Found 21 talks width keyword high-redshift galaxies
The flow of gas from the cosmic web into galaxies provides the necessary fuel for star formation and galaxy assembly. I will review our current knowledge about gas accretion into galaxies and its consequences for galaxy formation at high and low redshifts. Special attention will be given to the detectability of cold streams as Lyman-alpha blobs or Lyman-Limit systems, as well as the current challenges to the cold-flow picture.
How do the first galaxies form and evolve? Optical and near-infrared deep surveys are now finding galaxies at very high redshifts. However, they are typically small, not massive and present some but not very high star formation. But now the Herschel Multi-tiered Extragalactic Survey (HerMES), the largest project that has being carried out with the Herschel Space Observatory, in collaboration with other groups, has discovered a massive, maximum-starburst galaxy at a redshift of 6.34. The presence of galaxies like HFLS3 in the early Universe challenges current theories of galaxy fomation and evolution. I will describe the method we have developed to find these galaxies, the follow-up observations with different facilities and the main physical properties of this extreme object.
Taking advantage of the ultra-deep near-infrared imaging obtained with the Hubble Space Telescope on the Hubble Ultra Deep Field, we detect and explore for the first time the properties of the stellar haloes of two Milky Way-like galaxies at z~1. We find that the structural properties of those haloes (size and shape) are similar to the ones found in the local universe. However, these high-z stellar haloes are approximately three magnitudes brighter and exhibit bluer colours ((g-r)<0.3 mag) than their local counterparts. The stellar populations of z~1 stellar haloes are compatible with having ages <1 Gyr. This implies that the stars in those haloes were formed basically at 1<z<2. This result matches very well the theoretical predictions that locate most of the formation of the stellar haloes at those early epochs. A pure passive evolutionary scenario, where the stellar populations of our high-z haloes simply fade to match the stellar halo properties found in the local universe, is consistent with our data.
Evolution of galaxies is relatively well known up to z ~ 5, but beyond this limit and regarding the few number of galaxies confirmed by spectroscopy, their evolution is still uncertain. In the last five years, many projects and instruments aiming at pushing the limits of the Universe have emerged. Among them, the WIRCam Ultra Deep Survey (WUDS), a very large (~400 arcmin^2 field of view) and deep (m_H=27.00 AB) survey covering wavelength from Y to Ks bands, dedicated to select the brightest sources at z > 4.5, has just been finished.This survey takes benefit from the deep images from the CFHT-LS (Groth Strip) in u, g, r, i and z-band to improve the wavelength coverage and thus the determination of photometric redshift in each sample. The evolution of galaxies has been studied through the evolution of the UV Luminosity Function from z~5 up to z~9. During this talk I will present you the WIRCam Ultra Deep Survey and the most popular method used to select the very high-redshift sources. Then I will focus on the determination of the luminosity function and on the implications of this evolution on the Epoch of Reionization. I will finish this presentation by giving some perspectives, and especially the results that we can expected from futures instruments and telescopes (e.g. EMIR @ GTC, KMOS and MUSE @ VLT, JWST, E-ELT).
Morphologies of star-forming galaxies at z>1 are typically irregular containing a handful of dominant bright regions. Recent observational evidence suggest that many of these galaxies are governed by disc-like rotation. Using Halpha galaxy kinematics from OSIRIS+LGSAO we find that within z~1 turbulent discs star-forming regions have average sizes of 1.5 kpc and average Jeans masses of 4.2x10^9 \Msun, in total accounting for 20-30% of the stellar mass of the discs. These findings lend observational support to models that predict larger star-forming regions will form as a result of higher disc velocity dispersions driven-up by cosmological gas accretion. As a consequence of the changes in global environment, it may be predicted that star-forming regions at high redshift should not resemble star-forming regions locally. Yet despite the increased sizes and dispersions, high-z star-forming regions and HII regions are found to follow tight scaling relations over the range z=0-2 for Halpha size, velocity dispersion, luminosity and mass when comparing >2000 HII regions locally and 30 regions at z>1. While the turbulence of discs may have important implications for the size and luminosity of regions which form within them, the same processes likely govern their formation from high redshift to the current epoch. We are now able to test this conclusion with first results from a new sample of z=0.1-0.2 highly star-forming turbulent galaxies from the Sloan Digital Sky Survey.
