2,120 research outputs found
Likelihood Analysis of Cosmic Shear on Simulated and VIRMOS-DESCART Data
We present a maximum likelihood analysis of cosmological parameters from
measurements of the aperture mass up to 35 arcmin, using simulated and real
cosmic shear data. A four-dimensional parameter space is explored which
examines the mean density \Omega_M, the mass power spectrum normalization
\sigma_8, the shape parameter \Gamma and the redshift of the sources z_s.
Constraints on \Omega_M and \sigma_8 (resp. \Gamma and z_s) are then given by
marginalizing over \Gamma and z_s (resp. \Omega_M and \sigma_8). For a flat
LCDM cosmologies, using a photometric redshift prior for the sources and \Gamma
\in [0.1,0.4], we find \sigma_8=(0.57\pm0.04) \Omega_M^{(0.24\mp 0.18)
\Omega_M-0.49} at the 68% confidence level (the error budget includes
statistical noise, full cosmic variance and residual systematic). The estimate
of \Gamma, marginalized over \Omega_M \in [0.1,0.4], \sigma_8 \in [0.7,1.3] and
z_s constrained by photometric redshifts, gives \Gamma=0.25\pm 0.13 at 68%
confidence. Adopting h=0.7, a flat universe, \Gamma=0.2 and \Omega_m=0.3 we
find \sigma_8=0.98 \pm0.06 . Combined with CMB, our results suggest a non-zero
cosmological constant and provide tight constraints on \Omega_M and \sigma_8.
We finaly compare our results to the cluster abundance ones, and discuss the
possible discrepancy with the latest determinations of the cluster method. In
particular we point out the actual limitations of the mass power spectrum
prediction in the non-linear regime, and the importance for its improvement.Comment: 11 pages, submitted to A&
Evolution of hierarchical clustering in the CFHTLS-Wide since z~1
We present measurements of higher order clustering of galaxies from the
latest release of the Canada-France-Hawaii-Telescope Legacy Survey (CFHTLS)
Wide. We construct a volume-limited sample of galaxies that contains more than
one million galaxies in the redshift range 0.2<z<1 distributed over the four
independent fields of the CFHTLS. We use a counts in cells technique to measure
the variance and the hierarchical moments S_n = /^(n-1)
(3<n<5) as a function of redshift and angular scale.The robustness of our
measurements if thoroughly tested, and the field-to-field scatter is in very
good agreement with analytical predictions. At small scales, corresponding to
the highly non-linear regime, we find a suggestion that the hierarchical
moments increase with redshift. At large scales, corresponding to the weakly
non-linear regime, measurements are fully consistent with perturbation theory
predictions for standard LambdaCDM cosmology with a simple linear bias.Comment: 17 pages, 11 figures, submitted to MNRA
Spitzer bright, UltraVISTA faint sources in COSMOS: the contribution to the overall population of massive galaxies at z=3-7
We have analysed a sample of 574 Spitzer 4.5 micron-selected galaxies with
[4.5]24 (AB) over the UltraVISTA ultra-deep COSMOS field. Our
aim is to investigate whether these mid-IR bright, near-IR faint sources
contribute significantly to the overall population of massive galaxies at
redshifts z>=3. By performing a spectral energy distribution (SED) analysis
using up to 30 photometric bands, we have determined that the redshift
distribution of our sample peaks at redshifts z~2.5-3.0, and ~32% of the
galaxies lie at z>=3. We have studied the contribution of these sources to the
galaxy stellar mass function (GSMF) at high redshifts. We found that the
[4.5]24 galaxies produce a negligible change to the GSMF
previously determined for Ks_auto<24 sources at 3=<z<4, but their contribution
is more important at 4=~50% of the galaxies with stellar
masses Mst>~6 x 10^10 Msun. We also constrained the GSMF at the highest-mass
end (Mst>~2 x 10^11 Msun) at z>=5. From their presence at 5=<z<6, and virtual
absence at higher redshifts, we can pinpoint quite precisely the moment of
appearance of the first most massive galaxies as taking place in the ~0.2 Gyr
of elapsed time between z~6 and z~5. Alternatively, if very massive galaxies
existed earlier in cosmic time, they should have been significantly
dust-obscured to lie beyond the detection limits of current, large-area, deep
near-IR surveys.Comment: 18 pages, 15 figures, 4 tables. Updated to match version in press at
the Ap
The VIRMOS deep imaging survey: I. overview and survey strategy
This paper presents the CFH12K-VIRMOS survey: a deep B, V, R and I imaging
survey in four fields totalling more than 17 deg^2, conducted with the 30x40
arcmin^2 field CFH-12K camera. The survey is intended to be a multi-purpose
survey used for a variety of science goals, including surveys of very high
redshift galaxies and weak lensing studies.
