28 research outputs found
Dark matter halo properties from galaxy-galaxy lensing
We present results for a galaxy-galaxy lensing study based on imaging data
from the Canada-France-Hawaii Telescope Legacy Survey Wide. From a 12 million
object multi-colour catalogue for 124 deg^2 of photometric data in the
u*g'r'i'z' filters we compute photometric redshifts (with a scatter of
\sigma_{\Delta z/(1+z)} = 0.033 and an outlier rate of \eta=2.0 per cent for
i'<=22.5) and extract galaxy shapes down to i'=24.0. We select a sample of
lenses and sources with 0.05 < z_d <= 1 and 0.05 < z_s <= 2. We fit three
different galaxy halo profiles to the lensing signal, a singular isothermal
sphere (SIS), a truncated isothermal sphere (BBS) and a universal density
profile (NFW). We derive velocity dispersions by fitting an SIS out to 100
h^{-1} kpc to the excess surface mass density \Delta\Sigma and perform maximum
likelihood analyses out to a maximum scale of 2 h^{-1} Mpc to obtain halo
parameters and scaling relations. We find luminosity scaling relations of
\sigma_{red} ~ L^{0.24+-0.03} for the red lens sample, \sigma_{blue} ~
L^{0.23+-0.03} for blue lenses and \sigma ~ L^{0.29+-0.02} for the combined
lens sample with zeropoints of \sigma*_{red}=162+-2 km/s, \sigma*_{blue}=115+-3
km/s and \sigma*=135+-2 km/s at a chosen reference luminosity L*_{r'} = 1.6
\times 10^10 h^{-2} L_{r',sun}. The steeper slope for the combined sample is
due to the different zeropoints of the blue and red lenses and the fact that
blue lenses dominate at low luminosities and red lenses at high luminosities.
The mean effective redshifts for the lens samples are =0.28 for red
lenses, =0.35 for blue lenses and =0.34 for the combined lens
sample.Comment: 62 pages, 55 figures, accepted for publication in MNRAS, abridged
abstract, includes corrections from final proof. Our created catalogues
(photometry, photometric redshifts and shears) are publicly available at
http://www.usm.uni-muenchen.de/people/stella/GGL
Mining the gap: evolution of the magnitude gap in X-ray galaxy groups from the 3 square degree XMM coverage of CFHTLS
We present a catalog of 129 X-ray galaxy groups, covering a redshift range
0.04<z<1.23, selected in the ~3 square degree part of the CFHTLS W1 field
overlapping XMM observations performed under the XMM-LSS project. We carry out
a statistical study of the redshift evolution out to redshift one of the
magnitude gap between the first and the second brightest cluster galaxies of a
well defined mass-selected group sample. We find that the slope of the relation
between the fraction of groups and the magnitude gap steepens with redshift,
indicating a larger fraction of fossil groups at lower redshifts. We find that
22.26% of our groups at z0.6 are fossil groups. We compare our
results with the predictions of three semi-analytic models based on the
Millennium simulation. The intercept of the relation between the magnitude of
the brightest galaxy and the value of magnitude gap becomes brighter with
increasing redshift. This trend is steeper than the model predictions which we
attribute to the younger stellar age of the observed brightest cluster
galaxies. This trend argues in favor of stronger evolution of the feedback from
active galactic nuclei at z<1 compared to the models. The slope of the relation
between the magnitude of the brightest cluster galaxy and the value of the gap
does not evolve with redshift and is well reproduced by the models, indicating
that the tidal galaxy stripping, put forward as an explanation of the
occurrence of the magnitude gap, is both a dominant mechanism and is
sufficiently well modeled
X-Ray Groups of Galaxies in the Aegis Deep and Wide Fields
We present the results of a search for extended X-ray sources and their
corresponding galaxy groups from 800-ks Chandra coverage of the All-wavelength
Extended Groth Strip International Survey (AEGIS). This yields one of the
largest X-ray selected galaxy group catalogs from a blind survey to date. The
red-sequence technique and spectroscopic redshifts allow us to identify 100
of reliable sources, leading to a catalog of 52 galaxy groups. The groups span
the redshift range and virial mass range
. For the 49 extended
sources which lie within DEEP2 and DEEP3 Galaxy Redshift Survey coverage, we
identify spectroscopic counterparts and determine velocity dispersions. We
select member galaxies by applying different cuts along the line of sight or in
projected spatial coordinates. A constant cut along the line of sight can cause
a large scatter in scaling relations in low-mass or high-mass systems depending
on the size of cut. A velocity dispersion based virial radius can more
overestimate velocity dispersion in comparison to X-ray based virial radius for
low mass systems. There is no significant difference between these two radial
cuts for more massive systems. Independent of radial cut, overestimation of
velocity dispersion can be created in case of existence of significant
substructure and also compactness in X-ray emission which mostly occur in low
mass systems. We also present a comparison between X-ray galaxy groups and
optical galaxy groups detected using the Voronoi-Delaunay method (VDM) for
DEEP2 data in this field.Comment: Accepted for publication in AP
BRIGHTEST X-RAY CLUSTERS OF GALAXIES IN THE CFHTLS WIDE FIELDS : CATALOG AND OPTICAL MASS ESTIMATOR
Peer reviewe
Weak lensing mass estimates of galaxy groups and the line-of-sight contamination
Weak lensing is an important technique to determine the masses of galaxy
groups. However, the distortion imprint on the shape of the background galaxies
is affected by all the mass content along the line-of-sight. Using COSMOS shear
mock data we study the shear profile of 165 groups and investigate the level at
which the neighbouring groups can enhance or suppress the shear signal from the
main halo. Our mock data are based on CFHT and Subaru observations and the
information on the galaxy groups is taken from the COSMOS X-ray catalogue of
extended sources. The expected gravitational shear field of these groups is
calculated assuming that the haloes follow NFW density profiles. We conclude
that, on average, the signal-to-noise for a detection of the main halo is
affected by ~15%x\sqrt{ngal/30} with respect to the signal-to-noise the same
halo would have if it was isolated in the sky. Groups with neighbours that are
close in projected distance (<1') are the most affected, but haloes located at
larger angular distances also cause a measurable shear signal, which can be
interpreted as uncorrelated large-scale structure. The average bias in the mass
excess estimate of individual groups that is introduced by the external haloes
is zero with an rms of ~6-72%, depending on the aperture size used. The shear
signal introduced by large-scale structure acts as an external source of noise.
