Constraining stellar properties of intervening damped Ly{\alpha} and MgII absorbing galaxies toward GRB 050730

TL;DR

This study used deep multi-band imaging after a gamma-ray burst to search for and constrain the properties of galaxies causing intervening absorption systems, finding they are likely dwarf galaxies with low star formation rates.

Contribution

It provides the first constraints on the stellar masses and star-formation rates of intervening absorber host galaxies using post-burst imaging, avoiding QSO glare.

Findings

Host galaxies are undetected, with upper limits on flux.

Star-formation rates are less than 2.5 and 1.0 solar masses per year for different systems.

Stellar masses are estimated to be a few times 10^9 solar masses or smaller.

Abstract

We performed multi-band deep imaging of the field around GRB 050730 to identify the host galaxies of intervening absorbers, which consist of a damped Ly{\alpha} absorption (DLA) system at zabs=3.564, a sub-DLA system at zabs=3.022, and strong MgII absorption systems at zabs=1.773 and 2.253. Our observations were performed after the gamma-ray burst afterglow had disappeared. Thus, our imaging survey has a higher sensitivity to the host galaxies of the intervening absorbers than the normal imaging surveys in the direction of QSOs, for which the QSO glare tends to hide the foreground galaxies. In this deep imaging survey, we could not detect any unambiguous candidates for the host galaxies of the intervening absorbers. Using the 3sigma upper limit of the flux in the optical to mid-infrared observing bands, which corresponds to the UV to optical bands in the rest-frame of the intervening absorbers, we constrained the star-formation rates and stellar masses of the hosts. We estimated the star-formation rates for the intervening absorbers as < 2.5 Msun/yr for z>3 DLAs and < 1.0 Msun/yr for z~2 MgII systems. Their stellar masses are estimated to be several times 10^9 Msun or smaller for all intervening galaxies. These properties are comparable to dwarf galaxies, rather than the massive star-forming galaxies commonly seen in the z>2 galaxy surveys based on emission-line selection or color selection.