Multi-wavelength campaign on NGC 7469

I. The rich 640 ks RGS spectrum

¹ Department of Physics, Technion, 32000 Haifa, Israel
e-mail: behar@physics.technion.ac.il
² Department of Astronomy, University of Maryland, College Park, MD 20742-2421, USA
³ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
⁴ SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
⁵ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
⁶ Department of Physics, Virginia Tech, Blacksburg, VA 24061, USA
⁷ Dipartimento di Matematica e Fisica, Università degli Studi Roma Tre, via della Vasca Navale 84, 00146 Roma, Italy
⁸ Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey, RH5 6NT, UK
⁹ INAF-IASF Bologna, via Gobetti 101, 40129 Bologna, Italy
¹⁰ Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse, 85748 Garching, Germany
¹¹ Department of Astronomy, University of Geneva, 16 chemin d’Ecogia, 1290 Versoix, Switzerland
¹² European Space Astronomy Centre, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
¹³ School of Physics and Astronomy, Tel Aviv University, 69978 Tel Aviv, Israel
¹⁴ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France

Received: 22 October 2016
Accepted: 22 December 2016

Abstract

Aims. Outflows in active galaxies (AGNs) are common, although their launching mechanism, location, and physical impact on the host galaxy remain controversial. We conducted a multi-wavelength six-month campaign to observe the nearby Seyfert galaxy NGC 7469 with several observatories in order to better understand and quantify the outflow in this AGN.

Methods. We report on the time-integrated line-resolved X-ray spectrum of NGC 7469 obtained with the Reflection Grating Spectrometer (RGS) on board XMM-Newton. We used the RGS spectrum to discern the many AGN outflow components and applied a global fit to obtain their physical parameters.

Results. We find that the AGN wind can be well described by three narrow velocity components at ~–650, –950, and –2050 km s^-1. The RGS clearly resolves the –2050 km s^-1 component in C⁵⁺ Ly α, while the –650 km s^-1 and –950 km s^-1 velocities are blended. Similar velocities (±200 km s^-1) are resolved in the UV. The H-equivalent column densities of these components are, respectively, N_H ~ 7 × 10²⁰, 2.2 × 10²¹, and 10²⁰ cm^-2, for a total of ~3 × 10²¹ cm^-2, which was also measured in 2004, indicating the absorber did not significantly change. The –650 km s^-1 component shows a broad ionization distribution (−1 ≲ log ξ ≲ 2,ξ being the ionization parameter in erg s^-1 cm). We identify a photo-ionized emission component blue-shifted by ~–450 km s^-1, somewhat broad (FWHM = 1400 km s^-1), and with −1 ≲ log ξ ≲ 1 erg s^-1 cm, which we ascribe to the same outflow that produces the absorption lines. We also find a collisionally ionized component at kT = 0.35 keV that we associate with the circum-nuclear star-formation activity of NGC 7469, as it follows the L_FIR/L_X ≈ 10⁴ relation found in star forming galaxies. The elemental abundance ratios of C, N, Ne, S, and Fe to O in the outflow tend to be between one and two times solar. Preliminary estimates of the absorber distance from the AGN center suggest it is at least a few pc away from the center, but more advanced methods need to be applied in order to obtain better constraints.

Conclusions. The complex X-ray spectrum of NGC 7469 demonstrates the richness of high energy phenomena taking place in AGN cores. The subtle spectroscopic differences between the various components require deep, high-resolution observations, such as the present RGS spectrum, if one is to resolve them and perform quantitative plasma diagnostics.