UV Properties and Evolution of High-redshift Galaxies (original) (raw)
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The Properties of Ultraviolet-luminous Galaxies at the Current Epoch
Astrophysical Journal, 2005
We have used the first matched set of GALEX and SDSS data to investigate the properties of a sample of 74 nearby galaxies with far-ultraviolet luminosities chosen to overlap the luminosity range of typical high-z Lyman Break Galaxies (LBGs). GALEX deep surveys have shown that ultraviolet-luminous galaxies (UVLGs) similar to these are the fastest evolving component of the UV galaxy population. Model fits to the combined GALEX and SDSS photometry yield typical FUV extinctions similar to LBGs. The implied star formation rates are SFR ~ 3 to 30 solar mass per year. This overlaps the range of SFRs for LBGs. We find a strong inverse correlation between galaxy mass and far-ultraviolet surface brightness, and on this basis divide the sample into ``large'' and ``compact'' UVLGs. The compact UVLGs have half-light radii of a few kpc or less (similar to LBGs). They are relatively low mass galaxies (~10 billion solar masses) with typical velocity dispersions of 60 to 150 km/s. They span a range in metallicity from 0.3 to 1 times solar, have blue optical-UV colors, and are forming stars at a rate sufficient to build the present galaxy in ~a Gigayear. In all these respects they appear similar to the LBG population. These ``living fossils'' may therefore provide an opportunity for detailed investigation of the physical processes occurring in typical star forming galaxies in the early universe.
The Astrophysical Journal Supplement Series, 1994
In this paper we present new chemo-spectrophotometric models of elliptical galaxies in which infall of primordial gas is allowed to occur. They aim to simulate the collapse of a galaxy made of two components, i.e. luminous material and dark matter. The mass of the dark component is assumed to be constant in time, whereas that of the luminous material is supposed to accrete at a suitable rate. They also include the effect of galactic winds powered by supernova explosions and stellar winds from massive, early-type stars. The models are constrained to match a number of properties of elliptical galaxies, i.e. the slope and mean colours of the colour-magnitude relation (CMR), V versus (V-K), the UV excess as measured by the colour (1550-V) together with the overall shape of the integrated spectral energy distribution (ISED) in the ultraviolet, the relation between the Mg 2 index and (1550-V), the mass to blue luminosity ratio M/L B as a function of the B luminosity, and finally the broad-band colours (U-B), (B-V), (V-I), (V-K), etc. The CMR is interpreted as a mass-metallicity sequence of old, nearly coeval objects, whose mean age is 15 Gyr. Assuming the law of star formation to be proportional to M k g (t) with k = 1, the rate of star formation as function of time starts small, grows to a maximum, and then declines thus easily avoiding the excess of metal-poor stars found by BCF with the closed-box scheme (the analog of the G-Dwarf Problem in the solar vicinity). Owing to their stellar content, infall models can easily reproduce all the basic data of the galaxies under examination. As far as the UV excess is concerned, the same sources proposed by BCF are found to hold also with the infall scheme. H-HB and AGB manqué stars of high metallicity play the dominant role, and provide a robust explanation of the correlation between the (1550-V) colour and the luminosity, mass and metallicity of the galaxies. Furthermore, these models con-⋆ Send offprint requests to: C. Chiosi firm the potential of the (1550-V) colour as an age indicator in cosmology as already suggested by BCF. In the rest frame of a massive and metal-rich elliptical galaxy, this colour suffers from one major variation: at the onset of the so-called H-HB and AGB-manqué stars (age about 5.6 Gyr). This transition occurs at reasonably small redshifts and therefore could be detected with the present-day instrumentation.
