Abstract
We report the discovery of massive $łog(M/M_ødot)=10.74^+0.18_-0.16$
galaxy at the same redshift as a carbon-monoxide bearing sub-damped Lyman
$\alpha$ absorber (sub-DLA) seen in the spectrum of the QSO J1439+1117. The
galaxy, J1439B, is located 4.7" from the QSO sightline, a projected distance of
38 physical kpc at $z=2.4189$, and exhibits broad optical emission lines
($\sigma_O III=303 12$ km s$^-1$) with ratios characteristic of
excitation by an active galactic nucleus (AGN). The galaxy has a factor of
$\sim$10 lower star formation than is typical of star-forming galaxies of the
same mass and redshift. The nearby DLA is highly enriched, suggesting its
galactic counterpart must be massive if it follows the $z\sim2$
mass-metallicity relationship. Metallic absorption associated with the DLA is
spread over a velocity range $\Delta v > 1000$ km s$^-1$, suggesting an
energetic origin. We explore the possibility that a different galaxy could be
responsible for the rare absorber, and conclude it is unlikely based on
imaging, integral field spectroscopy, and high-$z$ massive galaxy pair
statistics. We argue that the gas seen in absorption against the QSO was likely
ejected from the galaxy J1439B and therefore provides a unique observational
probe of AGN feedback in the distant universe.
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