Anatomy of the AGN in NGC 5548

II. The spatial, temporal, and physical nature of the outflow from HST/COS Observations^⋆

¹ Department of Physics, Virginia Tech, Blacksburg, VA 24061, USA
e-mail: arav@vt.edu
² Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
³ Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD 21218, USA
⁴ SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
⁵ Leiden Observatory, Leiden University, Post Office Box 9513, 2300 RA Leiden, The Netherlands
⁶ INAF−IASF Bologna, via Gobetti 101, 40129 Bologna, Italy
⁷ Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey, RH5 6NT, UK
⁸ Univ. Grenoble Alpes, IPAG, 38000 Grenoble, France
⁹ CNRS, IPAG, 38000 Grenoble, France
¹⁰ Instituto de Astronomía, Universidad Católica del Norte, Avenida Angamos 0610, Casilla 1280, Antofagasta, Chile
¹¹ Department of Physics, University of Oxford, Keble Road, Oxford, OX1 3RH, UK
¹² Department of Physics, Technion-Israel Institute of Technology, 32000 Haifa, Israel
¹³ Dipartimento di Matematica e Fisica, Università degli Studi Roma Tre, via della Vasca Navale 84, 00146 Roma, Italy
¹⁴ Department of Astronomy, University of Geneva, 16 Ch. d’Ecogia, 1290 Versoix, Switzerland
¹⁵ Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125, USA
¹⁶ Université de Toulouse, UPS-OMP, IRAP, 31028 Toulouse, France
¹⁷ CNRS, IRAP, 9 Av. colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
¹⁸ Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse, 85748 Garching, Germany
¹⁹ Department of Astronomy, The Ohio State University, 140W 18th Avenue, Columbus, OH 43210, USA
²⁰ Center for Cosmology & AstroParticle Physics, The Ohio State University, 191 West Woodruff Avenue, Columbus, OH 43210, USA
²¹ Institute of Astronomy, University of Cambridge, Madingley Rd, Cambridge, CB3 0HA, UK
²² Astronomisches Institut, Ruhr-Universität Bochum, Universitätsstraße 150, 44801 Bochum, Germany
²³ INAF/IAPS− via Fosso del Cavaliere 100, 00133 Roma, Italy
²⁴ Research Center for Measurement in Advanced Science, Faculty of Science, Rikkyo University 3-34-1 Nishi-Ikebukuro, Toshima-ku, Tokyo, Japan

Received: 7 November 2014
Accepted: 2 March 2015

Abstract

Context. AGN outflows are thought to influence the evolution of their host galaxies and of super massive black holes. Our deep multiwavelength campaign on NGC 5548 has revealed a new, unusually strong X-ray obscuration, accompanied by broad UV absorption troughs observed for the first time in this object. The X-ray obscuration caused a dramatic decrease in the incident ionizing flux on the outflow that produces the long-studied narrow UV absorption lines in this AGN. The resulting data allowed us to construct a comprehensive physical, spatial, and temporal picture for this enduring AGN wind.

Aims. We aim to determine the distance of the narrow UV outflow components from the central source, their total column-density, and the mechanism responsible for their observed absorption variability.

Methods. We study the UV spectra acquired during the campaign, as well as from four previous epochs (1998−2011). Our main analysis tools are ionic column-density extraction techniques, photoionization models based on the code CLOUDY, and collisional excitation simulations.

Results. A simple model based on a fixed total column-density absorber, reacting to changes in ionizing illumination, matches the very different ionization states seen in five spectroscopic epochs spanning 16 years. The main component of the enduring outflow is situated at 3.5 ± 1.1 pc from the central source, and its distance and number density are similar to those of the narrow-emitting-line region in this object. Three other components are situated between 5−70 pc and two are farther than 100 pc. The wealth of observational constraints and the anti-correlation between the observed X-ray and UV flux in the 2002 and 2013 epochs make our physical model a leading contender for interpreting trough variability data of quasar outflows.

Conclusions. This campaign, in combination with prior UV and X-ray data, yields the first simple model that can explain the physical characteristics and the substantial variability observed in an AGN outflow.