Day 659

Monday.

1405.3984
Revisiting the universality of (multiple) star formation in present-day star formation regions
Marks, Leigh, Giersz, Pfalzner, Pflamm-Altenburg, Oh

Dynamical interactions in clustered regions change star populations; but stellar density-dependent modification of a universal initial binary population (efficiency of binary disruption is thought to be determined by stellar density) cannot explain the observations.  Re-analyze data with different model assumptions: (1) non-universality without dynamical modification and (2) universality with dynamics.  Illustrate that the standard model does account for all known populations if regions were significantly denser in the past.  Some of the effects of using present-day cluster properties as proxies for their past values are emphasized and that the degeneracy between age and density of a SF region can not be omitted when interpreting multiplicity data.  A new analysis of the Corona Australis sregion is performed within the standard model.  It is found that this region is likely as involved as Taurus and an initial density of ~190 Msun/pc^3 is required to produce the presently observed binary population, which is close to its present-day density.

1405.4285
Mass and galaxy distributions of four massive galaxy clusters from Dark Energy Survey Science Verification data
Melchior ... Huff, Rykoff, Gruen, Armstrong, Bacon, Bernstein, Bridle, Jain, Krause, ... et al

Measure the WL masses and galaxy distributions of four massive galaxy clusters observed during the Science Verification phase of the DES with the purpose of 1) validating the DECam imager for the task of measuring WL shapes, and 2) utilizing DECam's large FoV to map out the clusters and their environments over 90 arcmin.  Conduct a series of rigorous tests on astrometry, photometry, image quality, PSF modeling, and shear measurement accuracy to single out flaws in the data and also to identify the optical data processing steps and parameters.  Find Science Verification data from DECam to be suitable for lensing analyses.  The PSF is generally well-behaved, but the modeling is rendered difficult by a flux-dependent PSF width.  Employ photometric redshifts to distinguish between FG and BG galaxies, and a red-sequence cluster finder to provide cluster richness estimates and cluster-galaxy distributions.  By fitting NFW profiles to the clusters in this study, determine WL masses that are in agreement with previous work.  For Abell 3261, provide the first estimates of redshift, WL mass, and richness.  In addition, the cluster-galaxy distributions indicate the existence of filaments attached to 1E 0657-56 and RXC J2248.7-4431, stretching out as far as 1 degree (approximately 20 Mpc), showcasing the potential of DECam and DES for detailed studies of degree-scale features on the sky.