Day 1096

Tuesday.

1605.04307
What does the Bullet Cluster tell us about self-interacting dark matter?
Robertson, Massey, Eke

Perform numerical sim of the merging Bullet Cluster, including the effects of elastic DM scattering.  In a similar manner to the stripping of gas by ram pressure, DM self-interactions would transfer momentum between the two galaxy cluster DM haloes, causing them to lag behind the collisionless galaxies.  The absence of an observed separation between the dark matter and stellar components in the Bullet cluster has been used to place upper limits on the cross-section for DM scattering.  Emphasize the importance of analyzing simulations in an observationally-motivated matter, finding that the way in which the positions of the various components are measured can have a larger impact on derived constraints on DM's self-interaction cross-section than reasonable changes to the initial conditions for the merger.  In particular, find that the methods used in previous studies to place some of the tightest constraints on the cross-section do not reflect what is done observationally, and overstate the Bullet Cluster's ability to constrain the particle properties of DM.  Introduce the first simulations of the Bullet Cluster including both self-interacting DM and gas.  Find that as the gas is stripped it introduces radially-dependent asymmetries into the stellar and DM distributions.  As the techniques used to determine the positions of the DM and galaxies are sensitive to different radial scales, these asymmetries can lead to erroneously measured offsets between DM and galaxies even when they are spatial coincident.


1605.04309
The PCA Lens-Finder: application to CFHTLS
Paraficz, Courbin, et al

Present the realists of a new search for galaxy-scale SL systems in CFHTLS wide.  The lens-finding technique involves a preselection of potential lens galaxies, applying simple cuts in size and magnitude.  Then perform a PCA of the galaxy images, ensuring a clean removal of the light profile.  Lensed features are searched for in the residual images using the clustering topometric algorithm DBSCAN.  Find 1098 lens candidates that are visually inspected, leading to a cleaned sample of 109 new lens candidates.  Using realistic image simulations, estimate the completeness of the sample and show that it is independent of source surface brightness, Einstein ring size (image separation) or lens redshift.  Compare the properties of the sample to previous lens searches in CFHTLS.  Including the present search, the total number of lenses found int CFHTLS amounts to 678, which corresponds to ~4 lenses per square degree down to i=24.8.  This is equivalent to ~60,000 lenses in total in a survey as wide as Euclid, but at the CFHTLS resolution and depth.


1605.04319
A look to the inside of haloes: a characterization of the halo shape as a function of overdensity in the Planck cosmology
Despali, Giocoli, et al

From simulation, discuss how halo triaxiality increases with (i) mass, (ii) redshift and (iii) overdensity.  Also examine how the orientation of the different ellipsoidal shells are aligned with each other and what is the gradient in internal shapes for haloes with different viral configurations.  Findings highlight that the internal part of the halo retains memory of the violent formation process keeping the major axis oriented toward the preferential direction of the infalling material while the outer part becomes rounder due to continuous isotropic merging events; this effect is clearly evident in high mass haloes - which formed recently - while it is more blurred in low mass haloes.  Present simple distributions that may be used as priors for various mass reconstruction algorithms, operating in different wavelengths, in order to recover a more complex and realistic DM distribution of isolated and relaxed systems.


1605.04357
The rise of the first stars: supersonic streaming, radiative feedback, and 21-cm cosmology
Barkana

Since the universe was filled with H atoms at early times, the most promising probe of the epoch of the first stars is the prominent 21-cm spectral line of H.  Current observational efforts are focus on the cosmic reionization era, but observations of the pre-reioniation cosmic down are also promising.  While observationally unexplored, theoretical studies predict a rich variety of observational signatures from cosmic dawn.  As the first stars formed, their radiation (plus that from stellar remnants) produced significant cosmic events including Lyman-alpha coupling at z~25, and early X-ray heating.  Much focus has gone to studying the angle-averaged power spectrum of 21-cm fluctuations.  Additional probes include the global (sky-averaged) 21-cm spectrum, and the LOS anisotropy of the 21-cm power spectrum.  A particularly striking signature may result from the recently recognized effect of a supersonic relative velocity between the DM and gas.  Work in this field, focused on understanding the whole era of reionization and cosmic dawn with analytical models and numerical simulations, is likely to grow in intensity and importance, as the theoretical predictions are finally expected to confront 21-cm observations  the coming years.