The Dark Matter Halos of HI Selected Galaxies

TL;DR

This paper analyzes the distribution of neutral hydrogen in galaxies, deriving relations between HI mass, velocity, and halo mass, revealing how baryonic processes influence gas content across different galaxy types and masses.

Contribution

It introduces new HI mass and velocity width functions from ALFALFA data and establishes scaling relations between HI properties and halo mass, highlighting differences between red and blue galaxy populations.

Findings

The HI mass function is dominated by blue galaxies at low masses and red galaxies at high masses.

The $M_{HI} - M_{h}$ relation shows a steep slope at low masses and flattens at higher masses.

The transition halo mass for HI content is smaller than that for stellar mass, indicating different baryonic process efficiencies.

Abstract

We present the neutral hydrogen mass ($M_{\text{HI}}$) function (HIMF) and velocity width ($w_{50}$) function (HIWF) based on a sample of 7857 galaxies from the 40% data release of the ALFALFA survey ($\alpha.40$). The low mass (velocity width) end of the HIMF (HIWF) is dominated by the blue population of galaxies whereas the red population dominates the HIMF (HIWF) at the high mass (velocity width) end. We use a deconvolution method to estimate the HI rotational velocity ($V_{\text{rot}}$) functions (HIVF) from the HIWF for the total, red, and blue samples. The HIWF and HIVF for the red and blue samples are well separated at the knee of the function compared to their HIMFs. We then use recent stacking results from the ALFALFA survey to constrain the halo mass ($M_{\text{h}}$) function of HI-selected galaxies. This allows us to obtain various scaling relations between $M_{\text{HI}} - w_{50} - V_{\text{rot}} - M_{\text{h}}$, which we present. The $M_{\text{HI}} - M_{\text{h}}$ relation has a steep slope ~2.10 at small masses and flattens to ~0.34 at masses larger than a transition halo mass, $\log_{10}(M_{\text{ht}} h^2_{70}/M_{\odot})=10.62$. Our scaling relation is robust and consistent with a volume-limited sample of $\alpha.40$. The $M_{\text{HI}} - M_{\text{h}}$ relation is qualitatively similar to the $M_{\text{star}} - M_{\text{h}}$ relation but the transition halo mass is smaller by ~1.4 dex compared to that of the $M_{\text{star}} - M_{\text{h}}$ relation. Our results suggest that baryonic processes like heating and feedback in larger mass halos suppress HI gas on a shorter time scale compared to star-formation.