18 research outputs found
Evolution of the X-ray Profiles of Poor Clusters from the XMM-LSS Survey
A sample consisting of 27 X-ray selected galaxy clusters from the XMM-LSS
survey is used to study the evolution in the X-ray surface brightness profiles
of the hot intracluster plasma. These systems are mostly groups and poor
clusters, with temperatures 0.6-4.8 keV, spanning the redshift range 0.05 to
1.05. Comparing the profiles with a standard beta-model motivated by studies of
low redshift groups, we find 54% of our systems to possess a central excess,
which we identify with a cuspy cool core. Fitting beta-model profiles, allowing
for blurring by the XMM point spread function, we investigate trends with both
temperature and redshift in the outer slope (beta) of the X-ray surface
brightness, and in the incidence of cuspy cores. Fits to individual cluster
profiles and to profiles stacked in bands of redshift and temperature indicate
that the incidence of cuspy cores does not decline at high redshifts, as has
been reported in rich clusters. Rather such cores become more prominent with
increasing redshift. Beta shows a positive correlation with both redshift and
temperature. Given the beta-T trend seen in local systems, we assume that
temperature is the primary driver for this trend. Our results then demonstrate
that this correlation is still present at z~0.3, where most of our clusters
reside.Comment: Accepted for publication in MNRAS. 15 pages, 12 figure
High redshift X-ray cooling-core cluster associated with the luminous radio loud quasar 3C186
We present the first results from a new, deep (200ks) Chandra observation of
the X-ray luminous galaxy cluster surrounding the powerful (L ~10^47 erg/s),
high-redshift (z=1.067), compact-steep-spectrum radio-loud quasar 3C186. The
diffuse X-ray emission from the cluster has a roughly ellipsoidal shape and
extends out to radii of at least ~60 arcsec (~500 kpc). The centroid of the
diffuse X-ray emission is offset by 0.68(+/-0.11) arcsec (5.5+/-0.9 kpc) from
the position of the quasar. We measure a cluster mass within the radius at
which the mean enclosed density is 2500 times the critical density,
r_2500=283(+18/-13)kpc, of 1.02 (+0.21/-0.14)x10^14 M_sun. The gas mass
fraction within this radius is f_gas=0.129(+0.015/-0.016). This value is
consistent with measurements at lower redshifts and implies minimal evolution
in the f_gas(z) relation for hot, massive clusters at 0<z<1.1. The measured
metal abundance of 0.42(+0.08/-0.07) Solar is consistent with the abundance
observed in other massive, high redshift clusters. The spatially-resolved
temperature profile for the cluster shows a drop in temperature, from kT~8 keV
to kT~3 keV, in its central regions that is characteristic of cooling core
clusters. This is the first spectroscopic identification of a cooling core
cluster at z>1. We measure cooling times for the X-ray emitting gas at radii of
50 kpc and 25 kpc of 1.7(+/-0.2)x10^9 years and 7.5(+/-2.6)x 10^8 years, as
well as a nominal cooling rate (in the absence of heating) of
400(+/-190)M_sun/year within the central 100 kpc. In principle, the cooling gas
can supply enough fuel to support the growth of the supermassive black hole and
to power the luminous quasar. The radiative power of the quasar exceeds by a
factor of 10 the kinematic power of the central radio source, suggesting that
radiative heating may be important at intermittent intervals in cluster cores.Comment: 15 pages, 9 figures, ApJ in pres
Luminosity Functions of XMM-LSS C1 Galaxy Clusters
CFHTLS optical photometry has been used to study the galaxy luminosity
functions of 14 X-ray selected clusters from the XMM-LSS survey. These are
mostly groups and poor clusters, with masses (M_{500}) in the range 0.6 to
19x10 ^{13} M_solar and redshifts 0.05-0.61. Hence these are some of the
highest redshift X-ray selected groups to have been studied. Lower and upper
colour cuts were used to determine cluster members. We derive individual
luminosity functions (LFs) for all clusters as well as redshift-stacked and
temperature-stacked LFs in three filters, g', r' and z', down to M=-14.5. All
LFs were fitted by Schechter functions which constrained the faint-end slope,
alpha, but did not always fit well to the bright end. Derived values of alpha
ranged from -1.03 to as steep as -2.1. We find no evidence for upturns at faint
magnitudes. Evolution in alpha was apparent in all bands: it becomes shallower
