2,902 research outputs found
The Luminosity Function of Field Galaxies in the CNOC1 Redshift Survey
We have computed the luminosity function for 389 field galaxies from the
Canadian Network for Observational Cosmology cluster redshift survey (CNOC1),
over redshifts z = 0.2-0.6. We find Schechter parameters M^* - 5 log h = -19.6
\pm 0.3 and \alpha = -0.9 \pm 0.2 in rest-frame B_{AB}. We have also split our
sample at the color of a redshifted but nonevolving Sbc galaxy, and find
distinctly different luminosity functions for red and blue galaxies. Red
galaxies have a shallow slope \alpha \approx -0.4 and dominate the bright end
of the luminosity function, while blue galaxies have a steep \alpha \approx
-1.4 and prevail at the faint end. Comparisons of the CNOC1 results to those
from the Canada-France (CFRS) and Autofib redshift surveys show broad agreement
among these independent samples, but there are also significant differences
which will require larger samples to resolve. Also, in CNOC1 the red galaxy
luminosity density stays about the same over the range z = 0.2-0.6, while the
blue galaxy luminosity density increases steadily with redshift. These results
are consistent with the trend of the luminosity density vs. redshift relations
seen in the CFRS, though the normalizations of the luminosity densities appear
to differ for blue galaxies. Comparison to the local luminosity function from
the Las Campanas redshift survey (LCRS) shows that the luminosity density at z
\approx 0.1 is only about half that seen at z \approx 0.4. A change in the
luminosity function shape, particularly at the faint end, appears to be
required to match the CNOC1 and LCRS luminosity functions, if galaxy evolution
is the sole cause of the differences seen. However, it should be noted that the
specific details of the construction of different surveys may complicate the
comparison of results and so may need to be considered carefully.Comment: 22 pages, including 6 postscript figures, uses AASTEX v4.0 style
files. Corrected minor typos and updated references. Results and conclusions
unchanged. Final version to appear in the Astrophysical Journa
Probing the Relation Between X-ray-Derived and Weak-Lensing-Derived Masses for Shear-Selected Galaxy Clusters: I. A781
We compare X-ray and weak-lensing masses for four galaxy clusters that
comprise the top-ranked shear-selected cluster system in the Deep Lens Survey.
The weak-lensing observations of this system, which is associated with A781,
are from the Kitt Peak Mayall 4-m telescope, and the X-ray observations are
from both Chandra and XMM-Newton. For a faithful comparison of masses, we adopt
the same matter density profile for each method, which we choose to be an NFW
profile. Since neither the X-ray nor weak-lensing data are deep enough to well
constrain both the NFW scale radius and central density, we estimate the scale
radius using a fitting function for the concentration derived from cosmological
hydrodynamic simulations and an X-ray estimate of the mass assuming
isothermality. We keep this scale radius in common for both X-ray and
weak-lensing profiles, and fit for the central density, which scales linearly
with mass. We find that for three of these clusters, there is agreement between
X-ray and weak-lensing NFW central densities, and thus masses. For the other
cluster, the X-ray central density is higher than that from weak-lensing by 2
sigma. X-ray images suggest that this cluster may be undergoing a merger with a
smaller cluster. This work serves as an additional step towards understanding
the possible biases in X-ray and weak-lensing cluster mass estimation methods.
Such understanding is vital to efforts to constrain cosmology using X-ray or
weak-lensing cluster surveys to trace the growth of structure over cosmic time.Comment: 14 pages, 7 figures, matches version in Ap
Intracluster medium of the merging cluster Abell 3395
We present a detailed imaging and spectral analysis of the merging
environment of the bimodal cluster A3395 using X-ray and radio observations.
X-ray images of the cluster show five main constituents of diffuse emission :
A3395 NE, A3395 SW, A3395 NW, A3395 W, and a filament connecting NE to W. X-ray
surface-brightness profiles of the cluster did not show any shock fronts in the
cluster. Temperature and entropy maps show high temperature and high entropy
regions in the W, the NW, the filament and between the NE and SW subclusters.
The NE, SW and W components have X-ray bolometric luminosities similar to those
of rich clusters of galaxies but have relatively higher temperatures.
Similarly, the NW component has X-ray bolometric luminosity similar to that of
isolated groups but with much higher temperature. It is, therefore, possible
that all the components of the cluster have been heated by the ongoing mergers.
