text:
in: Trope, Futuristic Tech Index, Applied Phlebotinum, Comm Links
Comm Links
Lovely little ultra-portable pieces of Applied Phlebotinum that keep the cast in constant communication across vast distances, usually without any sort of lag or static, excepting outside interference. How they work is rarely explained—they just do. They are standard equipment for any starship or superhero team. Frequently, they can patch into any other communication network with ease. They usually don't have any visible means of selecting who to talk to, but somehow this is never a problem.
Sometimes cell-phone-like (and indeed, in works set in the present, cell phones usually fill this role), sometimes small enough to be worn on the shirt or in the ear.
Basically, just a plot device to ensure members of the cast can stay in touch over long distances.
The good twin of Reinventing the Telephone.
Compare: Video Phone.
Examples of Comm Links include:
6 Newspaper Comics
7 Tabletop Games
9 Web Comics
10 Web Original
11 Western Animation
12 Truth in Television
13 Fanfiction
In an episode of Trigun, Vash has access to a pair of these, despite radio being Lost Technology.
Seto Kaiba has that thing on his collar he's always talking to.
In Code Geass, Knightmare Frames could communicate with each other, and some sort of earpieces were in use (mostly by the Britannians). Also, cell phones were commonly used for sensitive communications, but with visible hardware modifications for encryption purposes.
The Devices of Magical Girl Lyrical Nanoha have communication capabilities that allow its users to keep in contact even across dimensions. They also have text messaging capabilities (with less pushing of little buttons since the AI can recognize speech) and can send transmissions to ordinary earth Cell Phones.
The calculator-esque and later wrist communicators in Sailor Moon. One wonders just what kind of infrastructure makes them work.
Bleach: This two-way system keeps shinigami in contact with communications division (a unit of the 12th division) while on missions, allowing shinigami and Seireitei to remain in contact even though the shinigami is in the human world and Seireitei is in the spirit world. There have been two styles shown to date. A radio-headset style which is carried in the uniform rather than clipped to an ear, as used by Rangiku and Yumichika, and a phone style, as used by Rukia.
Science Ninja Team Gatchaman (AKA Battle of the Planets). G-Force had wrist band communications devices which also allowed them to change between their team uniforms and civilian clothing.
Some versions of X-Men have communicators in the X's on their costumes.
Green Lanterns can use their rings to communicate with each other.
DC's Legion of Super-Heroes has several variants, most notably the omnicom, which is essentially an iPhone on steroids and which was introduced decades before cellular phones were developed. Various incarnations of the Legion have also incorporated hyperspace communications into their flight rings, and "telepathic earplugs" which serve as a combination comlink and Universal Translator.
The members of The Authority communicate by using nanomachinery to send each other messages through the Carrier.
The Avengers' Identicard is essentially a smartphone the size and shape of a credit card, which also serves as Avengers ID. When in use, the image of the person you're talking to replaces your ID photo.
The 1980's British Starblazer had the Wrist Vis-Phone. With some engineering creativity it could create a nerve torturing blast of sonic vibrations.
Star Wars has comlinks. Lando Calrissian has a "wrist radio" version in The Empire Strikes Back.
The Mission Impossible movies had camera-radios built into eyeglasses.
They Live. The aliens use wrist radios to communicate with each other. They can also be used to make short-range teleports.
Used in the climactic battle in Avatar, despite the main location being incredibly bad for all other electronics.
Buckaroo Banzai. Buckaroo and Rawhide have small communicators that can transmit across New Jersey.
In Peter F. Hamilton's The Nights Dawn Trilogy, Adamists (baseline or near-baseline humans) communicate with neural nanonics, brain-interfacing nanotech that allows a form of technological telepathy. This form of communication carries the usual technical limitations (network availability, interference and the speed of light). Edenists (genetically modified telepathic humans) use their "affinity gene" which allows real, instantaneous telepathy. At one point an interface device is used to allow an Adamist ship to make use of the Edenist affinity capability.
In David Drake's Hammers Slammers world, each soldier is fitted out with a tiny communicator that's implanted in the jawbone. It's activated by clenching the teeth and can even pick up subvocal speech. Handy things.
The Axis Of Time trilogy by John Birmingham has portable net-enabled laptops from Twenty Minutes Into the Future transported back to World War Two, where they function much like a wrist radio or Star Trek communicator. Notable in that, thanks to no satellites floating in orbit, the connections are often crappy, but work, thanks to a side feature of bouncing communications off the atmosphere... or something like that.
Uglies has skintennas that work like cell-phones but are built in to your body and only have a 1 km range.
In a Star Trek Expanded Universe novel, Mackenzie Calhoun is given, among other things, a newly-developed communicator that can send and receive messages over enormous distances by piggybacking on any carrier wave. Mac first tests it by accident when he jokingly says "Mackenzie to Jellico" and hears Admiral Jellico on the other end a second later, even though Jellico is on another planet.
In Michael Crichton's Timeline, a comm link was created that could fit in one's ear (it was described as looking like a hearing aid). It could also translate spoken languages into the wearer's ear. Both the distance and the amount of languages aren't specified, but the book emphasized that its batteries have a shelf-life of 36 hours.
E. E. "Doc" Smith's Lens is an uber-example of this, combining instantaneous communication, translation, code-breaking and identification functions. The latter is very, very specific - a particular Lens is matched uniquely to an individual wearer's mind, and attempting to wear or even handle one that isn't yours is instantly lethal (it disintegrates upon death to avoid being a permanent menace).
Star Trek is the Trope Maker here. The original series had cell phone-like devices, while The Next Generation had them built into the Starfleet badges.
No, the modern world has Star Trek Communicator-like devices.
In How William Shatner Changed The World, Motorala chief engineer and inventor of the cell phone Martin Cooper states that he invented the cell phone because he wanted a real life star trek communicator.
Farscape: the crew of Moya have small badge-like communicators which are threaded through Moya. It also fits the "patch into other networks" as, in the (pre-miniseries) Grand Finale, John uses his to talk to his dad through the phone...from the moon.
Leverage has Hardison inventing an earpiece in the pilot that everyone on the team uses throughout the first season to keep in contact over surprisingly vast distances.
Babylon 5 had comm links that attached to the back of their hands. The spinoff series Crusade had bracelet variants. In neither case were they used across extremely large distances, making them essentially two-way radios. They also avert the "have no visible means of selecting who to talk to" by requiring the call initiator to specify the call's destination through some kind of, probably automated, switchboard. This can be a person or a location. Also, they can be used as remote controls for their TVs/comm screens on the station and have biometric anti-theft features.
The comlinks are specially designed to only stick to living tissue using molecular bonding. An assassin kills a station security guard and steals his comlink, replacing it with a fake. The fake is discovered and is demonstrated by sticking it to the bulkhead, since the fake uses regular glue.
Also, that anti-theft feature? The link can only be used by its owner (as identified by their DNA somehow). The only time this came up, was when he needed to use someone else's link to call Security for help. Very frustrating for the character, although it worked out in the end, since the link sent its location to the Security office to report the theft, thus making them realize something was wrong.
The Mighty Morphin Power Rangers had communicators that also happened to tap into their mentor's teleportation system. Later Power Rangers teams had either wrist-mounted or Cell Phone morphers that had communications built in.
A TV series named Probe had agents with remote TV cameras that would fit onto a cuff-link or tie-tac, and implanted voice communications. Oh yes, the TV cameras weren't limited to visible light.
According to Wikipedia, 'Probe' was the pilot movie for an early 1970's television series called 'Search.' (There was a late 1980s series called 'Probe,' about an eccentric genius and his ditzy assistant.)
In the Doctor Who 2009 easter special, the Doctor finds a pair of "internal comms" lying around, one of which he gives to the Classy Cat Burglar before she does her mission impossible sequence into the depths of the ship.
Comms that fit perfectly into the humanoid ear, despite being owned by insectoid aliens with the heads of flies.
Happens occasionally in Kamen Rider, predominantly in Faiz where all five Riders have fully-functioning cell phones as their Transformation Trinket. Den-O has the Keitaros cell phone which activates Climax Form, but a more literal example is Hana's otherwise ordinary cell, which can apparently connect with the phone in the dining car of the time-traveling DenLiner.
In Knight Rider, Michael communicates with KITT and Devon through use of comm links. When outside of KITT, this device is in his wrist watch, which also has camera and scanner functions when KITT needs more info than what Michael can describe. KITT himself has a comm link in the console.
The remake replaces the watch with an earpiece.
In Andromeda, the crew of the Andromeda Ascendant use comms implanted into their necks. They work over long distances and allow them to communicate with the ship in orbit. Also, they can apparently record and transmit video while being implanted. Not really used on the ship, as the AI can route calls there.
The Torchwood team has Bluetooth-like devices in their ears. It is not made clear whether they are regular Bluetooth attachments (i.e., they keep their cell phones hidden), slightly modified Earth technology, or completely Imported Alien Phlebotinum made to look like Earth tech.
Dick Tracy had a radio wristwatch in an era when real radios still had vacuum tubes.
Later upgraded to a two-way wrist TV.
Later still upgraded to a two-way wrist computer which includes additional functions like forensic scanners and a Lie Detector function.
In Rogue Trader every class starts with one of these, called a Micro-bead, which fits in the ear and has a mike which stretches around the face, rather like a 360 headset. Other helmets have them built in, which is very useful.
And (Unusually for this trope) it has a range of about a kilometer.
Shadowrun introduced Commlinks after the second Matrix Crash. They're customizable, ultra portable computers that are so ubiquitous nearly everyone in the world owns one.
Traveller has them, starting at TL 8 they have an integrated computer (just like a cellphone) and at TL 10 they can be implanted.
Paranoia routinely includes com units as part of assigned mission equipment. Like everything else in Alpha Complex, they tend to break down when you want them to work, and work fine when you wish they didn't. (Like when The Computer contacts you while you're busy shooting Commies. Or treasonously shooting loyal citizens.) In the latest editions, they've been upgraded to Personal Digital Companions (basically PDAs), and collect spam and viruses like mad.
Final Fantasy V has an awesome variation. Apparently, on the second world, communicators come in the form of grass.
Final Fantasy IV also has a variation, the whisperweed functions as a communicator once.
In World of Warcraft, there is a questline where you use communicators to talk to Brann Bronzebeard (at least on the horde side, where normal communication would be difficult to say the least).
Also in WoW are Hearthstones, little enchanted trinkets that let you warp back to your home camp once an hour. On roleplaying servers, Hearthstones are said to also be communication devices, thus explaining how players are chatting across a zone or continent without stepping out of character.
The codec system in Metal Gear Solid, which was so advanced there was no external component, only a system of nanites.
Handwaved frequently throughout the series. The codec is super advanced, apparently: it uses an extremely small cochlear implant to directly stimulate the bones in the ear that are responsible for hearing. It can't be jammed, ever, as long as burst transmission is used (this is actually pretty close to reality), though local transmission can have troubles. The nanites in the body turn the entire human physiological system into a radio antenna for communication...the list goes on.
Although at no point is it explained how you're viewing the video feed being transmitted to your inner ear, or how it's more secure to talk to someone a few feet away from you using codec (see Metal Gear Solid 2 Sons of Liberty) than just face-to-face. I guess it's just magic.
The team in Mass Effect has ear-bead communication systems with enough range to contact a starship in orbit.
There's probably a system (possibly an advanced communication suite, and I feel like it might have even been mentioned at some point) built into the hardsuits that the team wear. Supported by the fact that they always seem to put their hand to their ear, and even talk into their elbow a little when they're communicating with the ship.
Jack from MadWorld uses two of these, both ear pieces, each to a different person. Strange how only one of them hears the other talk.
Sonic Adventure 2 features radios that the characters often use. What's odd is that both sides of the story (Hero and Dark) have the same kind of radio.
In Max Payne 2, Max and Mona keep in touch via seeming indestructible (and undetectable, since Mona's doesn't get taken when she gets arrested) Comm Links throughout most of the game.
Final Fantasy XI has Linkshells and Linkpearls that allow communication across continents, dimensions, and time itself. It's a game mechanic, as well, but at least one that's explained.
Star Ocean Till the End of Time features a Comm Link with an effective range of one light year, that also triples as a translation device and an impromptu but powerful explosive.
Fridge Brilliance: Any device powerful enough to broadcast over one light year would have to put several kilowatts into its signal, and thus would need correspondingly powerful batteries. Ever heard of cell phone batteries bursting into flames? The exploding communicator would be the same thing turned Up to Eleven.
Cole in In Famous uses what looks like a cell phone to communicate, though the sound effects indicate it is either a radio or in "push-to-talk" mode. Rather cleverly, it closely resembles a real Motorola phone from the old Nextel service, which had both push-to-talk and rubber insulation. Given that Cole accidentally fries most electronics, it's probably the only one he can use.
So how does he recover memory card from dead drops?
Quake IV uses wrist based comms that seem to work though several miles of Strogg Architecture.
The various Legend of Zelda games solve this in different ways. Many games it's just plain ol telepathy that lets Princess Zelda talk to Link. Wind Waker had the Pirate's Charm, which initially allowed Tetra, and later the King of Red Lions, to talk to Link.
Space Quest V: The Next Mutation, being a parody of Star Trek, uses flip communicators for Roger to contact the ship.
Dead Space and Dead Space 2 have RIG transmissions, both video and audio, that work reliably in adverse conditions and only fail for plot reasons.
Schlock Mercenary has hypernet communicators.
In Antihero for Hire, Shadehawk has one that keeps him in touch with Wrench. They appear to be standard gear for superheroes; Crossroad has one for connecting with Echo, and the Civic Champions all have them as well.
Web Original
Fatebane in Associated Space has a computer built into his brain that can function as a communicator.
The body-surfing AI O'Malley from Red vs. Blue uses radio waves to hop from host to host. Shutting off the helmet radios everyone uses is a frequent plot point for the Blue team.
The DCAU Justice League have their own communicators as well—ultra-slick tech that fits in the ear. In the comics, on the other hand, J'onn usually just keeps everyone telepathically networked.
The Teen Titans have hand-held clamshell devices that function as communicators. In the final season of the cartoon, the Brotherhood of Evil managed to capture one and used it to track down all the heroes and capture them one by one. Robin had to re-wire his so it could detonate a secret explosive inside each one.
Kim Possible has her "Kimmunicator", which is shaped like a compact. It's like a PDA with Everything Sensors built in, not to mention a seriously powerful battery, extendable robot arms and whatever else might come in handy.
In one episode, Drakken locked Kim in a vault and threw the vault into a deep water-filled pit after confiscating her Kimmunicator. Kim then remembered that her class ring had a back-up Kimmunicator that also doubled as a laser torch and emergency rebreather!
Totally Spies. The girls use a Compowder to communicate (so called because it looks like a make-up kit, which often contain powder puffs).
In both Teenage Mutant Ninja Turtles cartoons, the turtles have communicators. In the first the bad guys also have them, and even the dimensional port in the Technodrome can double as such. And with two parallel systems, it is no wonder that both sides sometimes used the communicators to hack each others' frequencies. The second series Turtles use special modified Cell Phones instead.
Static and Richie (later Gear) in Static Shock make gadgets called Shock Boxes, which work like walkie talkies. In one episode, Static managed to use his powers to boost their range to across the planet, somehow.
On The Venture Brothers, Brock Samson and Thaddeus, Hank, and Dean Venture have communicator wristwatches they can use to contact each other or HELPeR. Jonas Venture, Jr, has his communicator built into his shirt collar, which is more accessible but lacks a video screen.
The Centurions use wristwatch-like communicators.
This is, of course, the essence of what two-way radios are for. Modern radios can include a variety of features including selectable frequencies, programmable encryption, and even the ability to get around enemy jamming. You could program a radio so that you could talk to specific people by flipping a dial to a specific pre-set channel, though it's not quite the same as just saying who you want to talk to.
Comm badges actually exist already, though so far their only real market is hospitals, where specific doctors need to be summoned quickly for meetings or to tend to patient emergencies (the other method for reaching them, of course, is paging him via a beeper or the hospital PA system).
In the Harry Potter fic Make a Wish, a mad scientist friend of Harry's came up with miniature Floo systems that worked mostly for communication-only purposes and could be handily enclosed in a Zippo lighter.
Futuristic Tech Index


