European Astronomical Society Publications Series (2)
Symposium - International Astronomical Union (2)
News from z ~ 6 − 10 galaxy candidates found behind gravitational lensing clusters
D. Schaerer, A. Hempel, R. Pello, E. Egami, J. Richard, J.-P. Kneib, M. Wise
Published online by Cambridge University Press: 01 August 2006, p. 425
Following up on the detailed results from our searches for z~ 6–10 galaxies using gravitional lensing clusters descrived in Richard et al. (2006), we have obtained new observations, which are presented here. For a general overview of the project see Schaerer et al. (2006). First, deep HST/ACS observations in the z-band confirm 17 out of 18 high redshift candidates as optical drop-out objects; the remaining object appears faint and star-like. Second, Spitzer/IRAC images at 3.6, 4.5, 5.8 and 8.0 μm have been obtained. 11 out of 18 candidates are in "free", uncominated regions. These 11 high-z candidates are undetected, with upper limits which are compatible with their SED if these objects are blue star-forming galaxies at high redshift (see Fig. 1). In conclusion, our new observations corroborate so far the high-z nature of the majority of the candidates.
The Strong Transformation of Spiral Galaxies Infalling into Massive Clusters at z~ 0.2
L. Cortese, D. Marcillac, J. Richard, H. Bravo-Alfaro, J.-P. Kneib, G. Rieke, G. Covone, E. Egami, J. Rigby, O. Czoske, J. Davies
We report the discovery of two peculiar galaxies infalling into the lensing clusters of galaxies Abell 1689 (z~ 0.18) and 2667 (z~ 0.23). Hubble Space Telescope images show extraordinary trails composed by blue bright knots and stellar streams associated with both these systems, an ~L* and ~0.1L* galaxy. Under the combined action of tidal interaction with the cluster potential and of ram pressure by the intra-cluster medium the morphologies and star formation histories of these two galaxies are strongly perturbed. While in the massive system tidal interactions are the dominant effect and are able to produce a sinking of gas towards the galaxy center triggering a strong burst of star formation and changing galaxy's morphology, in the smaller galaxy the effects of gravitation are reduced by ram pressure stripping which blows away the neutral hydrogen from the galactic disk, quenching the star formation activity and transforming a gas rich late type spiral into quiescent disk dominated early type system. This result is a new additional evidence that galaxy mass represents the main driver of galaxy evolution, even during their dive into the harsh cluster environment and can give additional insights on the origin of S0s and dwarf cluster galaxies.
New constraints on the co-moving star formation rate in the redshift interval 6<z<10
Richard S. Ellis, Daniel P. Stark, Johan Richard, Andrew J. Bunker, Eiichi E. Egami, Jean-Paul Kneib
Journal: Proceedings of the International Astronomical Union / Volume 2 / Issue 14 / August 2006
Recent progress in measuring the optical depth of neutral hydrogen in distant quasars and that of electron scattering of microwave background photons suggests that most of the sources responsible for cosmic re-ionisation probably lie in the redshift interval 6 to 10. We present two new observational results which, together, provide valuable constraints on the contribution from star-forming sources in this redshift interval. First, using a large sample of v-band dropouts with unconfused Spitzer-IRAC detections, we determine the integrated stellar mass density at z = 5. This provides a valuable 'integral constraint' on past star formation. It seems difficult to reconcile the observed stellar mass at z = 5 with the low abundance of luminous i-z- and J-band dropouts in deep Hubble Space Telescope data. Accordingly, we explore whether less luminous star-forming sources in the redshift interval 6 to 10 might be the dominant cause of cosmic re-ionization. In the second component of our research, we report on the results of two surveys for weak Lymanα emitters and z- and J-band dropouts highly-magnified by foreground lensing clusters. Although some promising z = 8–9 candidates are found, it seems unlikely that low luminosity sources in this redshift interval can dominate cosmic reionization. If our work is substantiated by more extensive and precise surveys, the bulk of the re-ionizing photons may come from yet earlier sources lying at redshifts z>10.
Relaxed and unrelaxed clusters of galaxies seen in X-rays
G.A. Mamon, F. Combes, C. Deffayet, B. Fort, F. Durret, G.B. Lima Neto, C. Adami, J. Bagchi, G. Covone, W. Forman, J.-P. Kneib, E. Slezak, G. Soucail
Journal: European Astronomical Society Publications Series / Volume 20 / 2006
Published online by Cambridge University Press: 19 May 2006, pp. 183-186
Recent X-ray observations have been showing that the old vision of clusters as peacefully relaxed structures is in most cases absolutely wrong. Coupled with optical and radio observations, these X-ray data show evidence for violent mechanisms. Results based on XMM-Newton gas temperature maps for four clusters will be presented here.
Mass distribution and Dynamical State of Galaxy Clusters in the LZLS Sample
G.A. Mamon, F. Combes, C. Deffayet, B. Fort, L.E. Campusano, E.S. Cypriano, L. Jr. Sodré, J.-P. Kneib
We use the weak gravitational lensing effect to study the mass distribution of a sample of 50 southern Abell clusters (0.05 < z < 0.3) having LX > 5 × 1044 erg s-1 observed with ESO-VLT under uniform sky conditions and subarsecond (0.6'') image quality. Their dynamical equibrium is assesed through comparison of the clusters mass estimates made by weak-lensing, velocity-dispersions and X-ray techniques. So far, for 24 clusters (Cypriano et al. 2004), we find: a) the center of their mass and light distributions are coincident for 77% of the sample; b) the elongations of the fitted mass profiles and of the light of the cD galaxies generally match with each other; c) although most of the clusters are found to be in dynamical equilibrium, those with TX ≥ 8 keV (or σv ≥ 1120 km s-1) are the discordant ones. The preliminary bright arc statistics for our whole sample (LZLS) suggests the presence of a cut-off at z ~ 0.07 which is qualitatively consistent with predictions done in a ΛCDM cosmology (Meneghetti et al. 2003).
