Constraining stellar properties of intervening damped Lyα and Mg: II absorbing galaxies toward GRB 050730

Abstract

We performed multiband deep imaging of the field around GRB050730 to identify the host galaxies of intervening absorbers, which consist of a damped Lyα absorption (DLA) system at z abs = 3.564, a sub-DLA system at z abs = 3.022, and strong Mg II absorption systems at z abs = 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 3σ 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 to be ≲ 2.5 M ⊙ yr -1 for z > 3 DLAs and ≲ 1.0 M ⊙ yr -1 for z ∼ 2 Mg II systems. Their stellar masses are estimated to be several times 10 9 M ⊙ 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. © © 2012. The American Astronomical Society. All rights reserved.