699 research outputs found
X ray opacity in cluster cooling flows
We have calculated the emergent x-ray properties for a set of spherically symmetric, steady-state cluster cooling flow models including the effects of radiative transfer. Opacity due to resonant x-ray lines, photoelectric absorption, and electron scattering have been included in these calculations, and homogeneous and inhomogeneous gas distributions were considered. The effects of photoionization opacity are small for both types of models. In contrast, resonant line optical depths can be quite high in both homogeneous and inhomogeneous models. The presence of turbulence in the gas can significantly lower the line opacity. We find that integrated x-ray spectra for the flow cooling now are only slightly affected by radiative transfer effects. However x-ray line surface brightness profiles can be dramatically affected by radiative transfer. Line profiles are also strongly affected by transfer effects. The combined effects of opacity and inflow cause many of the lines in optically thick models to be asymmetrical
The Insignificance of Global Reheating in the Abell 1068 Cluster: X-Ray Analysis
We report on a Chandra observation of the massive, medium redshift (z=0.1386)
cooling flow cluster Abell 1068. We detect a clear temperature gradient in the
X-ray emitting gas from kT ~ 5 keV in the outer part of the cluster down to
roughly 2 keV in the core, and a striking increase in the metallicity of the
gas toward the cluster center. The total spectrum from the cluster can be fit
by a cooling flow model with a total mass deposition rate of 150 solar
masses/yr. Within the core (r < 30 kpc), the mass depositon rate of 40 solar
masses/yr is comparable to estimates for the star formation rate from optical
data. We find an apparent correlation between the cD galaxy's optical isophotes
and enhanced metallicity isocontours in the central ~100 kpc of the cluster. We
show that the approximate doubling of the metallicity associated with the cD
can be plausibly explained by supernova explosions associated with the cD's
ambient stellar population and the recent starburst. Finally, we calculate the
amount of heating due to thermal conduction and show that this process is
unlikely to offset cooling in Abell 1068.Comment: Accepted for publication in ApJ, 26 pages, 12 b+w figures, 3 color
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Late Pop III Star Formation During the Epoch of Reionization: Results from the Renaissance Simulations
We present results on the formation of Pop III stars at redshift 7.6 from the
Renaissance Simulations, a suite of extremely high-resolution and physics-rich
radiation transport hydrodynamics cosmological adaptive-mesh refinement
simulations of high redshift galaxy formation performed on the Blue Waters
supercomputer. In a survey volume of about 220 comoving Mpc, we found 14
Pop III galaxies with recent star formation. The surprisingly late formation of
Pop III stars is possible due to two factors: (i) the metal enrichment process
is local and slow, leaving plenty of pristine gas to exist in the vast volume;
and (ii) strong Lyman-Werner radiation from vigorous metal-enriched star
formation in early galaxies suppresses Pop III formation in ("not so") small
primordial halos with mass less than 3 10 M. We
quantify the properties of these Pop III galaxies and their Pop III star
formation environments. We look for analogues to the recently discovered
luminous Ly emitter CR7 (Sobral et al. 2015), which has been
interpreted as a Pop III star cluster within or near a metal-enriched star
forming galaxy. We find and discuss a system similar to this in some respects,
however the Pop III star cluster is far less massive and luminous than CR7 is
inferred to be.Comment: 8 pages, 4 figures, 3 tables. Accepted by Ap
Probing The Ultraviolet Luminosity Function of the Earliest Galaxies with the Renaissance Simulations
In this paper, we present the first results from the Renaissance Simulations,
a suite of extremely high-resolution and physics-rich AMR calculations of high
redshift galaxy formation performed on the Blue Waters supercomputer. These
simulations contain hundreds of well-resolved galaxies at , and
make several novel, testable predictions. Most critically, we show that the
ultraviolet luminosity function of our simulated galaxies is consistent with
observations of high-z galaxy populations at the bright end of the luminosity
function (M), but at lower luminosities is essentially flat
rather than rising steeply, as has been inferred by Schechter function fits to
high-z observations, and has a clearly-defined lower limit in UV luminosity.
This behavior of the luminosity function is due to two factors: (i) the strong
dependence of the star formation rate on halo virial mass in our simulated
galaxy population, with lower-mass halos having systematically lower star
formation rates and thus lower UV luminosities; and (ii) the fact that halos
with virial masses below M do not universally
contain stars, with the fraction of halos containing stars dropping to zero at
M. Finally, we show that the brightest of our
simulated galaxies may be visible to current and future ultra-deep space-based
surveys, particularly if lensed regions are chosen for observation.Comment: 7 pages, 4 figures, accepted by The Astrophysical Journal Letter
Scaling Relations for Galaxies Prior to Reionization
The first galaxies in the Universe are the building blocks of all observed
galaxies. We present scaling relations for galaxies forming at redshifts when reionization is just beginning. We utilize the ``Rarepeak'
cosmological radiation hydrodynamics simulation that captures the complete star
formation history in over 3,300 galaxies, starting with massive Population III
stars that form in dark matter halos as small as ~. We make
various correlations between the bulk halo quantities, such as virial, gas, and
stellar masses and metallicities and their respective accretion rates,
quantifying a variety of properties of the first galaxies up to halo masses of
. Galaxy formation is not solely relegated to atomic cooling
halos with virial temperatures greater than K, where we find a dichotomy
in galaxy properties between halos above and below this critical mass scale.
Halos below the atomic cooling limit have a stellar mass -- halo mass
relationship .
We find a non-monotonic relationship between metallicity and halo mass for the
smallest galaxies. Their initial star formation events enrich the interstellar
medium and subsequent star formation to a median of and
, respectively, in halos of total mass that
is then diluted by metal-poor inflows, well beyond Population III
pre-enrichment levels of . The scaling relations presented
here can be employed in models of reionization, galaxy formation and chemical
evolution in order to consider these galaxies forming prior to reionization.Comment: 10 pages, 10 figures. Accepted to Ap
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