Day 878

Thursday.


1504.07629
Gravitational lens modeling with basis sets
Birrer, Amara, Refregier

Present a lensing modeling technique based on versatile basis sets for the lens and source planes.  The method uses high performance MC algorithms, allows for an adaptive build up of complexity and bridges the gap between parametric and pixel based reconstruction methods.  Apply the method to a HST image of the strong lens system RXJ1131-1231 and show that the method finds a reliable solution and is able to detect substructure in the lens and source planes simultaneously.  Using mock data, show that the method is sensitive to sub-clumps with masses four orders of magnitude smaller than the main lens, which corresponds to about 1e8 Msun, without prior knowledge on the position and mass of the sub-clump.  The modeling approach is flexible and maximises automation to facilitate the analysis of the large number of strong lensing systems expected in upcoming wide field surveys.  The resulting search for dark sub-clumps in these systems, without M/L priors, offers promise for probing physics beyond the standard model in the DM sector.


1504.07632
On detecting halo assembly bias with galaxy populations
Lin, Mandelbaum, Huang, Huang, Dalal, Diemer, Jian, Kravtsov

The fact that the clustering and concentration of DM haloes depend not only on their mass, but also the formation epoch, is a prominent, albeit subtle, feature of the CDM structure formation theory, and is known as assembly bias.  At low mass scales (~1e12 Msun/h), early-forming haloes are predicted to be more strongly clustered than the late-forming ones.  In this study, aim to robustly detect the signature of assembly bias observationally, making use of formation time indicators of central galaxies in low mass haloes as a proxy for the halo formation history.  WL is employed to ensure the early- and late- forming halo samples have similar masses, and are free of contamination of satellites from more massive haloes.  For the two formation time indicators used (resolved SFH and current sSFR), do not find convincing evidence of assembly bias.  For a pair of early- and late-forming galaxy samples with mean mass M_200c~9e11 Msun/h, the relative bias is 1.00±0.12.  Attribute the lack of detection to the possibilities that either the current measurements of these indicators are too noisy, or they do not correlate well with the halo formation history.  Alternative proxies for the halo formation history that should perform better are suggested for future studies.


1504.07686
A pilot survey for CIII] Emission in the reionization era: gravitationally-lensed z$\sim7-8$ galaxies in the Frontier Fields Cluster Abell 2744
Zitrin, Ellis, Belli, Stark

Report results of a search for CIII] ll1907,1909 A emission using Keck's MOSFIRE spectrograph in a sample of 7 z_phot~7-8 candidates (H~27) lensed by the HFF cluster A2744.  Earlier work has suggested the promise of using the CIII] doublet for z confirmation of galaxies in the reionization era given Lya (l1216A) is likely attenuated by the neutral IGM.  The primary challenge of the approach is the feasibility of locating CIII] emission without advanced knowledge of the spectroscopic z.  With an integration time of 5 hrs in the H-band, reach a 5 sigma median flux limit (in between the sky lines) of 1.5e-18 ergs/cm2/sec, but no convincing CIII] emission found.  Also incorporate preliminary measurements from to two other CLASH/HFF clusters in which, similarly, no line was detected, but these were observed to lesser depth.  Using the known distribution of OH emission and the photometric z likelihood distribution of each lensed candidate, present statistical upper limits on the mean total CIII] rest-frame equivalent width for the z~7-8 sample.  For a signal/noise ratio of 5, estimate the typical CIII] doublet rest-frame equivalent width is, with 95% confidence, <26±5A.  Although consistent with the strength of earlier detection in brighter objects at z~6-7, the study illustrates the necessity of studying more luminous or strongly-lensed examples prior to the launch of JWST.