The distribution of dark galaxies and spin bias

TL;DR

This paper revisits predictions of dark galaxy distributions based on spin bias, updating models with Planck18 parameters and comparing them with recent observations of dark galaxies, highlighting a correlation between halo spin and galaxy luminosity.

Contribution

The study updates the Toomre stability-based predictions for dark galaxy distributions using Planck18 cosmological parameters and compares them with recent observational data, emphasizing the role of spin bias.

Findings

Dark galaxy spin parameters are near the stability threshold.

Higher predicted number densities occur where spins are more reliably measured.

Evidence supports a bias in galaxy formation related to halo spin.

Abstract

In the light of the discovery of numerous (almost) dark galaxies from the ALFALAFA and LITTLE THINGS surveys, we revisit the predictions of Jimenez et al. 1997, based on the Toomre stability of rapidly-spinning gas disks. We have updated the predictions for $\Lambda$CDM with parameters given by Planck18, computing the expected number densities of dark objects, and their spin parameter and mass distributions. Comparing with the data is more challenging, but where the spins are more reliably determined, the spins are close to the threshold for disks to be stable according to the Toomre criterion, where the expected number density is highest, and reinforces the concept that there is a bias in the formation of luminous galaxies based on the spin of their parent halo.