186 research outputs found
Effects of Selection and Covariance on X-ray Scaling Relations of Galaxy Clusters
We explore how the behavior of galaxy cluster scaling relations are affected
by flux-limited selection biases and intrinsic covariance among observable
properties. Our models presume log-normal covariance between luminosity (L) and
temperature (T) at fixed mass (M), centered on evolving, power-law mean
relations as a function of host halo mass. Selection can mimic evolution; the
\lm and \lt relations from shallow X-ray flux-limited samples will deviate from
mass-limited expectations at nearly all scales while the relations from deep
surveys (10^{-14} \cgsflux) become complete, and therefore unbiased, at
masses above \sims 2 \times 10^{14} \hinv \msol. We derive expressions for
low-order moments of the luminosity distribution at fixed temperature, and show
that the slope and scatter of the \lt relation observed in flux-limited samples
is sensitive to the assumed \lt correlation coefficient. In addition, \lt
covariance affects the redshift behavior of halo counts and mean luminosity in
a manner that is nearly degenerate with intrinsic population evolution.Comment: 5pages, 4 Figures, Submitted to MNRA
Statistics of X-ray observables for the cooling-core and non-cooling core galaxy clusters
We present a statistical study of the occurrence and effects of the cooling cores in the clusters of galaxies in a flux-limited sample, HIFLUGCS, based on ROSAT and ASCA observations. About 49% of the clusters in this sample have a significant, classically-calculated cooling-flow, mass-deposition rate. The upper envelope of the derived mass-deposition rate is roughly proportional to the cluster mass, and the fraction of cooling core clusters is found to decrease with it. The cooling core clusters are found to have smaller core radii than non-cooling core clusters, while some non-cooling core clusters have high values (> 0.8). In the relation of the X-ray luminosity vs. the temperature and the mass, the cooling core clusters show a significantly higher normalization. A systematic correlation analysis, also involving relations of the gas mass and the total infrared luminosity, indicates that this bias is shown to be mostly due to an enhanced X-ray luminosity for cooling core clusters, while the other parameters, like temperature, mass, and gas mass may be less affected by the occurrence of a cooling core. These results may be explained by at least some of the non-cooling core clusters being in dynamically young states compared with cooling core clusters, and they may turn into cooling core clusters in a later evolutionary stage
Astrophysical Tests of Modified Gravity: A Screening Map of the Nearby Universe
Astrophysical tests of modified modified gravity theories in the nearby
universe have been emphasized recently by Hui, Nicolis and Stubbs (2009) and
Jain and VanderPlas (2011). A key element of such tests is the screening
mechanism whereby general relativity is restored in massive halos or high
density environments like the Milky Way. In chameleon theories of gravity,
including all f(R) models, field dwarf galaxies may be unscreened and therefore
feel an extra force, as opposed to screened galaxies. The first step to study
differences between screened and unscreened galaxies is to create a 3D
screening map. We use N-body simulations to test and calibrate simple
approximations to determine the level of screening in galaxy catalogs. Sources
of systematic errors in the screening map due to observational inaccuracies are
modeled and their contamination is estimated. We then apply our methods to
create a map out to 200 Mpc in the Sloan Digital Sky Survey footprint using
data from the Sloan survey and other sources. In two companion papers this map
will be used to carry out new tests of gravity using distance indicators and
the disks of dwarf galaxies. We also make our screening map publicly available.Comment: 21 pages, 10 figure
Non-parametric modeling of the intra-cluster gas using APEX-SZ bolometer imaging data
We demonstrate the usability of mm-wavelength imaging data obtained from the
APEX-SZ bolometer array to derive the radial temperature profile of the hot
intra-cluster gas out to radius r_500 and beyond. The goal is to study the
physical properties of the intra-cluster gas by using a non-parametric
de-projection method that is, aside from the assumption of spherical symmetry,
free from modeling bias. We use publicly available X-ray imaging data from the
XMM-Newton observatory and our Sunyaev-Zel'dovich Effect (SZE) imaging data
from the APEX-SZ experiment at 150 GHz to de-project the density and
temperature profiles for the relaxed cluster Abell 2204. We derive the gas
density, temperature and entropy profiles assuming spherical symmetry, and
obtain the total mass profile under the assumption of hydrostatic equilibrium.
