28 research outputs found
The mass distribution in an assembling super galaxy group at
We present a weak gravitational lensing analysis of supergroup SG11201202,
consisting of four distinct X-ray-luminous groups, that will merge to form a
cluster comparable in mass to Coma at . These groups lie within a
projected separation of 1 to 4 Mpc and within km s and
form a unique protocluster to study the matter distribution in a coalescing
system.
Using high-resolution {\em HST}/ACS imaging, combined with an extensive
spectroscopic and imaging data set, we study the weak gravitational distortion
of background galaxy images by the matter distribution in the supergroup. We
compare the reconstructed projected density field with the distribution of
galaxies and hot X-ray emitting gas in the system and derive halo parameters
for the individual density peaks.
We show that the projected mass distribution closely follows the locations of
the X-ray peaks and associated brightest group galaxies. One of the groups that
lies at slightly lower redshift () than the other three groups
() is X-ray luminous, but is barely detected in the
gravitational lensing signal. The other three groups show a significant
detection (up to in mass), with velocity dispersions between
and km s and masses between
and , consistent with independent measurements. These groups are
associated with peaks in the galaxy and gas density in a relatively
straightforward manner. Since the groups show no visible signs of interaction,
this supports the picture that we are catching the groups before they merge
into a cluster.Comment: 10 pages, 10 figures, accepted for publication by Astronomy &
Astrophysic
On the shear estimation bias induced by the spatial variation of colour across galaxy profiles
The spatial variation of the colour of a galaxy may introduce a bias in the
measurement of its shape if the PSF profile depends on wavelength. We study how
this bias depends on the properties of the PSF and the galaxies themselves. The
bias depends on the scales used to estimate the shape, which may be used to
optimise methods to reduce the bias. Here we develop a general approach to
quantify the bias. Although applicable to any weak lensing survey, we focus on
the implications for the ESA Euclid mission.
Based on our study of synthetic galaxies we find that the bias is a few times
10^-3 for a typical galaxy observed by Euclid. Consequently, it cannot be
neglected and needs to be accounted for. We demonstrate how one can do so using
spatially resolved observations of galaxies in two filters. We show that HST
observations in the F606W and F814W filters allow us to model and reduce the
bias by an order of magnitude, sufficient to meet Euclid's scientific
requirements. The precision of the correction is ultimately determined by the
number of galaxies for which spatially-resolved observations in at least two
filters are available. We use results from the Millennium Simulation to
demonstrate that archival HST data will be sufficient for the tomographic
cosmic shear analysis with the Euclid dataset.Comment: MNRAS submitted, 18 pages, 13 Figure
CFHTLenS: Co-evolution of galaxies and their dark matter haloes
Galaxy-galaxy weak lensing is a direct probe of the mean matter distribution
around galaxies. The depth and sky coverage of the CFHT Legacy Survey yield
statistically significant galaxy halo mass measurements over a much wider range
of stellar masses ( to ) and redshifts () than previous weak lensing studies. At redshift , the
stellar-to-halo mass ratio (SHMR) reaches a maximum of percent as a
function of halo mass at . We find, for the first
time from weak lensing alone, evidence for significant evolution in the SHMR:
the peak ratio falls as a function of cosmic time from percent at
to percent at , and shifts to lower
stellar mass haloes. These evolutionary trends are dominated by red galaxies,
and are consistent with a model in which the stellar mass above which star
formation is quenched "downsizes" with cosmic time. In contrast, the SHMR of
blue, star-forming galaxies is well-fit by a power law that does not evolve
with time. This suggests that blue galaxies form stars at a rate that is
balanced with their dark matter accretion in such a way that they evolve along
the SHMR locus. The redshift dependence of the SHMR can be used to constrain
the evolution of the galaxy population over cosmic time.Comment: 18 pages, MNRAS, in pres
CFHTLenS: A Weak Lensing Shear Analysis of the 3D-Matched-Filter Galaxy Clusters
