On the two high-metallicity DLAs at z = 2.412 and 2.583 towards Q 0918+1636
Vestergaard, M.; Fynbo, J. P. U.; Krühler, T.; Maund, J. R.; Christensen, L.; Møller, P.; Ledoux, C.; Gallazzi, A.; Rivera-Thorsen, T.; Krogager, J. -K.; Noterdaeme, P.; Geier, S. J.
Denmark, Spain, Italy, Chile, United Kingdom, Germany, France, Sweden, United States
Abstract
The quasar Q0918+1636 (z = 3.07) has two intervening high-metallicity Damped Lyman α Absorbers (DLAs) along the line of sight, at redshifts of z = 2.412 and 2.583. The z = 2.583 DLA is located at a large impact parameter of 16.2 kpc, and despite this large impact parameter it has a very high metallicity (consistent with solar), a substantial fraction of H2 molecules and it is dusty as inferred from the reddened spectrum of the background QSO. The z = 2.412 DLA has a metallicity of [M/H] = -0.6 (based on Zn II and Si II). In this paper we present new observations of this interesting sightline consisting of deep multiband imaging and further VLT spectroscopy. By fitting stellar population synthesis models to the photometric Spectral Energy Distribution we constrain the physical properties of the z = 2.583 DLA galaxy, and we infer its morphology by fitting a Sérsic model to its surface brightness profile. We find it to be a relatively massive (M⋆ ≈ 1010 M⊙), strongly star-forming (SFR ≈ 30 M⊙ yr-1), dusty (E(B - V) = 0.4) galaxy with a disc-like morphology. We detect strong emission lines from the z = 2.583 DLA ([O II] λ3727, [O III] λλ4960, 5007, Hβ and Hα, albeit at low signal-to-noise ratio except for the [O III] λ5007 line). The metallicity derived from the emission lines is consistent with the absorption metallicity (12 + log (O/H) = 8.8 ± 0.2). We also detect [O III] λ5007 emission from the galaxy counterpart of the z = 2.412 DLA at a small impact parameter (<2 kpc). Overall our findings are consistent with the emerging picture that high-metallicity DLAs are associated with relatively luminous and massive galaxy counterparts, compared to typical DLAs.