Day 1022

Friday.


1512.03050
Introducing decorated HODs: modeling assembly bias in the galaxy-halo connection
Hearing, Zentner, van den Bosch, Campbell, Tollerud

The connection between galaxies and dark matter haloes is often inferred form data using probabilistic models, such as the Halo Occupation Distribution (HOD).  Conventional HOD formulations assume that only halo mass governs the galaxy-halo connection.  Violations of this assumption, known as galaxy assembly bias, threaten the HOD program.  Introduce decorated HODs, a new, flexible class of models designed to account for assembly bias.  Decorated HODs minimally expand the parameter space and maximize the independence between traditional and novel HOD parameters.  Use decorated HODs to quality the influence of assembly bias on clustering and lensing statistics.  For SDSS-like samples, the impact of assembly bias on galaxy clustering can be as large as a factor of two on r~200 kpc scales and ~15% in the linear regime.  Assembly bias can either enhance or diminish clustering on large scales, but generally increases clustering on scales r<~1 Mpc.  Performed the calculations with Halotools, an open-source, community-driven python package for studying the galaxy-halo connection.  Conclude by describing the use of decorated HODs to treat assembly bias in otherwise conventional likelihood analyses.


1512.03062
Observation and confirmation of six strong lensing systems in the Dark Energy Survey Science Verification Data
Nord et al

In DES SV, identify 53 candidate systems, the obtain spectroscopic follow-up of 21 candidates using GMOS at Gemini South and IMACS at Magellan/Baade.  Confirmed 6 candidates as gravitational lenses:  Three of the systems are newly discovered, and the remaining three were previously known.  Of the 21 observed candidates, the remaining 15 were either not detected in spectra observations, were observed and did not exhibit continuum emission (or spectral features), or were ruled out as lensing system.  The confirmed sample consists of one group-scale and five galaxy cluster-scale lenses.  The lensed sources range in redshift z~0.80-3.2, and in i-band surface brightness i_SB~23-25 mag/sq-arcsec (2" aperture) . For each of the 6 systems, estimate the Einstein rides and the enclosed mass, which have ranges ~5.0-8.6" and ~7.5e12-6.4e13 Msun, respectively.


1512.03402
Recovering the tidal field in the projected galaxy distribution
Alonso, Hadzhiyska, Strauss

Present a method to recover and study the projected gravitational tidal forces from a galaxy survey containing little or no redshift information.  The method and the physical interpretation of the recovered tidal maps as a tracer of the cosmic web are described in detail.  First apply the method to a simulated galaxy survey and study the accuracy with which the cosmic web can be recovered in the presence of different observational effects, showing that the projected tidal field can be estimated with reasonable precision over large regions of the sky.  Then apply the method to the 2MASS survey and present a publicly available full-sky map of the projected tidal forces in the local Universe.  As an example of an application of these data, further study the distribution of galaxy luminosities across the different elements of the cosmic web, finding that, while more luminous objects are found preferentially in the most dense environments, there is no further segregation by tidal environment.