Reeves, J and Porquet, D and Braito, V and Nardini, E and Lobban, A and Turner, J (2016) A deep X-ray view of the bare AGN Ark 120. I. Revealing the Soft X-ray Line Emission. Astrophysical Journal, 828 (2). ISSN 0004-637X

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Abstract

The Seyfert 1 galaxy, Ark 120, is a prototype example of the so-called class of bare nucleus AGN, whereby there is no known evidence for the presence of ionized gas along the direct line of sight. Here deep ($>400$ ks exposure), high resolution X-ray spectroscopy of Ark 120 is presented, from XMM-Newton observations which were carried out in March 2014, together with simultaneous Chandra/HETG exposures. The high resolution spectra confirmed the lack of intrinsic absorbing gas associated with Ark 120, with the only X-ray absorption present originating from the ISM of our own Galaxy, with a possible slight enhancement of the Oxygen abundance required with respect to the expected ISM values in the Solar neighbourhood. However, the presence of several soft X-ray emission lines are revealed for the first time in the XMM-Newton RGS spectrum, associated to the AGN and arising from the He and H-like ions of N, O, Ne and Mg. The He-like line profiles of N, O and Ne appear velocity broadened, with typical FWHM widths of $\sim5000$ km s$^{-1}$, whereas the H-like profiles are unresolved. From the clean measurement of the He-like triplets, we deduce that the broad lines arise from gas of density $n_{\rm e}\sim10^{11}$ cm$^{-3}$, while the photoionization calculations infer that the emitting gas covers at least 10 percent of $4\pi$ steradian. Thus the broad soft X-ray profiles appear coincident with an X-ray component of the optical-UV Broad Line Region on sub-pc scales, whereas the narrow profiles originate on larger pc scales, perhaps coincident with the AGN Narrow Line Region. The observations show that Ark 120 is not intrinsically bare and substantial X-ray emitting gas exists out of our direct line of sight towards this AGN.

Item Type: Article
Additional Information: © IOP Science; This is the accepted author manuscript (AAM). The final published version Reeves, J.N. et al., 2016. A DEEP X-RAY VIEW OF THE BARE AGN ARK 120. I. REVEALING THE SOFT X-RAY LINE EMISSION. The Astrophysical Journal, 828(2), p.98 is available online via IOP Science at http://dx.doi.org/10.3847/0004-637x/824/1/20. Please refer to any applicable terms of use of the publisher.
Uncontrolled Keywords: galaxies, active, individual (Ark 120), Seyfert, X-rays
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Faculty of Natural Sciences > School of Physical and Geographical Sciences
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Depositing User: Symplectic
Date Deposited: 09 Dec 2016 14:08
Last Modified: 09 Dec 2016 14:08
URI: http://eprints.keele.ac.uk/id/eprint/2589

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