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New large-scale solar energy system is taking form in New Mexico
October 11, 2016	0 By Bret Williams
Xcel Energy to purchase electricity from new solar energy system
NextEra Energy, a prominent energy developer, will be building a new, large-scale solar energy system in New Mexico. The project costs an estimated $260 million and will span some 1,400 acres near Roswell. Once completed, the solar farm will be operated by five full-time employees, with electricity that the solar farm generates being purchased by Xcel Energy. The solar power system is estimated to generate enough electricity to power approximately 40,000 average homes.
Company continues to look for renewable energy sources to make use of
Xcel Energy is looking to expand its use of renewable energy and solar power has caught the company's attention. The company has formed a 25-year power purchase agreement with NextEra Energy. Through the agreement, Xcel Energy will purchase a portion of the electricity that the new solar energy system generates. This electricity will then be provided to customers in New Mexico and, potentially, Texas. Currently, approximately 20% of Xcel Energy's electrical power in both New Mexico and Texas is derived from renewable sources.
Solar energy market continues to grow in the US
Solar renewable energy has begun to gather a great deal of attention and support in recent years. New Mexico is home to a very promising solar market, largely due to the abundant sunlight that it experiences on a year-round basis. The growth of solar energy, and other forms of clean power, is being fueled by government policies. Some of these policies, namely new emissions regulations coming from the federal government, are forcing utilities to make more use of clean energy. Many utilities have chosen to support solar power, though they are also investing in wind power and other forms of clean power.
Xcel Energy has high hopes for solar power
Xcel Energy believes that solar energy has a very promising future. The company suggests that using solar power to generate electricity is more cost effective than using natural gas. Xcel Energy's support of solar energy is likely to expand, especially as new large-scale projects begin to take form in favorable markets. The company is expected to benefit from the continued growth of the solar energy market.
CategorySolar Energy Hydrogen news United States
Tagsnew mexico new mexico solar energy NextEra Energy renewable energy solar energy solar energy news solar energy projects solar power texas xcel energy
Hyundai to launch new businesses based on hydrogen fuel cells
Many developers use Production Tax Credit to renovate their wind energy systems

redpajama_set_name: RedPajamaCommonCrawl


text:
Make Your Personal Mind Map Today To Chase What Matters Most To You {Samples Included}
The ultimate truth, our inevitable death, is raw humanity. To be vulnerable together, in the company of someone who is sick or dying, is a roller coaster of emotions. It is witnessing strength, acceptance and peace amidst chaos, despair and pain. It's an honor to be in the presence of someone during this difficult and very private time. And if its a cat that's dying, a living being who can't speak his feelings out, it's the most humbling experience of a lifetime.
How To Reframe Our Reality Through Cognitive Reappraisal:
We have a lot of cognitive biases through which we perceive our reality. Learn how to mitigate them. Read about it HERE.
Productivity And Mindfulness Resources For Adults
A Comprehensive Toolkit Of Resources For Mental Health, Personal Development And Digital Wellbeing
Life shrinks or expands in proportion to one's courage. ~ Anais Nin
How To Start Your Own Business, Even If You're a Youngin'
* What's Stopping You? Do you ever feel like you aren't taken seriously just because you're young? While there is something to be said for experience and wisdom, kids can – and should – do amazing things! Starting a business can be one of them. With the...
Top 4 Social Media Fails That Lead Employees To Get Canned From Companies
* * Want To Listen To The Article Instead? * Cited Works: https://sba.thehartford.com/managing-employees/employees-getting-canned-over-social-media/ * The Future Of Work And The Role Of Non-Cognitive Skills: Read more...
Who Are Road Scientists And How To Work In STEM As A Digital Nomad
* The Road Scientist: Working a STEM-related job and trying to live remotely is rarely straightforward, but it is possible. Whether you specialize in science, technology, engineering, or mathematics, in this article, I'll provide a few key strategies to help...
The Top 3 Trends That Are Going To Shape The Future Of Work Around The World In 2023
* https://youtu.be/WArC4ZaxDxA * Want To Listen To The Article Instead? * Works Cited: https://www.linkedin.com/news/story/say-goodbye-to-the-9-to-5-workday-6107738/...
A Pictorial Depiction Of How 33 Powerful Mindset Shifts Can Help Supercharge Your Value Proposition
* In the book, Drive, author Daniel Pink says that our intrinsic motivation is determined by our autonomy, competency and relatedness. When we feel like we have a stake in something or understand why we have to do what we have to do, that increases our...
Ask A Business Owner What Courage Is. They Know A Thing Or Two About Being Relentless.
* Courage is a topic close to my heart. Ask me , I am business owner. Every day, I feel vulnerable and weak as an entrepreneur. But, being a small business owner has taught me a few things. It has taught me the courage to be imperfect. It has made me do what I...


