The MURALES survey

I. A dual AGN in the radio galaxy 3C 459?^⋆

¹ INAF – Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate, Italy
e-mail: balmaverde@oato.inaf.it
² INAF – Osservatorio Astrofisico di Torino, Via Osservatorio 20, 10025 Pino Torinese, Italy
³ Dipartimento di Fisica e Astronomia, Università di Firenze, via G. Sansone 1, 50019 Sesto Fiorentino (Firenze), Italy
⁴ INAF – Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, 50125 Firenze, Italy
⁵ Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD, 21210 USA
⁶ Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD, 21218 USA
⁷ Department of Physics and Astronomy, University of Southampton, Highfield, SO17 1BJ UK
⁸ INAF – Osservatorio Astronomico di Bologna, Via Gobetti 93/3, 40129 Bologna, Italy
⁹ INAF – IASFBO, Via Gobetti 101, 40129 Bologna, Italy
¹⁰ Department of Physics and Astronomy, University of Manitoba, Winnipeg, MB R3T 2N2 Canada
¹¹ Leiden Observatory, Leiden University, PO Box 9513 2300 RA Leiden, The Netherlands
¹² Department of Physics and Yale Center for Astronomy & Astrophysics, Yale University, 217 Prospect Street, New Haven, CT, 06511 USA
¹³ University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, MD, 21250 USA
¹⁴ School of Physics & Astronomy, Rochester Institute of Technology, Rochester, 14623 NY, USA
¹⁵ Carlson Center for Imaging Science, Rochester Institute of Technology, Rochester, 14623 NY, USA

Received: 28 May 2018
Accepted: 2 August 2018

Abstract

We observed the FR II radio galaxy 3C 459 (z = 0.22) with the MUSE spectrograph at the Very Large Telescope (VLT) as part of the MURALES project (a MUse RAdio Loud Emission line Snapshot survey). We detected diffuse nuclear emission and a filamentary ionized gas structure forming a one-sided, triangular-shaped region extending out to ∼80 kpc. The central emission line region is dominated by two compact knots of similar flux: the first (N1) cospatial with the radio core and the (N2) second located 1″.2 (5.3 kpc) to the SE. The two regions differ dramatically from the point of view of velocity (with an offset of ∼400 km s⁻¹), line widths, and line ratios. This suggests that we are observing a dual AGN system formed by a radio loud AGN and type 2 QSO companion, which is the result of the recent merger that also produced its disturbed host morphology. The alternative possibility that N2 is just a bright emission line knot resulting from, for example, a jet-cloud interaction, is disfavored because of (1) the presence of a high ionization bicone whose apex is located at N2; (2) the observed narrow line widths; (3) its line luminosity (∼10⁴² erg s⁻¹) typical of luminous QSOs; and (4) its location, which is offset from the jet path. The putative secondary AGN must be highly obscured, since we do not detect any emission in the Chandra and infrared Hubble Space Telescope images.