I will present new deep and wide narrow-band surveys undertaken with UKIRT, Subaru and the VLT; a unique combined effort to select large, robust samples of H-alpha (Ha) emitters at z=0.40, 0.84, 1.47 and 2.23 (corresponding to look-back times of 4.2, 7.0, 9.2 and 10.6 Gyrs) in a uniform manner over ~2 sqdeg in the COSMOS and UDS fields. The deep multi-epoch Ha surveys are sensitive to Milky-Way SFRs out to z=2.2 for the first time, while the wide area and the coverage over two independent fields allows to greatly overcome cosmic variance. A total of over 600 sources per epoch are homogeneously selected. Overall, the evolution seen in Ha is in good agreement with the evolution seen using inhomogeneous compilations of other tracers of star formation, such as FIR and UV, jointly pointing towards the bulk of the evolution in the last 11 Gyrs being driven by a strong luminosity/SFR increase from z~0 to z~2.2. Our uniform analysis allows to derive the Ha star formation history of the Universe, for which a simple time-parametrisation is a good approximation for the last 11Gyrs. Both the shape and normalisation of the Ha star formation history are consistent with the measurements of the stellar mass density growth, confirming that our Ha analysis traces the bulk of the formation of stars in the Universe up to z~2.2. We are also exploring the large, multi-epoch and homogeneously selected samples of Ha emitters to conduct detailed morphology, dust, clustering, environment and mass studies which are providing us with a unique view on the evolution of star-forming galaxies and what has been driving it for the past 11 Gyrs.
In recent years, major changes were done at the IRAM Plateau de Bure interferometer and 30-meter telescope, in particular in the areas of receivers and back-ends. These enhancements increased in significant ways both the sensitivity and the efficiency of both IRAM facilities. I will present results obtained on high-z (2 < 6.4) sub-millimeter galaxies and quasars that illustrate the progress that has been made, emphasizing recent follow-up observations of sources that were uncovered in the Herschel surveys. The talk will end with a presentation of the future projects that are currently under discussion at IRAM, including the NOrthern Extended Millimeter Array (NOEMA), as well as the prospects offered by ALMA.
AbstractMassive (≥ 1011 M⊙) galaxies at high redshift (z ≥ 1.5) remain mysterious objects. Their extremely small sizes (effective radii of 1-2 kpc) make them as dense as modern globular clusters. It is thought that a highly dissipational merger is needed to create such compact type of galaxies. We will discuss this issue, along with state-of-the-art morphological and kinematic observations of these objects. In the present day Universe massive galaxies show large sizes, and harbor old and metal-rich stellar populations. In order to explore their development, we present near-IR IFU observations with SINFONI@VLT for ten massive galaxies at z=1.4 solely selected by their high stellar mass which allow us to retrieve velocity dispersions, kinematic maps and dynamical masses. We joined this with data and works coming from the GOODS NICMOS Survey, the largest sample of massive galaxies (80 objects) with high-resolution imaging at high redshift (1.7 < z < 3) acquired to date. As a result, we show how their morphology changes possibly through elusive minor merging.
AbstractIn this talk, I will cover our contribution to the study of extremely red galaxy (ERG) populations presenting a multi-wavelength analysis of these objects, selected in the GOODS-South/Chandra Deep Field South field. By using all the photometric (from X-rays to radio) and spectroscopic information available on large deep samples of extremely red objects (EROs, 645 sources), infrared EROs (IEROs, 294 sources) and distant red galaxies (DRGs, 350 sources), we derive redshift distributions, identify AGN powered and star-formation powered galaxies (based on X-ray properties and a new IR AGN diagnostic developed by us), and, using the radio observations of this field, estimate robust (AGN- and dust-unbiased) star formation rate densities (SFRD) for these populations. Applying a redshift separation (1 ≤ z < 2 and 2 ≤ z ≤ 3) we find a significant rise (a factor of 1.5 — 3) of SFRD for EROs and DRGs toward high-z, while none is observed for IEROs. As expected, we find a significant overlap between the ERG populations, and investigate the properties of "pure" (galaxies that conform to only one of the three considered ERG criteria) and "combined" (galaxies conforming to all three criteria) sub-populations. We find ERG sub-populations with no AGN activity and intense star-formation rates. With average values of ~180 M⊙/yr at 2 ≤ z < 3, they reasonably contribute to the global star-formation rate density, reaching a > 20% level. Strong AGN behaviour is not observed in the ERG population, with AGN only increasing the average radio luminosity of ERGs by 10 — 20%. However, AGN are frequently found (in up to 27% of the ERG population), and would increase the SFRD estimate by over 100%. Thus, and while the contribution of SF processes to the radio luminosity in galaxies with AGN remains uncertain, a comprehensive identification of AGN in these populations is necessary to obtain meaningful results. The dust content to each population is also derived by correlating UV and Radio SFRs, giving a higher obscuration for more active SF sources. Also, know to be amongst the most massive galaxies in the high-z universe, I will show that ERGs may constitute up to 60% of the total mass in the universe at 1 ≤ z ≤ 3. Finally, preliminary and promising results are presented on the morphologies of ERGs (CAS and Gini/M20 parameters) based on the v1.9 ACS GOODS-S images.
Luminous high-redshift radio galaxies (HzRGs) are associated with the most massive known galaxies in the early Universe. These galaxies have the properties expected of the progenitors of dominant galaxies in rich clusters.
I shall describe the properties of HzRGs and demonstrate how they can be used to study the formation and evolution of galaxies and clusters. I shall also show how LOFAR, the new European radio telescope, can be used to extend these probes into the epoch of reionisation.
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