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China announces sanctions on nearly 30 ex-Trump administration officials
U.S. coronavirus death toll surpasses 400,000 in final hours of Trump presidency
Trump pardons Flynn despite ex-national security adviser's guilty plea in Russia probe
by: Associated Press, Kareen Wynter
President Donald Trump pardoned his former national security adviser Michael Flynn on Wednesday, ending a yearslong prosecution in the Russia investigation that saw Flynn twice plead guilty to lying to the FBI and then reverse himself before the Justice Department stepped in to dismiss his case.
"It is my Great Honor to announce that General Michael T. Flynn has been granted a Full Pardon," Trump tweeted. "Congratulations to @GenFlynn and his wonderful family, I know you will now have a truly fantastic Thanksgiving!"
The pardon, in the waning weeks of Trump's single term, is part of a broader effort by Trump to undo the results of a Russia investigation that shadowed his administration and yielded criminal charges against a half-dozen associates. It comes just months after the president commuted the sentence of another associate, Roger Stone, days before he was to report to prison.
The move is likely to energize supporters who have taken up Flynn as a cause celebre and rallied around the retired Army lieutenant general as the victim of what they assert is an unfair prosecution, even though Flynn twice admitted guilt. Trump has repeatedly spoken warmly about Flynn and, in an indication of his personal interest in his fate, asked then-FBI Director James Comey in February 2017 to end a criminal investigation into the national security adviser.
In a statement, Flynn's family thanked Trump "for answering our prayers and the prayers of a nation" by issuing the pardon.
Democrats lambasted the pardon as undeserved and unprincipled. House Speaker Nancy Pelosi called it "an act of grave corruption and a brazen abuse of power," while Rep. Adam Schiff, the Democratic chair of the House Intelligence Committee, said a "pardon by Trump does not erase" the truth of Flynn's guilty plea, "no matter how Trump and his allies try to suggest otherwise."
"The President's enablers have constructed an elaborate narrative in which Trump and Flynn are victims and the Constitution is subject to the whims of the president," House Judiciary Committee Chair Jerry Nadler said in a statement. "Americans soundly rejected this nonsense when they voted out President Trump. "
The pardon is the final step in a case defined by twists and turns. The most dramatic came in May when the Justice Department abruptly moved to dismiss the case, insisting that Flynn should not have been interviewed by the FBI in the first place, only to have U.S. District Justice Emmet Sullivan resist the request and appoint a former judge to argue against the federal government's position and to evaluate whether Flynn should be held in criminal contempt for perjury.
That former judge, John Gleeson, called the Justice Department's dismissal request an abuse of power and said its grounds for dropping the case were ever-evolving and "patently pretextual."
As Sullivan declined to immediately dismiss the prosecution, Flynn lawyer Sidney Powell sought to bypass the judge by asking a federal appeals court to direct him to drop the matter. A three-judge panel did exactly that, but the full court overturned that decision and sent case back to Sullivan.
Appeals court keeps Michael Flynn's case alive, permits scrutiny of DOJ's request to dismiss it
Appeals court orders dismissal of case against ex-Trump adviser Michael Flynn, who had admitted to lying in Russia probe
Push to dismiss Michael Flynn case is 'gross abuse' of power, former judge says
At a hearing in September, Powell told Sullivan that she had discussed Flynn's case with Trump but also said she did not want a pardon — presumably because she wanted him to be vindicated in the courts.
Powell emerged separately in recent weeks as a public face of Trump's efforts to overturn the results of his election loss to President-elect Joe Biden, but the Trump legal team distanced itself from her after she advanced a series of uncorroborated conspiracy claims.
The pardon spares Flynn the possibility of any prison sentence, which Sullivan could potentially have imposed had he ultimately rejected the Justice Department's dismissal request. That request was made after a review of the case by a federal prosecutor from St. Louis who had been specially appointed by Attorney General William Barr.
At issue in the prosecution was an FBI interview of Flynn, days after Trump's inauguration, about a conversation he had during the presidential transition period with the then-Russian ambassador.
Flynn acknowledged lying during that interview by saying he had not discussed with the diplomat, Sergey Kislyak, sanctions that the outgoing Obama administration had just been imposed on Russia for election interference. During that conversation, Flynn advised that Russia be "even-keeled" in response to the punitive measures, and assured him "we can have a better conversation" about relations between the countries after Trump became president.
The conversation alarmed the FBI, which at the time was investigating whether the Trump campaign and Russia had coordinated to sway the election. In addition, White House officials were stating publicly that Flynn and Kislyak had not discussed sanctions, which the FBI knew was untrue.
Flynn was ousted from his position in February 2017 after news broke that Obama administration officials had warned the White House that Flynn had indeed discussed sanctions with Kislyak and was vulnerable to blackmail. He pleaded guilty months later to a false statement charge.
But last May, after years of defending the prosecution, the Justice Department abruptly reversed its position.
It asserted the FBI had no basis to interview Flynn about Kislyak and that any statements he made during the interview were not material to the FBI's broader counterintelligence probe. The department also pointed to internal FBI notes showing agents had planned to close out the investigation weeks before interviewing Flynn about Kislyak.
Flynn, of Middletown, Rhode Island, was among the first people charged in Mueller's investigation and provided such extensive cooperation that prosecutors did not recommend any prison time, leaving open the possibility of probation.
But the morning he was to have been sentenced, after a stern rebuke about his behavior from Sullivan, Flynn asked for the hearing to be cut short so that he could continue cooperating and earn credit toward a more lenient sentence.
After that, he hired new attorneys — including Powell, a conservative commentator and outspoken critic of Mueller's investigation — who took a far more confrontational stance to the government and tried to withdraw his guilty plea.
by Los Angeles Times / Jan 20, 2021
Now it's really official.
Moments after swearing in as the 46th president of the United States, Joe Biden crossed another important milestone in the democratic transfer of power: He took over the @POTUS Twitter account.
In one of the inaugurations's most talked about moments, poet Amanda Gorman summoned images dire and triumphant Wednesday as she called out to the world "even as we grieved, we grew."
The 22-year-old Gorman referenced everything from Biblical scripture and "Hamilton," and at times echoed the oratory of John F. Kennedy and the Rev. Martin Luther King Jr. With urgency and assertion he began by asking "Where can we find light/In this never-ending shade?" and used her own poetry and life story as an answer. The poem's very title, "The Hill We Climb," suggested both labor and transcendence.
A full-throated, supremely confident Lady Gaga belted out the national anthem Wednesday in a very Gaga way — with flamboyance, fashion and passion.
The Grammy winner wore a large dove pin and an equally large red and billowing sculpted skirt as she sang into a golden microphone, delivering an emotional and powerful rendition of "The Star-Spangled Banner." She was followed by Jennifer Lopez, dressed all in white, delivering a moving medley of "This Land is Your Land" and "America the Beautiful."
Kamala Harris of California makes history as 1st woman and 1st Black and South Asian person to be VP
Capitol police officer hailed as hero for actions during insurrection accompanies Harris at inauguration
Trump follows presidential tradition, leaves note behind for Biden
Philip Rivers retiring after 17 years in NFL, 16 with Chargers
With California's influence on higher education, some believe SAT and ACT could be headed for demise
Wednesday forecast: More wind, but not as widespread
Indian village cheers for Kamala Harris before swearing-in as U.S. vice president
Fierce winds fan California wildfires, topple trees and flip big rigs
Inauguration Day: President-elect Biden attends church with bipartisan group from Congress
Local news / 5 mins ago
California / 1 hour ago


With tremendous excitement, we are happy to announce the launch of The Race to raise awareness and support for the eradication of malaria. The Race is an attempt to break the Transatlantic speed record. It symbolizes urgency, provides excitement and fun and is the vehicle to bring awareness and support to eradicate malaria, an epidemic that *kills nearly a half a million people yearly, mostly children under the age of five!
Two LightSpeed ferries are now under construction in Seattle, Washington. Scheduled to be completed by the end of 2019. At which time they will begin a national tour down the west coast, through the Panama Canal, across the gulf coast, and up the Atlantic coast stopping at 20 ports to publicize The Race, and to raise awareness and support for the eradication of malaria. Mid-summer 2021 the pair of LightSpeed ferries will cross the Atlantic to London for The Race European awareness event and the start of The Race to New York city and effort to break the record now held by Sir Richard Branson! Upon completion of The Race a worldwide televised concert will take place in celebration and announcement of progress made to date to eradicate malaria and cast a vision for future work together.


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\section{Introduction} \label{s:intro}

The star formation rate density of the universe has changed
considerably since $z \sim 2$, decreasing by approximately an order of
magnitude.  This decrease has been widely discussed
\citep[e.g.][]{b:madau96, b:pei99, b:somerville01, b:hopkins04}
because the evolution of the star formation rate density acts to
constrain all models of galaxy formation and evolution.
Redshift-dependent luminosity densities (such as the $R$ band
luminosity density $l_R(z)$) and star formation rate densities (\SFRDz
) remain some of the best constraints on these models.  The value of
$l_R(z)$ at $z \approx 0$ constrains the evolution of stellar mass
\citep{b:madau98}.  Likewise, the value of \SFRDz\ at $z \approx 0$
helps determine the relative contributions of burst and quiescent star
formation \citep{b:somerville01} and the chemical evolution of the
universe \citep{b:pei95}.  Estimates of \SFRD\ from previous studies
span a factor of two or more, and do not always agree within their
stated uncertainties, as shown in Table \ref{t:sfrd}.  All surveys
suffer biases, however, and these may explain the large discrepancies
between the densities derived from each.

The process of star formation leaves measurable signatures across the
electromagnetic spectrum, allowing numerous methods for selecting
star-forming galaxies, each with its own set of biases.  For example,
objective prism surveys for emission line galaxies
\citep[e.g.][]{b:gallego95, b:gronwall97} result in a large,
consistent bias towards galaxies with high surface brightness, high
equivalent width emission lines \citep[e.g.][]{b:salzer89}.
Ultraviolet (UV) surveys \citep[e.g.][]{b:treyer98} are biased against
galaxies highly attenuated by dust.  Conversely, far-infrared (FIR)
\citep[e.g.][]{b:flores99, b:perez05} or sub-millimeter surveys select
galaxies by the presence of dust-reprocessed optical and UV light,
resulting in a bias against galaxies possessing little dust.
Similarly, 1.4 GHz radio surveys \citep[e.g.][]{b:serjeant02} bias
against systems with low dust content \citep{b:bell03}; in addition,
the correlation between radio flux and FIR flux (which is then used to
calculate star formation rate) is not linear, resulting in a
pronounced bias against low luminosity galaxies
\citep{b:devereux89,b:yun01}.

The 21-cm spectral line of neutral hydrogen ({\sc Hi} ) presents a useful
starting point for star formation surveys.  New stars form out of the
interstellar medium, of which {\sc Hi}\ is a key component.  While it is
the molecular component of the ISM from which new stars form, a strong
correlation has been found between {\sc Hi}\ surface density and star
formation intensity \citep{b:kennicutt98}.  {\sc Hi}\ flux is unaffected by
dust extinction, and has been measured in every type of star-forming
galaxy.  As a result, selecting targets by {\sc Hi}\ mass creates a sample
set free of the common optical biases.  For this, we use the {\sc Hi}\
Parkes All Sky Survey ({\sc HiPASS} ), an {\sc Hi}\ survey of the southern sky
($\delta \le +2^{\circ}$) over a velocity range from $-1280$ to +12700
km s$^{-1}$ obtained with the 21-cm multibeam receiver
\citep{b:staveley96} at the 64m Parkes radio telescope
\citep{b:barnes01}.

We have commenced the Survey of Ionization in Neutral Gas Galaxies
(SINGG) to survey star formation in the {\sc HiPASS}\ galaxies.
\citet[][hereafter Paper I]{b:meurer06} introduce the SINGG survey,
including sample selection, methods used, and basic measurements.  In
total the SINGG sample set includes 468 {\sc Hi} -selected targets covering
the mass range $7.0 \le \log(\mbox{${\cal M}_{\rm HI}$}/\mbox{${\cal M}_\odot$} ) \le 11.0$ in approximately
equal numbers per decade of mass.  Distance was also used in the
selection process; the nearest sources were preferentially selected at
each mass to improve physical resolution and avoid confusion.

To measure star formation, SINGG uses \Hline{\mbox{$\alpha$}}, the most readily
accessible optical tracer of star formation at low redshifts.
\Hline{\mbox{$\alpha$}}\ is a recombination line primarily resulting from hydrogen
photoionization.  Because this requires ionizing UV photons, the
majority of \Hline{\mbox{$\alpha$}}\ flux will be produced near the most massive O
stars, whose extremely short lifespans ($\lesssim 10$ Myr) make them
good indicators of the current star formation rate.  SINGG uses $R$
band measurements for continuum subtraction, which also provide useful
measurements of the existing stellar populations.  Observations
presented in Paper I consist of the 93 {\sc HiPASS}\ extragalactic {\sc Hi}\
targets fully processed to date.  Due to the large beam size of
{\sc HiPASS}, 13 of these {\sc Hi}\ targets contain between two and four
distinct \Hline{\mbox{$\alpha$}}\ objects.  As a result, the SINGG sample includes a
total of 111 individual \Hline{\mbox{$\alpha$}} -emitting galaxies, which we refer to
as SINGG Release 1, or SR1.  We however exclude one {\sc Hi}\ target,
J0403-01, and its single \Hline{\mbox{$\alpha$}} -emitting galaxy due to excessive sky
uncertainties and foreground field contamination.  The results
included in this paper are entirely generated from the data presented
in Paper I.

This paper uses the SINGG observations to derive the \Hline{\mbox{$\alpha$}}\ and $R$
band luminosity densities of the local universe, designated $\mbox{$l_{\rm H\alpha}$}(z)$
and $l_R(z)$ respectively, where $z$ indicates the mean redshift of
the survey.  For this and most of the other local ($z \approx 0$)
studies, we will omit the $(z)$ notation except where required.
Combined with the {\sc Hi}\ data from {\sc HiPASS} , these yield the star
formation rate density of the local universe, the stellar luminosity
density, the density of the neutral ISM, and the cosmic gas cycling
time.  Section~\ref{s:method} explains the methodology used to
determine the various volume densities and their uncertainties.
Section~\ref{s:results} gives the results of our calculations.
Section~\ref{s:disc} gives the results and compares to those of other
surveys, while Section~\ref{s:concl} discusses some of the
implications of our results.  We use a $\Lambda$CDM cosmology
($\Omega_{0}$ = 0.3, $\Omega_{\Lambda}$= 0.7) with a Hubble constant
of $H_{0}$ = 70\ km s$^{-1}$ Mpc$^{-1}$, and a \citet{b:salpeter55}
IMF between 0.1 and 100 \mbox{${\cal M}_\odot$} .

