How does the surface density and size of disc galaxies measured in hydrodynamic simulations correlate with the halo spin parameter?

Abstract

Late-type low surface brightness galaxies (LSBs) are faint disc galaxies with central maximum stellar surface densities below 100 M⊙ pc−2. The currently favoured scenario for their origin is that LSBs have formed in fast-rotating haloes with large angular momenta. We present the first numerical evidence for this scenario using a suite of self-consistent hydrodynamic simulations of a 2.3 × 1011 M⊙ galactic halo, in which we investigate the correlations between the disc stellar/gas surface densities and the spin parameter of its host halo. A clear anticorrelation between the surface densities and the halo spin parameter λ is found. That is, as the halo spin parameter increases, the disc cutoff radius at which the stellar surface density drops below 0.1 M⊙ pc−2 monotonically increases, while the average stellar surface density of the disc within that radius decreases. The ratio of the average stellar surface density for the case of λ = 0.03 to that for the case of λ = 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.