Volume 625, May 2019
|Number of page(s)||5|
|Section||Letters to the Editor|
|Published online||17 May 2019|
Letter to the Editor
Gaia-assisted selection of a quasar reddened by dust in an extremely strong damped Lyman-α absorber at z = 2.226
Instituto de Astrofísica de Canarias, Vía Láctea, s/n, 38205 La Laguna, Tenerife, Spain
2 Gran Telescopio Canarias (GRANTECAN), 38205 San Cristóbal de La Laguna, Tenerife, Spain
3 Centre for Astrophysics and Cosmology, Science Institute, University of Iceland, Dunhagi 5, 107 Reykjavík, Iceland
4 Cosmic Dawn Center (DAWN), Copenhagen, Denmark
5 Niels Bohr Institute, University of Copenhagen, Lyngbyvej 2, 2100 Copenhagen Ø, Denmark
6 European Southern Observatory, Alonso de Córdova 3107, Vitacura, Casilla 19001, Santiago, Chile
7 DARK, Niels Bohr Institute, University of Copenhagen, Lyngbyvej 2, 2100 Copenhagen Ø, Denmark
8 Institut d’Astrophysique de Paris, CNRS-UPMC, UMR7095, 98bis Boulevard Arago, 75014 Paris, France
9 European Southern Observatory, Karl-Schwarzschildstraße 2, 85748 Garching, Germany
Accepted: 4 April 2019
Damped Lyman-α absorbers (DLAs) as a class of quasi-stellar object (QSO) absorption-line systems are currently our most important source of detailed information on the cosmic chemical evolution of galaxies. However, the degree to which this information is biased by dust remains to be understood. One strategy is to specifically search for QSOs that are reddened by metal-rich and dusty foreground absorbers. In this Letter, we present the discovery of a z = 2.60 QSO that is strongly reddened by dust in an intervening extremely strong DLA at z = 2.226. This QSO was identified through a novel selection that combined the astrometric measurements from ESA’s Gaia satellite with extisting optical and near- to mid-infrared photometry. We infer a total neutral atomic-hydrogen column density of log N(H I) = 21.95 ± 0.15 and a lower limit on the gas-phase metallicity of [Zn/H] > −0.96. This DLA is also remarkable in that it exhibits shielded neutral gas that is visible in C I, and it shows tentative detections of CO molecular bands. The spectral energy distribution of the QSO is well accounted for by a spectral energy distribution that is normal for a QSO and is reddened by dust from a DLA with 10% solar metallicity, a dust extinction of AV = 0.82 ± 0.02 mag, and an extinction curve that resembles that of the Large Magellanic Cloud, including the characteristic 2175 Å extinction feature. Such QSO absorption-line systems have been shown to be very rare in previous surveys, which have mostly revealed sight-lines with low extinction. The present case therefore suggests that previous samples have under-represented the fraction of dusty absorbers. Building a complete sample of such systems is required to assess the significance of this effect.
Key words: quasars: general / quasars: absorption lines / quasars: individual: GQ1218+0832 / dust, extinction
© ESO 2019
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