Day 705

Tuesday.

1407.4996
Galaxy and Mass Assembly (GAMA): merging galaxies and their properties
De Propis et al

Derive the close pair fractions and volume merger rates as a function of luminosity and morphology for galaxies in the GAMA survey with -23<M(r)<-17 at 0.01<z<0.22.  The merger fraction is about 0.015 at all luminosities (assuming 1/2 of pairs merge) and the volume merger rate is about 0.00035 per cubic Mpc per Gyr.  Dry mergers (between red or spheroidal galaxies) are uncommon and decrease with decreasing luminosity.  Fainter mergers are wet, between blue or disk galaxies.  Damp mergers (one of each type) follow the average of dry and wet mergers.  In the brighter luminosity bin (-23<M(r)<-20) the merger rate evolution is flat, irrespective of color or morphology.  The makeup of the merging population does not change since z=0.2.  Major mergers and dry mergers appear comparatively unimportant in the buildup of the red sequence over the past 2 Gyr.  Compare the color, morphology, environmental density and degree of activity of galaxies in pairs to those of more isolated objects in the same volume.  Galaxies in close pairs tend to be both redder and slightly more spheroid-dominated.  This may be due to "harassment" in multiple previous passes prior to the current interaction.  Galaxy pairs do not appear to prefer significantly denser environments.  There is no evidence of an enhancement in the AGN fraction in pairs, compared to other galaxies in the same volume.  

1407.4730
A universal model for halo concentrations
Diemer, Kravtsov

Present a numerical study of DM halo concentrations in LCDM and self-similar cosmologies.  Show that the relation between concentration c and peak height nu exhibits the smallest deviations from universality if halo masses are defined wrt the critical density of the universe.  These deviations can be explained by the residual dependence of concentration on the local slope of the matter PS n, which affects both the normalization and shape of the c-nu relation.  In particular, there is no well-defined floor in the concentration values.  Instead, the minimum concentration depends on redshift: at fixed nu, haloes at higher z experience steeper slopes n, and thus have lower minimum concentrations.  Show that the concentrations in the simulations can be accurately described by a universal 7-parameter function of only nu and n.  This model matches the LCDM results to ~<5% accuracy up to z=6, and matches scale-free Omega_m=1 models to ~<15%.  The model also reproduces the low concentration values of Earth-mass haloes at z~30, and thus correctly extrapolates over 16 orders of magnitude in halo mass.  The predictions of the model differ significantly from all models previously proposed n the literature at high masses and redshifts.  This model is in excellent agreement with recent lensing measurements of cluster concentrations.

1407.5120
Isophotal shapes of early-type galaxies to very faint levels
Chaware, Cannon, Kembhavi, Pandey

Isophotal shapes of early-type galaxies to very faint levels, reaching ~0.1% of the sky brightness.  From integrated exposures of 1 to 4 hours in the SDSS riz bands at the Palomar 5m Hale telescope.  The shapes of isophotes of early-type galaxies are important as they are correlated with the physical properties of the galaxies and are influenced by galaxy formation processes.  In this paper, report on a sample of 132 E and SO galaxies in one LFC field (53 with redshifts).  The shapes of early-type galaxies often vary with radius.  Derive average values of isophotal shape parameters in 4 different radial bins along the semi-major axis in each galaxy.  Obtain empirical fitting formulae for the probability distribution of the isophotal parameters in each bin and investigate for possible correlations with other global properties of the galaxies.  The main finding: the isophotal shapes of the inner regions are statistically different from those in the outer regions [how?].  This suggests that the outer and inter parts of early-type galaxies have evolved somewhat independently.

1407.5151
Estimating luminosities and stellar masses of galaxies photometrically without determining redshifts
Hsieh, Yee

Direct estimate of these quantities using training sets, bypassing photometric redshift determination: Direct Empirical Photometric method (DEmP).  DEmP applies two techniques to minimize the effects arising from the non-uniform distribution of training-set galaxy redshifts from a flux-limited sample.  First, for each input galaxy, fitting is performed using a subset of the training-set galaxies with photometry and colors closest to those of the input galaxy.  Second, the training set is artificially resampled to produce a flat distribution in redshift, or other properties (e.g. luminosity).  To test the performance of DEmP, use a 4-filter band mock catalog to examine its ability to recover z, L, M*, and L-M* functions.  Also compare the results to those from two publicly available template-fitting methods, finding that the DEmP algorithm outperforms both.  Find resampling the training set to have uniform z distribution produces the best results not only in photometric redshift, but also in estimating luminosity and stellar mass.  The DEmP method is especially powerful in estimating quantities such as NIR luminosities and stellar mass sing only data from a small number of optical bands.

1407.5350
Weak gravitational lensing as a probe of physical properties of substructures in dark matter haloes
Shirasaki

A novel method to select satellite galaxies in outer regions of galaxy groups or clusters using weak gravitational lensing.  The method is based on the theoretical expectation that the tangential shear pattern around satellite galaxies would appear with negative values at the offset distance from the center of the main halo.  Thus locate the satellite galaxies statistically with a offset distance of several lensing smoothing scales by using the standard reconstruction of surface mass density maps from WL observation.  Test the idea using high res cosmo sims. Show that sub haloes separated from the center of the host halo are successfully located even without assuming the position of the center.  For a number of such subhaloes, the characteristic mass and the offset length can be also estimated on a statistical basis.  Perform a Fisher analysis to show how well upcoming WL surveys can constrain the mass density profile of satellite galaxies.  In the case of LSST with a sky coverage of 20k sq deg, the mass of the member galaxies in the outer region of galaxy clusters can be constrained with an accuracy of ~0.1 dex for galaxy clusters with mass of 1e14 Msun/h at z=0.15.  Finally, explore the detectability of tidal stripping features for sub haloes having a wide range of masses: 1e10-13 Msun/h.

1407.5453
Constraining primordial non-Gaussianity via multi-tracer technique with Euclid and SKA
Yamauchi, Takahashi, Oguri

Forecast constraints on f_NL with Euclid and a continuum galaxy survey by SKA, and their combination.  Derive a general expression for the covariance matrix of the PS estimates of multiple tracers to show how the multi-tracer technique improves constraints on f_NL.  Clarify the role of the overlap fraction of multiple tracers and the divisio method of the tracers.  The Fisher matrix analysis indicates that stringent constraints of sigma(f_NL)<1 can be obtained even with a single survey, assuming 5 mass bins.  When Euclid and SKA phase 1(2) are combined, constraints of f_NL are improved to sigma(f_NL)=0.34(0.31).