<p>Yes, the main processes that create elements heavier than Helium all involve stars:  Some elements are formed in stellar cores, some in neutron star collisions (but you can only get neutron stars from regular stars), some are formed in supernovae, some by neutron capture. All these processes require stars at some point.</p>
<p>So if a galaxy is becoming more metal-rich, that would mean that star formation is occurring. In particular, large stars are forming and dying.</p>

CC BY-SA 4.0
2022-08-08T09:57:42.587Z
2022-08-08T09:57:42.587Z
James K
<p>High metallicity indicates the presence of hot, massive stars - which implies it's a site where star formation exists <em>actively</em> - which in turn means there's a lot of gas left for massive stars to sustain numerous blue stars at once.</p>
<p>Moreover, any element past Helium in the periodic table is considered a &quot;metal&quot; here by astronomers. So lithium, oxygen (chemically non-metals) and likewise are all assumed &quot;metals&quot;. The point of this is to separate stars that don't form lots of oxygen, which tend to be low mass stars (which shine red strongly than blue, and appears red) from the high mass stars (which as I stated earlier, shines blue). A low star forming galaxy would be dominated by low metallicity, looks red, and have exhausted available gas and begins forming low mass stars instead of high mass.</p>
<p>So in short, metallicity indicates how young and massive the stars in it are, which in turn can shed light into the galaxy's evolution and age.</p>

CC BY-SA 4.0
2022-08-09T15:44:22.063Z
Your answer seems very similar to the other existing answer. Is there anything that differentiates yours?
WarpPrime
CC BY-SA 4.0
2022-08-09T15:44:25.753Z
Your answer could be improved with additional supporting information. Please [edit] to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers [in the help center](/help/how-to-answer).
Community
CC BY-SA 4.0
2022-08-09T15:52:22.463Z
@fasterthanlight I've added a whole paragraph now.
Karthik
CC BY-SA 4.0
2022-08-09T16:20:28.430Z
Do you have any materials that you could cite?
WarpPrime
CC BY-SA 4.0
2022-08-09T15:24:14.310Z
2022-08-09T15:51:57.480Z
2022-08-09T15:51:57.480Z
Karthik
<p>For example, if there is a galaxy and its metallicity increase or decrease from high redshift to present day (We can see it from simulation like TNG or EAGLE). What physical process we can know?</p>
<p>Metallicity defined as (Mz/Mtot, where Z = any element above He)</p>
<p>My answer is that if metallicity of a galaxy increase, that means this galaxy is star-forming because new stars are thought to be with higher metallicity. I don't know if it is right.</p>

CC BY-SA 4.0
2022-08-07T18:57:11.707Z
Question:  what do you mean by "its metallicity increase or decrease from high redshift to present day"  We can only observe a galaxy at its current redshift. We can never observe a galaxy "in the present day" except for the Milky way. We can't observe the evolution of a galaxy, as we don't have billions of years.  We can observe different galaxies at different redshifts.
James K
CC BY-SA 4.0
2022-08-08T07:44:27.717Z
We can do it from simulation
Jinning Liang
CC BY-SA 4.0
2022-08-08T07:46:54.610Z
You should mention some details about your simulation in the question.
James K
CC BY-SA 4.0
2022-08-08T16:05:02.407Z
"My answer" suggests that you are asking for someone to provide an answer for an exam or assessment question.
ProfRob
<galaxy><cosmology><stellar-evolution><metallicity><galactic-evolution>
What physical process can Metallicity(Z) of a galaxy tell us?
Jinning Liang
# What physical process can Metallicity(Z) of a galaxy tell us?

(Asked by: username_0 on 2022-08-07)

For example, if there is a galaxy and its metallicity increase or decrease from high redshift to present day (We can see it from simulation like TNG or EAGLE). What physical process we can know?

Metallicity defined as (Mz/Mtot, where Z = any element above He)

My answer is that if metallicity of a galaxy increase, that means this galaxy is star-forming because new stars are thought to be with higher metallicity. I don't know if it is right.

**Tags:** galaxy, cosmology, stellar-evolution, metallicity, galactic-evolution
> **Comments:**
> **username_1**: Question:  what do you mean by "its metallicity increase or decrease from high redshift to present day"  We can only observe a galaxy at its current redshift. We can never observe a galaxy "in the present day" except for the Milky way. We can't observe the evolution of a galaxy, as we don't have billions of years.  We can observe different galaxies at different redshifts.  
> **username_0**: We can do it from simulation  
> **username_1**: You should mention some details about your simulation in the question.  
> **username_2**: "My answer" suggests that you are asking for someone to provide an answer for an exam or assessment question.  

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## 2 answers

### Answer by username_1 on 2022-08-08. Score: 2

Yes, the main processes that create elements heavier than Helium all involve stars: Some elements are formed in stellar cores, some in neutron star collisions (but you can only get neutron stars from regular stars), some are formed in supernovae, some by neutron capture. All these processes require stars at some point.

So if a galaxy is becoming more metal-rich, that would mean that star formation is occurring. In particular, large stars are forming and dying.


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### Answer by username_3 on 2022-08-09. Score: -1

High metallicity indicates the presence of hot, massive stars - which implies it's a site where star formation exists *actively* - which in turn means there's a lot of gas left for massive stars to sustain numerous blue stars at once.

Moreover, any element past Helium in the periodic table is considered a "metal" here by astronomers. So lithium, oxygen (chemically non-metals) and likewise are all assumed "metals". The point of this is to separate stars that don't form lots of oxygen, which tend to be low mass stars (which shine red strongly than blue, and appears red) from the high mass stars (which as I stated earlier, shines blue). A low star forming galaxy would be dominated by low metallicity, looks red, and have exhausted available gas and begins forming low mass stars instead of high mass.

So in short, metallicity indicates how young and massive the stars in it are, which in turn can shed light into the galaxy's evolution and age.

> **Comments:**
> **username_4**: Your answer seems very similar to the other existing answer. Is there anything that differentiates yours?  
> **username_5**: Your answer could be improved with additional supporting information. Please [edit] to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers [in the help center](/help/how-to-answer).  
> **username_3**: @fasterthanlight I've added a whole paragraph now.  
> **username_4**: Do you have any materials that you could cite?  

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