The halo mass function of late-type galaxies from HI kinematics

TL;DR

This paper introduces an empirical method to derive the galaxy halo mass function using HI kinematics, confirming consistency with $ ext{Lambda}$CDM predictions for certain mass ranges and providing insights into gas-poor massive halos.

Contribution

The study presents a novel empirical approach linking HI line-widths to halo masses, enabling the derivation of the galaxy halo mass function from large HI surveys.

Findings

The empirical HMF fits a Schechter function and aligns with $ ext{Lambda}$CDM predictions between $10^{10.5}$ and $10^{12} ext{M}_\odot$.

More massive halos are gas-poor, maintaining the $ ext{Lambda}$CDM power law.

No discrepancy found at low halo masses; the lowest probed mass is near the Local Group missing satellite scale.

Abstract

We present an empirical method to measure the halo mass function (HMF) of galaxies. We determine the relation between the \hi\ line-width from single-dish observations and the dark matter halo mass ($M_{200}$) inferred from rotation curve fits in the SPARC database, then we apply this relation to galaxies from the \hi\ Parkes All Sky Survey (HIPASS) to derive the HMF. This empirical HMF is well fit by a Schecther function, and matches that expected in $\Lambda$CDM over the range $10^{10.5} < M_{200} < 10^{12}\;\mathrm{M}_{\odot}$. More massive halos must be poor in neutral gas to maintain consistency with the power law predicted by $\Lambda$CDM. We detect no discrepancy at low masses. The lowest halo mass probed by HIPASS, however, is just greater than the mass scale where the Local Group missing satellite problem sets in. The integrated mass density associated with the dark matter halos of \hi-detected galaxies sums to $\Omega_{\rm m,gal} \approx 0.03$ over the probed mass range.