\section{Methodology} \label{s:method}

\subsection{{\sc Hi}\ mass}

Since the SINGG sample is not volume complete, we tie our results to
an {\sc Hi}\ Mass Function ({\sc HiMF}).  {\sc Hi}\ parameters are primarily derived
from the data given in our two main source catalogs: {\sc HiCAT} , the
final {\sc HiPASS}\ catalog \citep{b:meyer04}, and BGC, the {\sc HiPASS}\ Bright
Galaxy Catalog \citep{b:koribalski04}.  These catalogs have 95\%\
completeness limits in velocity-integrated 21 cm flux densities of
$\int S_{\nu}\ d\rm v \sim $ 5 and 25 Jy km s$^{-1}$, respectively.
The {\sc Hi}\ mass of a galaxy at a distance of $D$ Mpc is derived using
the standard relation $\mbox{${\cal M}_{\rm HI}$}\ [\mbox{${\cal M}_\odot$} ]= 2.36 \times 10^{5} D^{2} \int
S_{\nu}\ d$v [Jy km s$^{-1}$] \citep{b:roberts62}.  As a result, the
flux density limits for these two samples correspond to {\sc Hi}\ mass
limits of 1.2 and 5.9 $\times\ 10^{6}\ D^{2}\ \mbox{${\cal M}_\odot$} $, respectively.
The SR1 sources have distances of 4 -- 73 Mpc (with the majority
falling within the 10 -- 20 Mpc range) and {\sc Hi}\ masses of $10^{7.5}$
-- $10^{10.6}$ \mbox{${\cal M}_\odot$} .  Detailed information about the {\sc Hi}\ masses of
the SINGG galaxies can be found in the original catalog publications
and Paper I.

Distances for most sources are derived from radial velocities using
the model of \citet{b:mould00}, which corrects for infalls towards the
Virgo cluster, Great Attractor, and Shapley supercluster.  Distances
to the nearest galaxies are taken from \citet{b:karachentsev04}.  This
alters the distances and {\sc Hi}\ masses for many SINGG galaxies when
compared to other {\sc HiPASS}\ papers \citep{b:zwaan05}, and marginally
alters the {\sc Hi}\ Mass Function used to correct for incompleteness.  The
values given throughout this paper are those derived using the Mould
model for the full {\sc HiPASS}\ sample.

We use the standard Schechter function to parameterize the {\sc HiMF}:
\begin{equation}
\theta(\mbox{${\cal M}_{\rm HI}$} )\ d\mbox{${\cal M}_{\rm HI}$}\ = \theta_{\ast} \left( \frac{\mbox{${\cal M}_{\rm HI}$} }{\mbox{${\cal M}_\star$}
} \right)^{\alpha} e^{- \left( \frac{\mbox{${\cal M}_{\rm HI}$} }{\mbox{${\cal M}_\star$} } \right) }\
d\left( \frac{\mbox{${\cal M}_{\rm HI}$} }{\mbox{${\cal M}_\star$} } \right)
\end{equation}
where $\theta(\mbox{${\cal M}_{\rm HI}$} )$ represents the number density of galaxies as a
function of {\sc Hi}\ mass (in Mpc$^{-3}$), \mbox{${\cal M}_\star$}\ is the characteristic
mass, $\alpha$ is the ``faint'' end slope and $\theta_\ast$ is the
normalization factor.  We calculate Schechter fits to raw, binned
$\theta(\mbox{${\cal M}_{\rm HI}$} )$ data from \citet{b:zwaan05}, and adjusted to the
distance of \citet{b:mould00} for $H_0 = 70\, {\rm km\ s^{-1}\
Mpc^{-1}}$.  This yields $\mbox{${\cal M}_\star$} = 10^{9.92 \pm 0.04}\ h_{70}^{-2}$
\mbox{${\cal M}_\odot$} , $\alpha = -1.41 \pm 0.05$ and $\theta_{\ast} = (3.86 \pm 0.7)
\times 10^{-3}\ h_{70}^{3}$ Mpc$^{-3}$ dex$^{-1}$; these values are
compared to other {\sc Hi}\ Mass Functions in Table~\ref{t:himf}.  As is
usually the case, the errors on \mbox{${\cal M}_\star$}\ and $\theta_{\ast}$ are highly
correlated.

For the 13 SR1 {\sc Hi}\ targets containing multiple \Hline{\mbox{$\alpha$}}\ sources,
{\sc HiPASS}\ can only provide the total {\sc Hi}\ mass for each target, with no
ability to distinguish the contributions of each individual galaxy.
When calculating our luminosity densities, the luminosities of the
individual galaxies within each {\sc Hi}\ target are combined and the total
is treated as a single aggregate object.  As the mass function given
above was generated using similarly combined {\sc Hi}\ masses, this
approach should not substantially bias our results.

\subsection{Volume densities} \label{s:calc}

Using the {\sc HiMF} , we derive the $R$ continuum luminosity density
$l_R$, \Hline{\mbox{$\alpha$}}\ luminosity density \mbox{$l_{\rm H\alpha}$} , and {\sc Hi}\ mass density
\rhoHI\ for the local universe.  We denote values uncorrected for
internal extinction with a prime ($'$) symbol.

The volume density of a quantity $x$ is found using:
\begin{equation}
n_{x} = \int\ \theta (\mbox{${\cal M}_{\rm HI}$} )\ x(\mbox{${\cal M}_{\rm HI}$} ) \
d\left(\frac{\mbox{${\cal M}_{\rm HI}$}}{\mbox{${\cal M}_\star$}}\right)
\label{e:rhox}
\end{equation}
where $x = L_{\rm H\alpha}$ when calculating \mbox{$l_{\rm H\alpha}$}, $x = L_R$ when
calculating $l_R$, $x = 1.0$ when calculating the number density $n$,
or $x = \mbox{${\cal M}_{\rm HI}$}$ when calculating \rhoHI .

By separating our data into {\sc Hi}\ mass bins and combining the results
within each bin, Eq.~\ref{e:rhox} is replaced by:
\begin{equation}
n_{x} = \ln (10) \sum_{i=1}^{N_{bins}} \frac{\Delta
\log(\mbox{${\cal M}_{\rm HI}$})_{i}}{N_{i}} \sum_{j=1}^{N_{i}} \theta (\mbox{${\cal M}_{\rm HI}$}_{j})\
x_{j} \left(\frac{\mbox{${\cal M}_{\rm HI}$}_{j}}{\mbox{${\cal M}_\star$}}\right)
\label{e:rhox2}
\end{equation}
Here, $i$ represents the array of mass bins, while $j$ represents the
individual {\sc HiPASS}\ targets within each bin.  $\Delta \log(\mbox{${\cal M}_{\rm HI}$})_{i}$
is the logarithmic width of each mass bin; our bins are 0.5 decades
wide for all bins except the lowest ($7.0 \le \log(\mbox{${\cal M}_{\rm HI}$}/\mbox{${\cal M}_\odot$} ) \le
8.0$), as shown in Table~\ref{t:bindata}.

The SR1 \Hline{\mbox{$\alpha$}}\ and $R$ luminosities are given in Paper I, along with
lists of targets containing multiple emission line galaxies.  These
luminosities are derived from fluxes extracted using elliptical
apertures, supplemented with the flux from outer disk {\sc Hii}\ regions.
Full discussions of our $R$ and \Hline{\mbox{$\alpha$}}\ flux extraction procedures
are given in Paper I.

To calculate the Star Formation Rate (SFR) for each galaxy, we adopt
the conversion from \Hline{\mbox{$\alpha$}}\ luminosity to SFR given by
\citet{b:kennicutt94}.  This relationship is derived using a single
power law Initial Mass Function (IMF) having a \citet{b:salpeter55}
slope and spanning the mass range of 0.1 to 100 \mbox{${\cal M}_\odot$} .  The resulting
conversion is
\begin{equation}
SFR\ [\mbox{${\cal M}_\odot$}\ \mbox{\rm yr}^{-1}] = \left(\frac{L_{\rm H\alpha}\ [\rm
erg\ s^{-1}]}{1.26 \times 10^{41}}\right)
\label{e:sfr}
\end{equation}
We adopt this conversion to maintain consistency with numerous other
studies.  The choice in IMF is a major source of systematic
uncertainty, since the conversion of $L_{\rm H\alpha}$ to SFR depends
entirely on the fraction of stars falling within the mass range
responsible for ionizing hydrogen.  For example, the various IMFs of
\citet{b:scalo86} would decrease the conversion factor to anywhere
from $1.7 \times 10^{40}$ to $8.4 \times 10^{40}$
\citep{b:kennicutt94}, and that of \citet{b:kroupa01} would give a
conversion of $1.9 \times 10^{41}$ \citep{b:brinchmann04}.  However,
all \Hline{\mbox{$\alpha$}}\ surveys suffer from this bias equally, and so as with
$H_{0}$, we convert other \Hline{\mbox{$\alpha$}}\ surveys to our chosen IMF before
comparison.

\subsection{Flux corrections}

To calculate star formation rates, we first have to correct the flux
data for foreground and internal extinction, [{\sc Nii}] contamination, and
stellar absorption.  The foreground extinction corrections are
accomplished using the \citet{b:schlegel98} extinction maps.  Since our
selection avoids the Galactic plane and the Magellanic clouds, the
foreground extinction correction increases the derived values of
\mbox{$l_{\rm H\alpha}$}\ and $l_R$ by an average of only 10\%.  Stellar absorption,
as explained in Paper I, causes our measurements to consistently
underestimate \Hline{\mbox{$\alpha$}}\ flux by 2 -- 6\% \citep{b:brinchmann04}.  To
adjust for this, we increase each of our \Hline{\mbox{$\alpha$}}\ fluxes by 4\%.

For the [{\sc Nii}] correction and internal dust absorption,
$A(\Hline{\mbox{$\alpha$}})_{\rm int}$, we adopt the relationships with $R$ band
absolute magnitude prior to dust absorption corrections, $M_R'$, given
by \citet{b:helmboldt04} and converted to the AB magnitude system, as
explained in Paper I.  Each galaxy's individual [{\sc Nii}]/\Hline{\mbox{$\alpha$}}\
correction is based on its {\sc Hi}\ velocity, velocity width, and the
narrow-band transmission profile, as detailed in Paper I.  Integrated
over our entire sample, the [{\sc Nii}] correction decreases \mbox{$l_{\rm H\alpha}$}\ by 15\%;
$l_R$ is not affected.  The internal extinction correction
$A(\Hline{\mbox{$\alpha$}})_{\rm int}$ increases our estimate of \mbox{$l_{\rm H\alpha}$}\ by a factor of
2.1 (0.82 mag).  As noted in Paper I, we assume that the $R$ band
internal dust absorption, $A(R)_{\rm int}$, is half that of
$A(\Hline{\mbox{$\alpha$}})_{\rm int}$, due to the well-known phenomenon of increased
extinction in {\sc Hii}\ regions compared to the field
\citep{b:fanelli88,b:calzetti94}, and so $l_R$ increases by 0.41
magnitudes after extinction correction.

