466 research outputs found
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 than at , 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 () and half-mass radius () as
functions of halo mass and redshift , in a cosmological -CDM
-body simulation. In the range , we find
and , close to
the values expected for homologous virialized systems. At fixed in the
range we find
and . We show that
such evolution of the halo scaling laws is driven by individual haloes growing
in mass following the evolutionary tracks and , consistent with simple dissipationless merging models in
which the encounter orbital energy is accounted for. We compare the -body
data with ETGs observed at by populating the haloes with
a stellar component under simple but justified assumptions: the resulting
galaxies evolve consistently with the observed ETGs up to , but the
model has difficulty reproducing the fast evolution observed at .
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
. 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 , 7.665, and 8.499. We then supplement our
sample with a photometric-redshift selection, and identify five additional
candidates at . 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 Myr) of
sub-solar metallicity () and little dust attenuation
(). 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- 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
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