CFHTLenS: The Canada-France-Hawaii telescope lensing survey - Imaging data and catalogue products
Monthly Notices of the Royal Astronomical Society 433:3 (2013) 2545-2563
Abstract:
We present data products from the Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS). CFHTLenS is based on the Wide component of the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). It encompasses 154 deg2 of deep, optical, high-quality, sub-arcsecond imaging data in the five optical filters u′g′r′i′z′. The scientific aims of the CFHTLenS team are weak gravitational lensing studies supported by photometric redshift estimates for the galaxies. This paper presents our data processing of the complete CFHTLenS data set. We were able to obtain a data set with very good image quality and high-quality astrometric and photometric calibration. Our external astrometric accuracy is between 60 and 70 mas with respect to Sloan Digital Sky Survey (SDSS) data, and the internal alignment in all filters is around 30 mas. Our average photometric calibration shows a dispersion of the order of 0.01-0.03 mag for g′r′i′ z′ and about 0.04 mag for u* with respect to SDSS sources down to iSDSS ≤ 21. We demonstrate in accompanying papers that our data meet necessary requirements to fully exploit the survey for weak gravitational lensing analyses in connection with photometric redshift studies. In the spirit of the CFHTLS, all our data products are released to the astronomical community via the Canadian Astronomy Data Centre at http://www.cadc-ccda.hia-iha.nrc-cnrc. gc.ca/community/CFHTLens/query.html. We give a description and how-to manuals of the public products which include image pixel data, source catalogues with photometric redshift estimates and all relevant quantities to perform weak lensing studies.© 2013 The Authors.The Hard X-Ray spectrum of NGC 1365: Scattered light, not black hole Spin
Astrophysical Journal Letters 773:1 (2013)
Abstract:
Active galactic nuclei (AGNs) show excess X-ray emission above 10 keV compared with extrapolation of spectra from lower energies. Risaliti et al. have recently attempted to model the hard X-ray excess in the type 1.8 AGN NGC 1365, concluding that the hard excess most likely arises from Compton-scattered reflection of X-rays from an inner accretion disk close to the black hole. Their analysis disfavored a model in which the hard excess arises from a high column density of circumnuclear gas partially covering a primary X-ray source, despite such components being required in the NGC 1365 data below 10 keV. Using a Monte Carlo radiative transfer approach, we demonstrate that this conclusion is invalidated by (1) use of slab absorption models, which have unrealistic transmission spectra for partial covering gas, (2) neglect of the effect of Compton scattering on transmitted spectra, and (3) inadequate modeling of the spectrum of scattered X-rays. The scattered spectrum is geometry-dependent and, for high global covering factors, may dominate above 10 keV. We further show that, in models of circumnuclear gas, the suppression of the observed hard X-ray flux by reprocessing may be no larger than required by the "light bending" model invoked for inner disk reflection, and the expected emission line strengths lie within the observed range. We conclude that the time-invariant "red wing" in AGN X-ray spectra is probably caused by continuum transmitted through and scattered from circumnuclear gas, not by highly redshifted line emission, and that measurement of black hole spin is not possible. © 2013. The American Astronomical Society. All rights reserved.CFHTLenS tomographic weak lensing: Quantifying accurate redshift distributions
Monthly Notices of the Royal Astronomical Society 431:2 (2013) 1547-1564
Abstract:
The Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS) comprises deep multicolour (u*g'r'i'z') photometry spanning 154 deg2, 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 zp < 1.3.We present cosmological constraints using tomographic weak gravitational lensing by large-scale structure. We use two broad redshift bins 0.5 < zp ≤ 0.85 and 0.85 < zp ≤ 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 Canada-France-Hawaii Telescope Legacy Survey data analyses, does not affect the CFHTLenS data. For a flat Λ cold dark matter model and a fixed matter density Ωm = 0.27, we find the normalization of the matter power spectrum σ8 = 0.771 ± 0.041. When combined with cosmic microwave background data (Wilkinson Microwave Anisotropy Probe 7-year results), baryon acoustic oscillation data (BOSS) and a prior on the Hubble constant from the Hubble Space Telescope distance ladder, we find that CFHTLenS improves the precision of the fully marginalized parameter estimates by an average factor of 1.5-2. Combining our results with the above cosmological probes, we find Ωm = 0.2762 ± 0.0074 and σ8 = 0.802 ± 0.013. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.CFHTlens: The environmental dependence of galaxy halo masses from weak lensing
Monthly Notices of the Royal Astronomical Society 431:2 (2013) 1439-1452
Abstract:
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 deg2 of high-quality shape data. Using the photometric redshifts, we divide the sample of lens galaxies with stellar masses in the range 109-1010.5M⊙ 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. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.Defining a weak lensing experiment in space
Monthly Notices of the Royal Astronomical Society 431:4 (2013) 3103-3126