\section{Results} \label{s:results}

\subsection{Volume densities} \label{s:voldens}

The $R$ band luminosity density, corrected only for Galactic
extinction, is found to be
\begin{equation}
l_R' = (4.4 \pm 0.7) \times 10^{37}\ h_{70}\ \rm erg\ s^{-1}\
{\rm \AA}^{-1}\ Mpc^{-3}
\end{equation}
while the \Hline{\mbox{$\alpha$}}\ luminosity density, corrected for [{\sc Nii}]
contamination and Galactic extinction, is
\begin{equation}
\mbox{$l'_{\rm H\alpha}$} = (9.4 \pm 1.8) \times 10^{38}\ h_{70}\ \rm erg\ s^{-1}\ Mpc^{-3}.
\end{equation}
With our adopted IMF and resultant star formation rate conversion,
Eq.~\ref{e:sfr}, the local star formation rate density (uncorrected for
internal extinction) is
\begin{eqnarray}
\log(\SFRDp\ [\mbox{${\cal M}_\odot$}\ \mbox{\rm yr}^{-1}\ \mbox{\rm Mpc}^{-3}]) &=&
-2.13\ ^{+0.08}_{-0.09}(ran.) \\ &\pm& 0.03(sys.) + \log(h_{70})
\nonumber
\end{eqnarray}

Corrected for internal dust extinction, these equations become:
\begin{eqnarray}
l_R\ &=& 7.0\ ^{+1.5}_{-0.3} \times 10^{37}\ h_{70}\ \rm erg\ s^{-1}\ {\rm \AA}^{-1}\ Mpc^{-3} \\
\mbox{$l_{\rm H\alpha}$} &=& 2.0\ ^{+0.6}_{-0.4} \times 10^{39}\ h_{70}\ \rm erg\ s^{-1}\ Mpc^{-3}
\end{eqnarray}
\begin{eqnarray}
\log(\SFRD\ [\mbox{${\cal M}_\odot$}\ \mbox{\rm yr}^{-1} \mbox{\rm Mpc}^{-3}]) &=&
-1.80\ ^{+0.13}_{-0.07}(ran.) \\ &\pm& 0.03(sys.) + \log(h_{70})
\nonumber
\end{eqnarray}
The uncertainties in each variable are explained in detail in
subsections~\ref{s:random} and \ref{s:system}.

Additionally, we derive the {\sc Hi}\ mass density to be
\begin{equation}
\rhoHI = 5.17 \pm 0.38 \times 10^{7}\ h_{70}\ \mbox{${\cal M}_\odot$}\ \rm Mpc^{-3}
\end{equation}
and the mean number density of {\sc Hi} -rich galaxies to be
\begin{equation}
n = 0.112\ ^{+0.017}_{-0.024}\ h_{70}\ \rm Mpc^{-3}
\end{equation}
within our mass range, $7.0 \le \log(\mbox{${\cal M}_{\rm HI}$}/\mbox{${\cal M}_\odot$} ) \le 11.0$.  Unlike
the luminosity densities, this number density is completely dependent
on the lower boundary chosen, as the integrated function increases as
\mbox{${\cal M}_{\rm HI}$}\ decreases.  Fig.~\ref{f:ldensity} shows the dependence of the
luminosity densities (and, by extension, derived quantities such as
\SFRD ) on \mbox{${\cal M}_{\rm HI}$} , along with the systematic uncertainty in the total
value due to each bin.  The plotted quantity is the fraction of the
total luminosity density coming from one decade of mass.

For comparison, we also derive \SFRD\ and \rhoHI\ for other mass
functions, using the simpler distance model favored by {\sc HiPASS} ; these
values are given in Table~\ref{t:himf}.  Only the {\sc HiMF}\ weighting of
each \Hline{\mbox{$\alpha$}}\ source is altered; the distances and fluxes remain
unchanged.  While the differences in individual {\sc HiMF}\ parameters are
relatively small, the resulting integrated mass and luminosity
densities in Table~\ref{t:himf} vary by 0.20 -- 0.22 dex, primarily
due to the low-mass slope, $\alpha$.  While this discrepancy is
comparable to the total uncertainties in each density, it is
significantly larger than the $\sim 0.03$ dex uncertainty caused by
the uncertainties in the {\sc HiMF}\ parameters themselves.

\subsection{Random errors} \label{s:random}

Since the calculations of luminosity densities involve many different
variables, most of which have their own uncertainties, the simple
methods of error propagation would result in heavily correlated
uncertainties.  To better quantify the random uncertainties, we
utilize Monte Carlo and ``bootstrap'' algorithms.

We consider the following sources of random error: (1) the {\sc HiMF}: the
limited number of {\sc HiPASS}\ sources used to derive each {\sc HiMF}\ results
in uncertainties in the parameters used to fit that {\sc HiMF}, and hence
on luminosity densities; (2) error due to the limited SINGG SR1
sample; (3) $R$ and \Hline{\mbox{$\alpha$}}\ flux uncertainties due to sky
subtraction; (4) \Hline{\mbox{$\alpha$}}\ flux uncertainty due to continuum
subtraction; (5) the uncertainty in the \Hline{\mbox{$\alpha$}}\ flux calibration, and
(6-7) error due to the dispersion in the fits used to generate our
[{\sc Nii}] and $A(\Hline{\mbox{$\alpha$}})_{\rm int}$ corrections.  The random errors are
presented in Table~\ref{t:error}; we consider each of these terms in
detail.

To estimate the uncertainty due to the {\sc HiMF} , we create one hundred
realizations of the {\sc HiMF}\ using a bootstrap resampling of the
original data in {\sc HiCAT}\ and adopting the \citet{b:mould00} distance
model.  The {\sc HiMF}\ in each realization is created using the same two
dimensional stepwise maximum likelihood technique of
\citet{b:zwaan05}.  Each realized {\sc HiMF}\ is fit to a Schechter
function, which is used in Eq.~\ref{e:rhox2} to determine the
resulting luminosity densities of each realization.  The random
uncertainty in each luminosity density due to the {\sc HiMF}\ is then the
dispersion about the mean luminosity density for all the realizations.

To quantify the SR1 sampling error we use a ``bootstrap'' resampling
method, drawing 92 objects at random (with duplication allowed) from
our data set.  As with our other uncertainties, this randomization is
repeated ten thousand times, with the overall sampling uncertainty
defined as the standard deviation of the resulting distribution.

The errors due to the uncertainties in the continuum scaling ratio and
background sky level for each galaxy are quantified through another
form of Monte Carlo logic.  For each of ten thousand iterations, we
vary the sky level or continuum ratio within Gaussian distributions
having the uncertainties derived from our error models, which in turn
alter the measured flux (and by extension, the star formation rate)
for each galaxy.  Again, the luminosity densities are recalculated for
each iteration, and the dispersion about the mean is quoted as the
resulting uncertainty.  Additionally, we have an uncertainty due to
our flux calibration method, as explained in Paper I; we estimate this
uncertainty to be 0.04 magnitudes for images requiring our 6568/28
narrow-band filter, and 0.02 magnitudes for all others.

To find the random error due to our $A(\Hline{\mbox{$\alpha$}})_{\rm int}$ and [{\sc Nii}]
corrections, we use the $M_R'$ fits given in \citet{b:helmboldt04},
each of which has a dispersion of 0.23 dex (Helmboldt, priv.\ comm.).
We make a series of realizations of our sample; within each
realization, each galaxy's $\log(A(\Hline{\mbox{$\alpha$}})_{\rm int})$ or
$\log(F_{\rm [NII]6583}/F_{\rm H\alpha})$ correction is perturbed by a
Gaussian random deviate with the above dispersion.  Luminosity
densities are re-derived, and the dispersion about the mean simulated
luminosity density is our random error.  Separate sets of realizations
are done to determine the errors due to $A(\Hline{\mbox{$\alpha$}})_{\rm int}$ and
those due to the [{\sc Nii}] correction, with all other terms held fixed.

Applied to the SINGG sample, we find the uncertainties as listed in
Table~\ref{t:error}.  We find that the random uncertainties are
dominated by the internal dust extinction (for the corrected
luminosity densities only), the SR1 sampling error, and to a lesser
extent the {\sc HiMF}\ uncertainties.  While the sky and continuum
subtraction uncertainties dominate the measurements of many individual
galaxies, when evaluated over our entire sample their contributions to
the error budget are relatively small.

\subsection{Systematic errors} \label{s:system}

The SINGG results also suffer from a series of systematic
uncertainties.  We consider the following sources of systematic error:
(1 -- 2) uncertainty in the zeropoints of our [{\sc Nii}] and $A(\Hline{\mbox{$\alpha$}})_{\rm
int}$ corrections; (3) variation due to our choice of distance model;
(4) variation due to our choice of {\sc HiMF} .

In addition to the dispersion mentioned in Section~\ref{s:random}, our
$A(\Hline{\mbox{$\alpha$}})_{\rm int}$ and [{\sc Nii}] corrections include an uncertainty
in the fit from \citet{b:helmboldt04} itself.  This zeropoint
uncertainty corresponds to the discrepancy in luminosity density for
fits one standard deviation of mean away from the best fit, generated
from the 196 sources of \citet{b:jansen00}.

Our distance model is a significant source of systematic uncertainty,
as most SINGG targets are located within a distance of 20 Mpc.
Variations in the distances used can result in large changes in
observed luminosities as well as the underlying {\sc Hi}\ Mass Function,
and as a result alter the derived star formation rates.  To quantify
this effect, we calculate \SFRD\ using both our default
\citet{b:mould00} distance model as well as the simpler local-group
model used by \citet{b:zwaan05}, and quote the difference as our
uncertainty.

Finally, we calculate our luminosity densities using a variety of {\sc Hi}\
mass functions and the local-group distance model, with results shown
in Table~\ref{t:himf}.  While the {\sc HiPASS}\ team has produced several
{\sc Hi}\ mass functions, each supersedes the one before, with the work of
\citet{b:zwaan05} comprising the most complete version.  As a result,
while the resulting values of \SFRD\ vary by non-negligible amounts,
the earlier {\sc HiMF}\ values are only for comparison purposes, and we do
not include this error in our final uncertainties.

Our quoted systematic uncertainties are completely dominated by our
choice of distance model.

\subsection{Equivalent width}

We define the volume-averaged \Hline{\mbox{$\alpha$}}\ equivalent width to be the
ratio of \Hline{\mbox{$\alpha$}}\ flux density to $R$ band flux density.  We find the
volume-averaged equivalent width of our sample to be
\begin{equation}
EW'(\Hline{\mbox{$\alpha$}}) = 21.2\ ^{+4.2}_{-3.5}\ {\rm \AA}
\end{equation}
without internal extinction corrections, and
\begin{equation}
EW(\Hline{\mbox{$\alpha$}}) = 28.8\ ^{+7.2}_{-4.7}\ {\rm \AA}
\end{equation}
after all corrections have been applied.  The difference between these
two values is due to the differential nature (line versus continuum)
of the extinction law applied \citep[][Paper I]{b:calzetti94}.

The \Hline{\mbox{$\alpha$}}\ equivalent width is a measure of the rate of
transformation of the ISM into stars, relative to the existing stellar
population.  Comparison of the dust-corrected equivalent width to the
theoretical curves of \citet{b:kennicutt94} yields the birthrate
parameter $b$, corresponding to the ratio of the star formation rate
at the present time to that averaged over the age of the galactic
disk.  This interpretation is heavily dependent on the IMF used; for
our adopted \citet{b:salpeter55} IMF, we find
\begin{equation}
b = 0.26\ ^{+0.10}_{-0.06}
\end{equation}
which supports the common assertion that the cosmic star formation
density has decreased substantially since $z \sim 1.5$ within
star-forming galaxies.  Other IMFs result in greater values of $b$,
ranging as high as 2.8 for bottom-heavy IMFs such as
\citet{b:scalo86}.

\subsection{Gas cycling timescale} \label{s:tgas}

Using the SINGG data, we determine the gas cycling timescale
\mbox{$t_{\rm gas}$} , the time it would take for star formation to process the
existing neutral and molecular ISM of a galaxy at its current rate of
star formation.  This value can be derived from {\sc Hi}\ data if two
assumptions are made.  First, we assume that {\sc Hi}\ emission occurs
predominantly at low optical depth.  Second, we assume that the ratio
of molecular hydrogen to neutral atomic hydrogen remains constant,
independent of the other characteristics of the galaxy.

To calculate \mbox{$t_{\rm gas}$}\ we use the equation given in Paper I,
\begin{equation}
\mbox{$t_{\rm gas}$}\ \approx 2.3 \left({\mbox{${\cal M}_{\rm HI}$}\ \over SFR}\right)
\label{e:tgas}
\end{equation}
where ${\cal M}_{gas}$ = 2.3 \mbox{${\cal M}_{\rm HI}$}, derived from the observations of
\citet{b:young96}, accounts for the typical molecular hydrogen as well
as the helium content of the ISM.