We present the cluster mass-richness scaling relation calibrated by a weak
lensing analysis of >18000 galaxy cluster candidates in the
Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS). Detected using the
3D-Matched-Filter cluster-finder of Milkeraitis et al., these cluster
candidates span a wide range of masses, from the small group scale up to
, and redshifts 0.2 0.9. The total
significance of the stacked shear measurement amounts to 54. We compare
cluster masses determined using weak lensing shear and magnification, finding
the measurements in individual richness bins to yield 1 compatibility,
but with magnification estimates biased low. This first direct mass comparison
yields important insights for improving the systematics handling of future
lensing magnification work. In addition, we confirm analyses that suggest
cluster miscentring has an important effect on the observed 3D-MF halo
profiles, and we quantify this by fitting for projected cluster centroid
offsets, which are typically 0.4 arcmin. We bin the cluster candidates
as a function of redshift, finding similar cluster masses and richness across
the full range up to 0.9. We measure the 3D-MF mass-richness scaling
relation . We find a normalization , and a logarithmic slope of
, both of which are in 1 agreement with results
from the magnification analysis. We find no evidence for a redshift-dependence
of the normalization. The CFHTLenS 3D-MF cluster catalogue is now available at
cfhtlens.org.Comment: 3D-MF cluster catalog is NOW AVAILABLE at cfhtlens.org.
Magnification-shear mass comparison in Figure 10. 19 pages, 10 figures.
Accepted to MNRA
CFHTLenS tomographic weak lensing: Quantifying accurate redshift distributions
The Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS) comprises deep
multi-colour (u*g'r'i'z') photometry spanning 154 square degrees, with accurate
photometric redshifts and shape measurements. We demonstrate that the redshift
probability distribution function summed over galaxies provides an accurate
representation of the galaxy redshift distribution accounting for random and
catastrophic errors for galaxies with best fitting photometric redshifts z_p <
1.3.
We present cosmological constraints using tomographic weak gravitational
lensing by large-scale structure. We use two broad redshift bins 0.5 < z_p <=
0.85 and 0.85 < z_p <= 1.3 free of intrinsic alignment contamination, and
measure the shear correlation function on angular scales in the range ~1-40
arcmin. We show that the problematic redshift scaling of the shear signal,
found in previous CFHTLS data analyses, does not afflict the CFHTLenS data. For
a flat Lambda-CDM model and a fixed matter density Omega_m=0.27, we find the
normalisation of the matter power spectrum sigma_8=0.771 \pm 0.041. When
combined with cosmic microwave background data (WMAP7), baryon acoustic
oscillation data (BOSS), and a prior on the Hubble constant from the HST
distance ladder, we find that CFHTLenS improves the precision of the fully
marginalised parameter estimates by an average factor of 1.5-2. Combining our
results with the above cosmological probes, we find Omega_m=0.2762 \pm 0.0074
and sigma_8=0.802 \pm 0.013.Comment: 17 pages, 12 figures, submitted to MNRA
Probing Galaxy Dark Matter Haloes in COSMOS with Weak Lensing Flexion
Current theories of structure formation predict specific density profiles of
galaxy dark matter haloes, and with weak gravitational lensing we can probe
these profiles on several scales. On small scales, higher-order shape
distortions known as flexion add significant detail to the weak lensing
measurements. We present here the first detection of a galaxy-galaxy flexion
signal in space-based data, obtained using a new Shapelets pipeline introduced
here. We combine this higher-order lensing signal with shear to constrain the
average density profile of the galaxy lenses in the Hubble Space Telescope
COSMOS survey. We also show that light from nearby bright objects can
significantly affect flexion measurements. After correcting for the influence
of lens light, we show that the inclusion of flexion provides tighter
constraints on density profiles than does shear alone. Finally we find an
average density profile consistent with an isothermal sphere.Comment: 14 pages, 14 figures. Accepted for publication in MNRA
CFHTLenS: co-evolution of galaxies and their dark matter haloes
