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Star-forming galaxies constitute the majority of galaxies with stellar masses >10^10 M_Sun/h^2 at z~2 and dominate the star-formation rate density of the Universe at this early epoch. It is thus critical to understand their origins, evolution, and connection to the underlying dark matter distribution. To this end, we identify the dark matter halos (including subhalos) that are likely to contain star-forming galaxies at z~2 (z2SFGs) within a large dissipationless cosmological simulation and then use halo merger histories to follow the evolution of z2SFG descendants to z~1 and z~0. The evolved halos at these epochs are then confronted with an array of observational data in order to uncover the likely descendants of z2SFGs. Though the evolved halos have clustering strengths comparable to red galaxies at z~1 and z~0, we find that the bulk of z2SFGs do not evolve into red galaxies, at either epoch. This conclusion is based primarily on the fact that the space density of z2SFGs is much higher than that of lower redshift red galaxies, even when accounting for the merging of z2SFG descendants, which decreases the number density of z2SFG descendants by at most a factor of two by z~0. Of the ~50% of z2SFGs that survive to z~0, ~70% reside at the center of z~0 dark matter halos with M>10^12 M_Sun/h. Halo occupation modeling of z~0 galaxies suggests that such halos are occupied by galaxies with M_r<-20.5, implying that these z2SFGs evolve into ``typical'' ~ L* galaxies today, including our own Galaxy. The remaining ~30% become satellite galaxies by z~0, and comparison to halo occupation modeling suggests that they are rather faint, with M_r<-19.5. (ABRIDGED), Comment: 13 pages, 5 figures. ApJ in press

We discuss new observational constraints on the abundance of faint high redshift Lyman-alpha emitters secured from a deep Keck near-infrared spectroscopic survey which utilizes the strong magnification provided by lensing galaxy clusters at intermediate redshift (z=0.2-0.5). In each of 9 clusters we have undertaken a systematic `blind' search for line emission with NIRSPEC in the J-band within carefully-selected regions which offer very high magnifications (>10-50x) for background sources with redshifts z~10. The high magnification enables the detection of emission at unprecedented limits (10^41 - 10^42 erg/s), much fainter than those of conventional narrow band imaging and other spectroscopic searches. As the comoving volumes probed are small, our survey is designed to address the important question of whether intrinsically feeble star forming galaxies could provide the dominant ionizing flux at z~10. Our survey has yielded six promising (>5 sigma) candidate Lyman-alpha emitters which lie between z=8.7 and z=10.2. While the predicted reionization photon budget depends upon a large number of physical assumptions, our first glimpse at the z~10 Universe suggests that low luminosity star-forming galaxies contribute a significant proportion of the UV photons necessary for cosmic reionization. [Abridged], Comment: Submitted to ApJ, with changes to reflect referee's comments, 27 pages, 12 figures, for higher resolution figures, see http://www.astro.caltech.edu/~dps/papers/nirscrit.pdf

We discuss the observational properties of a remarkably faint triply-imaged galaxy revealed in a deep z-band ACS observation of the lensing cluster A2218. A well-constrained mass model for the cluster, which incorporates the outcome of recent Keck spectroscopic campaigns, suggests that the triple system arises via a z>6 source viewed at high magnification (~x25). Optical and IR photometry from HST and Keck confirms the lensing hypothesis and suggests a significant discontinuity occurs in the spectral energy distribution within 9250-9850A. If this break is associated with Gunn-Peterson absorption from neutral hydrogen,6.6

We derive the luminosity function of high-redshift Lyman alpha emitting sources from a deep, blind, spectroscopic survey that utilized strong-lensing magnification by intermediate-redshift clusters of galaxies. We observed carefully selected regions near 9 clusters, consistent with magnification factors generally greater than 10 for the redshift range 4.5L) proportional to L^-1 over 10^41 to 10^42.5 erg/s. When combined with the results of other surveys, limited at higher luminosities, our results suggest evidence for the suppression of star formation in low-mass halos, as predicted in popular models of galaxy formation., Comment: 22 pages, 14 figures, submitted to ApJ

Lyman-alpha emission from high-redshift galaxies may be a powerful probe of the ionization history of the IGM at z>6: the observed Lyman-alpha emission line is sensitive to the neutral fraction of IGM hydrogen in the range 0.1-1. We present calculations of observed Lyman-alpha emission lines from z>6 galaxies, illustrating the effect of varying the many free parameters associated with the emitting galaxy, its halo, and the IGM around the galaxy. In particular, we use a dynamic model of the IGM that includes the effect of IGM infall toward the emitting galaxy. Galactic winds may play a crucial role in determining observed Lyman-alpha line fluxes. We compare our model predictions with observations of two z=6.5 galaxies and conclude that, if galactic winds are allowed for, existing observations place no constraint on the neutral fraction of the IGM at z=6.5. Future space-based observations will constrain the importance of galactic winds; if winds are unimportant for the observed z=6.5 galaxies, our models suggest that the IGM neutral fraction at z=6.5 is <~0.1., Comment: 17 pages, 25 figures, submitted to MNRAS

We present an observational test of the spectrum of the ionizing background at z~5; the test is sufficiently sensitive to determine whether Pop II or Pop III stars are the dominant source of ionizing radiation. The ionizing background at z~5 may reflect the nature of the sources responsible for the final overlap phase of reionization. We find that rest-frame extreme-UV HeI absorption will be detectable in deep spectral observations of some rare z~5 quasars; the ratio of HeI to HI absorption reflects the shape of the ionizing background in the photon energy range between 13.6 and 24.6 eV. Most z~5 quasars have too much HI absorption along their line of sight for HeI absorption to be observed. However, based on current measurements of HI absorber statistics, we use Monte Carlo simulations to demonstrate that the Sloan Digital Sky Survey (SDSS) will discover a sufficient number of z~5 quasars to turn up a quasar suitable for measuring HeI absorption (and we illustrate a selection method to identify that quasar). From simulated observations of a suitable z~5 quasar with a 10-meter telescope, we show that a constraint on the spectral slope of the ionizing background at that redshift can be obtained., Comment: 12 pages, 12 figures, submitted to MNRAS

We calculate the contribution to the cosmic infrared background from very massive metal-free stars at high redshift. We explore two plausible star-formation models and two limiting cases for the reprocessing of the ionizing stellar emission. We find that Population III stars may contribute significantly to the cosmic near-infrared background if the following conditions are met: (i) The first stars were massive, with M > ~100 M_sun. (ii) Molecular hydrogen can cool baryons in low-mass haloes. (iii) Pop III star formation is ongoing, and not shut off through negative feedback effects. (iv) Virialized haloes form stars at about 40 per cent efficiency up to the redshift of reionization, z~7. (v) The escape fraction of the ionizing radiation into the intergalactic medium is small. (vi) Nearly all of the stars end up in massive black holes without contributing to the metal enrichment of the Universe., Comment: 11 pages, 6 figures, expanded discussion, added mid-IR to Fig 6, MNRAS in press