The values of \mbox{$t_{\rm gas}$}\ for our array of mass bins are given in Table
\ref{t:bindata}.  The volume-averaged gas cycling timescale for our
sample can be derived from \mbox{$t_{\rm gas}$}\ $\approx 2.3 \left(\rhoHI
/\SFRD \right)$; with the values for \rhoHI\ and \SFRD\ presented in
Section~\ref{s:voldens}, we find this timescale to be $\mbox{$t_{\rm gas}$}\ = 7.5\
^{+1.3}_{-2.1}$ Gyr.  This is somewhat less than the Hubble time,
consistent with the previous findings of \citet{b:kennicutt94}.
Fig.~\ref{f:gastime} shows the gas cycling timescales for each of the
SINGG galaxies, as well as the average within each {\sc Hi}\ mass bin.
While the galaxy-to-galaxy variation in \mbox{$t_{\rm gas}$}\ is substantial (0.54
dex), the mean value does not appear to vary greatly with \mbox{${\cal M}_{\rm HI}$} .

Our choices of distance model and {\sc Hi}\ Mass Function have much smaller
impacts on the cosmic \mbox{$t_{\rm gas}$}\ than they do on \SFRD, and have no effect
on the gas cycling times of the individual galaxies within our sample.
Using the other {\sc Hi}\ Mass Functions given in Table~\ref{t:himf} result
in cosmic \mbox{$t_{\rm gas}$}\ values of 7.0 to 7.3 Gyr, well within the error bars
of our adopted {\sc HiMF} .

One should not take these gas cycling timescales too literally, as
several of the assumptions behind them may be questioned.  Much of the
neutral interstellar medium may have a large optical depth, which
would imply larger values of \mbox{${\cal M}_{\rm HI}$}\ than measured, causing \mbox{$t_{\rm gas}$}\ to be
somewhat underestimated.  This effect probably results in a
discrepancy of less than 20\% \citep{b:haynes84}.  As mentioned in
Paper I, the observed ratio of $\left(\mbox{${\cal M}_{\rm H2}$} /\mbox{${\cal M}_{\rm HI}$} \right)$ used to
derive Eq.~\ref{e:tgas} has a dispersion of 0.58 dex, or almost a
factor of 4; the ratio of CO luminosity to H$_{2}$ mass also has a
large uncertainty.  Hence, the \mbox{$t_{\rm gas}$}\ estimate of any single galaxy is
likely to be highly uncertain.  Similarly, we have not accounted for
systematic effects.  It is well known that more massive and higher
surface brightness galaxies are easier to detect in CO emission than
dwarfs.  In addition, our scenario does not include the ``hot phase''
of the ISM.  This accounts for the X-ray emitting halos around
galaxies as well as the intracluster medium and the intergalactic
medium.  This is likely to be the largest baryonic component of the
universe \citep{b:fukugita98}.  We also do not account for the return
to the ISM of material processed by stars, the stellar yield.  Because
of these limitations we are careful not to imply that \mbox{$t_{\rm gas}$}\ is a
consumption timescale; rather, it is simply the time it would take for
the present rate of star formation to form the mass of observed
neutral ISM and inferred molecular ISM into new stars.

\subsection{Dynamical parameters} \label{s:dyn}

The dynamical mass located within the optical radius of a galaxy,
\mbox{${\cal M}_{\rm dyn}$}, is a useful way to estimate its mass (including both
baryonic and dark matter) from easily observable quantities.  The
corresponding orbital time, \mbox{$t_{\rm orb}$} , is also used for comparison with
various models of galaxy evolution.  To find these values, we first
approximate the circular velocity of the edge of the galaxy from the
FWHM spread in the velocities measured by {\sc HiPASS} , corrected for the
estimated inclination of each galaxy.  That is,
\begin{equation}
v_{\rm circ} = \left(\frac{W_{50}}{2\ sin(i)}\right).
\label{e:vcirc}
\end{equation}
where our inclination angle, $i$, is defined as
\begin{equation}
sin^{2}(i) = \left(\frac{a^2 - b^2}{a^2 - c^{2}}\right)
\end{equation}
\citep{b:bottinelli83}, where $a,c$ are the axial lengths of the
oblate spheroid fit to each galaxy, and $a,b$ are the axial lengths of
the elliptical aperture used to measure optical fluxes.  Since we do
not wish to include any dependence on morphological classifications in
the SINGG methodology, we assume a constant $(c/a) = 0.20$, except in
three cases where our estimated $(b/a)$ is less than this amount,
where we simply set $c = b$.  To reduce uncertainty in \mbox{${\cal M}_{\rm dyn}$}\ we
exclude the 13 {\sc Hi}\ targets with multiple emission line galaxies, as
well as 14 additional face-on galaxies ($(b/a) \geq 0.8$, or $i \leq
38^{\circ}$).

We then find the mass contained within the observed limit of each
galaxy to be
\begin{equation}
\mbox{${\cal M}_{\rm dyn}$} = \left(\frac{v_{\rm circ}^{2}\ \mbox{$r_{\rm max}$}}{G}\right)
\end{equation}
and the orbital time to be
\begin{equation}
\mbox{$t_{\rm orb}$} = \left(\frac{2\pi\ \mbox{$r_{\rm max}$}}{v_{\rm circ}}\right).
\label{e:torb}
\end{equation}

\mbox{${\cal M}_{\rm dyn}$}\ is evaluated using the radius at which we truncate our light
profiles, \mbox{$r_{\rm max}$} . This radius is found using only the optical light of
the galaxy, therefore matter located outside it will not be included.
\mbox{${\cal M}_{\rm dyn}$}\ is not a true total mass; rather, it is a crude estimate of the
mass contained within the optical radius.  Since {\sc Hi}\ typically
extends beyond \mbox{$r_{\rm max}$}\ with a flat rotation curve, the total mass
(including dark matter) is larger, and our \mbox{${\cal M}_{\rm dyn}$}\ estimates are thus
lower limits to the total mass.  \mbox{${\cal M}_{\rm dyn}$}\ is compared with our {\sc HiPASS}
-derived values of \mbox{${\cal M}_{\rm HI}$}\ in Fig.~\ref{f:massscatter}a, and with our
observed $R$ band luminosity, $L_R$, in Fig.~\ref{f:massscatter}b.
After excluding galaxies as explained above and fitting with a robust
least absolute deviation fit, we find:
\begin{eqnarray}
\log(\mbox{${\cal M}_{\rm dyn}$}) =& 1.26\ \log(\mbox{${\cal M}_{\rm HI}$}) &-\ 1.36 \pm 0.37 \label{e:mdynvsmhi}\\
\log(\mbox{${\cal M}_{\rm dyn}$}) =& 0.79\ \log(L_{R}) &+\ 2.83 \pm 0.36 \label{e:mdynvslr}
\end{eqnarray}
Eq.~\ref{e:mdynvsmhi} implies that the fraction of \mbox{${\cal M}_{\rm dyn}$}\ made of {\sc Hi}\
is typically more than six times higher for our lowest {\sc Hi}\ masses
(\mbox{${\cal M}_{\rm HI}$}\ $\approx 10^{7.5}$ \mbox{${\cal M}_\odot$} ) than it is for those at our
high-mass extreme (\mbox{${\cal M}_{\rm HI}$}\ $\approx 10^{10.6}$ \mbox{${\cal M}_\odot$} ).  Likewise, if we
were to assume that $\cal M$/$L$ remains constant over our range of
dynamical masses, Eq.~\ref{e:mdynvslr} would imply that the visible
mass fraction is up to 10 times larger for our most massive galaxies
as for our least massive.  For any further equations requiring \mbox{${\cal M}_{\rm dyn}$} ,
we use the fit of Eq.~\ref{e:mdynvslr} to set the dynamical mass of
those galaxies exluded from our fit because of inclination or multiple
\Hline{\mbox{$\alpha$}}\ sources.  While Eq.~\ref{e:mdynvslr} is reminiscent of the
classic relations of \citet{b:tully77}, our \mbox{${\cal M}_{\rm dyn}$}\ depends both on the
width of the {\sc Hi}\ velocity profile and the optical radius, \mbox{$r_{\rm max}$}.  As
a result, our result should not be directly compared to the
Tully-Fisher relationship, $\mbox{${\cal M}_\star$} \sim v_{\rm circ}^{3.1}$.

We are primarily interested in \mbox{$t_{\rm orb}$}\ because it lets us address the
redshift evolution of SFR in conjunction with the star formation law
of \citet{b:kennicutt98}, which states that the global star formation
law of galaxies is equivalent to galaxies converting 21\%\ of their
ISM mass within one orbital time \mbox{$t_{\rm orb}$}\ evaluated at the radius where
the {\sc Hii}\ region distribution is truncated, \mbox{$r_{\rm HII}$} .  We have not
measured \mbox{$r_{\rm HII}$}\, as such, for our sample.  However, Paper I provides
two radii that should bracket this: $r_{90}(\Hline{\mbox{$\alpha$}})$, the radius
enclosing 90\%\ of the \Hline{\mbox{$\alpha$}}\ flux, and \mbox{$r_{\rm max}$}; for most sources,
\mbox{$r_{\rm max}$}\ contains all the discernable emission in both $R$ and \Hline{\mbox{$\alpha$}} .
We evaluate the orbital time, \mbox{$t_{\rm orb}$} , at these two radii.  As with our
determination of \mbox{${\cal M}_{\rm dyn}$}, \mbox{$t_{\rm orb}$}\ is ill-determined for galaxies which
have $i \leq 38^{\circ}$ or are in multiple ELG systems.  In those
cases we estimate $\log(\mbox{$t_{\rm orb}$})$ from $L_{R}$ using least absolute
deviation fits, similar to Eq.~\ref{e:mdynvslr}:
\begin{eqnarray}
\log(\mbox{$t_{\rm orb}$}(\mbox{$r_{\rm max}$})) &=& 0.099\ \log(L_{R}) - 1.04 \pm 0.20 \\
\log(\mbox{$t_{\rm orb}$}(r_{90}(\Hline{\mbox{$\alpha$}}))) &=& 0.106\ \log(L_{R}) - 1.35 \pm 0.23
\end{eqnarray}
These fits are then used to set orbital times for the excluded
galaxies, in the same manner as for \mbox{${\cal M}_{\rm dyn}$}.

As with {\sc Hi}\ mass, we use \mbox{${\cal M}_{\rm dyn}$}\ to find the local dynamical mass
density, $\rho_{\rm dyn}$, with Eq.~\ref{e:rhox2}.  We find
\begin{equation}
\rho_{\rm dyn} = 9.3\ ^{+1.4}_{-1.6} \times 10^8\ h_{70}\ \mbox{${\cal M}_\odot$}\
\rm Mpc^{-3}.
\end{equation}
Again, we emphasize that this is only the mass density of the local
universe residing within the optical radii of {\sc Hi} -rich galaxies.  Of
this density, 15\%\ is found in galaxies with multiple \Hline{\mbox{$\alpha$}}\
sources, while an additional 34\%\ is found in the face-on galaxies
excluded from Eq.~\ref{e:mdynvslr}.  Comparing to our {\sc Hi}\ mass
density, \rhoHI , we estimate that 5.6\%\ of the dynamical mass of
local galaxies consists of neutral hydrogen in stars.

\section{Discussion} \label{s:disc}

\subsection{Completeness} \label{s:complete}

One of our goals is to determine how representative an {\sc Hi} -selected
sample is.  To do this, we compare the $R$ band luminosity density
$l_R'$ and dynamical mass density $\rho_{\rm dyn}$ derived from an {\sc Hi}
-selected sample to those derived from more ``complete'' samples, such
as the full SDSS sample set.

