arXiv subjects

Robert J. Thacker

Publications and source records attributed to Robert J. Thacker.

21 records · Page 2Linked to original sources

arXiv2003

Temporal Bias in the Clustering of Massive Cosmological Objects

It is a well-established fact that massive cosmological objects exhibit a ``geometrical bias'' that boosts their spatial correlations with respect to the underlying mass distribution. Although this geometrical bias is a simple function of mass, this is only half of the story. We show using numerical simulations that objects that are in the midst of accreting material also exhibit a ``temporal bias,'' which further boosts their clustering far above geometrical bias levels. These results may help to resolve a discrepancy between spectroscopic and clustering mass estimates of Lyman Break Galaxies, a population of high-redshift galaxies that are caught in the act of forming large numbers of new stars.

astro-ph↗

arXiv2003

On the Spatial Correlations of Lyman Break Galaxies

Motivated by the observed discrepancy between the strong spatial correlations of Lyman break galaxies (LBGs) and their velocity dispersions, we consider a theoretical model in which these starbursting galaxies are associated with dark matter halos that experience appreciable infall of material. We show using numerical simulation that selecting halos that substantially increase in mass within a fixed time interval introduces a ``temporal bias'' which boosts their clustering above that of the underlying population. If time intervals consistent with the observed LBGs star formation rates of 50 solar masses per year are chosen, then spatial correlations are enhanced by up to a factor of two. These values roughly correspond to the geometrical bias of objects three times as massive. Thus, it is clear that temporal biasing must be taken into account when interpreting the properties of Lyman break galaxies.

astro-ph↗

arXiv2001

High-Redshift Galaxy Outflows and the Formation of Dwarf Galaxies

We examine the effects of galaxy outflows on the formation of dwarf galaxies in numerical simulations of the high-redshift Universe. Using a Smoothed Particle Hydrodynamic code, we conduct two detailed simulations of a (5.2 Mpc/h)^3 comoving volume of the Universe. In both simulations we implement simple, well-motivated models of galaxy identification and star formation, while our second simulation also includes a simple ``blow-out'' model of galaxy outflows in which supernova driven winds from newly formed disk galaxies punch-out and shock the intergalactic medium while leaving the host galaxies intact. A direct comparison between these simulations suggests that there are two major mechanisms by which outflows affect dwarf formation. Firstly, the formation of an outflow slows down the further accretion of gas onto a galaxy, causing an overall decrease of approximately 50% in the total gas mass accreted by the objects in our simulations. Additionally, our simulations uncover a significant population of approximately 10^9 solar mass objects whose formation is suppressed by the mechanism of ``baryonic stripping,'' in which outflows from early galaxies strip the gas out of nearby overdense regions that would have otherwise later formed into dwarf galaxies. This mechanism may be important in explaining the observed discrepancy between the number of dwarf galaxies predicted and observed in the local group and provide a natural explanation for the formation of empty halos which may be required by the existence of the extremely gas-poor extra-galactic High-Velocity Clouds.

astro-ph↗