A deep X-ray view of the bare AGN Ark 120. I. Revealing the Soft X-ray Line Emission - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue Astrophys.J. Année : 2016

A deep X-ray view of the bare AGN Ark 120. I. Revealing the Soft X-ray Line Emission

J.N. Reeves
  • Fonction : Auteur
V. Braito
  • Fonction : Auteur
E. Nardini
  • Fonction : Auteur
A. Lobban
  • Fonction : Auteur
T.J. Turner
  • Fonction : Auteur

Résumé

The Seyfert 1 galaxy Ark 120 is a prototype example of the so-called class of bare nucleus active galactic nuclei (AGNs), 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 that were carried out in 2014 March, together with simultaneous Chandra/High Energy Transmission Grating 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 interstellar medium (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 neighborhood. However, the presence of several soft X-ray emission lines are revealed for the first time in the XMM-Newton RGS spectrum, associated with 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 FWHMs of ∼5000 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 a gas of density n (e) ∼ 10(11) cm(−)(3), while the photoionization calculations infer that the emitting gas covers at least 10% of 4π steradian. Thus the broad soft X-ray profiles appear coincident with an X-ray component of the optical–UV broad-line region on sub-parsec scales, whereas the narrow profiles originate on larger parsec 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 toward this AGN.

Dates et versions

hal-01554044 , version 1 (03-07-2017)

Identifiants

Citer

J.N. Reeves, D. Porquet, V. Braito, E. Nardini, A. Lobban, et al.. A deep X-ray view of the bare AGN Ark 120. I. Revealing the Soft X-ray Line Emission. Astrophys.J., 2016, 828 (2), pp.98. ⟨10.3847/0004-637X/828/2/98⟩. ⟨hal-01554044⟩
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