The HI Mass Function of the Local Universe: Combining Measurements from HIPASS, ALFALFA and FASHI

TL;DR

This paper combines data from three large HI surveys to accurately measure the local universe's HI mass function, revealing a double Schechter function fit and precise cosmic HI abundance estimates.

Contribution

It provides the first HIMF measurement from the FASHI survey and combines multiple surveys for a comprehensive, unbiased local universe HIMF analysis.

Findings

Best-fit Schechter function with alpha = -1.30 and M* = 10^9.86 solar masses

Double Schechter function better describes the HIMF with two knee masses

Cosmic HI abundance omega_HI = 0.000454

Abstract

We present the first HI mass function (HIMF) measurement for the recent FAST All Sky HI (FASHI) survey and the most complete measurements of HIMF in the local universe thus far. We obtained these results by combining the HI catalogues from HI Parkes All Sky Survey (HIPASS), Arecibo Legacy Fast ALFA (ALFALFA) and FASHI surveys at redshift 0 < z < 0.05, covering 76% of the entire sky. We adopted the same methods to estimate the distances, calculate the sample completeness, and determine the HIMF for all three surveys. The best-fit Schechter function for the total HIMF shows a low-mass slope parameter of alpha = -1.30 and a knee mass log(Ms) = 9.86, along with a normalisation of phi_s = 0.00658. This gives us the cosmic HI abundance: omega_HI= 0.000454. We find that a double Schechter function with the same slope alpha better describes our HIMF, where the two different knee masses are log(Ms1) = 9.96 and log(Ms2) = 9.65. We verify that the measured HIMF is marginally affected by the choice of distance estimates. The effect of cosmic variance is significantly suppressed by combining the three surveys and this provides a unique opportunity to obtain an unbiased estimate of the HIMF in the Local Universe.