The first galaxies: instrument requirements and concept study for OWL
J.-G. Cuby, J.-P. Kneib, F. Hammer, E. Prieto, M. Marteaud, P. Vola, P. Jagourel, P.-E. Blanc, T. Fusco
Journal: Proceedings of the International Astronomical Union / Volume 1 / Issue S232 / November 2005
A highlight science case for the European ELT is: First light - The First Galaxies and the Ionization State of the Early Universe. It aims at understanding the formation and evolution of the first sources of light at the end of the Dark Ages and of the re-ionization of the Universe. The corresponding instrument requirements are: a few tens of integral field units with spatial sampling $\sim$20mas and individual fields of ${\sim}1''$ over a wide field of view of $5' \times 5'$ or larger. Multi-Object Adaptive Optics is required to locally provide significant image quality enhancement. Spectroscopic observations are required in the near IR domain with a spectral resolution of a few 1000. MOMFIS is a preliminary instrument concept designed for OWL around this science case. The instrument concept and preliminary design are presented. Development efforts are estimated, as well as development risks and required R&D activities.
Physical properties of lensed high-redshift galaxies
M. Lemoine-Busserolle, T. Contini, R. Pello, J.-F. Le Borgne, J.-P. Kneib, J. Richard, M. Kissler-Patig, S. F. Sanchez
Journal: Proceedings of the International Astronomical Union / Volume 1 / Issue C199 / March 2005
Published online by Cambridge University Press: 06 October 2005, pp. 439-441
We report the results obtained from optical and near-infrared spectroscopy and also broad-band photometry of lensed low-luminosity galaxies ($1.3\leq z\leq 2.3$) located in the core of lensing clusters. The amplification factor allowed us to obtain the physical properties (SFR, abundance ratios, mass, age of the burst, dust contents, etc.) of star-forming galaxies, 1 to 2 magnitudes fainter than galaxies in a blank field, using the same indicators as in studies of low-redshift galaxies. A part of this study was concentrated on the dynamics of distant lensed galaxies using Integral Field Spectroscopy (SINFONI/VLT science verification programme).
Very High-Redshift Lensed Galaxies
R. Pelló, D. Schaerer, J. Richard, J.- F. Le Borgne, J.- P. Kneib
Journal: Proceedings of the International Astronomical Union / Volume 2004 / Issue IAUS225 / July 2004
Published online by Cambridge University Press: 15 June 2005, pp. 373-386
Print publication: July 2004
We review in this paper the main results recently obtained on the identification and study of very high-z galaxies using lensing clusters as natural gravitational telescopes. We present in detail our pilot survey with ISAAC/VLT, aimed at the detection of z$>7$ sources. Evolutionary synthesis models for extremely metal-poor and PopIII starbursts have been used to derive the observational properties expected for these high-$z$ galaxies, such as expected magnitudes and colors, line fluxes for the main emission lines, etc. These models have allowed to define fairly robust selection criteria to find z$\sim 7-10$ galaxies based on broad-band near-IR photometry in combination with the traditional Lyman drop-out technique. The first results issued from our photometric and spectroscopic survey are discussed, in particular the preliminary confirmation rate, and the global properties of our high-z candidates, including the latest results on the possible z=10.0 candidate A1835-1916. The search efficiency should be significantly improved by the future near-IR multi-object ground-based and space facilities. However, strong lensing clusters remain a factor of $\sim$ 5-10 more efficient than blank fields in the z $\sim$ 7-11 domain, within the FOV of a few arcminutes around the cluster core, for the typical depth required for this survey project.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html
Gravitational Lensing and Deep Infrared Surveys
Leo Metcalfe, B. Mcbreen, J.-P. Kneib, B. Altieri
Journal: Symposium - International Astronomical Union / Volume 204 / 2001
ISO's infrared camera was used to make deep mid-infrared (MIR) images through three gravitationally lensing clusters of galaxies. Observations were made at 7 μm and 15 μm covering more than 50 square arcminutes, with the lensing increasing the sensitivity to background sources significantly.
A large number of MIR sources were detected behind the lenses and provide source counts, corrected for cluster contamination and lensing distortion effects, which exceed by a factor of 10 the expectation from local counts assuming a no-evolution model. The results are consistent with larger-area surveys and the detected population resolves a substantial fraction (of order 60%) of the background MIR radiation intensity into discrete sources.
We discuss the evidence, in large part derived from lensing cluster observations, for overlap of the ISO 15 μm faint galaxy population with the 850 μm submillimetre and the 0.5 to 7 keV X-ray populations. We find that the ISO data shows substantial overlap with both the submillimetre and the X-ray source populations, with roughly 25% of ISO sources being detected at submillimetre wavelengths and a significant number of Chandra X-ray sources being detected in the ISO data.
Optical Imaging Of B1422+231 – Prospects For Determining the Hubble Constant
J. Hjorth, A.O. Jaunsen, A.R. Patnaik, J.-P. Kneib
We report on observations indicating that the bright quadruple lens B1422+231 may be variable in the optical on a time scale of hours. We also find that a model can reproduce the optical positions and magnifications. Unfortunately, the system may be affected by possible microlensing and external shear. HST should provide a good model for the lens, the system should be monitored for several nights in superb seeing (0.3-0.4 arcsec FWHM), and the redshifts of the south-east galaxies should be determined. With this extra information, improved modeling will tell whether it is realistic to obtain H 0 from the time delays of B1422+231.