Four high galactic latitude fields, each 2x2 deg^2, have been selected along
the celestial equator: 0226-04, 1003+01, 1400+05, and 2217+00. The 16 deg^2 of
the "wide" survey are covered with exposure times of 2h, 1.5h, 1h, 1h, while
the 1.3x1 deg^2 area of the "deep" survey at the center of the 0226-04 field is
covered with exposure times of 7h, 4.5h, 3h, 3h, in B,V,R and I respectively.
The data is pipeline processed at the Terapix facility at the Institut
d'Astrophysique de Paris to produce large mosaic images. The catalogs produced
contain the positions, shape, total and aperture magnitudes for the 2.175
million objects. The depth measured (3sigma in a 3 arc-second aperture) is
I_{AB}=24.8 in the ``Wide'' areas, and I_{AB}=25.3 in the deep area. Careful
quality control has been applied on the data as described in joint papers.
These catalogs are used to select targets for the VIRMOS-VLT Deep Survey, a
large spectroscopic survey of the distant universe (Le F\`evre et al., 2003).
First results from the CFH12K-VIRMOS survey have been published on weak lensing
(e.g. van Waerbeke & Mellier 2003).
Catalogs and images are available through the VIRMOS database environment
under Oracle ({\tt http://www.oamp.fr/virmos}). They will be open for general
use on July 1st, 2003.Comment: 17 pages including 9 figures, submitted to A&
The VIRMOS deep imaging survey: III. ESO/WFI deep U-band imaging of the 0226-04 deep field
In this paper we describe the U-band imaging of the F02 deep field, one of
the fields in the VIRMOS Deep Imaging Survey. The observations were done at the
ESO/MPG 2.2m telescope at La Silla (Chile) using the 8k x 8k Wide-Field Imager
(WFI). The field is centered at alpha(J2000)=02h 26m 00s and
delta(J2000)=-04deg 30' 00", the total covered area is 0.9 deg**2 and the
limiting magnitude (50% completeness) is U(AB) ~ 25.4 mag. Reduction steps,
including astrometry, photometry and catalogue extraction, are first discussed.
The achieved astrometric accuracy (RMS) is ~ 0.2" with reference to the I-band
catalog and ~ 0.07" internally (estimated from overlapping sources in different
exposures). The photometric accuracy including uncertainties from photometric
calibration, is < 0.1 mag. Various tests are then performed as a quality
assessment of the data. They include: (i) the color distribution of stars and
galaxies in the field, done together with the BVRI data available from the
VIMOS survey; (ii) the comparison with previous published results of U-band
magnitude-number counts of galaxies.Comment: 10 pages, 13 figures, accepted for publication on Astronomy and
Astrophysic
Dark energy constraints and correlations with systematics from CFHTLS weak lensing, SNLS supernovae Ia and WMAP5
We combine measurements of weak gravitational lensing from the CFHTLS-Wide
survey, supernovae Ia from CFHT SNLS and CMB anisotropies from WMAP5 to obtain
joint constraints on cosmological parameters, in particular, the dark energy
equation of state parameter w. We assess the influence of systematics in the
data on the results and look for possible correlations with cosmological
parameters.
We implement an MCMC algorithm to sample the parameter space of a flat CDM
model with a dark-energy component of constant w. Systematics in the data are
parametrised and included in the analysis. We determine the influence of
photometric calibration of SNIa data on cosmological results by calculating the
response of the distance modulus to photometric zero-point variations. The weak
lensing data set is tested for anomalous field-to-field variations and a
systematic shape measurement bias for high-z galaxies.
Ignoring photometric uncertainties for SNLS biases cosmological parameters by
at most 20% of the statistical errors, using supernovae only; the parameter
uncertainties are underestimated by 10%. The weak lensing field-to-field
variance pointings is 5%-15% higher than that predicted from N-body
simulations. We find no bias of the lensing signal at high redshift, within the
framework of a simple model. Assuming a systematic underestimation of the
lensing signal at high redshift, the normalisation sigma_8 increases by up to
8%. Combining all three probes we obtain -0.10<1+w<0.06 at 68% confidence
(-0.18<1+w<0.12 at 95%), including systematic errors. Systematics in the data
increase the error bars by up to 35%; the best-fit values change by less than
0.15sigma. [Abridged]Comment: 14 pages, 10 figures. Revised version, matches the one to be
published in A&A. Modifications have been made corresponding to the referee's
suggestions, including reordering of some section
Clustering properties of a type-selected volume-limited sample of galaxies in the CFHTLS
(abridged) We present an investigation of the clustering of i'AB<24.5
galaxies in the redshift interval 0.2<z<1.2. Using 100,000 precise photometric
redshifts in the four ultra-deep fields of the Canada-France Legacy Survey, we
construct a set of volume-limited galaxy catalogues. We study the dependence of
the amplitude and slope of the galaxy correlation function on absolute B-band
rest-frame luminosity, redshift and best-fitting spectral type. We find: 1. The
comoving correlation length for all galaxies decreases steadily from z~0.3 to
z~1. 2. At all redshifts and luminosities, galaxies with redder rest-frame
colours have clustering amplitudes between two and three times higher than
