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

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(2016)cite arxiv:1601.07909Comment: 5 pages, 3 figures, accepted for publication in Astrophysical Journal Letters.

Abstract

We report a Giant Metrewave Radio Telescope (GMRT) search for HI 21cm emission from a large sample of star-forming galaxies at $z 1.18 - 1.34$, 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$_HI < 2.5 \mu$Jy on the average HI 21cm flux density of the 857 galaxies, at a velocity resolution of $315$ km s$^-1$. This yields the $3\sigma$ constraint M$_HI < 2.1 \times 10^10 łeft\Delta V/315 km/s \right^1/2 M_ødot$ 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 $\rm M_GAS/M_* < 0.5$, 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 star-forming galaxies at $z 1.3$ is $Ømega_GAS < 3.7 10^-4$, significantly lower than $Ømega_GAS$ estimates in both galaxies in the local Universe and damped Lyman-$\alpha$ absorbers at $z 2.2$. Blue star-forming galaxies thus do not appear to dominate the neutral atomic gas content of the Universe at $z 1.3$.

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