Day 972

Tuesday.


1509.05784
A weak gravitational lensing recalibration of the scaling relations linking the gas properties of dark haloes to their mass
Wang, White, Mandelbaum, Henriques, Anderson, Han

Use WL to measure mean mass profiles around Locally Bright Galaxies.  These are selected from SDSS DR7 spec and photo catalogs to be brighter than any neighbor projected within 1.0 Mpc and differing in z by <1000 km/s.  Most (>83%) are expected to be the central galaxies of their DM haloes.  Previous stacking analyses have used this LBG sample to measure mean SZ flux and mean X-ray luminosity as a function of LBG stellar mass.  In both cases, a simulation of the formation of the galaxy population was used to estimate effective halo mass for LBGs of given stellar mass, allowing the derivation of scaling relations between the gas properties of haloes and their mass. By comparing results form a variety of sims to the lensing data, show that this procedure has signifiant model dependence reflecting: (i) the failure of any given sim to reproduce observed galaxy abundances exactly; (ii) a dependent on the cosmo underlying the simulations; and (iii) a dependence on the details of how galaxies populate haloes.  Use the lensing results to recalibrate the scaling relations, eliminating most of this model dependence and explicitly accounting both for residual modeling uncertainties and for observational uncertainties in the lensing results.  The resulting scaling relations link the mean gas properties of dark haloes to their mass over an unprecedentedly wide range, 12.5 < log(M500/Msun) < 14.5, and should fairly and robustly represent the full halo population.


1509.06096
Direct shear mapping: prospects for weak lensing studies of individual galaxy-galaxy lensing systems
de Burge-Day, Taylor, Webster, Hopkins

Investigate (using both theoretical and empirical approach) the frequency of low redshift gg-lensing systems in which the signature of WL might be directly detectable.  Find good agreement between these two approaches.  In order to make a theoretical estimate of the WL shear, gamma, for each galaxy in a catalogue, made an estimate of the asymptotic circular velocity from the stellar mass using 3 different approaches: from a simulation based relation, from an empirically-derived relation, and using the baryonic Tully-Fisher relation.  Using data from the Galaxy and Mass Assembly redshift survey, estimate the frequency of detectable WL at low redshift.  Find that to z~0.6, the probability of a galaxy being weakly lensed by at least gamma=0.02 is ~0.01.  A scatter in the M*-Mh relation results in a shift towards higher measured shears for a given population of galaxies.  Given this, and the good probability of WL at low redshifts, investigate the feasibility of measuring the scatter in the M*-Mh relation using shear statistics.  This is a novel measurement, and is made possible because DSM is able to make individual shape direct shape [?] shear measurements, in contrast to traditional WL techniques which can only make statistical measurements.  Estimate that for a shear measurement error of Delta gamma =0.02 (consistent with the sensitivity of DSM), a sample of ~50k spatially and spectrally resolved galaxies would allow a measurement of the scatter in the M*-Mh relation to be made.  While there are no currently existing IFU surveys of this size, there are upcoming surveys which will provide this data (HETDEX, SKA).