134 research outputs found
The prevalence and physical properties of extremely low-luminosity galaxies in the early universe
Large scale structure and cosmolog
Understanding the Observed Evolution of the Galaxy Luminosity Function from z=6-10 in the Context of Hierarchical Structure Formation
Recent observations of the Lyman-break galaxy (LBG) luminosity function (LF)
from z~6-10 show a steep decline in abundance with increasing redshift.
However, the LF is a convolution of the mass function of dark matter halos
(HMF)--which also declines sharply over this redshift range--and the
galaxy-formation physics that maps halo mass to galaxy luminosity. We consider
the strong observed evolution in the LF from z~6-10 in this context and
determine whether it can be explained solely by the behavior of the HMF. From
z~6-8, we find a residual change in the physics of galaxy formation
corresponding to a ~0.5 dex increase in the average luminosity of a halo of
fixed mass. On the other hand, our analysis of recent LF measurements at z~10
shows that the paucity of detected galaxies is consistent with almost no change
in the average luminosity at fixed halo mass from z~8. The LF slope also
constrains the variation about this mean such that the luminosity of galaxies
hosted by halos of the same mass are all within about an order-of-magnitude of
each other. We show that these results are well-described by a simple model of
galaxy formation in which cold-flow accretion is balanced by star formation and
momentum-driven outflows. If galaxy formation proceeds in halos with masses
down to 10^8 Msun, then such a model predicts that LBGs at z~10 should be able
to maintain an ionized intergalactic medium as long as the ratio of the
clumping factor to the ionizing escape fraction is C/f_esc < 10.Comment: 15 pages, 2 figures; results unchanged; accepted by JCA
Dust mass and dust production efficiencies on the redshift frontier
Interstellar matter and star formatio
Mean Hα+[N ii]+[S ii] EW inferred for star-forming galaxies atz ~ 5.1-5.4 using high-qualitySpitzer/IRAC photometry
Demonstrating the Feasibility of Line Intensity Mapping Using Mock Data of Galaxy Clustering from Simulations
Visbal & Loeb (2010) have shown that it is possible to measure the clustering
of galaxies by cross correlating the cumulative emission from two different
spectral lines which originate at the same redshift. Through this cross
correlation, one can study galaxies which are too faint to be individually
resolved. This technique, known as intensity mapping, is a promising probe of
the global properties of high redshift galaxies. Here, we test the feasibility
of such measurements with synthetic data generated from cosmological dark
matter simulations. We use a simple prescription for associating galaxies with
dark matter halos and create a realization of emitted radiation as a function
of angular position and wavelength over a patch of the sky. This is then used
to create synthetic data for two different hypothetical instruments, one aboard
the Space Infrared Telescope for Cosmology and Astrophysics (SPICA) and another
consisting of a pair of ground based radio telescopes designed to measure the
CO(1-0) and CO(2-1) emission lines. We find that the line cross power spectrum
can be measured accurately from the synthetic data with errors consistent with
the analytical prediction of Visbal & Loeb (2010). Removal of astronomical
backgrounds and masking bright line emission from foreground contaminating
galaxies do not prevent accurate cross power spectrum measurements.Comment: 12 pages, 6 figures, Submitted to JCA
The clustering and halo occupation distribution of Lyman-break galaxies at z ˜ 4
We investigate the clustering of Lyman-break galaxies (LBGs) at z ∼ 4. Using the hierarchical galaxy formation model GALFORM, we predict, for the first time using a semi-analytical model with feedback from active galactic nuclei (AGN), the angular correlation function (ACF) of LBGs and find agreement within 3σ with new measurements of the ACF from surveys including the Hubble eXtreme Deep Field (XDF) and Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) field. Our simulations confirm the conclusion reached using independent models that although the predicted ACFs reproduce the trend of increased clustering with luminosity, the dependence is less strong than observed. We find that for the detection limits of the XDF field, central LBGs at z ∼ 4 predominantly reside in haloes of mass ∼1011–1012 h−1 M⊙ and that satellites reside in larger haloes of mass ∼1012–1013 h−1 M⊙. The model predicts fewer bright satellite LBGs at z ∼ 4 than is inferred from measurements of the ACF at small scales. By analysing the halo occupation distribution (HOD) predicted by the model, we find evidence that AGN feedback affects the HOD of central LBGs in massive haloes. This is a new high-redshift test of this important feedback mechanism. We investigate the effect of photometric errors in the observations on the ACF predictions. We find that the observational uncertainty in the galaxy luminosity reduces the clustering amplitude and that this effect increases towards faint galaxies, particularly on small scales. To compare properties of model with observed LBGs, this uncertainty must be considered
The z ~ 6 Luminosity Function Fainter than -15 mag from the Hubble Frontier Fields: The Impact of Magnification Uncertainties
Large scale structure and cosmolog
Cosmic histories of star formation and reionization: An analysis with a power-law approximation
With a simple power-law approximation of high-redshift () star
formation history, i.e., , we
investigate the reionization of intergalactic medium (IGM) and the consequent
Thomson scattering optical depth for cosmic microwave background (CMB) photons.
A constraint on the evolution index is derived from the CMB optical
depth measured by the {\it Wilkinson Microwave Anisotropy Probe} (WMAP)
experiment, which reads ,
where the free parameter is the number of the escaped
ionizing ultraviolet photons per baryon. Moreover, the redshift for full
reionization, , can also be expressed as a function of as well as
. By further taking into account the implication of the
Gunn-Peterson trough observations to quasars for the full reionization
redshift, i.e., , we obtain
and .
For a typical number of of ionizing photons released per baryon of
normal stars, the fraction of these photons escaping from the stars, , can be constrained to within the range of .Comment: 10 pages, 4 figures, accepted for publication in JCA
High equivalent width of Hα+[N II] emission in z ~ 8 Lyman-break galaxies from IRAC 5.8 μm observations: evidence for efficient Lyman-continuum photon production in the Epoch of Reionization
Galaxie
The Lyman-Continuum Photon Production Efficiency ξ_ion of z ~ 4-5 Galaxies from IRAC-based Hα Measurements: Implications for the Escape Fraction and Cosmic Reionization
Interstellar matter and star formatio
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