Day 1092

Monday.

1605.01728
Alignments between galaxies, satellite systems and haloes
Shao et al

The spatial distribution of the satellite populations of the MW and Andromeda are puzzling in that they are nearly perpendicular to the disks of their central galaxies.  To understand the origin of such configurations, study the alignment of the central galaxy, satellite system and DM halo in the largest of the EAGLE simulation.  Find that centrals and their satellite systems tend to be well aligned with their haloes, with a median misalignment angle of 33deg in both cases.  While the centrals are better aligned with the inner 10 kpc halo, the satellite systems are better aligned with the entire halo indicating that satellites preferentially trace the outer halo.  The central - satellite alignment is weak (median misalignment angle of 52 deg) and find that around 20% of systems have a misalignment angle larger than 78deg, which is the value for the MW.  The central - satellite alignment is a consequence of the tendency of both components to align with the DM halo.  As a consequence, when the central is parallel to the satellite system, it also tends to be parallel to the halo.  In contrast, if the central is perpendicular to the satellite system, as in the case of MW and Andromeda, then the central - halo alignment is much weaker.  Dispersion-Dominated (spheroidal) centrals have stronger alignment with both their halo and their satellite than rotation-dominated (disk) centrals.  Also find that the halo, the central galaxy and the satellite system tend to be aligned with the surrounding large-scale distribution of matter, with the halo being the better aligned of the three.


1605.02036
Testing the log normality of the galaxy and weak lensing convergence distributions from Dark Energy Survey maps
Clerking, et al

It is well known that the PDF of galaxy density contrast is approximately lognormal; whether the PDF of mass fluctuations derived from WL convergence (kappa_WL) is lognormal is less well established.  Derive PDFs of the galaxy and projected matter density distributions via the counts in cells (CiC) method.  Use maps of galaxies and WL convergence produced from DES SV data over 139 deg^2.  Test whether the underlying density contrast is well described by a a lognormal distribution of the galaxies, the convergence and their joint PDF.  Confirm that the galaxy density contrast distribution is well modeled by a lognormal PDF convolved with Poisson noise at angular scales from 10-40 arcmin (corresponding to physical scales of 3-10 Mpc).  Note that as kappa_WL is a weighted sum of the mass fluctuations along the LoS, its PDF is expected to be only approximately lognormal.  And that the kappa-WL distribution is well modeled by lognormal PDF convolved with Gaussian shape noise at scales between 10 and 20 arcmin, with a best-fit chi^2/DOF of 1.11 compared to 1.84 for a Gaussian model, corresponding to p-values 0.35 and 0.07 respectively, at a scale of 10 arcmin.  Above 20 arcmin a simple Gaussian model is sufficient.  The joint PDF is also reasonably fitted by a bivariate lognormal. As a consistency check, compare the variances derived from the lognormal modeling with those directly measured via CiC.  The methods are validated against maps from the MICE Grand Challenge N-body simulation.