The averaged uncertainty introduced is \sigma_{\gamma_t}^{LSS}~0.006 per
component for an aperture size of ~5', which corresponds to 1.8% of the
one-component intrinsic ellipticity value. This large-scale structure noise
error becomes equal to intrinsic ellipticity noise if there are measurements
for ~3000 galaxies within a certain aperture, a number that is already achieved
by current deep surveys such as COSMOS and, therefore, should not be ignored.Comment: 23 pages, 20 figures. Accepted for publication in MNRA
First simultaneous optical/near-infrared imaging of an X-ray selected, high-redshift cluster of galaxies with GROND: the galaxy population of XMMU J0338.7+0030 at z=1.1
The XMM-Newton Distant Cluster Project is a serendipitous survey for clusters
of galaxies at redshifts z>=0.8 based on deep archival XMM-Newton observations.
... Low-significance candidate high-z clusters are followed up with the
seven-channel imager GROND (Gamma-Ray Burst Optical and Near-Infrared Detector)
that is mounted at a 2m-class telescope. ... The test case is XMMU
J0338.7+0030, suggested to be at z~1.45+/-0.15 from the analysis of the z-H vs
H colour-magnitude diagram obtained from the follow-up imaging. Later VLT-FORS2
spectroscopy enabled us to identify four members, which set this cluster at
z=1.097+/-0.002. To reach a better knowledge of its galaxy population, we
observed XMMU J0338.7+0030 with GROND for about 6 hr. The publicly available
photo-z code le Phare was used. The Ks-band number counts of the non-stellar
sources out of the 832 detected down to z'~26 AB-mag in the 3.9x4.3 square
arcmin region of XMMU J0338.7+0030 imaged at all GROND bands clearly exceed
those computed in deep fields/survey areas at ~20.5 - 22.5 AB-mag. The
photo-z's of the three imaged spectroscopic members yield z=1.12+/-0.09. The
spatial distribution and the properties of the GROND sources with a photo-z in
the range 1.01 - 1.23 confirm the correspondence of the X-ray source with a
galaxy over-density at a significance of at least 4.3 sigma. Candidate members
that are spectro-photometrically classified as elliptical galaxies define a red
locus in the i'-z' vs z' colour-magnitude diagram that is consistent with the
red sequence of the cluster RDCS J0910+5422 at z=1.106. XMMU J0338.7+0030 hosts
also a population of bluer late-type spirals and irregulars. The starbursts
among the photometric members populate both loci, consistently with previous
results. The analysis of the available data set indicates that XMMU
J0338.7+0030 is a low-mass cluster (M_200 ~ 1E14 M_sun) at z=1.1. (Abridged)Comment: accepted for publication in Astronomy & Astrophysics Main Journal, 27
pages, 24 figures, 1 tabl
CFHTLenS: weak lensing calibrated scaling relations for low-mass clusters of galaxies
We present weak lensing and X-ray analysis of 12 low-mass clusters from the Canada-France-Hawaii Telescope Lensing Survey and XMM-CFHTLS surveys. We combine these systems with high-mass systems from Canadian Cluster Comparison Project and low-mass systems from Cosmic Evolution Survey to obtain a sample of 70 systems, spanning over two orders of magnitude in mass. We measure core-excised LX-TX, M-LX and M-TX scaling relations and include corrections for observational biases. By providing fully bias-corrected relations, we give the current limitations for LX and TX as cluster mass proxies. We demonstrate that TX benefits from a significantly lower intrinsic scatter at fixed mass than LX. By studying the residuals of the bias-corrected relations, we show for the first time using weak lensing masses that galaxy groups seem more luminous and warmer for their mass than clusters. This implies a steepening of the M-LX and M-TX relations at low masses. We verify the inferred steepening using a different high-mass sample from the literature and show that variance between samples is the dominant effect leading to discrepant scaling relations. We divide our sample into subsamples of merging and relaxed systems, and find that mergers may have enhanced scatter in lensing measurements, most likely due to stronger triaxiality and more substructure. For the LX-TX relation, which is unaffected by lensing measurements, we find the opposite trend in scatter. We also explore the effects of X-ray cross-calibration and find that Chandra calibration leads to flatter LX-TX and M-TX relations than XMM-Newto
CFHTLenS: Weak lensing calibrated scaling relations for low mass clusters of galaxies
We present weak lensing and X-ray analysis of 12 low mass clusters from the
CFHTLenS and XMM-CFHTLS surveys. We combine these systems with high-mass
systems from CCCP and low-mass systems from COSMOS to obtain a sample of 70
systems, spanning over two orders of magnitude in mass. We measure core-excised
Lx-Tx, M-Lx and M-Tx scaling relations and include corrections for
observational biases. By providing fully bias corrected relations, we give the
current limitations for Lx and Tx as cluster mass proxies. We demonstrate that
Tx benefits from a significantly lower intrinsic scatter at fixed mass than Lx.
