Kavli Affiliate: Luis C. Ho
| First 5 Authors: Dharmender, Ravi Joshi, Michele Fumagalli, Pasquier Noterdaeme, Hum Chand
| Summary:
We aim to constrain the average star formation associated with neutral
hydrogen gas reservoirs at cosmic noon. Using a unprecedented sample of 1716
high column density Damped Ly-$alpha$ absorbers (DLAs) from the Sloan Digital
Sky Survey with log($N$(HI) / cm$^{-2}$) $ge$21, we generated the average
Ly-$alpha$ emission spectrum associated to DLAs, free from emission from the
background quasar. We measured Ly$alpha$ emission at $> 5.8sigma$ level with
luminosity $8.95pm 1.54 times rm 10^{40} text{erg} text{s}^{-1}$
(corresponding to about 0.02 L$^{star}$ at $z sim$ 2-3) in systems with
average log($N$(HI)/ $cm^{-2}$) $approx$21.2 and at median redshift of $z
sim$ 2.64. The peak of the Ly$alpha$ emission is apparently redshifted by
$sim$300 km s$^{-1}$ relative to the absorption redshift, which is seemingly
due to suppression of blue Ly-$alpha$ photons by radiative transfer through
expanding gas. We infer that DLAs form stars with an average rate of (0.08
$pm$ 0.01)/$text{f}_text{esc} rm text{M}_{odot} text{yr}^{-1}$, i.e,
$approx (0.54pm 0.09)rm text{M}_{odot} text{yr}^{-1}$ for a typical
escape fraction, $text{f}_{text{esc}} =0.15$, of Lyman-$alpha$ emitting
galaxies. DLA galaxies follows the star formation main sequence of star-forming
galaxies at high redshift, suggesting that the DLA population is dominated by
the lower mass end of Lyman-$alpha$ emitting galaxies.
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