Anatomy of the AGN in NGC 5548. V. A clear view of the X-ray narrow emission lines
Journal
ASTRONOMY & ASTROPHYSICS
Date Issued
2015
Author(s)
Whewell, M.
•
Branduardi-Raymont, G.
•
Kaastra, J. S.
•
Mehdipour, M.
•
Steenbrugge, K. C.
•
Bianchi, S.
•
Behar, E.
•
Ebrero, J.
•
•
Costantini, E.
•
De Marco, B.
•
Di Gesu, L.
•
Kriss, G. A.
•
Paltani, S.
•
Peterson, B. M.
•
Petrucci, P. -O.
•
•
DOI
10.1051/0004-6361/201526742
Description
The data used in this research are stored in the public archives of the satellites that are involved. We thank the International Space Science Institute (ISSI) in Bern for support. This work is based on observations obtained with XMM-Newton , an ESA science mission with instruments and contributions directly funded by ESA Member States and the USA (NASA). M. W. acknowledges the support of a Ph.D. studentship awarded by the UK Science Technology Facilities Council (STFC). SRON is supported financially by NWO, the Netherlands Organization for Scientific Research. M.M. acknowledges the support of a Studentship Enhancement Programme awarded by the UK Science Technology Facilities Council (STFC). K.C.S. acknowledges financial support from the Fondo Fortalecimiento de la Productividad Científica VRIDT 2013. E.B. is supported by grants from Israel’s MoST, ISF (1163/10), and I-CORE program (1937/12). B.M.P. acknowledges support from the US NSF through grant AST-1008882. M.C. and S.B. acknowledge INAF/PICS support. G.P. acknowledges support via an EU Marie Curie Intra-European fellowship under contract no. FP-PEOPLE-2012-IEF-331095. P.O.P. acknowledges funding support from the CNES and the French-Italian International Project of Scientific Collaboration: PICS-INAF project n181542. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This research has made use of NASA’s Astrophysics Data System Bibliographic Services’. M.W. thanks Mat Page for useful discussions. The authors thank the anonymous referee for the useful suggestions.
Abstract
Context. Our consortium performed an extensive multi-wavelength campaign of the nearby Seyfert 1 galaxy NGC 5548 in 2013-14. The source appeared unusually heavily absorbed in the soft X-rays, and signatures of outflowing absorption were also present in the UV. He-like triplets of neon, oxygen and nitrogen, and radiative recombination continuum (RRC) features were found to dominate the soft X-ray spectrum due to the low continuum flux.
Aims: Here we focus on characterising these narrow emission features using data obtained from the XMM-Newton RGS (770 ks stacked spectrum).
Methods: We use spex for our initial analysis of these features. Self-consistent photoionisation models from Cloudy are then compared with the data to characterise the physical conditions of the emitting region.
Results: Outflow velocity discrepancies within the O VII triplet lines can be explained if the X-ray narrow-line region (NLR) in NGC 5548 is absorbed by at least one of the six warm absorber components found by previous analyses. The RRCs allow us to directly calculate a temperature of the emitting gas of a few eV (~104 K), favouring photoionised conditions. We fit the data with a Cloudy model of log ξ = 1.45 ± 0.05 erg cm s-1, log NH = 22.9 ± 0.4 cm-2 and log vturb = 2.25 ± 0.5 km s-1 for the emitting gas; this is the first time the X-ray NLR gas in this source has been modelled so comprehensively. This allows us to estimate the distance from the central source to the illuminated face of the emitting clouds as 13.9 ± 0.6 pc, consistent with previous work.
Aims: Here we focus on characterising these narrow emission features using data obtained from the XMM-Newton RGS (770 ks stacked spectrum).
Methods: We use spex for our initial analysis of these features. Self-consistent photoionisation models from Cloudy are then compared with the data to characterise the physical conditions of the emitting region.
Results: Outflow velocity discrepancies within the O VII triplet lines can be explained if the X-ray narrow-line region (NLR) in NGC 5548 is absorbed by at least one of the six warm absorber components found by previous analyses. The RRCs allow us to directly calculate a temperature of the emitting gas of a few eV (~104 K), favouring photoionised conditions. We fit the data with a Cloudy model of log ξ = 1.45 ± 0.05 erg cm s-1, log NH = 22.9 ± 0.4 cm-2 and log vturb = 2.25 ± 0.5 km s-1 for the emitting gas; this is the first time the X-ray NLR gas in this source has been modelled so comprehensively. This allows us to estimate the distance from the central source to the illuminated face of the emitting clouds as 13.9 ± 0.6 pc, consistent with previous work.
Volume
581
Start page
A79
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