bluer ones. 3. For bright red and blue galaxies, the clustering amplitude is
invariant with redshift. 4. At z~0.5, less luminous galaxies have higher
clustering amplitudes of around 6 h-1 Mpc. 5. The relative bias between
galaxies with red and blue rest-frame colours increases gradually towards
fainter absolute magnitudes. One of the principal implications of these results
is that although the full galaxy population traces the underlying dark matter
distribution quite well (and is therefore quite weakly biased), redder, older
galaxies have clustering lengths which are almost invariant with redshift, and
by z~1 are quite strongly biased.Comment: 16 pages, 18 figures, accepted for publication in Astronomy and
Astrophysic
Rest-UV Absorption Lines as Metallicity Estimator: the Metal Content of Star-Forming Galaxies at z~5
We measure a relation between the depth of four prominent rest-UV absorption
complexes and metallicity for local galaxies and verify it up to z~3. We then
apply this relation to a sample of 224 galaxies at 3.5 = 4.8) in
COSMOS, for which unique UV spectra from DEIMOS and accurate stellar masses
from SPLASH are available. The average galaxy population at z~5 and log(M/Msun)
> 9 is characterized by 0.3-0.4 dex (in units of 12+log(O/H)) lower
metallicities than at z~2, but comparable to z~3.5. We find galaxies with
weak/no Ly-alpha emission to have metallicities comparable to z~2 galaxies and
therefore may represent an evolved sub-population of z~5 galaxies. We find a
correlation between metallicity and dust in good agreement with local galaxies
and an inverse trend between metallicity and star-formation rate (SFR)
consistent with observations at z~2. The relation between stellar mass and
metallicity (MZ relation) is similar to z~3.5, however, there are indications
of it being slightly shallower, in particular for the young, Ly-alpha emitting
galaxies. We show that, within a "bathtub" approach, a shallower MZ relation is
expected in the case of a fast (exponential) build-up of stellar mass with an
e-folding time of 100-200 Myr. Due to this fast evolution, the process of dust
production and metal enrichment as a function of mass could be more stochastic
in the first billion years of galaxy formation compared to later times.Comment: 20 pages, 13 figures, 4 tables; Submitted to Ap
The angular correlations of galaxies in the COSMOS field
We present measurements of the two-point galaxy angular correlation function
w(\theta) in the COSMOS field. Independent determinations of w(\theta) as a
function of magnitude limit are presented for both the HST ACS catalog and also
for the ground-based data from Subaru and the CFHT. Despite having
significantly different masks, these three determinations agree well. At bright
magnitudes (IAB<22), our data generally match very well with existing
measurements and with mock catalogs based on semi-analytic galaxy formation
calculations of Kitzbichler and White from the Millennium Simulation. The
exception is that our result is at the upper end of the expected cosmic
variance scatter for \theta > 10 arcmin, which we attribute to a particularly
rich structure known to exist at z~0.8. For fainter samples, however, the level
of clustering is somewhat higher than reported by some previous studies: in all
three catalogues we find w(\theta=1')~0.014 at a median IAB magnitude of 24. At
these very faintest magnitudes, our measurements agree well with the latest
determinations from the Canada-France Legacy Survey. This level of clustering
is approximately double what is predicted by the semi-analytic catalogs (at all
angles). The semi-analytic results allow an estimate of cosmic variance, which
is too small to account for the discrepancy. We therefore conclude that the
mean amplitude of clustering at this level is higher than previously estimated.Comment: Six pages, five figures. Accepted for publication in the ApJS COSMOS
special issue, Sept. 200
The Canada-France Deep Fields III: Photometric Redshift Distribution to I(AB) ~ 24
We compute accurate redshift distributions to I(AB) = 24 and R(AB) = 24.5
using photometric redshifts estimated from six-band UBVRIZ photometry in the
Canada-France Deep Fields-Photometric Redshift Survey (CFDF-PRS). Our
photometric redshift algorithm is calibrated using hundreds of CFRS
spectroscopic redshifts in the same fields. The dispersion in redshift is
\sigma/(1+z) \la 0.04 to the CFRS depth of I(AB) = 22.5, rising to \sigma/(1+z)
\la 0.06 at our nominal magnitude and redshift limits of I(AB) = 24 and z \le
1.3, respectively. We describe a new method to compute N(z) that incorporates
the full redshift likelihood functions in a Bayesian iterative analysis and we
demonstrate in extensive Monte Carlo simulations that it is superior to
distributions calculated using simple maximum likelihood redshifts. The
field-to-field differences in the redshift distributions, while not unexpected
theoretically, are substantial even on 30' scales. We provide I(AB) and R(AB)
redshift distributions, median redshifts, and parametrized fits of our results
in various magnitude ranges, accounting for both random and systematic errors
in the analysis.Comment: 19 Pages, 8 Tables, 13 Figures. Replaced to match published version.
Main results unchange
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