Day 1192

Wednesday.

1611.09362
Hints against the cold and collisionless nature of dark matter from the galaxy velocity function
Schneider, et al

The observed number of dwarf galaxies as a function of rotation velocity is significantly smaller than predicted by the LCDM model.  This discrepancy cannot be simply solved by assuming wrong baryonic processes, since they would violate the observed relation between maximum circular velocity (v_max) and baryon mass of galaxies.  A speculative possibility is that the mismatch between observation and theory points towards the existence of non-cold or non-collisionless DM.  In this paper, investigate the effects of warm, mixed (i.e. warm plus cold), and self-interacting DM scenarios on the abundance of dwarf galaxies and the relation between observed HI line-width and maximum circular velocity.  Both effects have the potential to alleviate the apparent mismatch between the observed and theoretical abundance of galaxies as a function of v_max.  For the case of warm and mixed DM, show that the discrepancy disappears, even for lukewarm models that evade stringent bounds from the Lyman-a forest.  Self-Interacting DM scenarios can also provide a solution as long as they lead to extended (>~1.5 kpc) DM cores in the density profiles of dwarf galaxies.  Only models with velocity-dependent cross sections can yield such cores without violating other observational constraints at larger scales.


1611.09366
Lensing constraints on the mass profile shape and splash back radius of galaxy clusters
Umetsu, Diemer

The lensing signal around galaxy clusters can, in principle, be used to test detailed predictions of their average mass profile from numerical simulations.  However, the intrinsic shape of the profiles can be smeared out when a sample that spans a wide range of cluster masses is averaged in physical length units.  This effect especially conceals rapid changes in gradient such as the steep drop associated with the splash back radius, a sharp edge corresponding to the outermost caustic in accreting halos.  Optimize the extraction of such local features by scaling individual halo profiles to a number of spherical overdensity radii, and apply this method to 16 Xray-selected high-mass clusters targeted in the Cluster Lensing and Supernova survey with Hubble (CLASH).  By forward-modeling the weak and strong lensing data presented in Umetsu et al., show that, regardless of the scaling overdensity, the projected ensemble density profile is remarkably well described by an NFW or Einasto profile out to R~2.5 Mpc/h, beyond which the profiles flatten.  Constrain the NFW concentration to c_200_c = 3.66±0.11 at M_200c~1e15 Msun/h, consistent with and improved from previous work that used conventionally stacked lensing profiles, and in excellent agreement with theoretical expectations.  Assuming the profile form of Diemer & Kravtsov and generic priors calibrated from numerical simulations, place a lower limit on the splash back radius of the cluster halos, if it exists, to be R_sp/r_200m>0.89 (R_sp>1.83 Mpc/h) at 68% confidence.  The corresponding density features is most pronounced when the cluster profiles are scaled by r_200m, and smeared out when scaled to higher overdensities.


1611.09459
How to find gravitationally lensed type Ia supernovae
Goldstein, Nugent

SNe Ia that are multiply imaged by GL can extend the SN Ia Hubble diagram to very high redshifts (z>~2), probe potential SN Ia evolution, and deliver high-precision constraints on H0, w, and Omega_m via time delays.  However, only one have been found to date, while many are needed to achieve these goals.  To increase the multiply imaged SN Ia discovery rate, present a simple algorithm for identifying gravitationally lensed SN Ia candidates in cadenced, wide-field optical imaging surveys.  The technique is to look for Se that appear to have an elliptical galaxy as their host with an absolute magnitude implied by the host's photometric redshift that is far brighter than the absolute magnitude of a normal SNIa (the brightest type of SN found in elliptical galaxies).  Importantly, this purely photometric method does not require the ability to resolve the lensed images for discovery.  The primary sources of contamination that affect the method are AGN and SF galaxies, but these can be controlled using catalog cross-matches and color cuts.  Highly magnified core-collapse SNe will also be discovered as a byproduct of the method.  Using MC sim, forecast that LSST can discover 500 multiply imaged SNe Ia using this technique in a 10-year z-band search, more than an order of magnitude improvement over previous estimates.  Also find the the Zwicky Transient Facility should find 10 multiply imaged SNe Ia using this technique in a 3-year R-band search -- despite the fact that this survey will not resolve a single system.