2,016 research outputs found
CARMA Measurements of the Sunyaev-Zel'dovich Effect in RXJ1347.5-1145
We demonstrate the Sunyaev-Zel'dovich (SZ) effect imaging capabilities of the
Combined Array for Research in Millimeter-wave Astronomy (CARMA) by presenting
an SZ map of the galaxy cluster RXJ1347.5-1145. By combining data from multiple
CARMA bands and configurations, we are able to capture the structure of this
cluster over a wide range of angular scales, from its bulk properties to its
core morphology. We find that roughly 9% of this cluster's thermal energy is
associated with sub-arcminute-scale structure imparted by a merger,
illustrating the value of high-resolution SZ measurements for pursuing cluster
astrophysics and for understanding the scatter in SZ scaling relations. We also
find that the cluster's SZ signal is lower in amplitude than suggested by a
spherically-symmetric model derived from X-ray data, consistent with
compression along the line of sight relative to the plane of the sky. Finally,
we discuss the impact of upgrades currently in progress that will further
enhance CARMA's power as an SZ imaging instrument.Comment: 8 pages, 6 figure
Constraints on the Thermal Contents of the X-ray Cavities of Cluster MS 0735.6+7421 with Sunyaev-Zel'dovich Effect Observations
Outbursts from active galactic nuclei (AGN) can inflate cavities in the
intracluster medium (ICM) of galaxy clusters and are believed to play the
primary role in offsetting radiative cooling in the ICM. However, the details
of how the energy from AGN feedback thermalizes to heat the ICM is not well
understood, partly due to the unknown composition and energetics of the
cavities. The Sunyaev-Zel'dovich (SZ) effect, a measure of the integrated
pressure along the line of sight, provides a means of measuring the thermal
contents of the cavities, to discriminate between thermal, nonthermal, and
other sources of pressure support. Here we report measurements of the SZ effect
at 30 GHz toward the galaxy cluster MS 0735.6+7421 (MS0735), using the Combined
Array for Research in Millimeter-wave Astronomy (CARMA). MS0735 hosts the most
energetic AGN outburst known and lobes of radio synchrotron emission coincident
with a pair of giant X-ray cavities across. Our CARMA maps show a
clear deficit in the SZ signal coincident with the X-ray identified cavities,
when compared to a smooth X-ray derived pressure model. We find that the
cavities have very little SZ-contributing material, suggesting that they are
either supported by very diffuse thermal plasma with temperature in excess of
hundreds of keV, or are not supported thermally. Our results represent the
first detection (with significance) of this phenomenon with the SZ
effect.Comment: 15 pages, 9 figures, submitted to ApJ Jun 2018, Accepted Dec 2018,
Published Jan 2019. This is the version of the article before editing, as
submitted by an author to ApJ. IOP Publishing Ltd is not responsible for any
errors or omissions in this version of the manuscript or any version derived
from it. The Version of Record is available online at
https://doi.org/10.3847/1538-4357/aaf88
Probing Hot Gas in Galaxy Groups through the Sunyaev-Zeldovich Effect
We investigate the potential of exploiting the Sunyaev-Zeldovich effect (SZE)
to study the properties of hot gas in galaxy groups. It is shown that, with
upcoming SZE surveys, one can stack SZE maps around galaxy groups of similar
halo masses selected from large galaxy redshift surveys to study the hot gas in
halos represented by galaxy groups. We use various models for the hot halo gas
to study how the expected SZE signals are affected by gas fraction, equation of
state, halo concentration, and cosmology. Comparing the model predictions with
the sensitivities expected from the SPT, ACT and Planck surveys shows that a
SPT-like survey can provide stringent constraints on the hot gas properties for
halos with masses M ~> 10^{13} h^{-1}Msun. We also explore the idea of using
the cross correlation between hot gas and galaxies of different luminosity to
probe the hot gas in dark matter halos without identifying galaxy groups to
represent dark halos. Our results show that, with a galaxy survey as large as
the Sloan Digital Sky Survey and with the help of the conditional luminosity
function (CLF) model, one can obtain stringent constraints on the hot gas
properties in halos with masses down to 10^{13} h^{-1}Msun. Thus, the upcoming
SZE surveys should provide a very promising avenue to probe the hot gas in
relatively low-mass halos where the majority of L*-galaxies reside.Comment: 22 pages, 16 figures, accepted for publication on MNRA
The Atacama Cosmology Telescope: Physical Properties and Purity of a Galaxy Cluster Sample Selected via the Sunyaev-Zel'dovich Effect
We present optical and X-ray properties for the first confirmed galaxy
cluster sample selected by the Sunyaev-Zel'dovich Effect from 148 GHz maps over
455 square degrees of sky made with the Atacama Cosmology Telescope. These
maps, coupled with multi-band imaging on 4-meter-class optical telescopes, have
yielded a sample of 23 galaxy clusters with redshifts between 0.118 and 1.066.