For comparison with X-ray spectroscopic temperature models, a re-analysis of
the recent Chandra observation is done with the latest calibration updates.
Using the non-parametric modeling we demonstrate a decrease of gas temperature
in the cluster outskirts, and also measure the gas entropy profile. These
results are obtained for the first time independently of X-ray spectroscopy,
using SZE and X-ray imaging data. The contribution of the SZE systematic
uncertainties in measuring T_e at large radii is shown to be small compared to
the Chandra systematic spectroscopic errors. The upper limit on M_200 derived
from the non-parametric method is consistent with the NFW model prediction from
weak lensing analysis.Comment: Replaced with the published version; A&A 519, A29 (2010
Deep Photometry of GRB 041006 Afterglow: Hypernova Bump at Redshift z=0.716
We present deep optical photometry of the afterglow of gamma-ray burst (GRB)
041006 and its associated hypernova obtained over 65 days after detection (55
R-band epochs on 10 different nights). Our early data (t<4 days) joined with
published GCN data indicates a steepening decay, approaching F_nu ~t^{-0.6} at
early times (<<1 day) and F_nu ~t^{-1.3} at late times. The break at
t_b=0.16+-0.04 days is the earliest reported jet break among all GRB
afterglows. During our first night, we obtained 39 exposures spanning 2.15
hours from 0.62 to 0.71 days after the burst that reveal a smooth afterglow,
with an rms deviation of 0.024 mag from the local power-law fit, consistent
with photometric errors. After t~4 days, the decay slows considerably, and the
light curve remains approximately flat at R~24 mag for a month before decaying
by another magnitude to reach R~25 mag two months after the burst. This
``bump'' is well-fitted by a k-corrected light curve of SN1998bw, but only if
stretched by a factor of 1.38 in time. In comparison with the other GRB-related
SNe bumps, GRB 041006 stakes out new parameter space for GRB/SNe, with a very
bright and significantly stretched late-time SN light curve. Within a small
sample of fairly well observed GRB/SN bumps, we see a hint of a possible
correlation between their peak luminosity and their ``stretch factor'', broadly
similar to the well-studied Phillips relation for the type Ia supernovae.Comment: ApJ Letters, accepted. Additional material available at
ftp://cfa-ftp.harvard.edu/pub/kstanek/GRB041006
The 400d Galaxy Cluster Survey Weak Lensing Programme: I: MMT/Megacam Analysis of CL0030+2618 at z=0.50
The mass function of galaxy clusters at high redshifts is a particularly
useful probe to learn about the history of structure formation and constrain
cosmological parameters. We aim at deriving reliable masses for a
high-redshift, high-luminosity sample of clusters of galaxies selected from the
400d survey of X-ray selected clusters. Here, we will focus on a particular
object, CL0030+2618 at z=0.50 Using deep imaging in three passbands with the
MEGACAM instrument at MMT, we show that MEGACAM is well-suited for measuring
gravitational shear. We detect the weak lensing signal of CL0030+2618 at 5.8
sigma significance, using the aperture mass technique. Furthermore, we find
significant tangential alignment of galaxies out to ~10 arcmin or >2r_200
distance from the cluster centre. The weak lensing centre of CL0030+2618 agrees
with several X-ray measurements and the position of the brightest cluster
galaxy. Finally, we infer a weak lensing virial mass of M_200=7.5 10^{14} M_sun
for CL0030+2618. Despite complications by a tentative foreground galaxy group
in the line of sight, the X-ray and weak lensing estimates for CL0030+2618 are
in remarkable agreement. This study paves the way for the largest weak lensing
survey of high-redshift galaxy clusters to date.Comment: 32 pages, 24 figures, submitted to Astronomy & Astrophysics; fixed
some LaTeX issues, now 30 pages v3: Improved version accepted by Astronomy &
Astrophysic
XMM-Newton Observations of A133: A Weak Shock Passing through the Cool Core
