The gas mass of star-forming galaxies at $z \approx 1.3$

TL;DR

This study uses GMRT observations to place the first direct constraints on the atomic gas mass of star-forming galaxies at redshift around 1.3, revealing a lower cosmic gas density than at lower redshifts.

Contribution

It provides the first direct upper limits on the atomic gas mass of galaxies at z > 1 using HI 21cm stacking, improving understanding of gas content evolution.

Findings

Upper limit on average HI mass: < 2.1 x 10^{10} M_sun.

Atomic gas mass fraction relative to stars: < 0.5.

Cosmological neutral atomic gas density: < 3.7 x 10^{-4}.

Abstract

We report a Giant Metrewave Radio Telescope (GMRT) search for HI 21cm emission from a large sample of star-forming galaxies at $z \approx 1.18 - 1.34$, lying in sub-fields of the DEEP2 Redshift Survey. The search was carried out by co-adding ("stacking") the HI 21cm emission spectra of 857 galaxies, after shifting each galaxy's HI 21cm spectrum to its rest frame. We obtain the $3\sigma$ upper limit S$_{\rm{HI}} < 2.5 \mu$Jy on the average HI 21cm flux density of the 857 galaxies, at a velocity resolution of $\approx 315$ km s$^{-1}$. This yields the $3\sigma$ constraint M$_{\rm{HI}} < 2.1 \times 10^{10} \times \left[\Delta {\rm V}/315 \rm{km/s} \right]^{1/2} \textrm{M}_\odot$ on the average HI mass of the 857 stacked galaxies, the first direct constraint on the atomic gas mass of galaxies at $z > 1$. The implied limit on the average atomic gas mass fraction (relative to stars) is ${\rm M}_{\rm GAS}/{\rm M}_* < 0.5$, comparable to the cold molecular gas mass fraction in similar star-forming galaxies at these redshifts. We find that the cosmological mass density of neutral atomic gas in massive star-forming galaxies at $z \approx 1.3$ is $\Omega_{\rm GAS} < 3.7 \times 10^{-4}$, significantly lower than $\Omega_{\rm GAS}$ estimates in both galaxies in the local Universe and damped Lyman-$\alpha$ absorbers at $z \geq 2.2$. Massive blue star-forming galaxies thus do not appear to dominate the neutral atomic gas content of the Universe at $z \approx 1.3$.