35 research outputs found
UV Luminosity Function at z~4, 3, and 2
We use very deep (R_lim=27) UGRI imaging to study the evolution of the faint
end of the UV-selected galaxy luminosity function from z~4 to z~2. We find that
the number of sub-L* galaxies increases from z~4 to z~3 while the number of
bright ones appears to remain constant. We find no evidence for continued
evolution to lower redshift, z~2. If real, this differential evolution of the
luminosity function suggests that differentially comparing key diagnostics of
dust, stellar populations, etc. as a function of z and L may let us isolate the
key mechanisms that drive galaxy evolution at high redshift and we describe
several such studies currently underway.Comment: To appear in proceedings of the conference "Starbursts - from 30
Doradus to Lyman break galaxies" (IoA, Cambridge UK, Sep 2004), Astrophysics
& Space Science Library, eds. de Grijs R., Gonzalez Delgado R.M. (Kluwer:
Dordrecht
Gas filaments of the cosmic web located around active galaxies in a protocluster
Cosmological simulations predict the Universe contains a network of intergalactic gas filaments, within which galaxies form and evolve. However, the faintness of any emission from these filaments has limited tests of this prediction. We report the detection of rest-frame ultraviolet Lyman-alpha radiation from multiple filaments extending more than one megaparsec between galaxies within the SSA 22 proto-cluster at a redshift of 3.1. Intense star formation and supermassive black-hole activity is occurring within the galaxies embedded in these structures, which are the likely sources of the elevated ionizing radiation powering the observed Lyman-alpha emission. Our observations map the gas in filamentary structures of the type thought to fuel the growth of galaxies and black holes in massive proto-clusters
Properties of Ly-alpha and Gamma Ray Burst selected starbursts at high redshifts
Selection of starbursts through either deep narrow band imaging of redshifted
Ly-alpha emitters, or localisation of host galaxies of gamma-ray bursts both
give access to starburst galaxies that are significantly fainter than what is
currently available from selection techniques based on the continuum (such as
Lyman-break selection). We here present results from a survey for Ly-alpha
emitters at z=3, conducted at the European Southern Observatory's Very Large
Telescope. Furthermore, we briefly describe the properties of host galaxies of
gamma-ray bursts at z>2. The majority of both Ly-alpha and gamma-ray burst
selected starbursts are fainter than the flux limit of the Lyman-break galaxy
sample, suggesting that a significant fraction of the integrated star formation
at z~3 is located in galaxies at the faint end of the luminosity function.Comment: invited talk, 6 pages, 3 figures, to appear in ``Starbursts from 30
Doradus to Lyman Break Galaxies'', eds. R. de Grijs, R. M. Gonzalez Delgado,
Astrophysics & Space Science Library Series, Kluwer (in press
The most metal-poor damped Lyα systems: insights into chemical evolution in the very metal-poor regime
We present a high spectral resolution survey of the most metal-poor damped Lyα absorption systems (DLAs) aimed at probing the nature and nucleosynthesis of the earliest generations of stars. Our survey comprises 22 systems with iron abundance less than 1/100 solar; observations of seven of these are reported here for the first time. Together with recent measures of the abundances of C and O in Galactic metal-poor stars, we reinvestigate the trend of C/O in the very metal-poor (VMP) regime and we compare, for the first time, the O/Fe ratios in the most metal-poor DLAs and in halo stars. We confirm the near-solar values of C/O in DLAs at the lowest metallicities probed, and find that their distribution is in agreement with that seen in Galactic halo stars. We find that the O/Fe ratio in VMP DLAs is essentially constant, and shows very little dispersion, with a mean [〈O/Fe〉]=+0.39 ± 0.12, in good agreement with the values measured in Galactic halo stars when the oxygen abundance is measured from the [O I] λ6300 line. We speculate that such good agreement in the observed abundance trends points to a universal origin for these metals. In view of this agreement, we construct the abundance pattern for a typical VMP DLA and compare it to model calculations of Population II and Population III nucleosynthesis to determine the origin of the metals in VMP DLAs. Our results suggest that the most metal-poor DLAs may have been enriched by a generation of metal-free stars; however, given that abundance measurements are currently available for only a few elements, we cannot yet rule out an additional contribution from Population II stars
A newly discovered DLA and associated Ly-alpha emission in the spectra of the gravitationally lensed quasar UM673A,B
The sightline to the brighter member of the gravitationally lensed quasar
pair UM 673A,B intersects a damped Lyman-alpha system (DLA) at z = 1.62650
which, because of its low redshift, has not been recognised before. Our high
quality echelle spectra of the pair, obtained with HIRES on the Keck I
telescope, show a drop in neutral hydrogen column density N(H I) by a factor of
at least 400 between UM 673A and B, indicating that the DLA's extent in this
direction is much less than the 2.7 kpc separation between the two sightlines
at z = 1.62650. By reassessing this new case together with published data on
other quasar pairs, we conclude that the typical size (radius) of DLAs at these
redshifts is R ~ (5 +/- 3) kpc, smaller than previously realised. Highly
ionized gas associated with the DLA is more extended, as we find only small
differences in the C IV absorption profiles between the two sightlines.
Coincident with UM 673B, we detect a weak and narrow Ly-alpha emission line
which we attribute to star formation activity at a rate SFR >~ 0.2 M_solar/yr.
The DLA in UM 673A is metal-poor, with an overall metallicity Z_DLA ~ 1/30
Z_solar, and has a very low internal velocity dispersion. It exhibits some
apparent peculiarities in its detailed chemical composition, with the elements
Ti, Ni, and Zn being deficient relative to Fe by factors of 2-3. The [Zn/Fe]
ratio is lower than those measured in any other DLA or Galactic halo star,
presumably reflecting somewhat unusual previous enrichment by stellar
nucleosynthesis. We discuss the implications of these results for the nature of
the galaxy hosting the DLA.Comment: 16 pages, 11 Figures, Accepted for publication in Monthly Notices of
the Royal Astronomical Society (updated to match the published version
The explosion energy of early stellar populations: the Fe-peak element ratios in low-metallicity damped Ly-alpha systems
The relative abundances of the Fe-peak elements (Ti–Zn) at the lowest metallicities are intimately linked to the physics of core-collapse supernova explosions. With a sample of 25 very metal poor damped Lyα systems (DLAs), we investigate the trends of the Fe-peak element ratios with metallicity. For nine of the 25 DLAs, a direct measurement (or useful upper limit) of one or more of the Ti, Cr, Co, Ni, Zn/Fe abundance ratios could be determined from detected absorption lines. For the remaining systems (without detections), we devised a new form of spectral stacking to estimate the typical Fe-peak element ratios of the DLA population in this metallicity regime. We compare these data to analogous measurements in metal-poor stars of the Galactic halo and to detailed calculations of explosive nucleosynthesis in metal-free stars. We conclude that most of the DLAs in our sample were enriched by stars that released an energy of ≲1.2 × 10^(51) erg when they exploded as core-collapse supernovae. Finally, we discuss the exciting prospect of measuring Fe-peak element ratios in DLAs with Fe/H < 1/1000 of solar when 30-m class telescopes become available. Only then will we be able to pin down the energy that was released by the supernovae of the first stars