Day 585

Monday, the day after the Superbowl.  Wednesday.

1401.7986
Reinterpreting short gamma ray burst progenitor kicks and time delays using the host galaxy-dark matter halo connection
Behroozi, Ramirez-Ruiz, Fryer

Nearly 20% of sGRBs have no observed host galaxies.  Combine this with constraints on galaxies' dark matter halo potential wells gives strong limits on the natal kick velocity distribution for sGRB progenitors [assuming that the sGRB originated in a galaxy?].  For the best-fitting velocity distribution, one in five sGRB progenitors receives a natal kick above 150 km/s [thus escaping the host galaxy?], consistent with merging NS models but not with merging WD binary models.  This progenitor model constraint is robust to a wide variety of systematic uncertainties, including the sGRB progenitor time-delay model, the Swift redshift sensitivity, and the shape of the natal kick velocity distribution  Also use constraints on the galaxy-halo connection to determine the host halo and host galaxy demographics for sGRBs, which match extremely well with available data.  Most sGRBs are expected to occur in halos near 1e12 Msun and in galaxies near 5e10 Msun (~L*); unobserved faint and high-z host galaxies contribute a small minority of the observed host less sGRB fraction.  Find that sGRB z distributions and host galaxy stellar masses weakly constrain the progenitor time-delay model; the active vs. passive fraction of sGRB host galaxies may offer a stronger constraint.  Discuss how searches for gravitational wave optical counterparts in the local Universe can reduce followup times using these findings.

1401.7990
Gravitational lens recovery with GLASS: measuring the mass profile and shape of a lens
Coles, Read, Saha

A new non-parametric gravitational modeling tool -- GLASS.  Used to determine what quality of data (SL, stellar kinematics, and/or stellar masses) are required to measure the circularly averaged mass profile of a lens and its shape.  GLASS uses an under-constrained adaptive grid of mass pixels to model the lens, searching through thousands of models to marginalize over model uncertainties.  Find: (i) for pure lens data, multiple sources with wide redshift separation give the strongest constraints [duh] as this breaks the well-known mass-sheet or steepness degeneracy [?]; (ii) a single quad with time delays also performs well, giving a good recovery of both the mass profile and its shape; (iii) stellar masses -- for lenses where the stars dominate the central potential -- can also break the steepness degeneracy, giving a recovery for doubles almost as good as having a quad with time delay data, or multiple source redshifts; (iv) stellar kinematics provides a robust measure of the mass at the half light radius of the stars r_1/2 that can also break the steepness degeneracy if the Einstein radius r_E != r_1/2; and (v) if r_E ~ r_1/2, then stellar kinematic data can be used to probe the stellar velocity anisotropy beta -- an interesting quantity in its own right.  Where information on the mass distribution from lensing and/or other probes becomes redundant, this opens up the possibility of using strong lensing to constrain cosmological models.

1401.7992
Super-sample CMB lensing
Manzotti, Hu, Benoit-Lévy

Lensing of the CMB by modes that are larger than the size of the survey dilates intrinsic scales in the temperature and polarization fields and coherently shifts their observed PS wrt the ensemble or all-sky mean.  The effect can be simply encapsulated as a contribution to the PS covariance matrix in accordance with the lensing trispectrum or as an additional parameter, the mean convergence in the field, for parameter estimation.  It should be included for upcoming surveys that precisely measure acoustic polarization features deep into the damping tail at multiples of l>1500 with <10% of sky.  Its omission may lead to seemingly conflicting values for the angular scale of the sound horizon which may then provide erroneous cosmological parameters when compared to BAO measurements.