By studying the residuals of the bias corrected relations, we show for the
first time using weak lensing masses that galaxy groups seem more luminous and
warmer for their mass than clusters. This implies a steepening of the M-Lx and
M-Tx relations at low masses. We verify the inferred steepening using a
different high mass sample from the literature and show that variance between
samples is the dominant effect leading to discrepant scaling relations. We
divide our sample into subsamples of merging and relaxed systems, and find that
mergers may have enhanced scatter in lensing measurements, most likely due to
stronger triaxiality and more substructure. For the Lx-Tx relation, which is
unaffected by lensing measurements, we find the opposite trend in scatter. We
also explore the effects of X-ray cross-calibration and find that Chandra
calibration leads to flatter Lx-Tx and M-Tx relations than XMM-Newton.Comment: Analysis modified to include bias correction. Updated CCCP
measurements. Comments are welcome, submitted to MNRAS, 26 pages, 20 figure
A pan-chromatic view of the galaxy cluster XMMU J1230.3+1339 at z=0.975 - Observing the assembly of a massive system
We present a comprehensive galaxy cluster study of XMMU J1230.3+1339 based on
a joint analysis of X-ray data, optical imaging and spectroscopy observations,
weak lensing results, and radio properties for achieving a detailed
multi-component view of this newly discovered system at z=0.975. We find an
optically very rich and massive system with
M200(4.20.8)10^14 M\sun, Tx5.3(+0.7--0.6)keV,
and Lx(6.50.7)10^44 erg/s, for which various widely used
mass proxies are measured and compared. We have identified multiple
cluster-related components including a central fly-through group close to core
passage with associated marginally extended 1.4GHz radio emission possibly
originating from the turbulent wake region of the merging event. On the cluster
outskirts we see evidence for an on-axis infalling group with a second
Brightest Cluster Galaxy (BCG) and indications for an additional off-axis group
accretion event. We trace two galaxy filaments beyond the nominal cluster
radius and provide a tentative reconstruction of the 3D-accretion geometry of
the system. In terms of total mass, ICM structure, optical richness, and the
presence of two dominant BCG-type galaxies, the newly confirmed cluster XMMU
J1230.3+1339 is likely the progenitor of a system very similar to the local
Coma cluster, differing by 7.6 Gyr of structure evolution.Comment: 26 pages, 14 color figures, accepted for publication in A&
The Cosmic Web and galaxy evolution around the most luminous X-ray cluster: RXJ1347.5-1145
In this paper we study the large scale structures and their galaxy content
around the most X-ray luminous cluster known, RX J1347.5-1145 at z=0.45. We
make use of ugriz CFHT MEGACAM photometry and VIMOS VLT spectroscopy to
identify structures around the RXJ1347 on a scale of 20x20 Mpc2. We construct
maps of the galaxy distribution and the fraction of blue galaxies. We study the
photometric galaxy properties as a function of environment, traced by the
galaxy density. We identify group candidates based on galaxy overdensities and
study their galaxy content. We also use available GALEX NUV imaging to identify
strong unobscured star forming galaxies. We find that the large scale structure
around RXJ1347 extends in the NE-SW direction for at least 20 Mpc, in which
most of the group candidates are located. As other studies, we find that the
fraction of blue galaxies (Fblue) is a function of galaxy number density, but
the bulk of the trend is due to galaxies belonging to massive systems. The
fraction of the UV-bright galaxies is also function of environment, but their
relative numbers compared to the blue population seems to be constant
regardless of the environment. These UV emitters also have similar properties
at all galaxy densities, indicating that the transition between galaxy types
occurs in short time-scales. Candidate galaxy groups show a large variation in
their galaxy content and Fblue in those groups display little dependence with
galaxy density. This may indicate possible differences in their evolutionary
status or the processes that are acting in groups are different than in
clusters. The large scale structure around rich clusters are dynamic places for
galaxy evolution. In the case of RXJ1347 the transformation may start within
infalling groups to finish with the removal of the cold gas once galaxies are
accreted in massive systems. (ABRIDGED)Comment: Accepted for publication in MNRA