15 research outputs found
Cosmological Applications of Gravitational Lensing
The last decade has seen an enormous increase of activity in the field of
gravitational lensing, mainly driven by improvements of observational
capabilities. I will review the basics of gravitational lens theory, just
enough to understand the rest of this contribution, and will then concentrate
on several of the main applications in cosmology. Cluster lensing, and weak
lensing, will constitute the main part of this review.Comment: 26 pages, including 2 figures (a third figure can be obtained from
the author by request) gziped and uuencoded postscript file; to be published
in Proceedings of the Laredo Advanced Summer School, Sept. 9
The redshift distribution and luminosity functions of galaxies in the Hubble Deep Field
Photometric redshifts have been determined for the galaxies in the Hubble Deep Field. The resulting redshift distribution shows two peaks: one at z ~ 0.6 and one at z ~ 2.2. Luminosity functions derived from the redshifts show strong luminosity evolution as a function of redshift. This evolution is consistent with the Babul and Rees scenario wherein massive galaxies form stars at high redshift while star formation in dwarf galaxies is delayed until after z = 1.Peer reviewed: YesNRC publication: N
The CNOC2 field galaxy redshift survey
The second Canadian Network for Observational Cosmology ( CNOC) galaxy redshift survey, CNOC2, is designed to investigate the relations between the dramatic evolution of field galaxies and their clustering over the redshift range 0 to 0.7. The sample of about 6000 galaxies with accurate velocities is spread over four sky patches with a total area of about 1.5deg2. Here we report preliminary results based on two of the sky patches and within the redshift range of 0.12 to 0.55. After classifying the galaxy spectral energy distributions relative to non–evolving references, we find that the early and intermediate–type populations can be described with nearly pure luminosity evolution, whereas the late–type population requires nearly pure density evolution. The spatial two–point correlation functions have a strong colour dependence with scale, and a weaker, apparently scale–free, luminosity dependence. The population most likely to be conserved with redshift is the high–luminosity galaxies. In particular, we choose galaxies with MRke ⩽−20 mag as our tracer population. We find that the evolution of the clustered density in proper co–ordinates at r ≲ 10h−1 Mpc, ρgg ∝ r0γ(1+z)3, is best described as a ‘de–clustering’, proportional to (1+z)0.6±0.4); or equivalently, there is a weak growth of clustering in co–moving co–ordinates, x0 ∝(1+z)(−0.3±0.2). This conclusion is supported by the pairwise peculiar velocities, which show no significant change with redshift. The cosmic virial theorem applied to the CNOC2 data gives Q3ΩM/b = 0.11 ± 0.04, where Q3 is the three–point correlation parameter and b the bias
The Average Mass Profile of Galaxy Clusters
The average mass density profile measured in the CNOC cluster survey is well
described with the analytic form rho(r)=A/[r(r+a_rho)^2], as advocated on the
basis on n-body simulations by Navarro, Frenk & White. The predicted core radii
are a_rho=0.20 (in units of the radius where the mean interior density is 200
times the critical density) for an Omega=0.2 open CDM model, or a_rho=0.26 for
a flat Omega=0.2 model, with little dependence on other cosmological parameters
for simulations normalized to the observed cluster abundance. The dynamically
derived local mass-to-light ratio, which has little radial variation, converts
the observed light profile to a mass profile. We find that the scale radius of
the mass distribution, 0.20<= a_rho <= 0.30 (depending on modeling details,
with a 95% confidence range of 0.12-0.50), is completely consistent with the
predicted values. Moreover, the profiles and total masses of the clusters as
individuals can be acceptably predicted from the cluster RMS line-of-sight
velocity dispersion alone. This is strong support of the hierarchical
clustering theory for the formation of galaxy clusters in a cool,
collisionless, dark matter dominated universe.Comment: Accepted for publication in ApJLetts. Also available at
http://manaslu.astro.utoronto.ca/~carlberg/cnoc/nfw/ave.ps.g
The Omega\_M-Omega\_Lambda Constraint from CNOC Clusters
The CNOC redshift survey of galaxy clusters measures Omega_M from Omega_e(z)=
M/L x j/\rho_c which can be applied on a cluster-by-cluster basis. The
mass-to-light ratios, M/L, are estimated from rich galaxy clusters, corrected
to the field population over the 0.18 to 0.55 redshift range. Since the
luminosity density depends on cosmological volumes, the resulting Omega_e(z)
has a strong dependence on cosmology which allows us to place the results in
the Omega_M-Omega_Lambda plane. The resulting Omega_M declines if
Omega_Lambda>0 and we find that Omega_Lambda<1.5.Comment: 4 pages LaTeX. To appear in "Fundamental Parameters in Cosmology,"
the proceedings of the XXXIIIrd Rencontres de Morion
The CNOC Cluster Survey: Omega, sigma\_8, Phi(L,z) Results, and Prospects for Lambda Measurement
Rich galaxy clusters are powerful probes of both cosmological and galaxy
evolution parameters. The CNOC cluster survey was primarily designed to
distinguish between Omega=1 and Omega~0.2 cosmologies. Projected foreground and
background galaxies provide a field sample of comparable size. The results
strongly support a low-density universe. The luminous cluster galaxies are
about 10-30% fainter, depending on color, than the comparable field galaxies,
but otherwise they show a slow and nearly parallel evolution. On the average,
there is no excess star formation when galaxies fall into clusters. These data
provide the basis for a simple Lambda measurement using the survey's clusters
and the field data. The errors in Omega_M, Lambda, sigma_8 and galaxy evolution
parameters could be reduced to a few percent with a sample of a few hundred
clusters spread over the 0<z<1 range.Comment: to appear in Ringberg Workshop on Large-Scale Structure (ed. D.
Hamilton) 14 pages, also available at
http://manaslu.astro.utoronto.ca/~carlberg/cnoc/conference/ring2.ps.g