[show abstract][hide abstract] ABSTRACT: We present the first galaxy-galaxy weak-lensing results using early data from the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). These results are based on ~22 deg2 of i' data. From these data, we estimate the average velocity dispersion for an L* galaxy at a redshift of 0.3 to be 137 ± 11 km s-1, with a virial mass, M200, of (1.1 ± 0.2) × 1012 h-1 M☉ and a rest-frame mass-to-light ratio of 173 ± 34 h M☉/L. We also investigate various possible sources of systematic error in detail. In addition, we separate our lens sample into two subsamples, divided by apparent magnitude and thus average redshift. From these early data we do not detect significant evolution in galaxy dark matter halo mass-to-light ratios at redshifts from 0.45 to 0.27. Finally, we test for nonspherical galaxy dark matter halos. Our results favor a dark matter halo with an ellipticity of ~0.3 at the 2 σ level when averaged over all galaxies. If the sample of foreground lens galaxies is selected to favor elliptical galaxies, the mean halo ellipticity and significance of this result increase.
The Astrophysical Journal 12/2008; 669(1):21. · 6.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: We present the first measurements of the weak gravitational lensing signal induced by the large scale mass distribution from data obtained as part of the ongoing Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). The data used in this analysis are from the Wide Synoptic Survey, which aims to image ~170 square degree in five filters. We have analysed ~22 deg2 (31 pointings) of i' data spread over two of the three survey fields. These data are of excellent quality and the results bode well for the remainder of the survey: we do not detect a significant `B'-mode, suggesting that residual systematics are negligible at the current level of accuracy. Assuming a Cold Dark Matter model and marginalising over the Hubble parameter h=[0.6,0.8], the source redshift distribution and systematics, we constrain sigma_8, the amplitude of the matter power spectrum. At a fiducial matter density Omega_m=0.3 we find sigma_8=0.85+-0.06. This estimate is in excellent agreement with previous studies. Combination of our results with those from the Deep component of the CFHTLS enables us to place a constraint on a constant equation of state for the dark energy, based on cosmic shear data alone. We find that w_0<-0.8 at 68% confidence.
The Astrophysical Journal 12/2005; · 6.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: We present the first cosmic shear measurements obtained from the T0001 release of the Canada-France-Hawaii Telescope Legacy Survey. The data set covers three uncorrelated patches (D1, D3 and D4) of one square degree each observed in u*, g', r', i' and z' bands, out to i'=25.5. The depth and the multicolored observations done in deep fields enable several data quality controls. The lensing signal is detected in both r' and i' bands and shows similar amplitude and slope in both filters. B-modes are found to be statistically zero at all scales. Using multi-color information, we derived a photometric redshift for each galaxy and separate the sample into medium and high-z galaxies. A stronger shear signal is detected from the high-z subsample than from the low-z subsample, as expected from weak lensing tomography. While further work is needed to model the effects of errors in the photometric redshifts, this results suggests that it will be possible to obtain constraints on the growth of dark matter fluctuations with lensing wide field surveys. The various quality tests and analysis discussed in this work demonstrate that MegaPrime/Megacam instrument produces excellent quality data. The combined Deep and Wide surveys give sigma_8= 0.89 pm 0.06 assuming the Peacock & Dodds non-linear scheme and sigma_8=0.86 pm 0.05 for the halo fitting model and Omega_m=0.3. We assumed a Cold Dark Matter model with flat geometry. Systematics, Hubble constant and redshift uncertainties have been marginalized over. Using only data from the Deep survey, the 1 sigma upper bound for w_0, the constant equation of state parameter is w_0 < -0.8. Comment: 14 pages, 16 figures, accepted A&A
Astronomy and Astrophysics 11/2005; · 5.08 Impact Factor
[show abstract][hide abstract] ABSTRACT: We present the findings of our weak lensing study of a sample of 116 CNOC2 galaxy groups. The lensing signal is used to estimate the mass-to-light ratio of these galaxy groups. The best fit isothermal sphere model to our lensing data has an Einstein radius of 0.88"+/-0.12", which corresponds to a shear-weighted velocity dispersion of 245+/-18 km/s. The mean mass-to-light ratio within 1 h^-1 Mpc is 185+/-28 h times solar in the B-band and is independent of radius from the group center. The signal-to-noise ratio of the shear measurement is sufficient to split the sample into subsets of "poor" and "rich" galaxy groups. The poor galaxy groups were found to have an average velocity dispersion of 193+/-38 km/s and a mass-to-light ratio of 134+/-26 h times solar in the B-band, while the rich galaxy groups have a velocity dispersion of 270+/-39 km/s and a mass-to-light ratio of 278+/-42 h times solar in the B-band, similar to the mass-to-light ratio of clusters. This steep increase in the mass-to-light ratio as a function of mass, suggests that the mass scale of ~10^13 solar masses is where the transition between the actively star-forming field environment and the passively-evolving cluster environment occurs. This is the first such detection from weak lensing. Comment: Accepted for publication in ApJ 6 pages, 6 figures, uses emulateapj
The Astrophysical Journal 08/2005; · 6.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: I will present the results from our weak lensing survey of CNOC2 galaxy groups. The detected shear is used to calculate the M/L of these groups and constrain the matter density of the universe. Galaxy groups are excellent cosmological probes because they dominate the mass and luminosity densities of the Universe, and thus their properties reflect closely the global properties of the universe. The mass-to-light ratio of the groups was calculated as a function of radius, and found to have an average value of 206 ±27 M&sun;/LR&sun;. The mass-to-light ratio appeared to rise in the outer regions of the galaxy groups, beyond the virial radius where dynamical estimates are valid. The signal-to-noise of the shear measurement was sufficient to allow us to split the sample into two halves: the ``rich'' galaxy groups and the ``poor'' galaxy groups. The rich galaxy groups were found to have an average velocity dispersion of 260 ±39 km/s while the small galaxies were found to have a velocity dispersion of 176 ±37 km/s. The mass-to-light ratio of the rich groups was nearly twice that of the poor groups. This indicates that the rising mass-to-light ratio of the full sample of galaxy groups is an artifact of averaging together many groups with different inherent mass-to-light ratios.
[show abstract][hide abstract] ABSTRACT: Galaxy groups dominate the mass density of the Universe, yet their mass-to-light ratios and dark matter profiles are poorly understood in comparison with galaxies or rich clusters. We have recently used the CNOC2 redshift survey to produce a catalogue of intermediate-redshift groups. The dynamical analysis suggests that the mass-to-light profile of galaxy groups rises by a factor of three to ten across their virialized extent. This unique dynamical sample is optimal for weak lensing studies by virtue of its median redshift (z ~ 0.4) and sky coverage (0.5 square degrees). We have nearly completed a weak lensing survey of CNOC2 fields to test the dynamical results and extend the mass profile measurement beyond the virialized regime, where dynamical methods fail. In this proposal, we demonstrate that these observations will give a >= 5 sigma detection of the rise in M/L with radius. The data will also be used to investigate galaxy-galaxy lensing and the morphological dependence of galaxy evolution in these groups. From the CFH12k data we have nearly-complete data for 3 of the 4 CNOC2 fields. However, in 2002B installation and commissioning of MegaCam is scheduled for the dates we require. In this proposal, we request 2 nights from the KPNO 4m+MOSAIC to complete the weak lensing survey by obtaining data for the 0223+05 field and completing observations of the 0920+37 field.