The Molecular Mass function of the Local Universe

TL;DR

This paper constructs the first comprehensive molecular mass function for the local universe using Herschel Reference Survey data, providing a baseline for understanding molecular gas evolution over cosmic time.

Contribution

It introduces a novel molecular mass function derived from a volume-limited, complete sample, using a copula method to relate K-band luminosity and molecular gas mass.

Findings

The molecular mass function spans from 4x10^6 to 10^10 solar masses.

It agrees with theoretical models at lower masses but may miss high-mass molecular-rich galaxies.

The local molecular gas density is approximately 1.5x10^7 solar masses per cubic Mpc.

Abstract

We construct the molecular mass function using the bivariate Kband-Mass Function of the Herschel Reference Survey, a volume-limited sample already widely studied at the entire electromagnetic spectrum. The molecular mass function is derived from the K-band and the gas mass cumulative distribution using a copula method described in detail in our previous papers. The H2 mass is relatively strong correlated with the K-band luminosity because of the tight relation between the stellar mass and the molecular gas mass within the sample with a scatter likely due to those galaxies which have lost their molecular content because of environmental effects or because of a larger gas consumption due to past star formation processes. The derived H2 Mass Function samples the molecular mass range from 4 10^6 to 10^10 solar masses, and when compared with theoretical models, it agrees well with the theoretical predictions at the lower end of the mass values, while at masses larger than 10^10 solar masses the HRS sample may miss galaxies with large content of molecular hydrogen and the outcomes are not conclusive. The value of the local density of the molecular gas mass inferred from our analysis is ~1.5x10^7 Mo Mpc^-3, and it is compared with the results at larger redshifts, confirming the lack of strong evolution of the molecular mass density between z=0 and z=4. This is the first Molecular Mass Function derived on a complete sample in the local Universe, which can be used as a reliable calibration at redshift $z$=0 for models aiming at predicting the evolution of the molecular mass density