The NE subcluster is the most massive and luminous constituent and other
subclusters are found to be gravitationally bound to it. The W component is
most probably either a clump of gas stripped off the SW due to ram pressure or
a separate subcluster that has merged or is merging with the SW. No X-ray
cavities are seen associated with the Wide Angle Tailed (WAT) radio source near
the centre of the SW subcluster. Minimum energy pressure in the radio
emission-peaks of the WAT galaxy is comparable with the external thermal
pressure. The radio spectrum of the WAT suggests a spectral age of ~10Myr
Scalar Field Theory in the AdS/CFT Correspondence Revisited
We consider the role of boundary conditions in the
correspondence for the scalar field theory. Also a careful analysis of some
limiting cases is presented. We study three possible types of boundary
conditions, Dirichlet, Neumann and mixed. We compute the two-point functions of
the conformal operators on the boundary for each type of boundary condition. We
show how particular choices of the mass require different treatments. In the
Dirichlet case we find that there is no double zero in the two-point function
of the operator with conformal dimension . The Neumann case leads
to new normalizations for the boundary two-point functions. In the massless
case we show that the conformal dimension of the boundary conformal operator is
precisely the unitarity bound for scalar operators. We find a one-parameter
family of boundary conditions in the mixed case. There are again new
normalizations for the boundary two-point functions. For a particular choice of
the mixed boundary condition and with the mass squared in the range
the boundary operator has conformal dimension comprised
in the interval . For mass squared
the same choice of mixed boundary condition leads to a boundary operator whose
conformal dimension is the unitarity bound.Comment: 22 pages, LaTeX, minor errors corrected, Conclusions and one
reference added, final version to be published in Nucl. Phys.
Spectral and temporal properties of RX J0520.5-6932 (LXP 8.04) during a type-I outburst
We observed RX J0520.5-6932 in the X-rays and studied the optical light curve
of its counterpart to verify it as a Be/X-ray binary. We performed an
XMM-Newton anticipated target of opportunity observation in January 2013 during
an X-ray outburst of the source in order to search for pulsations and derive
its spectral properties. We monitored the source with Swift to follow the
evolution of the outburst and to look for further outbursts to verify the
regular pattern seen in the optical light curve with a period of ~24.4 d. The
XMM-Newton EPIC light curves show coherent X-ray pulsations with a period of
8.035331(15) s (1 sigma). The X-ray spectrum can be modelled by an absorbed
power law with photon index of ~0.8, an additional black-body component with
temperature of ~0.25 keV and an Fe K line. Phase-resolved X-ray spectroscopy
reveals that the spectrum varies with pulse phase. We confirm the
identification of the optical counterpart within the error circle of XMM-Newton
at an angular distance of ~0.8 arcsec, which is an O9Ve star with known Halpha
emission. By analyzing the combined data from three OGLE phases we derived an
optical period of 24.43 d.The X-ray pulsations and long-term variability, as
well as the properties of the optical counterpart, confirm that RX J0520.5-6932
is a Be/X-ray binary pulsar in the Large Magellanic Cloud. Based on the X-ray
monitoring of the source we conclude that the event in January 2013 was a
moderately bright type-I X-ray outburst, with a peak luminosity of 1.79e36
erg/s.Comment: 10 pages, 9 figures, accepted A&
Suzaku Observations of AWM 7 Cluster of Galaxies: Temperature, Abundance and Bulk Motions
We carried out 3 observations of the cluster of galaxies AWM 7, for the
central region and 20'-east and 20'-west offset regions, with Suzaku.
Temperature and abundance profiles are measured out to 27'~ 570 /h_70 kpc,
which corresponded to ~0.35 r_180. The temperature of the intra-cluster medium
(ICM) slightly decreases from 3.8 keV at the center to 3.4 keV in ~0.35 r_180
region, indicating a flatter profile than those in other nearby clusters.
Abundance ratio of Si to Fe is almost constant in our observation, while Mg to
Fe ratio increases with radius from the cluster center. O to Fe ratio in the
west region shows increase with radius, while that in the east region is almost
flat, though the errors are relatively large. These features suggest that the
enrichment process is significantly different between products of type II
supernovae (O and Mg) and those by type Ia supernovae (Si and Fe). We also
examined positional shift of the central energy of He-like Fe-Ka line, in
search of possible rotation of the ICM. The 90% upper limit for the
line-of-sight velocity difference was derived to be v ~ 2000 km/s, suggesting
that the ellipticity of AWM 7 is rather caused by a recent directional infall
of the gas along the large-scale filament.Comment: 11 pages, 7 figures, accepted for publication in PAS
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