5,116 research outputs found
Low-Mass X-Ray Binaries, Millisecond Radio Pulsars, and the Cosmic Star Formation Rate
We report on the implications of the peak in the cosmic star-formation rate
(SFR) at redshift z ~ 1.5 for the resulting population of low-mass X-ray
binaries(LMXB) and for that of their descendants, the millisecond radio pulsars
(MRP). Since the evolutionary timescales of LMXBs, their progenitors, and their
descendants are thought be significant fractions of the time-interval between
the SFR peak and the present epoch, there is a lag in the turn-on of the LMXB
population, with the peak activity occurring at z ~ 0.5 - 1.0. The peak in the
MRP population is delayed further, occurring at z < 0.5. We show that the
discrepancy between the birthrate of LMXBs and MRPs, found under the assumption
of a stead-state SFR, can be resolved for the population as a whole when the
effects of a time-variable SFR are included. A discrepancy may persist for
LMXBs with short orbital periods, although a detailed population synthesis will
be required to confirm this. Further, since the integrated X-ray luminosity
distribution of normal galaxies is dominated by X-ray binaries, it should show
strong luminosity evolution with redshift. In addition to an enhancement near
the peak (z ~ 1.5) of the SFR due to the prompt turn-on of the relatively
short-lived massive X-ray binaries and young supernova remnants, we predict a
second enhancement by a factor ~10 at a redshift between ~ 0.5 and ~ 1 due to
the delayed turn-on of the LMXB population. Deep X-ray observations of galaxies
out to z ~ 1 by AXAF will be able to observe this enhancement, and, by
determining its shape as a function of redshift, will provide an important new
method for constraining evolutionary models of X-ray binaries.Comment: 13 pages, including 1 figure. Accepted for publication in ApJ Letter
The Next Generation Virgo Cluster Survey (NGVS). XVIII. Measurement and Calibration of Surface Brightness Fluctuation Distances for Bright Galaxies in Virgo (and Beyond)
We describe a program to measure surface brightness fluctuation (SBF)
distances to galaxies observed in the Next Generation Virgo Cluster Survey
(NGVS), a photometric imaging survey covering of the Virgo cluster
in the bandpasses with the Canada-France Hawaii Telescope. We
describe the selection of the sample galaxies, the procedures for measuring the
apparent -band SBF magnitude , and the calibration of the absolute
as a function of observed stellar population properties. The
multi-band NGVS data set provides multiple options for calibrating the SBF
distances, and we explore various calibrations involving individual color
indices as well as combinations of two different colors. Within the color range
of the present sample, the two-color calibrations do not significantly improve
the scatter with respect to wide-baseline, single-color calibrations involving
. We adopt the calibration as reference for the present
galaxy sample, with an observed scatter of 0.11 mag. For a few cases that lack
good photometry, we use an alternative relation based on a combination
of and colors, with only a slightly larger observed scatter of
0.12 mag. The agreement of our measurements with the best existing distance
estimates provides confidence that our measurements are accurate. We present a
preliminary catalog of distances for 89 galaxies brighter than
mag within the survey footprint, including members of the background M and W
Clouds at roughly twice the distance of the main body of the Virgo cluster. The
extension of the present work to fainter and bluer galaxies is in progress.Comment: ApJ accepte
Age- and sex-specific response to population density and sex ratio
Both population density and sex ratio shape competition for mates, resources and mating costs. Thus they may critically affect the intensity of sexual selection in the populations. Susceptibility to inter- and intrasexual competition, which changes with age in a large number of species, may additionally influence population response to these demographic factors. In this study, we monitored 16 seminatural populations of common lizards (Lacerta vivipara) to determine whether the reproductive output varied with male and female densities as a function of the individual sex and age. Our results suggest that the intensity of sexual selection was weaker in male-biased populations, supporting new theoretical models. In populations with a male-biased sex ratio, reproductive success was more equally distributed between males and, unlike female-biased populations, the choosiest females (middle-aged) did not obtain sires of higher quality than low-performance females. Our results also suggest that age may influence the intensity of sexual conflict. Middle-aged females (the class with the best performance) produced offspring with a lower body condition in male-biased populations, suggesting that they may be the preferred target of male harassment. By contrast, a male-biased sex ratio appeared to be beneficial for low-quality females, allowing these females to obtain higher quality sires and to produce offspring with a better body condition. These age- and sex-dependent responses to population density and sex ratio have important implications for population ecology and sexual selectio
Globular Cluster Systems and the Missing Satellite Problem: Implications for Cold Dark Matter Models
We analyze the metallicity distributions of globular clusters belonging to 28
early-type galaxies in the survey of Kundu & Whitmore (2001). A Monte Carlo
algorithm which simulates the chemical evolution of galaxies that grow
hierarchically via dissipationless mergers is used to determine the most
probable protogalactic mass function for each galaxy. Contrary to the claims of
Kundu & Whitmore, we find that the observed metallicity distributions are in
close agreement with the predictions of such hierarchical formation models. The