We use XMM-Newton observations of the cluster of galaxies A133 to study the
X-ray spectrum of the intracluster medium (ICM). We find a cold front to the
southeast of the cluster core. From the pressure profile near the cold front,
we derive an upper limit to the velocity of the core relative to the rest of
the cluster of <230 km s^-1. Our previous Chandra image of A133 showed a
complex, bird-like morphology in the cluster core. Based on the XMM-Newton
spectra and hardness ratio maps, we argue that the wings of this structure are
a weak shock front. The shock was probably formed outside the core of the
cluster, and may be heating the cluster core. Our Chandra image also showed a
``tongue'' of relatively cool gas extending from the center of the cD to the
center of the radio relic. The XMM-Newton results are consistent with the idea
that the tongue is the gas which has been uplifted by a buoyant radio bubble
including the radio relic to the northwest of the core. Alternatively, the
tongue might result from a cluster merger. The small velocity of the core
suggests that the bubble including the relic has moved by buoyancy, rather than
by motions of the core or the ICM. We do not find clear evidence for nonthermal
X-ray emission from the radio relic. Based on the upper limit on the inverse
Compton emission, we derive a lower limit on the magnetic field in the relic of
B>~1.5\mu G.Comment: 29 pages, ApJ in pres
X-ray Imaging Spectroscopy of Abell 1835
We present detailed spatially-resolved spectroscopy results of the
observation of Abell 1835 using the European Photon Imaging Cameras (EPIC) and
the Reflection Grating Spectrometers (RGS) on the XMM-Newton observatory. Abell
1835 is a luminous ( ergs ), medium redshift (),
X-ray emitting cluster of galaxies. The observations support the
interpretation that large amounts of cool gas are present in a multi-phase
medium surrounded by a hot (=8.2 keV) outer envelope. We detect O VIII
Ly and two Fe XXIV complexes in the RGS spectrum. The emission measure
of the cool gas below =2.7 keV is much lower than expected from
standard cooling-flow models, suggesting either a more complicated cooling
process than simple isobaric radiative cooling or differential cold absorption
of the cooler gas.Comment: 6 pages, 4 figures, Accepted by A&A letters, XMM issu
Evolution of BCGs structural parameters in the last 6 Gyr: feedback processes versus merger events
We present results on the evolution in the last 6 Gyr of the structural
parameters of two samples of brightest cluster galaxies (BCGs). The nearby
sample of BCGs consist on 69 galaxies from the WINGS survey spanning a redshift
range of 0.04z0.07. The intermediate redshift (0.3z0.6) sample is
formed by 20 BCGs extracted from the Hubble Space Telescope archive. Both
samples have similar spatial resolution and their host clusters have similar
X-ray luminosities. We report an increase in the size of the BCGs from
intermediate to local redshift. However, we do not detect any variation in the
S\'ersic shape parameter in both samples. These results are proved to be robust
since the observed tendencies are model independent. We also obtain significant
correlations between some of the BCGs parameters and the main properties of the
host clusters. More luminous, larger and centrally located BCGs are located in
more massive and dominant galaxy clusters. These facts indicate that the host
galaxy cluster has played an important role in the formation of their BCGs. We
discuss the possible mechanisms that can explain the observed evolution of the
structural parameters of the BCGs. We conclude that the main mechanisms that
can explain the increase in size and the non-evolution in the S\'ersic shape
parameter of the BCGs in the last 6 Gyr are feedback processes. This result
disagrees with semi-analytical simulation results supporting that merging
processes are the main responsible for the evolution of the BCGs until the
present epoch.Comment: Accepted for publication in ApJ; 17 pages, 7 figures; 10 table
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