Abstract
We present a detailed study of the emission from a z = 2:35 galaxy that
causes damped Lyman-alpha absorption in the spectrum of the background QSO,
SDSS J 2222-0946. We present the results of extensive analyses of the stellar
continuum covering the rest frame optical-UV regime based on broad-band HST
imaging, and of spectroscopy of the strong emission lines: Ly-alpha, OII,
OIII, NII, and the H-alpha and H-beta lines from VLT/X-Shooter. We compare
the metallicity from the absorption lines in the QSO spectrum with the oxygen
abundance inferred from the strong-line methods (R23 and N2). The two
emission-line methods yield consistent results: O/H = -0.30+/-0.13. Based on
the absorption lines in the QSO spectrum a metallicity of -0:52+/-0.05 is
inferred at an impact parameter of 6.3 kpc from the centre of the galaxy. The
star formation rates of the galaxy from the UV continuum and H-alpha line can
be reconciled assuming an amount of reddening of E(B-V) = 0.06+/-0.01, giving
an inferred SFR of 13+/-1 M_sun / yr (assuming a Chabrier IMF). From the HST
imaging, the galaxy associated with the absorption is found to be a compact
(re=1.12 kpc) object with a disclike, elongated (axis ratio 0.17) structure
indicating that the galaxy is seen close to edge on. Moreover, the absorbing
gas is located almost perpendicularly above the disc of the galaxy suggesting
that the gas causing the absorption is not co-rotating with the disc. We
investigate the stellar and dynamical masses from SED-fitting and emission-line
widths, respectively, and find consistent results of 2x10^9 M_sun. We suggest
that the galaxy is a young proto-disc with evidence for a galactic outflow of
enriched gas which cools down at a large distance. This galaxy hints at how
star-forming galaxies may be linked to the elusive population of damped
Lyman-alpha absorbers.
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