Monthly Notices of the Royal Astronomical Society, 2008
We combine deep optical and NIR (U BV RIzJK) photometry from the Multiwavelength Survey by Yale-Chile (MUSYC) with redshifts from the COMBO-17 survey to perform a large-scale study of the rest-frame ultraviolet (U V ) properties of 674 high-redshift (0.5 < z < 1) early-type galaxies, drawn from the Extended Chandra Deep Field South (E-CDFS). Galaxy morphologies are determined through visual inspection of Hubble Space Telescope (HST) images taken from the GEMS survey. We harness the sensitivity of the U V to young (< 1 Gyrs old) stars to quantify the recent star formation history of early-type galaxies across a range of luminosities (−23.5 < M (V ) < −18). Comparisons to simple stellar populations forming at high redshift indicate that ∼ 1.1 percent of early-types in this sample are consistent with purely passive ageing since z = 2 -this value drops to ∼ 0.24 percent and ∼ 0.15 percent for z = 3 and z = 5 respectively. Parametrising the recent star formation ('RSF') in terms of the mass fraction of stars less a Gyr old, we find that the early-type population as a whole shows a typical RSF between 5 and 13 percent in the redshift range 0.5 < z < 1. Early-types on the broad U V 'red sequence', show RSF values less than 5 percent, while the reddest early-types (which are also the most luminous) are virtually quiescent with RSF values of ∼ 1 percent. In contrast to their low-redshift (z < 0.1) counterparts, the high-redshift early-types in this sample show a pronounced bimodality in the rest-frame U V -optical colour, with a minor but significant peak centred on the blue cloud. Furthermore, star formation in the most active early-types is a factor of 2 greater at z ∼ 0.7 than in the local Universe. Given that evolved sources of U V flux (e.g. horizontal-branch stars) should be absent at z > 0.5, implying that the U V is dominated by young stars, we find compelling evidence that early-types of all luminosities form stars over the lifetime of the Universe, although the bulk of their star formation is already complete at high redshift. This 'tail-end' of star formation is measurable and not negligible, with luminous (−23 < M (V ) < −20.5) early-types potentially forming 10-15 percent of their mass since z = 1, with less luminous earlytypes (M (V ) > −20.5) potentially forming 30-60 percent of their mass after z = 1. This, in turn, implies that intermediate-age stellar populations should be abundant in local early-type galaxies, as expected in hierarchical cosmology.
The UV Properties of Star Forming Galaxies I: HST WFC3 Observations of Very-high Redshift Galaxies
2011
The acquisition of deep Near-IR imaging with Wide Field Camera 3 on the Hubble Space Telescope has provided the opportunity to study the very-high redshift Universe. For galaxies up to z ≈ 7.7 sufficient wavelength coverage exists to probe the rest-frame ultraviolet (UV) continuum without contamination from either Lyman-α emission or the Lyman-α break. In this work we use Near-IR imaging to measure the rest-frame UV continuum colours of galaxies at 4.7 < z < 7.7. We are have carefully defined a colourcolour selection to minimise any inherent bias in the measured UV continuum slope for the drop-out samples. For the highest-redshift sample (6.7 < z < 7.7), selected as z f 850lp -band dropouts, we find mean UV continuum colours approximately equal to zero (AB), consistent with a dust-free, solar metallicity, star forming population (or a moderately dusty population of low metallicity). At lower-redshift we find that the mean UV continuum colours of galaxies (over the same luminosity range) are redder, and that galaxies with higher luminosities are also slightly redder on average. One interpretation of this is that lower-redshift and more luminous galaxies are dustier, however this interpretation is complicated by the effects of the star formation history and metallicity and potentially the initial mass function on the UV continuum colours.
High redshift evolution of optically and IR-selected galaxies: a comparison with CDM scenarios
1999
A combination of ground-based (NTT and VLT) and HST (HDF-N and HDF-S) public imaging surveys have been used to collect a sample of 1712 I-selected and 319 Kleq21K\leq 21Kleq21 galaxies. Photometric redshifts have been obtained for all these galaxies. The results have been compared with the prediction of an analytic rendition of the current CDM hierarchical models for galaxy formation. We focus in particular on two observed quantities: the galaxy redshift distribution at K<21 and the evolution of the UV luminosity density. The derived photometric redshift distribution is in agreement with the hierarchical CDM prediction, with a fraction of only 5% of galaxies detected at z>2. This result strongly supports hierarchical scenarios where present-day massive galaxies are the result of merging processes. The observed UV luminosity density in the I-selected sample is confined within a factor of 4 over the whole range 0<z<4.5. CDM models in a critical Universe are not able to produce the density of UV photons that is observed at z>3. CDM models in Lambda\LambdaLambda-dominated universe are in better agreement at 3<z<4.5, but predict a pronounced peak at z~1.5 and a drop by a factor of 8 from z=1.5 to z=4 that is not observed in the data. We conclude that improvements are required in the treatment of the physical processes directly related to the SFR, e.g. the starbust activity in merger processes and/or different feedback to the star formation activity.
