Day 1168

Tuesday.

1610.02399
Statistics of dark matter substructure: III. Halo-to-halo variance
Jiang, van den Bosch

Present a study of unprecedented statistical power regarding the halo-to-halo variance of DM substructure.  Using a combination of N-body sims and a semi-analytical model, investigate the variance in subhalo mass fractions and subhalo occupation numbers, with an emphasis on how these statistics scale with halo formation time.  Demonstrate that the subhalo mass fraction, f_sub, is mainly a function of halo formation time, with earlier forming haloes having less substructure.  At fixed formation redshift, the average f_sub is virtually independent of halo mass, and the mass dependence of f_sub is therefore mainly a manifestation of more massive haloes assembling later.  Compare observational constraints on f_sub from gravitational lensing to the model predictions and simulations results.  Although the inferred f_sub are substantially higher than the median LCDM predictions, they fall within the 95th percentile due to halo-to-halo variance.  Show that while the halo occupation distribution of sub haloes, P(N|M), is super-poissonian for large <N>, a well established result, it becomes sub-Poissonian for <N> < 2.  Ignoring the non-Poissonity results in systematic errors of the clustering of galaxies of a few percent, and with a complicated scale-and luminosity-dependence.  Earlier-formed haloes have P(N|M) closer to a Poisson distribution, suggesting that the dynamical evolution of sub haloes drives the statistics towards Poissonian.  Contrary to a recent claim, the non-Poissonity of subhalo occupation statistics does not vanish by selecting haloes with fixed mass and fixed formation redshift.  Finally, use subhalo occupation statistics to put loose constraints on the mass and formation redshift of the MW halo.  Using observational constraints on the V_max of the most massive satellites, infer that 0.25<M_vir/1e12 Msun/h < 1.4 and 0.1<z_f<1.4 at 90% confidence.


1610.02485
An order statistics approach to the halo model for galaxies
Paul, Paranjape, Sheth

Use the Halo Model to explore the implications of assuming that galaxy luminosities in groups are randomly drawn from an underlying luminosity function.  Show that even the simplest of such order statistics models -- on in which this luminosity function p(L) is universal -- naturally produces a number of features associated with previous analyses based on the `central plus Poisson satellites' hypothesis.  These include the monotonic relation of mean central luminosity with halo mass, the Lognormal distribution around this mean, and the tight relation between the central and satellite mass scales.  In stark contrast to observations of galaxy clustering, however, this model predicts no luminosity dependence of large scale clustering.  Then show that an extended version of this model, based on the order statistics of a halo mass dependent luminosity function p(L|m), is in much better agreement with the clustering data as well as satellite luminosities, but systematically under-predicts central luminosities.  This brings into focus the idea that central galaxies constitute a distinct population that is affected by different physical processes than are the satellites.  Model this physical difference as a statistical brightening of the central luminosities, over and above the order statistics prediction.  The magnitude gap between the brightest and second brightest group galaxy is predicted as a by-product, and is also in good agreement with observations.  Propose that this order statistics framework provides a useful language in which to compare the Halo Model for galaxies with more physically motivated galaxy formation models.  


1610.02644
Quenching of satellite galaxies at the outskirts of galaxy clusters
Zinger, Dekel, Kravtsov, Nagai

Find, using cosmo sims of galaxy clusters, that the hot X-ray emitting intra-cluster medium (ICM) enclosed within the outer accretion shock extends out to R_shock~(2-3)R_vir, where R_vir is the standard virial radius of the halo.  Using a simple analytic model for satellite galaxies in the cluster, evaluate the effect of ram-pressure stripping of the gas in the inner discs and in the haloes at different distances from the cluster centre.  Find that significant removal of star-forming disc gas occurs only at r<~0.5 R_vir, while gas removal from the satellite halo is also efficient between R_vir and R_shock.  This leads to quenching of star formation by starvation over 2-3 Gyr, prior to the satellite entry to the inner cluster halo.  This can explain the presence of quenched galaxies, preferentially discs, at the outskirts of galaxy clusters, and the delayed quenching of satellites compared to central galaxies.


1610.02916
Building an inclusive AAS - The critical rote of diversity and inclusion training for AAS council and astronomy leadership
Brinkworth et al

... Diversity and inclusion training for AAS council and leadership, heads of astronomy departments, and faculty search committees should be a basic requirement throughout the field.