Down-the-barrel observations of a multi-phase quasar outflow at high redshift

VLT/X-shooter spectroscopy of the proximate molecular absorber at z = 2.631 towards SDSS J001514+184212^⋆

¹ Institut d’Astrophysique de Paris, CNRS-SU, UMR 7095, 98bis bd Arago, 75014 Paris, France
e-mail: noterdaeme@iap.fr
² Ioffe Institute, Polyteknicheskaya 26, 194021 Saint-Petersburg, Russia
³ Institute of Theoretical Astrophysics, University of Oslo, PO Box 1029 Blindern, 0315 Oslo, Norway
⁴ Cosmic Dawn Center (DAWN), University of Copenhagen, Jagtvej 128, 2200 Copenhagen N, Denmark
⁵ Inter-University Centre for Astronomy and Astrophysics, Pune University Campus, Ganeshkhind, Pune 411007, India
⁶ Niels Bohr Institute, University of Copenhagen, Jagtvej 128, 2200 Copenhagen N, Denmark

Received: 8 July 2020
Accepted: 3 December 2020

Abstract

We present ultraviolet to near infrared spectroscopic observations of the quasar SDSS J001514+184212 and its proximate molecular absorber at z = 2.631. The [O III] emission line of the quasar is composed of a broad (FWHM ∼ 1600 km s⁻¹), spatially unresolved component, blueshifted by about 600 km s⁻¹ from a narrow, spatially-resolved component (FWHM ∼ 650 km s⁻¹). The wide, blueshifted, unresolved component is consistent with the presence of outflowing gas in the nuclear region. The narrow component can be further decomposed into a blue and a red blob with a velocity width of several hundred km s⁻¹ each, seen ∼5 pkpc on opposite spatial locations from the nuclear continuum emission, indicating outflows on galactic scales. The presence of ionised gas on kpc scales is also seen from a weak C IV emission component, detected in the trough of a saturated C IV absorption that removes the strong nuclear emission from the quasar. Towards the nuclear emission, we observe absorption lines from atomic species in various ionisation and excitation stages and confirm the presence of strong H₂ lines originally detected in the SDSS spectrum. The overall absorption profile is very wide, spread over ∼600 km s⁻¹, and it roughly matches the velocities of the narrow blue [O III] blob. From a detailed investigation of the chemical and physical conditions in the absorbing gas, we infer densities of about n_H ∼ 10⁴ − 10⁵ cm⁻³ in the cold (T ∼ 100 K) H₂-bearing gas, which we find to be located at ∼10 kpc distances from the central UV source. We conjecture that we are witnessing different manifestations of a same AGN-driven multi-phase outflow, where approaching gas is intercepted by the line of sight to the nucleus. We corroborate this picture by modelling the scattering of Ly-α photons from the central source through the outflowing gas, reproducing the peculiar Ly-α absorption-emission profile, with a damped Ly-α absorption in which red-peaked, spatially offset, and extended Ly-α emission is seen. Our observations open up a new way to investigate quasar outflows at high redshift and shed light on the complex issue of AGN feedback.