Аннотация
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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