Star-Formation in Neutral Hydrogen Gas Reservoirs at Cosmic Noon

TL;DR

This study measures star formation in neutral hydrogen reservoirs at cosmic noon by analyzing Ly-alpha emission from a large sample of DLAs, revealing their star formation rates and relation to high-redshift galaxy populations.

Contribution

It provides the first average Ly-alpha emission spectrum for high column density DLAs and estimates their star formation rates at z~2-3, linking them to the star-forming galaxy main sequence.

Findings

Detected Ly-alpha emission at >5.8 sigma level with luminosity ~9 x 10^{40} erg/s.

Inferred average star formation rate of ~0.54 M_sun/yr for DLAs, assuming 15% escape fraction.

DLA galaxies align with the star formation main sequence at high redshift.

Abstract

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 $> 5.8\sigma$ level with luminosity $8.95\pm 1.54 \times \rm 10^{40}\ \text{erg}\ \text{s}^{-1}$ (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, $\approx (0.54\pm 0.09)\rm \text{M}_{\odot}\ \text{yr}^{-1}$ 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.