Beecroft Institute for Particle Astrophysics and Cosmology

Abstract:

We present cosmological constraints from 2D weak gravitational lensing by the large-scale structure in the Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS) which spans 154 deg2 in five optical bands. Using accurate photometric redshifts and measured shapes for 4.2 million galaxies between redshifts of 0.2 and 1.3, we compute the 2D cosmic shear correlation function over angular scales ranging between 0.8 and 350 arcmin. Using nonlinear models of the dark-matter power spectrum, we constrain cosmological parameters by exploring the parameter space with Population Monte Carlo sampling. The best constraints from lensing alone are obtained for the small-scale density-fluctuations amplitude σ8 scaled with the total matter density Ωm. For a flat Λcold dark matter (ΛCDM) model we obtain Σ8(Ωm/0.27)0.6 = 0.79 ± 0.03. We combine the CFHTLenS data with 7-year Wilkinson Microwave Anisotropy Probe (WMAP7), baryonic acoustic oscillations (BAO): SDSS-III (BOSS) and a Hubble Space Telescope distance-ladder prior on the Hubble constant to get joint constraints. For a flat ΛCDM model, we find Ωm = 0.283 ± 0.010 and Σ8 = 0.813 ± 0.014. In the case of a curved wCDM universe, we obtain Ωm = 0.27 ± 0.03, Σ8 = 0.83 ± 0.04, w0 = -1.10 ± 0.15 and Ωk = 0.006+0.006-0.004. We calculate the Bayesian evidence to compare flat and curved ΛCDM and dark-energy CDM models. From the combination of all four probes, we find models with curvature to be at moderately disfavoured with respect to the flat case. A simple dark-energy model is indistinguishable from ΛCDM. Our results therefore do not necessitate any deviations from the standard cosmological model. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.

Abstract:

We present the first direct measurement of the galaxy-matter bispectrum as a function of galaxy luminosity, stellar mass and type of spectral energy distribution (SED). Our analysis uses a galaxy-galaxy-galaxy lensing technique (G3L), on angular scales between 9 arcsec and 50 arcmin, to quantify (i) the excess surface mass density around galaxy pairs (excess mass hereafter) and (ii) the excess shear-shear correlations around single galaxies, both of which yield a measure of two types of galaxy-matter bispectra. We apply our method to the state-of-the-art Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS), spanning 154 square degrees. This survey allows us to detect a significant change of the bispectra with lens properties. Measurements for lens populations with distinct redshift distributions become comparable by a newly devised normalization technique. That will also aid future comparisons to other surveys or simulations. A significant dependence of the normalized G3L statistics on luminosity within-23=Mr=-18 and stellarmass within 5×109M⊙ =M* <2×1011M⊙ is found (h = 0.73). Both bispectra exhibit a stronger signal for more luminous lenses or those with higher stellar mass (up to a factor of 2-3). This is accompanied by a steeper equilateral bispectrum for more luminous or higher stellar mass lenses for the excess mass. Importantly, we find the excess mass to be very sensitive to galaxy type as recently predicted with semianalytic galaxy models: luminous (Mr < -21) late-type galaxies show no detectable signal, while all excess mass detected for luminous galaxies seems to be associated with early-type galaxies. We also present the first observational constraints on third-order stochastic galaxy biasing parameters. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Abstract:

Citizen science, in which volunteers work with professional scientists to conduct research, is expanding due to large online datasets. To plan projects, it is important to understand volunteers' motivations for participating. This paper analyzes results from an online survey of nearly 11,000 volunteers in Galaxy Zoo, an astronomy citizen science project. Results show that volunteers' primary motivation is a desire to contribute to scientific research. We encourage other citizen science projects to study the motivations of their volunteers, to see whether and how these results may be generalized to inform the field of citizen science.

Abstract:

We present the results of a new spectroscopic study of Fe K-band absorption in active galactic nuclei (AGN). Using data obtained from the Suzaku public archive we have performed a statistically driven blind search for Fe XXV Heα and/or Fe XXVI Lyα absorption lines in a large sample of 51 Type 1.0-1.9 AGN. Through extensive Monte Carlo simulations we find that statistically significant absorption is detected at E ≳ 6.7 keV in 20/51 sources at the PMC ≥ 95 per cent level, which corresponds to ~40 per cent of the total sample. In all cases, individual absorption lines are detected independently and simultaneously amongst the two (or three) available X-ray imaging spectrometer detectors, which confirms the robustness of the line detections. The most frequently observed outflow phenomenology consists of two discrete absorption troughs corresponding to Fe XXV Heα and Fe XXVI Lyα at a common velocity shift. From xstar fitting the mean column density and ionization parameter for the Fe K absorption components are log (NH/cm-2) ≈ 23 and log (ξ/erg cm s-1) ≈ 4.5, respectively. Measured outflow velocities span a continuous range from <1500 km s-1 up to ~100 000 km s-1, with mean and median values of ~0.1 c and ~0.056 c, respectively. The results of this work are consistent with those recently obtained using XMM-Newton and independently provides strong evidence for the existence of very highly ionized circumnuclear material in a significant fraction of both radio-quiet and radio-loud AGN in the local universe. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.