with increasing redshift; for example, in the z' band it flattened from -1.75
at low redshift to -1.22 in the redshift range z=0.43-0.61. Eight of our
systems lie at z~0.3, and we combine these to generate a galaxy LF in three
colours for X-ray selected groups and poor clusters at redshift 0.3. We find
that at z~0.3 alpha is steeper (-1.67) in the green (g') band than it is
(-1.30) in the red (z') band. This colour trend disappears at low redshift,
which we attribute to reddening of faint blue galaxies from z~0.3 to z~0. We
also calculated the total optical luminosity and found it to correlate strongly
with X-ray luminosity (L_X proportional to L_OPT^(2.1)), and also with ICM
temperature (L_OPT proportional to T^(1.62)), consistent with expectations for
self-similar clusters with constant mass-to-light ratio. We did not find any
convincing correlation of Schechter parameters with mean cluster temperature.Comment: 23 pages, 17 figure
The XMM-LSS Survey: A well controlled X-ray cluster sample over the D1 CFHTLS area
We present the XMM-LSS cluster catalogue corresponding to the CFHTLS D1 area.
The list contains 13 spectroscopically confirmed, X-ray selected galaxy
clusters over 0.8 deg2 to a redshift of unity and so constitutes the highest
density sample of clusters to date. Cluster X-ray bolometric luminosities range
from 0.03 to 5x10^{44} erg/s. In this study, we describe our catalogue
construction procedure: from the detection of X-ray cluster candidates to the
compilation of a spectroscopically confirmed cluster sample with an explicit
selection function. The procedure further provides basic X-ray products such as
cluster temperature, flux and luminosity. We detected slightly more clusters
with a (0.5-2.0 keV) X-ray fluxes of >2x10^{-14} erg/s/cm^{-2} than we expected
based on expectations from deep ROSAT surveys. We also present the
Luminosity-Temperature relation for our 9 brightest objects possessing a
reliable temperature determination. The slope is in good agreement with the
local relation, yet compatible with a luminosity enhancement for the 0.15 < z<
0.35 objects having 1 < T < 2 keV, a population that the XMM-LSS is identifying
systematically for the first time. The present study permits the compilation of
cluster samples from XMM images whose selection biases are understood. This
allows, in addition to studies of large-scale structure, the systematic
investigation of cluster scaling law evolution, especially for low mass X-ray
groups which constitute the bulk of our observed cluster population. All
cluster ancillary data (images, profiles, spectra) are made available in
electronic form via the XMM-LSS cluster database.Comment: 12 pages 5 figures, MNRAS accepted. The paper with full resolution
cluster images is available at
http://vela.astro.ulg.ac.be/themes/spatial/xmm/LSS/rel_pub_e.htm
The X-ray luminous cluster underlying the z = 1.04 quasar PKS1229-021
We present a 100 ks Chandra observation studying the extended X-ray emission
around the powerful z=1.04 quasar PKS1229-021. The diffuse cluster X-ray
emission can be traced out to ~15 arcsec (~120 kpc) radius and there is a drop
in the calculated hardness ratio inside the central 5 arcsec consistent with
the presence of a cool core. Radio observations of the quasar show a strong
core and a bright, one-sided jet leading to the SW hot spot and a second hot
spot visible on the counter-jet side. Although the wings of the quasar PSF
provided a significant contribution to the total X-ray flux at all radii where
the extended cluster emission was detected, we were able to accurately subtract
off the PSF emission using ChaRT and marx simulations. The resulting steep
cluster surface brightness profile for PKS1229-021 appears similar to the
profile for the FRII radio galaxy 3C444, which has a similarly rapid surface
brightness drop caused by a powerful shock surrounding the radio lobes (Croston
et al.). Using a model surface brightness profile based on 3C444, we estimated
the total cluster luminosity for PKS1229-021 to be L_X ~ 2 x 10^{44} erg/s. We
discuss the difficulty of detecting cool core clusters, which host bright X-ray
sources, in high redshift surveys.Comment: 10 pages, 9 figures, accepted by MNRA
The cosmological analysis of X-ray cluster surveys: I- A new method for interpreting number counts
We present a new method aiming to simplify the cosmological analysis of X-ray
