Exploring the cosmic dark ages with the next generation of space and ground-based facilities

This paper reviews our current understanding of the process of re-ionization of the Universe, focusing especially on those models where re-ionization is caused by UV radiation from massive stars. After reviewing the expected properties of stars at zero metallicity, I discuss the properties of primordial HII regions and their observability.Comment: 14 pages, 10 figures. To appear in the proceedings of the SPIE conference 4835 "Future research directions and visions for astronomy" held in Waikaloa, HI on August 25-26, 2002, A. Dressler Ed. Needs spie.cls (included

The very first Pop III stars and their relation to bright z~6 quasars

We discuss the link between dark matter halos hosting the first PopIII stars formed at redshift z > 40 and the rare, massive, halos that are generally considered to host bright z~6 quasars. We show that within the typical volume occupied by one bright high-z QSO the remnants of the first several thousands PopIII stars formed do not end up in the most massive halos at z~6, but rather live in a large variety of environments. The black hole seeds planted by these very first PopIII stars can easily grow to M > 10^{9.5} Msun by z=6 assuming Eddington accretion with radiative efficiency epsilon~0.1. Therefore quenching of the accretion is crucial to avoid an overabundance of supermassive black holes. We implement a simple feedback model for the growth of the seeds planted by PopIII stars and obtain a z~6 BH mass function consistent with the observed QSO luminosity function.Comment: 5 pages, to appear in the proceedings of "First Stars III", AIP Conference Series, T. Abel, A. Heger and B. O'Shea ed

The imprint of dark matter haloes on the size and velocity dispersion evolution of early-type galaxies

Early-type galaxies (ETGs) are observed to be more compact, on average, at $z \gtrsim 2$ than at $z\simeq 0$, at fixed stellar mass. Recent observational works suggest that such size evolution could reflect the similar evolution of the host dark matter halo density as a function of the time of galaxy quenching. We explore this hypothesis by studying the distribution of halo central velocity dispersion ($\sigma_0$) and half-mass radius ($r_{\rm h}$) as functions of halo mass $M$ and redshift $z$, in a cosmological $\Lambda$-CDM $N$-body simulation. In the range $0\lesssim z\lesssim 2.5$, we find $\sigma_0\propto M^{0.31-0.37}$ and $r_{\rm h}\propto M^{0.28-0.32}$, close to the values expected for homologous virialized systems. At fixed $M$ in the range $10^{11} M_\odot \lesssim M\lesssim 5.5 \times 10^{14} M_\odot$ we find $\sigma_0\propto(1+z)^{0.35}$ and $r_{\rm h}\propto(1+z)^{-0.7}$. We show that such evolution of the halo scaling laws is driven by individual haloes growing in mass following the evolutionary tracks $\sigma_0\propto M^{0.2}$ and $r_{\rm h}\propto M^{0.6}$, consistent with simple dissipationless merging models in which the encounter orbital energy is accounted for. We compare the $N$-body data with ETGs observed at $0\lesssim z\lesssim3$ by populating the haloes with a stellar component under simple but justified assumptions: the resulting galaxies evolve consistently with the observed ETGs up to $z \simeq 2$, but the model has difficulty reproducing the fast evolution observed at $z\gtrsim 2$. We conclude that a substantial fraction of the size evolution of ETGs can be ascribed to a systematic dependence on redshift of the dark matter haloes structural properties.Comment: 15 pages, 14 figures, 1 table. Matches the Accepted version from MNRA

The Dynamical Evolution of Substructure

The evolution of substructure embedded in non-dissipative dark halos is studied through N-body simulations of isolated systems, both in and out of initial equilibrium, complementing cosmological simulations of the growth of structure. We determine by both analytic calculations and direct analysis of the N-body simulations the relative importance of various dynamical processes acting on the clumps, such as the removal of material by global tides, clump-clump heating, clump-clump merging and dynamical friction. Our comparison between merging and disruption processes implies that spiral galaxies cannot be formed in a proto-system that contains a few large clumps, but can be formed through the accretion of many small clumps; elliptical galaxies form in a more clumpy environment than do spiral galaxies. Our results support the idea that the central cusp in the density profiles of dark halos is the consequence of self-limiting merging of small, dense halos. This implies that the collapse of a system of clumps/substructure is not sufficient to form a cD galaxy, with an extended envelope; plausibly subsequent accretion of large galaxies is required. Persistent streams of material from disrupted clumps can be found in the outer regions of the final system, and at an overdensity of around 0.75, can cover 10% to 30% of the sky.Comment: Accepted for publication in MNRAS. 61 pages, 22 figures; figures 2-7 and 21-22 are separate gif files. Complete paper plus high resolution figures available from http://www.stsci.edu/~mstiavel/Bing_et_al_02.htm

Physical Characterization of Early Galaxies in the Webb's First Deep Field SMACS J0723.3-7323

This paper highlights initial photometric analyses of JWST NIRCam imaging data in the sightline of SMACS0723, aiming to identify galaxies at redshift $z>7$. By applying a conservative Lyman-break selection followed by photometric redshift analysis and visual inspection, we identify four F090W-dropout and two F150W-dropout sources, three of which were recently confirmed in an independent spectroscopic analysis to $z=7.663$, 7.665, and 8.499. We then supplement our sample with a photometric-redshift selection, and identify five additional candidates at $7<z_{\rm phot}<13$. The NIRCam images clearly resolve all sources and reveal their sub-galactic components that were not resolved/detected in the previous imaging by Hubble Space Telescope. Our spectral energy distribution analysis reveals that the selected galaxies are characterized by young stellar populations (median age of $\sim50$ Myr) of sub-solar metallicity ($\sim0.2\,Z_\odot$) and little dust attenuation ($A_{V}\sim0.5$). In several cases, we observe extreme Hb+[OIII] lines being captured in the F444W band and seen as color excess, which is consistent with their observed high star formation rate surface density. Eight of the 11 sources identified in this study appear in at least one of the recent studies of the same fields (Adams et al., Atek et al., Donnan et al., Harikane et al., Yan et al.), implying the high fidelity of our selection. We cross-match all high-$z$ galaxy candidates presented in the five studies with our catalog and discuss the possible causes of discrepancy in the final lists.Comment: Resubmitted to ApJL after having addressed the reviewer's comments. This version includes a few updates, 1. identification of z>10 galaxy candidates, 2. estimates of number densities, and 3. comparison of the final candidates to those in other studies, all of which were pointed out during the review process. The analyses in this version are based on the latest stable version of NIRCam zeropoint