2017MNRAS.465..701J

We study the average Lyα emission associated with high-z strong (log N(H I) >= 21) damped Lyα systems (DLAs). We report Lyα luminosities (L_Lyα) for the full as well as various sub-samples based on N(H I), z, (r - i) colours of QSOs and rest equivalent width of Si IIλ1526 line (i.e. W₁₅₂₆). For the full sample, we find L_Lyα < 10⁴¹(3σ) erg s^- 1^ with a 2.8σ level detection of Lyα emission in the red part of the DLA trough. The L_Lyα is found to be higher for systems with higher W₁₅₂₆ with its peak, detected at >=3σ, redshifted by about 300-400 km s^–1 with respect to the systemic absorption redshift, as seen in Lyman break galaxies (LBGs) and Lyα emitters. A clear signature of a double-hump Lyα profile is seen when we consider W₁₅₂₆ >=0.4 Å and (r - i) < 0.05. Based on the known correlation between metallicity and W₁₅₂₆, we interpret our results in terms of star formation rate (SFR) being higher in high-metallicity (mass) galaxies with high velocity fields that facilitates easy Lyα escape. The measured Lyα surface brightness requires local ionizing radiation that is 4-10 times stronger than the metagalactic UV background at these redshifts. The relationship between the SFR and surface mass density of atomic gas seen in DLAs is similar to that of local dwarf and metal-poor galaxies. We show that the low-luminosity galaxies will contribute appreciably to the stacked spectrum if the size-luminosity relation seen for H I at low z is also present at high-z. Alternatively, large Lyα haloes seen around LBGs could also explain our measurements.