Day 1454

Tuesday.

1808.05619
Testing the uniqueness of gravitational lens mass models
Wals, Williams

The positions of images produced by the gravitational lensing of background sources provide unique insight into galaxy-lens mass distribution.  However, even quad images of extended sources are not able to fully characterize the central regions of the host galaxy. Most previous work has focused either on the radial density profile of the lenses or localized substructure clumps.  Here, concentrate on the azimuthal mass asymmetries near the image circle.  The motivation for considering such mass inhomogeneities is that the transition between the central stellar dominated region and the outer dark matter dominated region, though well represented by a power law density profile, is unlikely to be featureless, and encodes information about the dynamical state and assembly history of galaxies.  It also happens to roughly coincide with the Einstein radius.  Ask if galaxies that have mass asymmetries beyond ellipticity can be modeled with simpler lenses, i.e., can complex mass distributions masquerade as simple elliptical+shear lenses?  The preliminary study indicates that for galaxies with elliptical stellar and dark matter distributions, but with no mass asymmetry, and an extended source filling the diamond caustic, an elliptical+shear lens model can reproduce the images well, thereby hiding the potential complexity of the actual mass distribution.  For galaxies with non-zero mass asymmetry, the answer depends on the size and brightness distribution of the source, and its location within the diamond caustic.  In roughly half of the cases considered, the mass asymmetries can easily evade detection.


1808.05695
Reconciling the diversity and uniformity of galactic rotation curves with self-interacting dark matter
Ren, Kwa, Kaplinghat, Yu

Galactic rotation curves exhibit diverse behavior in the inner regions, while obeying an organizing principle, i.e., they can be approximately described by a radial acceleration relation or the Modified Newtonian Dynamics phenomenology.  Analyze the rotation curve data from the eSPARC sample, and explicitly demonstrate that both the diversity and uniformity are naturally reproduced in a hierarchical structure formation model with the addition of dark matter self-interactions.  The required concentrations of the dark matter haloes are fully consistent with the concentration-mass relation predicted by the Planck cosmological model.  The inferred stellar mass-to-light (3.6 um) ratios scatter around 0.5 Msun/Lsun, as expected from population synthesis models, leading to a tight radial acceleration relation and baryonic Tully-Fisher relation.  The inferred stellar-halo mass relation is consistent with the expectations from abundance matching.  These results indicate that the inner dark matter haloes of galaxies are thermalized due to the self-interactions of dark matter particles.


1808.05978
Larve Covariance Matrices: Accurate models without mocks
O'Connell, Eisenstein

Covariance matrix estimation is a persistent challenge for cosmology.  Focus on a class of model covariance matrices that can be generated with high accuracy and precision, using a tiny fraction of the computational resources that would be required to achieve comparably precise covariance matrices using mock catalogues.  In previous work, the free parameters in these models were determined using sample covariance matrices computed using a large number of mocks, but demonstrate that those parameters can be estimated consistently and with good precision by applying jackknife methods to a single survey volume.  This enables model covariance matrices that are calibrated from data alone, with no reference to mocks.