Galaxy-galaxy weak lensing is a direct probe of the mean matter distribution around galaxies. The depth and sky coverage of the Canada-France-Hawaii Telescope Legacy Survey yield statistically significant galaxy halo mass measurements over a much wider range of stellar masses (108.75 to 1011.3 M⊙) and redshifts (0.2<z<0.8) than previous weak lensing studies. At redshift z∼0.5, the stellar-to-halo mass ratio (SHMR) reaches a maximum of 4.0±0.2 per cent as a function of halo mass at ∼1012.25 M⊙. We find, for the first time from weak lensing alone, evidence for significant evolution in the SHMR: the peak ratio falls as a function of cosmic time from 4.5±0.3 per cent at z∼0.7 to 3.4±0.2 per cent at z∼0.3, and shifts to lower stellar mass haloes. These evolutionary trends are dominated by red galaxies, and are consistent with a model in which the stellar mass above which star formation is quenched ‘downsizes' with cosmic time. In contrast, the SHMR of blue, star-forming galaxies is well fitted by a power law that does not evolve with time. This suggests that blue galaxies form stars at a rate that is balanced with their dark matter accretion in such a way that they evolve along the SHMR locus. The redshift dependence of the SHMR can be used to constrain the evolution of the galaxy population over cosmic tim
CFHTLenS: a weak lensing shear analysis of the 3D-Matched-Filter galaxy clusters
We present the cluster mass-richness scaling relation calibrated by a weak lensing analysis of ≳ 18000 galaxy cluster candidates in the Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS). Detected using the 3D-Matched-Filter (MF) cluster-finder of Milkeraitis etal., these cluster candidates span a wide range of masses, from the small group scale up to∼1015 M⊙, and redshifts 0.2≲z≲0.9. The total significance of the stacked shear measurement amounts to 54σ. We compare cluster masses determined using weak lensing shear and magnification, finding the measurements in individual richness bins to yield 1σ compatibility, but with magnification estimates biased low. This first direct mass comparison yields important insights for improving the systematics handling of future lensing magnification work. In addition, we confirm analyses that suggest cluster miscentring has an important effect on the observed 3D-MF halo profiles, and we quantify this by fitting for projected cluster centroid offsets, which are typically∼0.4arcmin. We bin the cluster candidates as a function of redshift, finding similar cluster masses and richness across the full range up to z∼0.9. We measure the 3D-MF mass-richness scaling relation M200=M0(N200/20)β. We find a normalization , and a logarithmic slope of β∼1.4±0.1, both of which are in 1σ agreement with results from the magnification analysis. We find no evidence for a redshift dependence of the normalization. The CFHTLenS 3D-MF cluster catalogue is now available at cfhtlens.or
CFHTLenS: the environmental dependence of galaxy halo masses from weak lensing
We use weak gravitational lensing to analyse the dark matter haloes around satellite galaxies in galaxy groups in the Canada–France–Hawaii Telescope Lensing Survey (CFHTLenS) data set. This data set is derived from the Canada–France–Hawaii Telescope Legacy Survey Wide survey, and encompasses 154 deg^2 of high-quality shape data. Using the photometric redshifts, we divide the sample of lens galaxies with stellar masses in the range 10^(9)–10^(10.5) M_⊙ into those likely to lie in high-density environments (HDE) and those likely to lie in low-density environments (LDE). Through comparison with galaxy catalogues extracted from the Millennium Simulation, we show that the sample of HDE galaxies should primarily (∼61 per cent) consist of satellite galaxies in groups, while the sample of LDE galaxies should consist of mostly (∼87 per cent) non-satellite (field and central) galaxies. Comparing the lensing signals around samples of HDE and LDE galaxies matched in stellar mass, the lensing signal around HDE galaxies clearly shows a positive contribution from their host groups on their lensing signals at radii of ∼500–1000 kpc, the typical separation between satellites and group centres. More importantly, the subhaloes of HDE galaxies are less massive than those around LDE galaxies by a factor of 0.65 ± 0.12, significant at the 2.9σ level. A natural explanation is that the haloes of satellite galaxies are stripped through tidal effects in the group environment. Our results are consistent with a typical tidal truncation radius of ∼40 kpc