460 research outputs found
On the Kauffman bracket skein module of the quaternionic manifold
We use recoupling theory to study the Kauffman bracket skein module of the
quaternionic manifold over Z[A,A^{-1}] localized by inverting all the
cyclotomic polynomials. We prove that the skein module is spanned by five
elements. Using the quantum invariants of these skein elements and the Z_2
homology of the manifold, we determine that they are linearly independent.Comment: corrected summation signs in figures 14, 15, 17. Other minor change
Evidence for a constant IMF in early-type galaxies based on their X-ray binary populations
A number of recent studies have proposed that the stellar initial mass
function (IMF) of early type galaxies varies systematically as a function of
galaxy mass, with higher mass galaxies having bottom heavy IMFs. These bottom
heavy IMFs have more low-mass stars relative to the number of high mass stars,
and therefore naturally result in proportionally fewer neutron stars and black
holes. In this paper, we specifically predict the variation in the number of
black holes and neutron stars based on the power-law IMF variation required to
reproduce the observed mass-to-light ratio trends with galaxy mass. We then
test whether such variations are observed by studying the field low-mass X-ray
binary populations (LMXBs) of nearby early-type galaxies. In these binaries, a
neutron star or black hole accretes matter from a low-mass donor star. Their
number is therefore expected to scale with the number of black holes and
neutron stars present in a galaxy. We find that the number of LMXBs per K-band
light is similar among the galaxies in our sample. These data therefore
demonstrate the uniformity of the slope of the IMF from massive stars down to
those now dominating the K-band light, and are consistent with an invariant
IMF. Our results are inconsistent with an IMF which varies from a
Kroupa/Chabrier like IMF for low mass galaxies to a steep power-law IMF (with
slope =2.8) for high mass galaxies. We discuss how these observations
constrain the possible forms of the IMF variations and how future Chandra
observations can enable sharper tests of the IMF.Comment: 12 pages, 5 figures, 2 tables, submitted to Ap
Pseudorandom Number Generators and the Square Site Percolation Threshold
A select collection of pseudorandom number generators is applied to a Monte
Carlo study of the two dimensional square site percolation model. A generator
suitable for high precision calculations is identified from an application
specific test of randomness. After extended computation and analysis, an
ostensibly reliable value of pc = 0.59274598(4) is obtained for the percolation
threshold.Comment: 11 pages, 6 figure
Discovery of the Most-Distant Double-Peaked Emitter at z=1.369
We report the discovery of the most-distant double-peaked emitter, CXOECDFS
J033115.0-275518, at z=1.369. A Keck/DEIMOS spectrum shows a clearly
double-peaked broad Mg II emission line, with FWHM 11000 km/s for
the line complex. The line profile can be well fit by an elliptical
relativistic Keplerian disk model. This is one of a handful of double-peaked
emitters known to be a luminous quasar, with excellent multiwavelength coverage
and a high-quality X-ray spectrum. CXOECDFS J033115.0-275518 is a radio-loud
quasar with two radio lobes (FR II morphology) and a radio loudness of f_{5
GHz}/f_{4400 \AA}~429. The X-ray spectrum can be modeled by a power law with
photon index 1.72 and no intrinsic absorption; the rest-frame 0.5-8.0 keV
luminosity is erg/s. The spectral energy distribution (SED)
of CXOECDFS J033115.0-275518 has a shape typical for radio-loud quasars and
double-peaked emitters at lower redshift. The local viscous energy released
from the line-emitting region of the accretion disk is probably insufficient to
power the observed line flux, and external illumination of the disk appears to
be required. The presence of a big blue bump in the SED along with the
unexceptional X-ray spectrum suggest that the illumination cannot arise from a
radiatively inefficient accretion flow.Comment: 6 pages, 5 figures, ApJ in pres
The X-Ray Zurich Environmental Study (X-ZENS). I. Chandra and XMM-Newton observations of active galactic nuclei in galaxies in nearby groups
We describe X-ray observations with Chandra and XMM-Newton of 18 galaxy
groups (M_group ~ 1-6x10^13 Msolar, z~0.05) from the Zurich Environmental Study