cluster surveys. It is based on purely instrumental observable quantities,
considered in a two-dimensional X-ray colour-magnitude diagram (hardness ratio
versus count-rate). The basic principle is that, even in rather shallow
surveys, substantial information on cluster redshift and temperature is present
in the raw X-ray data and can be statistically extracted; in parallel, such
diagrams can be readily predicted from an ab initio cosmological modeling. We
illustrate the methodology for the case of a 100 deg2 XMM survey having a
sensitivity of ~10^{-14} ergs/s/cm^2 and fit at the same time, the survey
selection function, the cluster evolutionary scaling-relations and the
cosmology; our sole assumption -- driven by the limited size of the sample
considered in the case-study -- is that the local cluster scaling relations are
known. We devote special care to the realistic modeling of the count-rate
measurement uncertainties and evaluate the potential of the method via a Fisher
analysis. In the absence of individual cluster redshifts, the CR-HR method
appears to be much more efficient than the traditional approach based on
cluster counts (i.e. dn/dz, requiring redshifts). In the case where redshifts
are available, our method performs similarly as the traditional mass function
(dn/dM/dz) for the purely cosmological parameters, but better constrains
parameters defining the cluster scaling relations and their evolution. A
further practical advantage of the CR-HR method is its simplicity : this fully
top-down approach totally bypasses the tedious steps consisting in deriving
cluster masses from X-ray temperature measurements.Comment: 18 pages, 15 figures, 3 tables. Accepted for publication in MNRAS
(minor changes with respect to previous version
The XMM-LSS catalogue: X-ray sources and associated optical data. Version I
Following the presentation of the XMM-LSS X-ray source detection package by
Pacaud et al., we provide the source lists for the first 5.5 surveyed square
degrees. The catalogues pertain to the [0.5-2] and [2-10] keV bands and contain
in total 3385 point-like or extended sources above a detection likelihood of 15
in either band. The agreement with deep logN-logS is excellent. The main
parameters considered are position, countrate, source extent with associated
likelihood values. A set of additional quantities such as astrometric
corrections and fluxes are further calculated while errors on the position and
countrate are deduced from simulations. We describe the construction of the
band-merged catalogue allowing rapid sub-sample selection and easy
cross-correlation with external multi-wavelength catalogues. A small optical
CFHTLS multi-band subset of objects is associated wich each source along with
an X-ray/optical overlay. We make the full X-ray images available in FITS
format. The data are available at CDS and, in a more extended form, at the
Milan XMM-LSS database.Comment: 13 pages, 7 figures and 11 tables (fig. 1 and 6 are enclosed in
reduced resolution), MNRAS Latex, accepted by MNRA
Satellite abundances around bright isolated galaxies
We study satellite galaxy abundances in SDSS by counting photometric galaxies
around isolated bright primaries. We present results as a function of the
luminosity, stellar mass and colour of the satellites, and of the stellar mass
and colour of the primaries. For massive primaries the luminosity and stellar
mass functions of satellites are similar in shape to those of field galaxies,
but for lower mass primaries they are significantly steeper. The steepening is
particularly marked for the stellar mass function. Satellite abundance
increases strongly with primary stellar mass, approximately in proportion to
expected dark halo mass. Massive red primaries have up to a factor of 2 more
satellites than blue ones of the same stellar mass. Satellite galaxies are
systematically redder than field galaxies of the same stellar mass. Satellites
are also systematically redder around more massive primaries. At fixed primary
mass, they are redder around red primaries. We select similarly isolated
galaxies from mock catalogues based on the simulations of Guo et al.(2011) and
analyze them in parallel with the SDSS data. The simulation reproduces all the
above trends qualitatively, except for the steepening of the satellite
luminosity and stellar mass functions. Model satellites, however, are
systematically redder than in the SDSS, particularly at low mass and around