Of these 23 clusters, 10 are newly discovered. The selection of this sample is
approximately mass limited and essentially independent of redshift. We provide
optical positions, images, redshifts and X-ray fluxes and luminosities for the
full sample, and X-ray temperatures of an important subset. The mass limit of
the full sample is around 8e14 Msun, with a number distribution that peaks
around a redshift of 0.4. For the 10 highest significance SZE-selected cluster
candidates, all of which are optically confirmed, the mass threshold is 1e15
Msun and the redshift range is 0.167 to 1.066. Archival observations from
Chandra, XMM-Newton, and ROSAT provide X-ray luminosities and temperatures that
are broadly consistent with this mass threshold. Our optical follow-up
procedure also allowed us to assess the purity of the ACT cluster sample.
Eighty (one hundred) percent of the 148 GHz candidates with signal-to-noise
ratios greater than 5.1 (5.7) are confirmed as massive clusters. The reported
sample represents one of the largest SZE-selected sample of massive clusters
over all redshifts within a cosmologically-significant survey volume, which
will enable cosmological studies as well as future studies on the evolution,
morphology, and stellar populations in the most massive clusters in the
Universe.Comment: 20 pages, 15 figures, 6 tables. Accepted for publication in ApJ.
Higher resolution figures available at:
http://peumo.rutgers.edu/~felipe/e-prints
Parameterization Effects in the analysis of AMI Sunyaev-Zel'dovich Observations
Most Sunyaev--Zel'dovich (SZ) and X-ray analyses of galaxy clusters try to
constrain the cluster total mass and/or gas mass using parameterised models and
assumptions of spherical symmetry and hydrostatic equilibrium. By numerically
exploring the probability distributions of the cluster parameters given the
simulated interferometric SZ data in the context of Bayesian methods, and
assuming a beta-model for the electron number density we investigate the
capability of this model and analysis to return the simulated cluster input
quantities via three rameterisations. In parameterisation I we assume that the
T is an input parameter. We find that parameterisation I can hardly constrain
the cluster parameters. We then investigate parameterisations II and III in
which fg(r200) replaces temperature as a main variable. In parameterisation II
we relate M_T(r200) and T assuming hydrostatic equilibrium. We find that
parameterisation II can constrain the cluster physical parameters but the
temperature estimate is biased low. In parameterisation III, the virial theorem
replaces the hydrostatic equilibrium assumption. We find that parameterisation
III results in unbiased estimates of the cluster properties. We generate a
second simulated cluster using a generalised NFW (GNFW) pressure profile and
analyse it with an entropy based model to take into account the temperature
gradient in our analysis and improve the cluster gas density distribution. This
model also constrains the cluster physical parameters and the results show a
radial decline in the gas temperature as expected. The mean cluster total mass
estimates are also within 1 sigma from the simulated cluster true values.