The Astrophysical Journal, 1995
The cosmic evolution of the field galaxy population has been studied out to a redshift of z ∼ 1 using a sample of 730 I-band selected galaxies, of which 591 have secure redshifts with median < z >∼ 0.56. The tri-variate luminosity function φ(M, color, z) shows unambiguously that the population evolves and that this evolution is strongly differential with color and, less strongly, with luminosity. The luminosity function of red galaxies shows very little change in either number density or luminosity over the entire redshift range 0 < z < 1. In contrast, the luminosity function of blue galaxies shows substantial evolution at redshifts z > 0.5. By 0.5 < z < 0.75 the blue luminosity function appears to have uniformly brightened by approximately 1 magnitude. At higher redshifts, the evolution appears to saturate at the brightest magnitudes but continues at fainter levels leading to a steepening of the luminosity function. A significant excess of galaxies relative to the Loveday et al. (1992) local luminosity function is seen at low redshifts z < 0.2 around M AB (B) ∼ −18 and these galaxies may possibly represent the descendants of the evolving blue population seen at higher redshifts. The changes seen in the luminosity function are also apparent in color-magnitude diagrams constructed at different epochs and in the V /V max statistic computed as a function of spectral type. Finally, it is argued that the picture of galaxy evolution presented here is consistent with the very much smaller samples of field galaxies that have been selected in other wavebands, and with the results of studies of galaxies selected on the basis of Mg II 2799 absorption 1 Visiting Astronomer, Canada-France-Hawaii Telescope, which is operated by the National
The CANADA-FRANCE REDSHIFT SURVEY VI: Evolution of the galaxy luminosity function to z ~ 1
1995
The cosmic evolution of the field galaxy population has been studied out to a redshift of z ~ 1 using a sample of 730 I-band selected galaxies, of which 591 have secure redshifts with median ~ 0.56. The tri-variate luminosity function phi(M,color,z) shows unambiguously that the population evolves and that this evolution is strongly differential with color and, less strongly, with luminosity. The luminosity function of red galaxies shows very little change in either number density or luminosity over the entire redshift range 0 < z < 1. In contrast, the luminosity function of blue galaxies shows substantial evolution at redshifts z > 0.5. By 0.5 < z < 0.75, the blue luminosity function appears to have uniformly brightened by approximately 1 mag. At higher redshifts, the evolution appears to saturate at the brightest magnitudes but continues at fainter levels leading to a steepening of the luminosity function. A significant excess of galaxies relative to the Loveday et al. (1992) local luminosity function is seen at low redshifts z < 0.2 around M(B) ~ -18$ and these galaxies may possibly represent the descendants of the evolving blue population seen at higher redshifts. The changes seen in the luminosity function are also apparent in color-magnitude diagrams constructed at different epochs and in the V/V_max statistic computed as a function of spectral type. Finally, it is argued that the picture of galaxy evolution presented here is consistent with the very much smaller samples of field galaxies that have been selected in other wavebands, and with the results of studies of galaxies selected on the basis of Mg II 2799 absorption.
Late Stages of Stellar Evolution and their Impact on Spectrophotometric Properties of Galaxies
2007
The connection between AGB evolution of stellar populations and infrared vs. ultraviolet properties of the parent galaxies is reviewed relying on the updated lookout provided by population-synthesis theory. In particular, planetary-nebula events and hot horizontal-branch evolution are assessed in a unitary view to outline a plain general picture of galaxy spectrophotometric evolution. This will include a brief discussion of relevant phenomena such as the ``UV upturn'' in ellipticals and the stellar mass loss properties along the galaxy morphological sequence.