Our uncorrected value for $l_R'$, $4.4 \pm 0.7 \times 10^{37}\ h_{70}$
erg s$^{-1}$ {\rm \AA}$^{-1}$ Mpc$^{-3}$, compares well to the SDSS-derived
$^{0.1}r$ and $^{0.1}i$ band values of \citet{b:blanton03}, $6.17$ and
$6.70 \times 10^{37}\ h_{70}$ erg s$^{-1}$ {\rm \AA}$^{-1}$ Mpc$^{-3}$
respectively.  Interpolating between these two bands by wavelength
gives $l_R' \approx 6.30 \times 10^{37}\ h_{70}$ erg s$^{-1}$
{\rm \AA}$^{-1}$ Mpc$^{-3}$ for the Sloan survey, which we will use as our
``cosmic'' $R$ band density.  Our estimated $l_R'$ is approximately
70\% of this value; therefore, the majority of the stars comprising
the derived SDSS $R$ band luminosity density are located in galaxies
containing measurable quantities of {\sc Hi} .  If we were to assume that
our $l'_{R}$ is low due to gas-poor galaxies (ellipticals) being
absent from our sample, while our \mbox{$l'_{\rm H\alpha}$}\ is complete, then we can
derive a corrected ``cosmic'' $EW(\Hline{\mbox{$\alpha$}}) \approx\ \mbox{$l_{\rm H\alpha}$}/(l_{R}/0.70)
= 20.3\ ^{+5.9}_{-3.5}\ ${\rm \AA} .  This reduces the Salpeter-derived
birthrate parameter to $b \approx 0.16\ ^{+0.07}_{-0.03}$.

Note that the SR1 sample size implies that certain rare types of
galaxies simply won't be represented in these results.  For instance,
ultraluminous IR galaxies \citep[ULIRGs, defined as $L_{IR} \geq
10^{12} \mbox{$L_\odot$}$,][]{b:sanders96} are rare enough that the volume
contained within the {\sc HiPASS}\ redshift and declination limits would
only include roughly one ULIRG.  As the sample used in this paper
includes only 92 out of the 4315 {\sc HiPASS}\ targets, it was extremely
unlikely that any ULIRGs would be included in our observations.

When our dynamical mass density $\rho_{\rm dyn}$ is expressed as a
fraction of the critical Einstein-de Sitter mass density ($\rho_{crit}
= 1.36 \times 10^{11}\ h^{2}_{70}\ \mbox{${\cal M}_\odot$}\ $Mpc$^{-3}$), we find
$\Omega_{\rm dyn} = 0.0068\ h^{-1}_{70}$, or 2.3\% of $\Omega_{0}$ in
the concordance cosmology.  For comparison, \citet{b:cole01} estimates
the the $z \approx 0$ mass density of stars, $\Omega_{\rm stars}$, to
be between 0.0029 (from an IR luminosity function) and 0.0020 (from
star formation tracers).  Similarly, the {\sc Hi}\ Mass Function of
\citet{b:zwaan05} gives the local {\sc Hi}\ mass density to be $\approx
0.0004\ h^{-1}_{70}$, which would imply a gas density on the order of
$\Omega_{\rm gas} = 0.0009\ h^{-1}_{70}$ using the same logic as in
Section~\ref{s:tgas}.  As a result, our $\rho_{\rm dyn}$ implies that
around half of the mass located within the optical disks of nearby
galaxies consists of gas and stars, with the remainder most likely
consisting of dark matter.

This comparison must be viewed with some caution; our $\rho_{\rm
dyn}$ is a crude estimate of all matter within the optical radii of
{\sc Hi} -selected galaxies, including substantial quantities of dark
matter.  However, it excludes galactic gas (especially {\sc Hi} ) extending
beyond the optically-selected \mbox{$r_{\rm max}$} , and also samples little of the
hot plasma which resides in galaxy clusters and the intergalactic
medium.  We also do not sample any of the mass in {\sc Hi} -free galaxies,
predominantly early-type galaxies.  This comparison only shows that
the mass we sample is comparable to the baryon content of the local
star-forming galaxies, and that the ratio of baryonic matter to dark
matter within these galaxies is substantially different than that of
the universe as a whole.

\subsection{\SFRD\ and \mbox{$l_{\rm H\alpha}$}\ in context}

To compare our value of \SFRD\ to those found by other studies, we
refer to \citet{b:hopkins04}, which compiled the results of 33 other
star formation rate density papers and corrected each to a uniform
$\Lambda$CDM cosmology, a \citet{b:salpeter55} IMF, and with a Hubble
constant of $H_{0}$ = 70\ km s$^{-1}$ Mpc$^{-1}$, $\Omega_{0}$ = 0.3,
and $\Omega_{\Lambda}$= 0.7.  We also include the IR-derived \SFRDz\
data of \citet{b:perez05}.  The results before internal extinction
correction are plotted in Fig.~\ref{f:madau}a, while the corrected
values are plotted in Fig.~\ref{f:madau}b.

In Paper I we assert that SINGG is inherently less biased than other
surveys, due to selecting sources by ISM content at radio wavelengths.
Objective-prism surveys limit their samples by equivalent width and
surface brightness, while an {\sc Hi} -selected sample can include diffuse
sources or those with little star formation.  If this is the case, we
should expect to recover more star formation in the local universe.
However, there are many steps involved in turning measured fluxes into
luminosity density estimates; since techniques and assumptions vary
between groups it is important to compare our results in as consistent
a form as possible.  Few previous studies present actual \Hline{\mbox{$\alpha$}}\
luminosity densities, and so our primary comparison will be between
values of \SFRDpz\ corrected to our adopted IMF and extrapolated to $z
= 0$.  While some studies have only provided extinction-corrected
\SFRDz\ estimates, in most cases we are able to work backwards using
published corrections to derive \SFRDpz\ for each.

When the surveys located at $0.0 \le z \le 1.0$ are linearly fit to a
simple \SFRDz\ = \SFRDo\ $(1+z)^{\beta}$ relationship, we find $\beta
= 3.00 \pm 0.13$, which matches well with the $\beta = 3.2\
^{+0.7}_{-0.2}$ of \citet{b:lefloch05} and the $\beta = 3.1 \pm 0.5$
of \citet{b:perez05}.  As a result, we will use this proportionality
to extrapolate the star formation rate densities of low-redshift
surveys to $z \sim 0$; the results are given in Table~\ref{t:sfrd}.

The relative positions of the data points in Fig.~\ref{f:madau}a,b
change due to the internal extinction correction.  While the spread in
points noticeably decreases between the two figures, we cannot claim
to measure the highest corrected \SFRDo .  This is primarily due to
our relatively mild extinction correction of 0.82 magnitudes, while
the other samples noted in Table~\ref{t:sfrd} have corrections ranging
from 1.0 to 1.4 mag.  Although mild, our correction correlates well
with unpublished work from the 2dF Galaxy Redshift Survey
\citep{b:folkes99}, which used the Balmer decrement to estimate the
\Hline{\mbox{$\alpha$}}\ extinction of 160,000 line emitters; the typical value was
found to be approximately 0.8 magnitudes.  This discrepancy in
$A_{int}(\Hline{\mbox{$\alpha$}})$ is most likely caused by the same luminosity bias
mentioned above.

Even with a value of \SFRD\ comparable to other surveys, it is too
early to declare a consensus because of the differences between the
samples.  For instance, we assert that the objective-prism selection
method results in a large, consistent bias against non-starburst
galaxies.  Here we define starburst galaxies as those with \Hline{\mbox{$\alpha$}}\
equivalent widths within their half-light radii of $EW'_{50}(\Hline{\mbox{$\alpha$}})
\geq 50 ${\rm \AA} , without correction for internal extinction.  According
to \citet{b:heckman98}, starbursts are estimated to comprise 15 --
20\% of the population of the local universe.  In the UCM
spectroscopic survey, 72\% of the sample consists of galaxies with
equivalent widths above this threshold.  For SINGG SR1, 16 out of the
110 \Hline{\mbox{$\alpha$}}\ sources (14.5\%) met this criterion; these sources are
collectively responsible for 25\%\ of our final star formation rate
density.  If we assume that the {\sc Hi} -selected SINGG sample set is not
significantly biased towards or against these galaxies, emission
line-selected surveys (such as UCM) should be significantly
underestimating the value of \SFRD\ due to underrepresentation of the
non-starburst galaxies which appear to produce the majority of the
star formation in the local universe.

\subsection{Breakdown of luminosity density and \SFRD} \label{s:cumuhists}

Fig.~\ref{f:moreplots} shows the observed contributions to the $R$
band and \Hline{\mbox{$\alpha$}}\ luminosity densities as a function of a variety of
different quantities; this allows a comparison between our sample and
other local samples of galaxies.  Table~\ref{t:morestat} gives the
values of each parameter at the 10$^{th}$, 25$^{th}$, 50$^{th}$,
75$^{th}$, and 90$^{th}$ percentiles of each luminosity density.  In
all cases, extinction and [{\sc Nii}] corrections have been applied as
appropriate.

Plot (a) relates the luminosity densities to the {\sc HiPASS}\ {\sc Hi}\ mass.
We find that 72\% of $l_{R}$ and 70\% of \mbox{$l_{\rm H\alpha}$}\ are found in galaxies
with {\sc Hi}\ masses below our value of \mbox{${\cal M}_\star$}({\sc Hi}) .  However, 77\% of
\rhoHI\ falls below this value, so the stellar luminosity density and
\SFRD\ are slightly weighted towards higher {\sc Hi}\ masses than \rhoHI .

Plot (b) relates the luminosity densities to the dynamical mass, with
the fit from Fig.~\ref{f:massscatter}b used to estimate dynamical
masses for those galaxies with multiple sources or low axial ratios.
Galaxies with low dynamical masses contribute substantially more to
the \Hline{\mbox{$\alpha$}}\ luminosity than the $R$ band density, and the SINGG
sample extends across a wide range of \mbox{${\cal M}_{\rm dyn}$}\ values.

Plot (c) relates $l$ to the $R$ band luminosity by way of the absolute
magnitude, M$_{R}$.  As expected, galaxies with high $R$ band
luminosities contribute more to $l_R$ than to \mbox{$l_{\rm H\alpha}$}.  For comparison,
the study of \citet{b:brinchmann04} used a stellar mass function with
its knee at $\mbox{${\cal M}_\star$} = 10^{10.95} \mbox{${\cal M}_\odot$}$; as this is a stellar mass
(not simply {\sc Hi}\ mass), it should be approximately proportional to the
$R$ band luminosity.  The 10$^{th}$ and 50$^{th}$ percentiles for
\mbox{$l_{\rm H\alpha}$}\ in \citet{b:brinchmann04} were quoted as $\log(\mbox{${\cal M}_\star$}) = 9.0$
and $10.3$, respectively, a difference of 1.3 dex.  For comparison,
the corresponding SINGG values of M$_{R}$ for those percentiles differ
by 4.1 magnitudes (1.7 dex), as shown in Table~\ref{t:morestat}.

Plot (d) relates $l$ to the star formation rate of each galaxy
(directly proportional to \Hline{\mbox{$\alpha$}}\ luminosity, as shown in
Eq.~\ref{e:sfr}.)  As expected, galaxies with high \Hline{\mbox{$\alpha$}}\
luminosities contribute more to \mbox{$l_{\rm H\alpha}$}\ than $l_R$.  However, the
fraction of \Hline{\mbox{$\alpha$}}\ luminosity density caused by luminous galaxies in
SINGG is significantly lower than in other surveys.  Only 12.2\% of
the SINGG \mbox{$l_{\rm H\alpha}$}\ is caused by galaxies with observed star formation
rates greater than 10.0 \mbox{${\cal M}_\odot$}\ yr$^{-1}$ once extinction corrections
have been applied.  For comparison, we integrate the luminosity
functions quoted by other surveys; the UCM study of
\citet{b:gallego95} has 26.5\% of its \mbox{$l_{\rm H\alpha}$}\ come from galaxies above
this threshold, while \citet{b:tresse98} has 23.1\%.  At the extreme
cases, \citet{b:sullivan00} has only 9.3\%, while \citet{b:perez03}
has 51.4\% of its luminosity density come from galaxies with star
formation rates above 10.0 \mbox{${\cal M}_\odot$}\ yr$^{-1}$.  This further illustrates
that the apparent consensus in \SFRD\ may hide important differences
in the various surveys of local star formation.