(ZENS). We aim to establish the frequency and properties, unaffected by host
galaxy dilution and obscuration, of AGNs in central and satellite galaxy
members, also as a function of halo-centric distance. X-ray point-source
detections are reported for 22 of 177 observed galaxies, down to a limit of
f_(0.5-8 keV) ~ 5x10^-15 erg cm^-2 s^-1, corresponding to a limiting luminosity
of L_(0.5-8 keV)~3x10^40 erg s^-1. With the majority of the X-ray sources
attributed to AGNs of low-to-moderate levels (L/L_Edd>~10^-4), we discuss the
detection rate in the context of the occupation of AGNs to halos of this mass
scale and redshift, and compare the structural/morphological properties between
AGN-active and non-active galaxies of different rank and location within the
group halos. We see a slight tendency for AGN hosts to have either relatively
brighter/denser disks (or relatively fainter/diffuse bulges) than non-active
galaxies of similar mass. At galaxy mass scales <10^11 Msolar, central galaxies
appear to be a factor ~4 more likely to host AGNs than satellite galaxies of
similar mass. This effect, coupled with the tendency for AGNs to reside in
massive galaxies, explains the (weak) trend for AGNs to be preferentially found
in the inner regions of groups, with no detectable trend with halo-centric
distance in the frequency of AGNs within the satellite population. Finally, our
data support other analyses in finding that the rate of decline with redshift
of AGN activity in groups matches that of the global AGN population, indicating
that either AGNs occur preferentially in groups, or that the evolution rate is
independent of halo mass. These trends are of potential importance, and require
X-ray coverage of a larger sample to be solidly confirmed.Comment: 18 pages, 13 figures, submitted to The Astrophysical Journal, this is
a revised version that addresses the referee's comment
A conserved filamentous assembly underlies the structure of the meiotic chromosome axis.
The meiotic chromosome axis plays key roles in meiotic chromosome organization and recombination, yet the underlying protein components of this structure are highly diverged. Here, we show that 'axis core proteins' from budding yeast (Red1), mammals (SYCP2/SYCP3), and plants (ASY3/ASY4) are evolutionarily related and play equivalent roles in chromosome axis assembly. We first identify 'closure motifs' in each complex that recruit meiotic HORMADs, the master regulators of meiotic recombination. We next find that axis core proteins form homotetrameric (Red1) or heterotetrameric (SYCP2:SYCP3 and ASY3:ASY4) coiled-coil assemblies that further oligomerize into micron-length filaments. Thus, the meiotic chromosome axis core in fungi, mammals, and plants shares a common molecular architecture, and likely also plays conserved roles in meiotic chromosome axis assembly and recombination control
The growth of typical star-forming galaxies and their supermassive black holes across cosmic time since z~2
Understanding galaxy formation and evolution requires studying the interplay between the growth of galaxies and the growth of their black holes across cosmic time. Here, we explore a sample of Hα-selected star-forming galaxies from the High Redshift Emission Line Survey and use the wealth of multiwavelength data in the Cosmic Evolution Survey field (X-rays, far-infrared and radio) to study the relative growth rates between typical galaxies and their central supermassive black holes, from z = 2.23 to z = 0. Typical star-forming galaxies at z ∼ 1–2 have black hole accretion rates (M˙BHM˙BH) of 0.001–0.01 M⊙ yr−1 and star formation rates (SFRs) of ∼10–40 M⊙ yr−1, and thus grow their stellar mass much quicker than their black hole mass (3.3±0.2 orders of magnitude faster). However, ∼3 per cent of the sample (the sources detected directly in the X-rays) show a significantly quicker growth of the black hole mass (up to 1.5 orders of magnitude quicker growth than the typical sources). M˙BHM˙BH falls from z = 2.23 to z = 0, with the decline resembling that of SFR density or the typical SFR (SFR*). We find that the average black hole to galaxy growth (M˙BHM˙BH/SFR) is approximately constant for star-forming galaxies in the last 11 Gyr. The relatively constant M˙BHM˙BH/SFR suggests that these two quantities evolve equivalently through cosmic time and with practically no delay between the two
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