mass spectrum of protogalactic fragments for the galaxies in our sample has a
power-law behavior, with an exponent of roughly -2. This spectrum is
indistinguishable from the mass spectrum of dark matter halos predicted by cold
dark matter models for structure formation. We argue that these protogalactic
fragments, the likely sites of globular cluster formation in the early
universe, are the disrupted remains of the "missing" satellite galaxies
predicted by cold dark matter models. Our findings suggest that the solution to
the missing satellite problem is through the suppression of gas accretion in
low-mass halos after reionization, or via self-interacting dark matter, and
argue against models with suppressed small-scale power or warm dark matter.Comment: 28 pages, 19 postscript figures. Accepted for publication in the
Astrophysical Journa
The Chandra ACIS Survey of M33 (ChASeM33): Transient X-ray Sources Discovered in M33
The Chandra ACIS Survey of M33 (ChASeM33) has acquired 7 fields of ACIS data
covering M33 with 200 ks of exposure in each field. A catalog from the first 10
months of data, along with archival Chandra observations dating back to the
year 2000, is currently available. We have searched these data for transient
sources that are measured to have a 0.35-8.0 keV unabsorbed luminosity of at
least 4 erg s in one epoch and are not detected in
another epoch. This set of the survey data has yielded seven such sources,
including one previously-known supersoft source. We analyzed XMM-Newton data
from the archive distributed over the years 2000 to 2003 to search for
recurrent outbursts and to get a spectrum for the supersoft transient. We find
only one recurrent transient in our sample. The X-ray spectra, light curves,
and optical counterpart candidates of two of the other sources suggest that
they are high-mass X-ray binaries. Archival Spitzer photometry and high X-ray
absorption suggest that one of the sources is a highly variable background
active galactic nucleus. The other three sources are more difficult to
classify. The bright transient population of M33 appears to contain a large
fraction of high-mass X-ray binaries compared with the transient populations of
M31 and the Galaxy, reflecting the later morphology of M33.Comment: 33 pages, 2 tables, 10 figures, accepted for publication in Ap
The properties of the Malin 1 galaxy giant disk: A panchromatic view from the NGVS and GUViCS surveys
Low surface brightness galaxies (LSBGs) represent a significant percentage of
local galaxies but their formation and evolution remain elusive. They may hold
crucial information for our understanding of many key issues (i.e., census of
baryonic and dark matter, star formation in the low density regime, mass
function). The most massive examples - the so called giant LSBGs - can be as
massive as the Milky Way, but with this mass being distributed in a much larger
disk. Malin 1 is an iconic giant LSBG, perhaps the largest disk galaxy known.
We attempt to bring new insights on its structure and evolution on the basis of
new images covering a wide range in wavelength. We have computed surface
brightness profiles (and average surface brightnesses in 16 regions of
interest), in six photometric bands (FUV, NUV, u, g, i, z). We compared these
data to various models, testing a variety of assumptions concerning the
formation and evolution of Malin 1. We find that the surface brightness and
color profiles can be reproduced by a long and quiet star-formation history due
to the low surface density; no significant event, such as a collision, is
necessary. Such quiet star formation across the giant disk is obtained in a
disk model calibrated for the Milky Way, but with an angular momentum
approximately 20 times larger. Signs of small variations of the star-formation
history are indicated by the diversity of ages found when different regions
within the galaxy are intercompared.For the first time, panchromatic images of
Malin 1 are used to constrain the stellar populations and the history of this
iconic example among giant LSBGs. Based on our model, the extreme disk of Malin
1 is found to have a long history of relatively low star formation (about 2
Msun/yr). Our model allows us to make predictions on its stellar mass and
metallicity.Comment: Accepted in Astronomy and Astrophysic
Phases of the 2D Hubbard model at low doping
We show that the planar spiral phase of the 2D Hubbard model at low doping,
x, is unstable towards a noncoplanar spin configuration. The novel equilibrium
state we found at low doping is incommensurate with the inverse pitch of the
spiral varying as x^(1/2), but nevertheless has a dominant peak in the
susceptibility at (\pi,\pi). Relevance to the NMR and neutron scattering
experiments in La_2-xSr_xCuO_4 is disccussed.Comment: 12 pages, emtex v.3.
Pseudoseptic Arthritis: A Case Series and Review of the Literature
Purpose. Pseudoseptic arthritis is an acute inflammatory monoarthritis with a sterile synovial gram stain and culture. Pseudoseptic arthritis has been previously described in the literature in a variety of settings including rheumatoid arthritis and microcrystalline disease. Despite pseudoseptic arthritis being a described entity, there is little published data on this topic with no published reports since 1992.
Methods. This paper was a retrospective chart review over a 20-year period that identified all rheumatology inpatient consultations at our tertiary rural hospital for pseudoseptic arthritis.
Results. We identified 10 patients with pseudoseptic arthritis and presented 5 of those cases in this paper. Majority of these patients had known autoimmune inflammatory arthritis or microcrystalline inflammatory arthritis.
Conclusion. Pseudoseptic arthritis is a syndrome that should be in the differential diagnosis with patients with long standing inflammatory condition who present with an acute monoarthritis with no known bacterial source for septic arthritis
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