Day 1047

Wednesday.  Thursday.  Friday.  Monday.


1602.01099
Hierarchical galaxy growth and scatter in the stellar mass - halo mass relation
Gu, Conroy, Behroozi

The relation between galaxies and DM halos reflects the combined effects of many distinct physical processes.  Observations indicate that the z=0 SM-HM relation has remarkably small scatter in stellar mass at fixed halo mass (<0.2 dex) with little dependence on halo mass.  Investigate the origins of this scatter by combining N-body sims with observational constraints on the SMHM relation.  Find that at the group and cluster scale (Mvir > 1e14 Msun) the scatter due purely to hierarchical assembly is ~0.16 dex, which is comparable to recent direct observational estimates.  At lower masses, mass buildup since z~2 is driven largely by in-situ growth.  Include a model for the in-situ buildup of stellar mass and find that an intrinsic scatter in this growth channel of 0.2 dex produces a relation between scatter and halo mass that is consistent with observations from 1e12 Msun < Mvir < 1e14.75 Msun.  The approximately constant scatter across a wide range of halo masses at z=0 thus appears to be a coincidence as it is determined largely by in-situ growth at low masses and by hierarchical assembly at high masses.  These results indicate that the scatter in the SMHM relation can provide unique insight into the regularity of the galaxy formation process.


1602.02154
Accurate halo-model matter power spectra with dark energy, massive neutrinos and modified gravitational forces
Mead, Heymans, Lombriser, Peacock, Steele, Winther

Show that the tuned halo model method can predict the non-linear matter PS to measurements from sims of parameterized w(a) DE models at the few per cent level for k<10 h/Mpc, and present theoretically motivated extensions to cover non-minimally coupled scaler fields, massive neutrinos and Vainshtein screened modified gravity models that result in few per cent accurate power spectra for k<10 h/Mpc.  For Chameleon screened models, achieve only 10% accurate PS for the same range of scales.