Are we seeing accretion flows in a 250 kpc Lyα halo at z = 3?^⋆

¹ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
e-mail: jvernet@eso.org
² Sorbonne Universités, UPMC, Paris VI, CNRS UMR 7095, Institut d’Astrophysique de Paris, 98bis Bd Arago, 75014 Paris, France
³ Centro de Astrobiologìa (INTA-CSIC), Carretera de Ajalvir, km 4, 28850 Torrejòn de Ardoz, Madrid, Spain
⁴ Department of Physics and Astronomy, Johns Hopkins University, 3400 N. Charles St, Baltimore, MD 21218, USA
⁵ International Centre for Radio Astronomy Research, Curtin University, Perth WA 6845, Australia
⁶ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
⁷ Max-Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
⁸ Institut d’Astrophysique Spatiale, 91405 Orsay, Université Paris Sud et CNRS, France

Received: 24 March 2017
Accepted: 18 May 2017

Abstract

Using MUSE on the ESO-VLT, we obtained a four-hour exposure of the z = 3.12 radio galaxy MRC 0316-257. We detect features down to ~10^-19 erg s^-1 cm^-2 arcsec^-2, with the highest surface brightness regions reaching more than a factor of 100 higher. We find Lyα emission out to ~250 kpc in projection from the active galactic nucleus (AGN). The emission shows arc-like morphologies arising at 150−250 kpc from the nucleus in projection, with the connected filamentary structures reaching down into the circumnuclear region. The most distant arc is offset by ~700 km s^-1 relative to circumnuclear HeIIλ1640 emission, which we assume to be at the systemic velocity. As we probe emission closer to the nucleus, the filamentary emission narrows in projection on the sky, the relative velocity decreases to ~250 km s^-1, and the line full-width at half maximum ranges from ~300−700 km s^-1. From UV line ratios, the emission on scales of 10s of kpc from the nucleus along a wide angle in the direction of the radio jets is clearly excited by the radio jets and ionizing radiation of the AGN. Assuming ionization equilibrium, the more extended emission outside of the axis of the jet direction would require 100% or more illumination to explain the observed surface brightness. High-speed (≳300 km s^-1) shocks into rare gas would provide sufficiently high surface brightness. We discuss the possibility that the arcs of Lyα emission represent accretion shocks and the filamentary emission represents gas flows into the halo, and compare our results with gas accretion simulations.