37 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
DEMON: a Proposal for a Satellite-Borne Experiment to study Dark Matter and Dark Energy
We outline a novel satellite mission concept, DEMON, aimed at advancing our
comprehension of both dark matter and dark energy, taking full advantage of two
complementary methods: weak lensing and the statistics of galaxy clusters. We
intend to carry out a 5000 sqdeg combined IR, optical and X-ray survey with
galaxies up to a redshift of z~2 in order to determine the shear correlation
function. We will also find ~100000 galaxy clusters, making it the largest
survey of this type to date. The DEMON spacecraft will comprise one IR/optical
and eight X-ray telescopes, coupled to multiple cameras operating at different
frequency bands. To a great extent, the technology employed has already been
partially tested on ongoing missions, therefore ensuring improved reliability.Comment: 12 pages, 3 figures, accepted for publication in the SPIE conference
proceeding
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
Backsplash galaxies in isolated clusters
At modest radii from the centre of galaxy clusters, individual galaxies may
be infalling to the cluster for the first time, or have already visited the
cluster core and are coming back out again. This latter population of galaxies
is known as the backsplash population. Differentiating them from the infalling
population presents an interesting challenge for observational studies of
galaxy evolution. To attempt to do this, we assemble a sample of 14 redshift-
and spatially-isolated galaxy clusters from the Sloan Digital Sky Survey. We
clean this sample of cluster-cluster mergers to ensure that the galaxies
contained within them are (to an approximation) only backsplashing from the
centre of their parent clusters and are not being processed in sub-clumps. By
stacking them together to form a composite cluster, we find evidence for both
categories of galaxies at intermediate radii from the cluster centre.
Application of mixture modelling to this sample then serves to differentiate
the infalling galaxies (which we model on galaxies from the cluster outskirts)
from the backsplash ones (which we model on galaxies in the high density core
with low velocity offsets from the cluster mean). We find that the fraction of
galaxies with populations similar to the low velocity cluster core galaxies is
f = -0.052R/R_virial + 0.612 +/- 0.06 which we interpret as being the
backsplash population fraction at 1<R/R_virial<2. Although some interlopers may
be affecting our results, the results are demonstrated to be in concordance
with earlier studies in this area that support density-related mechanisms as
being the prime factor in determining the star formation rate of a galaxy.Comment: Accepted for publication in MNRA
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
BRIGHTEST X-RAY CLUSTERS OF GALAXIES IN THE CFHTLS WIDE FIELDS : CATALOG AND OPTICAL MASS ESTIMATOR
Peer reviewe
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
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&