20,461 research outputs found
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
Drastic change in transport of entropy with quadrupolar ordering in PrFeP
The antiferroquadrupolar ordering of PrFeP is explored by
probing thermal and thermoelectric transport. The lattice thermal conductivity
drastically increases with the ordering, as a consequence of a large drop in
carrier concentration and a strong electron-phonon coupling. The low level of
carrier density in the ordered state is confirmed by the anomalously large
values of the Seebeck and Nernst coefficients. The results are reminiscent of
URuSi and suggest that both belong to the same class of aborted
metal-insulator transitions. The magnitude of the Nernst coefficient, larger
than in any other metal, indicates a new route for Ettingshaussen cooling at
Kelvin temperatures.Comment: final published versio
The Effects of Halo Assembly Bias on Self-Calibration in Galaxy Cluster Surveys
Self-calibration techniques for analyzing galaxy cluster counts utilize the
abundance and the clustering amplitude of dark matter halos. These properties
simultaneously constrain cosmological parameters and the cluster
observable-mass relation. It was recently discovered that the clustering
amplitude of halos depends not only on the halo mass, but also on various
secondary variables, such as the halo formation time and the concentration;
these dependences are collectively termed assembly bias. Applying modified
Fisher matrix formalism, we explore whether these secondary variables have a
significant impact on the study of dark energy properties using the
self-calibration technique in current (SDSS) and the near future (DES, SPT, and
LSST) cluster surveys. The impact of the secondary dependence is determined by
(1) the scatter in the observable-mass relation and (2) the correlation between
observable and secondary variables. We find that for optical surveys, the
secondary dependence does not significantly influence an SDSS-like survey;
however, it may affect a DES-like survey (given the high scatter currently
expected from optical clusters) and an LSST-like survey (even for low scatter
values and low correlations). For an SZ survey such as SPT, the impact of
secondary dependence is insignificant if the scatter is 20% or lower but can be
enhanced by the potential high scatter values introduced by a highly correlated
background. Accurate modeling of the assembly bias is necessary for cluster
self-calibration in the era of precision cosmology.Comment: 13 pages, 5 figures, replaced to match published versio
Direct measurement of penetration length in ultra-thin and/or mesoscopic superconducting structures
We describe a method for direct measurement of the magnetic penetration
length in thin (10 - 100 nm) superconducting structures having overall
dimensions in the range 1 to 100 micrometers. The method is applicable for
broadband magnetic fields from dc to MHz frequencies.Comment: Accepted by Journal of Applied P:hysics (Jun 2006).5 pages, 5 figure
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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