1606.01318
The origin of weak lensing convergence peaks
Liu, Haiman
WL convergence peaks are a promising tool to probe nonlinear structure evolution at late teams, providing additional cosmo info beyond second-order statistics. Previous theoretical and observational studies have shown that the cosmo constraints on Omega_m and sigma_8 are improved by a factor of up to ~2 when peak counts are second-order statistics are combined, compared to using the latter alone. Study the origin of lensing peaks using observational data from the 154 deg2 CFHTLS. Find that while high peaks (with height kappa > 3.5 sigma_kappa, where sigma_kappa is the rms of the convergence kappa) are typically due to one single massive halo of ~1e15 Msun, low peaks (kappa<~sigma_kappa) are associated with constellations of 2-8 smaller haloes (<~1e13 Msun). In addition, halos responsible for forming low peaks are found to be significantly offset from the LoS towards the peak center (impact parameter >~ their viral radii), compared with ~0.25 viral radii for haloes linked with high peaks, hinting that low peaks are more immune to baryonic processes whose impact is confined to the inner regions of the DM haloes. Findings are in good agreement with results from the simulation work by Yang+2011.
1606.01516
The lopsided distribution of satellite galaxies
Libeskind, et al
The distribution of smaller satellite galaxies around large central galaxies has attracted attention because peculiar spatial and kinematic configurations have been detected in some systems. A particularly striking example of such behavior is seen in the satellite system of Andromeda, where around 80% are on the nearside of that galaxy, facing the MW. Motivated by this departure from anisotropy, examine the spatial distribution of satellites around pairs of galaxies in the SDSS. By stacking tens of thousands of satellites around galaxy pairs, find that satellites tend to bulge towards the other central galaxy, preferably occupying the space between the pair, rather than being spherically or axis-symmetrically distributed around each host. The bulging is a function of the opening angle examined, and is fairly strong -- there are up to ~10% more satellite in the space between the pair than expected from uniform. Consequently, it is a statistically very strong signal, being inconsistent with a uniform distribution at the 5 sigma level. The possibility that the observed signal is the result of the overlap of two haloes with extended satellite distributions, is ruled out by testing this hypothesis by performing the same test on isolated galaxies (and their satellites) artificially placed at similar separations. These findings highlight the unrelaxed and interacting nature of galaxies in pairs.
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