Day 710

 Monday.

1407.6708
The distribution of satellites around central galaxies in a cosmological hydrodynamical simulation
Dong, Lin, Kang, Wang, Dutton, Macciò

Observations have shown that the spatial distribution of satellite galaxies is not random, but rather, it is aligned with the major axes of central galaxies.  The strength of the alignment is dependent on the properties of both satellites and centrals.  Theoretical studies using dissipation less N-body sims are limited by their inability to directly predict the shape of central galaxies.  Using hydrodynamical simulations including gas cooling, SF and feedback, carry out a study of galaxy alignment and its dependence on galaxy properties predicted directly from the simulations.  Find that the observed alignment signal is well produced, as is the color dependence: red satellites and red centrals both show stronger alignments than their blue counterparts.  The reason for the stronger alignment of red satellites is that most of them stay in the inner region of the dark matter halo, where the shape of central galaxy traces better the DM distribution.  The dependence of alignment on the color of central galaxies arises from halo mass dependence, since the alignment between the shape of the central stellar component and the inner halo increases with halo mass.  Also find that the alignment of satellites is most strongly dependent on their metallicity, suggesting that the metallicity of satellites, rather than color, is a better tracer of galaxy alignment on small scales.  This could be tested in future observational studies.

1407.6715
Quenching depends on morphologies: implications from the ultraviolet-optical color distributions in Green Valley Galaxies
Pan, Li, Lin, Wang, Kong

Analyse the radial UV-optical color distributions in a sample of low redshift GV galaxies, with GALEX+SDSS images, to investigate the residual recent SF distribute in these galaxies.  Find that the dust-corrected u-r colors of ETGs are flat out to R_90, while the colors turn blue monotonously when r>0.5R_50 for LTGs.  More than a half of the ETGs are blue-cored and have remarkable positive NUV-r color gradients, suggesting that their SF are centrally concentrated; the rest have flat color distributions out to R_90.  The centrally concentrated SF activity in a large portion of ETGs is confirmed by the SDSS spectroscopy, showing that ~50% ETGs have EW(Ha)>6.0AA.  For the LTGs, 95% of them show uniform radial color profiles, which can be interpreted as a red bulge plus an extended blue disk.  The links between the two kinds of ETGs, e.g., those objects having remarkable "blue-cored" and those having flat color gradients, are less known and require future investigations.  It is suggested that the LTGs follow a general picture that quenching first occur in the core regions, and then finally extend to the rest of the galaxy.  This result can be re-examined and have important implications for the IFU surveys, such as MaNGA and SAMI.

1407.6740
The spatial distribution of satellite galaxies within halos: measuring the very small scale angular clustering of SDSS galaxies
Piscionere, Berlind, McBride, Scoccimarro

Measure the angular clustering of galaxies from SDSS DR7 in order to probe the spatial distribution of satellite galaxies within their DM haloes.  Specifically, measure the angular correlation function on very small scales (7-320") in a range of luminosity threshold samples (absolute r-band magnitudes of -18 up to -21) that are constructed from the subset of SDSS that has been spectroscopically observed more than once (plate overlap region).  Choose to measure angular clustering in this reduced survey footprint in order to minimize the effects of fiber collision incompleteness, which are otherwise substantial on these small scales.  Model clustering measurements using a fully numerical halo model that populates DM haloes in N-body sims to create realistic mock galaxy catalogs.  The model has free parameters that specify both the number and spatial distribution of galaxies within their host halos.  Adopt a flexible density profile for the spatial distribution of satellite galaxies that is similar to the DM NFW profile, except that the inner slope is allowed to vary.  Find that the angular clustering of the most luminous samples (Mr<-20 and -21) suggests that luminous satellite galaxies have substantially steeper inner density profiles than NFW.  Lower luminosity samples are less constraining, however, and are consistent with satellite galaxies having shallow density profiles.  Results confirm the findings of Watson+2012 while using different clustering measurements and modeling methodology.

1407.6990
The intrinsic alignment of galaxies and its impact on weak gravitational lensing in an era of precision cosmology
Troxel, Ishak

Cosmic shear measures the minute distributions of BG galaxy images by intervening cosmic structure, promising to be a powerful probe of astrophysics and cosmology.  However, the IA of galaxies --- their shape and orientation before being lensed --- poses a great challenge to the use of WL as an accurate probe, and has been identified as one of the primary physical systematic biases in cosmic shear studies.  Correlations between this IA and the lensing signal can persist even for large physical separations, and isolating the effect of IA from WL is not trivial.  Two decades of work in understanding and characterizing IA, which is also a direct and complementary probe of structure formation and evolution in its own right.  In this review, report the state of the understanding of IA of galaxies, with a particular emphasis on its large-scale impact on WL measurements and methods for its isolation or mitigation.