Cosmology

Abstract:

Recent evidence for a strong "hard excess" of flux at energies ≳ 20 keV in some Suzaku observations of type 1 active galactic nuclei (AGNs) has motivated an exploratory study of the phenomenon in the local type 1 AGN population. We have selected all type 1 AGNs in the Swift Burst Alert Telescope 58 month catalog and cross-correlated them with the holdings of the Suzaku public archive. We find the hard excess phenomenon to be a ubiquitous property of type 1 AGNs. Taken together, the spectral hardness and equivalent width of Fe Kα emission are consistent with reprocessing by an ensemble of Compton-thick clouds that partially cover the continuum source. In the context of such a model, ∼80% of the sample has a hardness ratio consistent with >50% covering of the continuum by low-ionization, Compton-thick gas. A more detailed study of the three hardest X-ray spectra in our sample reveal a sharp Fe K absorption edge at ∼7 keV in each of them, indicating that blurred reflection is not responsible for the very hard spectral forms. Simple considerations place the distribution of Compton-thick clouds at or within the optical broad-line region. © 2013. The American Astronomical Society. All rights reserved..

Abstract:

We present a finely binned tomographic weak lensing analysis of the Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS) mitigating contamination to the signal from the presence of intrinsic galaxy alignments via the simultaneous fit of a cosmological model and an intrinsic alignment model. CFHTLenS spans 154 square degrees in five optical bands, with accurate shear and photometric redshifts for a galaxy sample with a median redshift of zm = 0.70. We estimate the 21 sets of cosmic shear correlation functions associated with six redshift bins, each spanning the angular range of 1.5 < θ < 35 arcmin. We combine this CFHTLenS data with auxiliary cosmological probes: the cosmic microwave background with data from WMAP7, baryon acoustic oscillations with data from Baryon Oscillation Spectroscopic Survey and a prior on the Hubble constant from the Hubble Space Telescope distance ladder. This leads to constraints on the normalization of the matter power spectrum σ8 = 0.799 ± 0.015 and the matter density parameter ωm = 0.271 ± 0.010 for a flat Λ cold dark matter (ΛCDM) cosmology. For a flat wCDM cosmology, we constrain the dark energy equation-of-state parameter w = -1.02 ± 0.09. We also provide constraints for curved ΛCDM and wCDM cosmologies.We find the intrinsic alignment contamination to be galaxy-type dependent with a significant intrinsic alignment signal found for early-type galaxies, in contrast to the late-type galaxy sample for which the intrinsic alignment signal is found to be consistent with zero. © 2013 The Author. Published by Oxford University Press on behalf of the Royal Astronomical Society.

Abstract:

We present a quantitative analysis of the largest contiguous maps of projected mass density obtained from gravitational lensing shear. We use data from the 154 deg2 covered by the Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS). Our study is the first attempt to quantitatively characterize the scientific value of lensing maps, which could serve in the future as a complementary approach to the study of the dark universe with gravitational lensing. We show that mass maps contain unique cosmological information beyond that of traditional two-point statistical analysis techniques. Using a series of numerical simulations, we first show how, reproducing the CFHTLenS observing conditions, gravitational lensing inversion provides a reliable estimate of the projected matter distribution of large-scale structure. We validate our analysis by quantifying the robustness of the maps with various statistical estimators. We then apply the same process to the CFHTLenS data. We find that the two-point correlation function of the projected mass is consistent with the cosmological analysis performed on the shear correlation function discussed in the CFHTLenS companion papers. The maps also lead to a significant measurement of the third-order moment of the projected mass, which is in agreement with analytic predictions, and to a marginal detection of the fourth-order moment. Tests for residual systematics are found to be consistent with zero for the statistical estimators we used. A new approach for the comparison of the reconstructed mass map to that predicted from the galaxy distribution reveals the existence of giant voids in the dark matter maps as large as 3° on the sky. Our analysis shows that lensing mass maps are not only consistent with the results obtained by the traditional shear approach, but they also appear promising for new techniques such as peak statistics and the morphological analysis of the projected dark matter distribution. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.

Abstract:

We report the discovery of a giant HI tail in the intragroup medium of HCG 44 as part of the ATLAS3D survey. The tail is ~300 kpc long in projection and contains ~5 × 108 M ⊙of HI. We detect no diffuse stellar light at the location of the tail down to ~28.5 mag arcsec-2 in g band. We speculate that the tail might have formed as gas was stripped from the outer regions of NGC 3187 (a member of HCG 44) by the group tidal field. In this case, a simple model indicates that about 1/3 of the galaxy's HI was stripped during a time interval of <1 Gyr. Alternatively, the tail may be the remnant of an interaction between HCG 44 and NGC 3162, a spiral galaxy now ~650 kpc away from the group. Regardless of the precise formation mechanism, the detected HI tail shows for the first time direct evidence of gas stripping in HCG 44. It also highlights that deep HI observations over a large field are needed to gather a complete census of this kind of events inthe local Universe.©2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. © 2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.