Plot (e) relates $l$ to the narrow-band internal dust extinction
correction, A(\Hline{\mbox{$\alpha$}}).  While the extinction correction in our
overall \Hline{\mbox{$\alpha$}}\ luminosity density is 0.82 magnitudes, only 37\% of
the $R$ density comes from galaxies with smaller values, compared to
47\% of the \Hline{\mbox{$\alpha$}}\ density.  That is, $l_{R}$ is weighted towards
the more luminous galaxies, which have higher internal extinctions.

Plots (f) and (g) relate $l$ to the effective (50\%\ flux) radii found
in the $R$ and \Hline{\mbox{$\alpha$}}\ images, while plot (h) relates $l$ to the
ratio of these two radii.  Again, these plots support the
``downsizing'' model of star formation; galaxies with large radii tend
to contribute more to the $R$ band luminosity density than the
\Hline{\mbox{$\alpha$}}\ density, while galaxies with small radii contribute
substantially more to \mbox{$l_{\rm H\alpha}$}\ than $l_{R}$.  The luminosity density
contributions are evenly distributed over our range of
($r_{e}(\Hline{\mbox{$\alpha$}})/r_{e}(R)$).  Galaxies with centrally-located star
formation ($r_{e}(\Hline{\mbox{$\alpha$}})/r_{e}(R) \le 1.0$, suggestive of
starbursts) do not dominate the luminosity densities; this contradicts
what has been observed in other studies, such as the UCM survey of
\citet{b:gallego95}.

In all of the above plots, the smaller, less massive galaxies
contribute substantially more to the SINGG \Hline{\mbox{$\alpha$}}\ luminosity density
(and by extension, \SFRD ) than they do to the $R$ band density.  This
reinforces the ``downsizing'' model, where star formation activity
shifts to smaller galaxies over time \citep{b:cowie96}.

Plot (i) relates $l$ to the ratio of the 90\% flux radius to the
half-light radius in the $R$ band.  The inverse of this ratio
(referred to as the ``concentration index'') has been examined by
\citet{b:shimasaku01} using SDSS data.  In that work, it was estimated
that the boundary between bulge-dominated ``early-type'' and
disk-dominated ``late-type'' galaxies occurred at a ratio of
$r_{90}(r')/r_{e}(r') = 3.03$.  Given that definition, we estimate
that 71\% of our $R$ density ((3.2\ $\pm\ 0.5) \times 10^{37} h_{70}$\
erg s$^{-1}$\ {\rm \AA}$^{-1}$\ Mpc$^{-3}$ before extinction correction)
and 82\% of our \Hline{\mbox{$\alpha$}}\ density can be attributed to ``late-type''
galaxies, assuming the $r$-derived boundary does not change when
shifted to our $R$ band.  For comparison, \citet{b:hogg02} find that
38\% of the SDSS $^{0.1}i$ band luminosity density comes from
``red-type'' (assumed to be bulge-dominated early-type) galaxies,
meaning that a total of $4.1 \times 10^{37}\ h_{70}$ erg s$^{-1}\
${\rm \AA}$^{-1}$\ Mpc$^{-3}$ can be attributed to late-type galaxies.  As
their definition of red galaxies was conservative, this percentage
should include some early-type galaxies.  Likewise, \citet{b:baldry04}
fit a bimodal distribution to observed galaxy colors to determine that
58\% of the SDSS $^{0.1}r$ band luminosity density comes from blue
galaxies (for a density of $3.6 \times 10^{37}\ h_{70}$ erg s$^{-1}$
{\rm \AA}$^{-1}$\ Mpc$^{-3}$).  As a result, while the SINGG survey recovers
around 70\% of the SDSS $l_{R}$, we recover a larger fraction
(80 -- 90\%) of the luminosity density from late-type galaxies.

Plot (j) shows the dependence of $l$ on \Hline{\mbox{$\alpha$}}\ equivalent width.
The \SFRD\ derived from the UCM spectroscopic survey
\citep{b:gallego95} uses only galaxies with equivalent widths larger
than 10 {\rm \AA} .  According to our data, 24.1\% of the local
extinction-corrected $R$ band luminosity density and 4.5\% of the
corrected \Hline{\mbox{$\alpha$}}\ luminosity density come from galaxies with
equivalent widths below this threshold.

Plots (k) and (l) relate $l$ to surface brightnesses, $\mu_{e}(R)$ and
$\Sigma_{e}$(\Hline{\mbox{$\alpha$}}).  As expected, galaxies with high \Hline{\mbox{$\alpha$}}\
surface brightnesses (i.e., starbursts) contribute a much larger
fraction of \mbox{$l_{\rm H\alpha}$}\ than of $l_R$.  For comparison, the SDSS-derived
sample of \citet{b:blanton05} has a surface brightness limit of
$\mu_{e}(R)$ = 24.0 ABmag arcsec$^{-2}$; 1.1\%\ of our $l_R$ and
1.2\%\ of \mbox{$l_{\rm H\alpha}$}\ come from galaxies below this cutoff.

\subsection{Recent redshift evolution in \SFRDz} \label{s:evolution}

Fig.~\ref{f:madau}b shows that the \SFRDz\ has declined by
approximately a factor of ten from $z \sim 1$ to the present.
Specifically, fitting the internal dust corrected data with $z \leq 1$
with a robust (outlier resistant) linear fit
\begin{equation}
\log(\SFRDz) = \log(\SFRD) + \eta z
\label{e:slope}
\end{equation}
yields $\log(\SFRD\ [\mbox{${\cal M}_\odot$}\ $yr$^{-1}\ $Mpc$^{-3}]) = -1.73$ and $\eta =
1.02$ dex per redshift.  We can estimate the systematic uncertainties
in this fit by categorizing the \SFRDz\ data by the star formation
tracer used in each measurement: (1) optical emission lines; (2)
ultraviolet continuum; and (3) FIR or radio continuum.  This yields
$\log(\SFRD) = -1.80,\ -1.53,\ -1.94$, and $\eta = 1.05,\ 0.43,\
1.37$\ for survey types 1, 2, and 3, respectively.  This suggests that
the uncertainties in the zeropoint and slope are 0.20 and 0.47 dex,
respectively.

What causes the decrease in \SFRDz\ with cosmic time?  Recently,
\citet{b:kauffmann04} presented a model of the recent star formation
history of galaxies in the local universe that provides a useful
context to answering this question.  In their model, star formation
events occur when galaxies merge; subsequently, the SFR inside the
galaxy decays according to a prescription similar in nature to the
star formation laws of \citet{b:kennicutt98} and \citet{b:dopita94}.
They use a high-resolution Cold Dark Matter (CDM) simulation, identify
galaxy mergers with CDM halo mergers, and parameterize the form of
their star formation law by the average stellar mass density.
Essentially, the physics of their model can be separated into CDM
effects (the merger of halos), and baryonic physics (the star
formation law).  We can then rephrase the question above: is the
decrease in \SFRDz\ with cosmic time driven by CDM or baryonic
physics?  Are we seeing a recent decrease in the merger rate
of halos?  Or, are we seeing the secular decay of the SFR after a much
earlier decrease in the halo merger rate?

The dynamical information on our sample provided by the {\sc Hi}\ line
widths provides a means to address this question.  The orbital time,
\mbox{$t_{\rm orb}$} , has been evaluated at two radii, $r_{90}(\Hline{\mbox{$\alpha$}})$ and \mbox{$r_{\rm max}$} ,
as explained in Section~\ref{s:dyn}.  Using the same methods as those
in Section~\ref{s:cumuhists}, we find that the 25\%, median, and 75\%\
contributions to \mbox{$l_{\rm H\alpha}$}\ (and, by extension, \SFRD ) in our sample
occur for \mbox{$t_{\rm orb}$}\ = 0.30, 0.57, 0.60 Gyr when evaluated at
$r_{90}(\Hline{\mbox{$\alpha$}})$ and 0.56, 1.00, 1.03 when evaluated at \mbox{$r_{\rm max}$} .

We can use the orbital times to estimate the change in SFR with
redshift for the galaxies in our sample obeying Eq.~\ref{e:slope}.  If
we assume that the star formation law remains invariant over this
timescale, then consumption of 21\%\ of the ISM is equivalent to a
21\%\ decrease in the SFR over \mbox{$t_{\rm orb}$}\ \citep{b:kennicutt98}.
Translating \mbox{$t_{\rm orb}$}\ to a look back time, the logarithmic change in SFR
is given by
\begin{equation}
\frac{\delta\log(\rm SFR [\mbox{${\cal M}_\odot$}\ yr^{-1}])}{\delta z} \approx
\frac{1.43\ h_{70}}{\mbox{$t_{\rm orb}$}\ [\rm Gyr]}
\end{equation}
in the same units as the slope $\eta$ in Eq.~\ref{e:slope}.  The
median \mbox{$t_{\rm orb}$}\ translates to $\delta\log(\rm SFR)/\delta z = $ 2.5, 1.4
as defined by $r_{90}(\Hline{\mbox{$\alpha$}})$ and \mbox{$r_{\rm max}$} , while the interquartile
ranges are 4.8 -- 2.4 and 2.6 -- 1.4, respectively.  We see that the
SFR of the galaxies in our sample will decay over a wide range of
timescales.  However, a galaxy with \mbox{$t_{\rm orb}$}\ similar to the median
galaxy in our sample will have its star formation decay at a rate
similar to that observed in the universe as a whole.

\section{Conclusions} \label{s:concl}

Our measurement of the local star formation rate density, $\log(\SFRD\
[\mbox{${\cal M}_\odot$}\ \mbox{\rm yr}^{-1}\ \mbox{\rm Mpc}^{-3}]) = -1.80\ +
\log(h_{70})$, is similar to those of most previous $z \sim 0$
studies, as shown in Table~\ref{t:sfrd}.  When compared to the results
of other surveys, this agrees with the consensus that the star
formation rate density has decreased by an order of magnitude from a
redshift of $z \sim 1$ to the present.  While a consensus in \SFRD\
appears to be emerging, this may be largely illusory.  There remain
significant differences between the various surveys in terms of
extinction corrections and the contributions of various types of
galaxies to the totals.  Systematic effects are large and need to be
accounted for before a true consensus can emerge.

The decreasing \SFRDz\ with cosmic time has important implications for
models of galaxy evolution, as this trend suggests a shift from the
faster ``burst'' star formation process to the slower ``quiescent''
process, with the greater fraction of the total star formation
occurring in non-starburst galaxies.  This is supported by the results
presented in Section~\ref{s:evolution}, which suggest that the
decrease in \SFRDz\ with cosmic time is largely driven by the secular
decay in SFR after earlier accretion events.  That is, the current
evolution in \SFRDz\ is largely driven by interior baryon physics
rather than the merger of CDM dominated halos.  This interpretation is
consistent with the relatively small fraction of multiple ELG systems
and targets that look like recent mergers (15 out of 93 {\sc HiPASS}\
pointings included in SR1, see Paper I), as well as the work of
\citet{b:bell05}.  In contrast, at $z > 1$ field galaxies tend to have
a disturbed morphology suggesting a higher fraction of interacting and
merging systems and very few regular disk galaxies can be discerned.
It is tempting to speculate that $z \sim 1$ represents the epoch where
cosmic evolution transitions from being driven largely by CDM
interactions to being driven by the internal self-regulation of star
formation.

\acknowledgments

Partial finantial support for this work has been provided by NASA
grant NAG5-13083 (LTSA program) to G.R.\ Meurer, as well as the
Director's Discretionary Research Fund of the Space Telescope Science
Institute.  We would like to thank the many people whose feedback
helped in the development of this paper, including Jes\'us Gallego,
Pablo P\'erez-Gonz\'alez, Joe Helmboldt, and Jarle Brinchmann.  We
would also like to thank the National Optical Astronomy Observatory
(NOAO) for their support, especially the staff of the Cerro Tololo
Inter-American Observatory.

redpajama_set_name: RedPajamaArXiv