Day 966

Monday.


1509.03310
Time-delay cosmography: increased leverage with Angular Diameter Distances
Jee, Komatsu, Suyu, Huterer

Strong lensing time-delay systems constrain cosmo parameters via the so-called time-delay distance and the angular diameter distance to the lens.  In previous studies, only the former information was used.  In this paper, show that the cosmo constraints improve significantly when the latter information is also included.  Specifically, the angular diameter distance plays a crucial role in breaking the degeneracy between the curvature of the Universe and the time-varying equation of state of dark energy.  Using a mock sample of 55 bright quadruple lens systems based on expectations for ongoing/future imaging surveys, find that adding the angular diameter distance information to the time-delay distance information and the CMB data of Planck improves the constraint on the constant EoS by 30%, on the time variation in the EoS by a factor of two, and on the Hubble constant in the flat LCDM model by a factor of two.  Therefore, previous forecasts for the statistical power of time-delay systems were significantly underestimated, i.e., time-delay systems are more powerful than previously appreciated.


1509.03318
Mapping the galaxy color-redshift relation: optimal photometric redshift calibraiton strategies for cosmology surveys
Masters, Capak, Stern, Ilbert, Schmidt, Rhodes, ...Hoekstra, Hildebrandt, Coupon, ... et al

Calibrating the photometric redshifts of >1e9 galaxies for upcoming WL cosmo experiments is a major challenge for the astrophysics community.  The path to obtaining the required spectroscopic redshift for training and calibration is daunting, given the anticipated depths of the surveys and the difficulty in obtaining secure redshift for some faint galaxy populations.  Present an analysis of the problem based on the self-organizing map, a method of mapping the distribution of data in a high-dimensional space and projecting it onto a lower-dimensional representation.  Apply this method to existing photometric data from the COSMOS survey selected to approximated the anticipated Euclid WL sample, enabling us to robustly map the empirical distribution of galaxies in the multidimensional color space defined by the expected Euclid filters.  Making this multicolor distribution lets us determine where - in galaxy color space - redshifts from current spectroscopic surveys exist and where the are systematically missing.  Crucially, the method lets us determine whether a spectroscopic training sample is representative of the full spectroscopy need to map out the color-redshift relation, finding that sampling the galaxy distribution in color space in a systematic way can efficiently meet the calibration requirements.  While the analysis presented here focuses on the Euclid survey, similar analysis can be applied to other surveys facing the same calibration challenge, such as DES, LSST, and WFIRST.