1605.01056
Systematic tests for position-dependent additive shear bias
van Uitert, Schneider
Present new tests to identify stationary position-dependent additive shear biases in WL data sets. These tests are important diagnostics for currently ongoing and planned cosmic shear surveys, as such biases induce coherent shear patterns that can mimic and potentially bias the cosmic shear signal. The central idea of these tests is to determine the average ellipticity of all galaxies with shape measurements in a grid in the pixel plane. The distribution of the absolute values of these averaged ellipticities can be compared to randomized catalogues; a difference points to systematics in the data. In addition, introduce a method to quantify the spatial correlation of the additive bias, which suppresses the contribution from cosmic shear and therefore eases the identification of a position dependent additive shear bias in the data. Apply these tests to the publicly available shear catalogues from CFHTLenS and KiDS and find evidence for a small but non-negligible residual additive bias at small scales. As this residual bias is smaller than the error on the shear correlation signal at those scales, it is highly unlikely that it causes a significant bias in the published cosmic shear results of CFHTLenS. In CFHTLenS, the amplitude of this systematic signal is consistent with zero in fields where the number of stars used to model the PSF is higher than average, suggesting that the position-dependent additive shear bias originates from under sampled PSF variations across the image.
1605.01065
Intrinsic alignments in redMaPPer clusters -- I. central galaxy alignments and angular segregation of satellites
Huang, Mandelbaum, et al
The shapes of cluster central galaxies are not randomly oriented, but rather exhibit coherent alignments with the shapes of their parent clusters as well as with large-scale structure. In this work, undertake a comprehensive study of the alignments of central galaxies at low redshift. Based on a sample of 8237 clusters and 94817 members in the redMaPPer cluster catalog with 0.1<z0.35, first quantify the alignment between the projected central galaxy shapes and the distribution of member satellites, to understand what central galaxy and cluster properties most strongly correlate with these alignments. Next, investigate the angular segregation of satellites with respect to their central galaxy major axis directions, to identify the satellite properties that most strongly predict their angular segregation. Find that central galaxies are more aligned with their member galaxy distributions in clusters that are more elongated and have higher richness, and for central galaxies with larger physical size, higher luminosity and centering probability, and redder color. Satellites with redder color, higher luminosity, located closer to the central galaxy, and with smaller ellipticity show a stronger angular segregation toward their central galaxy major axes. Finally, provide physical explanations for some of the identified correlations, and discuss the connection to theories of central galaxy alignments, the impact of primordial alignments with tidal fields, and the importance of anisotropic accretion.
1605.01100
Cosmology with photometric weak lensing surveys: constraints with redshift tomography of convergence peaks and moments
Petri, May, Haiman
WL is becoming a mature technique for constraining cosmo parameters, and future surveys will be able to constrain the DE EoS w. When analyzing galaxy surveys, redshift information has proven to be a valuable addition to angular shear correlations. Forecast parameter constraints on the triples (Omega_m, w, sigma8) for an LSST-like photometric galaxy survey, using tomography of the shear-shear power spectrum, convergence peak counts and higher convergence moments. Find that redshift tomography with the power spectrum reduces the are of the 1 sigma confidence interval in (Omega_m, w) space by a factor of 8 with respect to the case of the single highest redshift bin. Also find that doing non-Gaussian information from the peak counts and higher-order moments of the convergence field and its spatial derivatives further reduces the constrained area in (Omega_m, w) by a a factor of 3 and 4, respectively. When CMB parameter priors from Planck are added to the analysis, tomography improves power spectrum constraints by a factor of 3. Adding moments yields and improvement by an additional factor of 2, and adding both moments and peaks improves by almost a factor of 3, over power spectrum tomography alone. Evaluate the effect of uncorrected systematic photometric redshift errors on the parameter constraints. Find that different statistics lead to different bias directions in parameter space, suggesting the possibility of eliminating this bias via self-calibration.
1605.01306
The search for HI emission at z $\approx0.4$ in gravitationally lensed galaxies with the green back telescope
Hunt, Pisano, Edel
HI is difficult to detect at high z due to weak emission, limited sensitivity of modern instruments, and terrestrial radio frequency interference (RFI) at low frequencies. Attempt to use GL to detect HI lie emission from 3 gravitationally lensed galaxies behind Abell 773, two at z of 0.398 and one at z=0.487, using the Green Bank Telescope. Find a 3 sigma upper limit for a galaxy with rotation velocity of 200 km/s. [...]
No comments:
Post a Comment