An N-body/SPH Study of Isolated Galaxy Mass Density Profiles

TL;DR

This study uses N-body/SPH simulations to explore how isolated galaxy mass density profiles evolve, revealing that the ratio of disk mass to halo spin parameter governs the development of a two-component profile.

Contribution

It demonstrates that the ratio of disk mass fraction to halo spin parameter controls the formation and characteristics of two-component density profiles in isolated galaxies.

Findings

Two-component profiles develop from a single exponential disk.

The ratio m_d/λ determines the break location and development speed.

Halo concentration influences the transition amplitude.

Abstract

We investigate the evolution of mass density profiles in secular disk galaxy models, paying special attention to the development of a two-component profile from a single initial exponential disk free of cosmological evolution (i.e., no accretion or interactions). As the source of density profile variations, we examine the parameter space of the spin parameter, halo concentration, virial mass, disk mass and bulge mass, for a total of 162 simulations in the context of a plausible model of star formation and feedback (GADGET-2). The evolution of the galaxy mass density profile, including the development of a two-component profile with an inner and outer segment, is controlled by the ratio of the disk mass fraction, $m_{d}$, to the halo spin parameter, $\lambda$. The location of the break between the two components and speed at which it develops is directly proportional to $m_{d}/\lambda$; the amplitude of the transition between the inner and outer regions is however controlled by the ratio of halo concentration to virial velocity. The location of the divide between the inner and outer profile does not change with time. (Abridged)