low-mass primaries. Simulated haloes of a given mass have satellite abundances
that are independent of central galaxy colour, but red centrals tend to have
lower stellar masses, reflecting earlier quenching of their star formation by
feedback. This explains the correlation between satellite abundance and primary
colour in the simulation. The correlation between satellite colour and primary
colour arises because red centrals live in haloes which are more massive, older
and more gas-rich, so that satellite quenching is more efficient.Comment: 29 pages, 24 figure
Fundamental properties of Fanaroff-Riley II radio galaxies investigated via Monte Carlo simulations
[Abridged] Radio galaxies and quasars are among the largest and most powerful
single objects known and are believed to have had a significant impact on the
evolving Universe and its large scale structure. We explore the intrinsic and
extrinsic properties of the population of FRII objects (kinetic luminosities,
lifetimes, and the central densities of their environments). In particular, the
radio and kinetic luminosity functions of FRIIs are investigated using the
complete, flux limited radio catalogues of 3CRR and Best et al. We construct
multidimensional Monte Carlo simulations using semi-analytical models of FRII
radio source growth to create artificial samples of radio galaxies. Unlike
previous studies, we compare radio luminosity functions found with both the
observed and simulated data to explore the fundamental source parameters. We
allow the source physical properties to co-evolve with redshift, and we find
that all the investigated parameters most likely undergo cosmological
evolution. Strikingly, we find that the break in the kinetic luminosity
function must undergo redshift evolution of at least (1+z)^3. The fundamental
parameters are strongly degenerate, and independent constraints are necessary
to draw more precise conclusions. We use the estimated kinetic luminosity
functions to set constraints on the duty cycles of these powerful radio
sources. A comparison of the duty cycles of powerful FRIIs with those
determined from radiative luminosities of AGN of comparable black hole mass
suggests a transition in behaviour from high to low redshifts, corresponding to
either a drop in the typical black hole mass of powerful FRIIs at low
redshifts, or a transition to a kinetically-dominated, radiatively-inefficient
FRII population.Comment: Accepted to MNRAS. 30 pages, 18 figures, 4 tables + online material
(in appendix): 9 pages, 14 figure
The XMM Cluster Survey: X-ray analysis methodology
The XMM Cluster Survey (XCS) is a serendipitous search for galaxy clusters
using all publicly available data in the XMM-Newton Science Archive. Its main
aims are to measure cosmological parameters and trace the evolution of X-ray
scaling relations. In this paper we describe the data processing methodology
applied to the 5,776 XMM observations used to construct the current XCS source
catalogue. A total of 3,675 > 4-sigma cluster candidates with > 50
background-subtracted X-ray counts are extracted from a total non-overlapping
area suitable for cluster searching of 410 deg^2. Of these, 993 candidates are
detected with > 300 background-subtracted X-ray photon counts, and we
demonstrate that robust temperature measurements can be obtained down to this
count limit. We describe in detail the automated pipelines used to perform the
spectral and surface brightness fitting for these candidates, as well as to
estimate redshifts from the X-ray data alone. A total of 587 (122) X-ray
temperatures to a typical accuracy of < 40 (< 10) per cent have been measured
to date. We also present the methodology adopted for determining the selection
function of the survey, and show that the extended source detection algorithm
is robust to a range of cluster morphologies by inserting mock clusters derived
from hydrodynamical simulations into real XMM images. These tests show that the
simple isothermal beta-profiles is sufficient to capture the essential details
of the cluster population detected in the archival XMM observations. The
redshift follow-up of the XCS cluster sample is presented in a companion paper,
together with a first data release of 503 optically-confirmed clusters.Comment: MNRAS accepted, 45 pages, 38 figures. Our companion paper describing
our optical analysis methodology and presenting a first set of confirmed
clusters has now been submitted to MNRA