Day 333

Friday.

1211.3120
Physical properties of simulated galaxy populations at z=2 -- II. Effects of physics ingredients other than cooling and outflows
Haas, Schaye, Booth, Vecchia, Springel, Theuns, Wiersma

Use hydrosims to investigate the dependence of the physical properties of galaxy populations at z=2 on the assumed star formation law, the equation of state imposed on the unresolved interstellar medium, the stellar IMF, the reionizaton history, and the assumed cosmology.  This work complements another paper, where the effects of varying models for galactic winds driven by SF and AGN were studied.  The normalization of the MPS strongly affects the galaxy mass function, but has a relatively small effect on the physical properties of galaxies residing in haloes of a fixed mass.  Reionization suppresses the stellar masses and gas fractions of low mass galaxies, but by z=2 the results are insensitive to the timing of reionization.  The IMF determines the physical properties of galaxies through its effects on the efficiency of the feedback, while changes in the recycled mass and metal fractions play a smaller role.  If we use a recipe for SF that reproduces the observed SF law independently of the assumed EoS of the unresolved ISM, then the latter is unimportant.  THe SF law (the gas consuption time scale as a function of surface density) determines the mass of dense, SF gas in galaxies, but affects neither the SFR nor the stellar mass.  This can be understood  in terms of self-regulation: the gas fraction adjusts until the outflow rate balances the inflow rate.

1211.3124
Angular momentum transfer to a milky way disk at high redshift
Tillson... Miller,... et al

An AMR cosmo resimulation analyzed to test whether filamentary flows of cold gas are responsible for the build-up of angular momentum within a MW like disk at z>=3.  A set of algorithms presented that takes advantage of the high spatial resolution of the simulation (12pc) to identify (i) the central gas disk and its plane of orientation, (ii) the complex individual filament trajectories that connect to the disk, and (iii) the infalling satellites.  The results show that two filaments at z>5.5, which later merge to form a single filament at z<4, drive the angular momentum and mass budget of the disk throughout its evolution, whereas luminous satellite mergers make negligible fractional contributions.  Combined with the ubiquitous presence of such filaments in all large-scale cosmological simulations that include hydrodynamics, these findings provide strong quantitative evidence that the growth of thin disks in haloes with masses below 1e12 Msun, which host the vast majority of galaxies, is supported via inflowing streams of cold gas at intermediate and high redshifts.

1211.3130
Removing BAO-peak shifts with local density transforms
McCullagh, Neyrinck, Szapudi, Szalay

Broadening of the BAO feature by large-scale bulk flows, and a small shift in the peak of the conventional overdensity correlation function (a mass-weighted statistic).  This shift occurs when high density peaks move toward each other.  Explore whether this shift can be removed by applying the density field a transform (eg. log) that gives fairer statistical weight to fluctuations in underdense regions.  Use configuration-space perturbation thoery in Zeldovich approximation, find that the log-density correlation function shows a much smaller shift in the position of BAO peak at low z than is seen in the overdensity correlation function.  Also show that if the initial Lagrangian density of matter parcels could be estimated at their Eulerian positions, giving a displaced-initial-density field, the peak shift would be even smaller,  In this model, these shifts in the peak position can be attributed to shift terms, involving the derivative of the linear correlation function, that entirely vanish in the displaced-initial-density field.

1211.3161
Galaxy pairs in the local group
Fattahi, Navarro, ... et al

Current models of galaxy formation: predict galaxy pairs of comparable magnitudes should become increasingly rare with decreasing luminosity.  At odds with Local Group observations.  Use literature data to show that ~30% of all satellites of MW and Andromeda M_V<-8 are found in likely physical pairs of comparable luminosity.  If confirmed in studies of larger samples, the high frequencey of dwarf galaxy pairings may provide interesting clues to the formation of faint galaxies in the current cosmological paradigm.