However, we find that for at least interferometric SZ analysis in practice at
the present time, there is no differences in the AMI visibilities between the
two models. This may of course change as the instruments improve.Comment: 19 pages, 13 tables, 24 figure
Reductions in hypothalamic Gfap expression, glial cells and α-tanycytes in lean and hypermetabolic Gnasxl-deficient mice
BACKGROUND: Neuronal and glial differentiation in the murine hypothalamus is not complete at birth, but continues over the first two weeks postnatally. Nutritional status and Leptin deficiency can influence the maturation of neuronal projections and glial patterns, and hypothalamic gliosis occurs in mouse models of obesity. Gnasxl constitutes an alternative transcript of the genomically imprinted Gnas locus and encodes a variant of the signalling protein Gαs, termed XLαs, which is expressed in defined areas of the hypothalamus. Gnasxl-deficient mice show postnatal growth retardation and undernutrition, while surviving adults remain lean and hypermetabolic with increased sympathetic nervous system (SNS) activity. Effects of this knock-out on the hypothalamic neural network have not yet been investigated. RESULTS: RNAseq analysis for gene expression changes in hypothalami of Gnasxl-deficient mice indicated Glial fibrillary acid protein (Gfap) expression to be significantly down-regulated in adult samples. Histological analysis confirmed a reduction in Gfap-positive glial cell numbers specifically in the hypothalamus. This reduction was observed in adult tissue samples, whereas no difference was found in hypothalami of postnatal stages, indicating an adaptation in adult Gnasxl-deficient mice to their earlier growth phenotype and hypermetabolism. Especially noticeable was a loss of many Gfap-positive α-tanycytes and their processes, which form part of the ependymal layer that lines the medial and dorsal regions of the 3(rd) ventricle, while β-tanycytes along the median eminence (ME) and infundibular recesses appeared unaffected. This was accompanied by local reductions in Vimentin and Nestin expression. Hypothalamic RNA levels of glial solute transporters were unchanged, indicating a potential compensatory up-regulation in the remaining astrocytes and tanycytes. CONCLUSION: Gnasxl deficiency does not directly affect glial development in the hypothalamus, since it is expressed in neurons, and Gfap-positive astrocytes and tanycytes appear normal during early postnatal stages. The loss of Gfap-expressing cells in adult hypothalami appears to be a consequence of the postnatal undernutrition, hypoglycaemia and continued hypermetabolism and leanness of Gnasxl-deficient mice, which contrasts with gliosis observed in obese mouse models. Since α-tanycytes also function as adult neural progenitor cells, these findings might indicate further developmental abnormalities in hypothalamic formations of Gnasxl-deficient mice, potentially including neuronal composition and projections
The Atacama Cosmology Telescope: Sunyaev Zel'dovich Selected Galaxy Clusters at 148 GHz in the 2008 Survey
We report on twenty-three clusters detected blindly as Sunyaev-Zel'dovich
(SZ) decrements in a 148 GHz, 455 square-degree map of the southern sky made
with data from the Atacama Cosmology Telescope 2008 observing season. All SZ
detections announced in this work have confirmed optical counterparts. Ten of
the clusters are new discoveries. One newly discovered cluster, ACT-CL
J0102-4915, with a redshift of 0.75 (photometric), has an SZ decrement
comparable to the most massive systems at lower redshifts. Simulations of the
cluster recovery method reproduce the sample purity measured by optical
follow-up. In particular, for clusters detected with a signal-to-noise ratio
greater than six, simulations are consistent with optical follow-up that
demonstrated this subsample is 100% pure. The simulations further imply that
the total sample is 80% complete for clusters with mass in excess of 6x10^14
solar masses referenced to the cluster volume characterized by five hundred
times the critical density. The Compton y -- X-ray luminosity mass comparison
for the eleven best detected clusters visually agrees with both self-similar
and non-adiabatic, simulation-derived scaling laws.Comment: 13 pages, 7 figures, Accepted for publication in Ap
Constraints on the Thermal Contents of the X-Ray Cavities of Cluster MS 0735.6+7421 with Sunyaev–Zel’dovich Effect Observations
Outbursts from active galactic nuclei (AGN) can inflate cavities in the intracluster medium (ICM) of galaxy clusters and are believed to play the primary role in offsetting radiative cooling in the ICM. However, the details of how the energy from AGN feedback thermalizes to heat the ICM is not well understood, partly due to the unknown composition and energetics of the cavities. The Sunyaev–Zel'dovich (SZ) effect, a measure of the integrated pressure along the line of sight, provides a means of measuring the thermal contents of the cavities, to discriminate between thermal, nonthermal, and other sources of pressure support. Here we report measurements of the SZ effect at 30 GHz toward the galaxy cluster MS 0735.6+7421 (MS0735), using the Combined Array for Research in Millimeter-wave Astronomy (CARMA). MS0735 hosts the most energetic AGN outburst known and lobes of radio synchrotron emission coincident with a pair of giant X-ray cavities ~200 kpc across. Our CARMA maps show a clear deficit in the SZ signal coincident with the X-ray identified cavities, when compared to a smooth X-ray derived pressure model. We find that the cavities have very little SZ-contributing material, suggesting that they are either supported by very diffuse thermal plasma with temperature in excess of hundreds of keV, or are not supported thermally. Our results represent the first detection (with 4.4σ significance) of this phenomenon with the SZ effect
Compressed representation of a partially defined integer function over multiple arguments
In OLAP (OnLine Analitical Processing) data are analysed in an n-dimensional cube. The cube may be represented as a partially defined function over n arguments. Considering that often the function is not defined everywhere, we ask: is there a known way of representing the function or the points in which it is defined, in a more compact manner than the trivial one
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