How Does the Surface Density and Size of Disk Galaxies Measured in Hydrodynamic Simulations Correlate with the Halo Spin Parameter?

TL;DR

This study uses hydrodynamic simulations to show that the surface density and size of disk galaxies are strongly anti-correlated with the halo spin parameter, supporting the idea that high-spin halos produce low surface brightness galaxies.

Contribution

First numerical evidence linking halo spin parameter to disk galaxy surface density and size, confirming the role of angular momentum in LSB galaxy formation.

Findings

Higher halo spin leads to larger disk cutoff radii.

Average stellar surface density decreases with increasing halo spin.

Result is robust against variations in baryon fraction.

Abstract

Late-type low surface brightness galaxies (LSBs) are faint disk galaxies with central maximum stellar surface densities below 100 Msun/pc^2. The currently favored scenario for their origin is that LSBs have formed in fast-rotating halos with large angular momenta. We present the first numerical evidence for this scenario using a suite of self-consistent hydrodynamic simulations of a 2.3e11 Msun galactic halo, in which we investigate the correlations between the disk stellar/gas surface densities and the spin parameter of its host halo. A clear anti-correlation between the surface densities and the halo spin parameter, lambda, is found. That is, as the halo spin parameter increases, the disk cutoff radius at which the stellar surface density drops below 0.1 Msun/pc^2 monotonically increases, while the average stellar surface density of the disk within that radius decreases. The ratio of the average stellar surface density for the case of lambda=0.03 to that for the case of lambda=0.14 reaches more than 15. We demonstrate that the result is robust against variations in the baryon fraction, confirming that the angular momentum of the host halo is an important driver for the formation of LSBs.