Issue |
A&A
Volume 555, July 2013
|
|
---|---|---|
Article Number | A79 | |
Number of page(s) | 14 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361/201321083 | |
Published online | 03 July 2013 |
The XMM Deep survey in the CDF-S
V. Iron K lines from active galactic nuclei in the distant Universe ⋆,⋆⋆
1
Instituto de Física de Cantabria (CSIC-UC),
39005
Santander,
Spain
e-mail: falocco@ifca.unican.es
2
Institute of Astronomy & Astrophysics, National
Observatory of Athens, Palaia
Penteli, 15236
Athens,
Greece
3
INAF-Osservatorio Astronomico di Bologna, via Ranzani
1, 40127
Bologna,
Italy
4
Dipartimento di Fisica ed Astronomia, Università di
Bologna, via Berti Pichat
6/2, 40127
Bologna,
Italy
5
ICREA and Institut de Ciències del Cosmos (ICC), Universitat de
Barcelona (IEEC-UB), 08028
Barcelona,
Spain
6
Department of Physics, University of Durham,
South Road, Durham
DH1 3LE,
UK
7
Max Planck Institute für Extraterrestriche Physik,
85748
Garching,
Germany
Received: 11 January 2013
Accepted: 22 April 2013
Context. X-ray spectroscopy of active galactic nuclei (AGN) offers the opportunity to directly probe the inner regions of the accretion disk. Reflection of the primary continuum on the circumnuclear accreting matter produces features in the X-ray spectrum that help to explore the physics and the geometry of the innermost region, close to the central black hole.
Aims. We present the results of our analysis of average AGN XMM-Newton X-ray spectra in the Chandra Deep Field South observation (hereafter, XMM CDFS), in order to explore the Fe line features in distant AGN up to z ~ 3.5.
Methods. We computed the average X-ray spectrum of a sample of 54 AGN with spectroscopic redshifts and signal-to-noise ratio in the 2–12 keV rest-frame band larger than 15 in at least one EPIC camera (for a total of 100 X-ray spectra and 181 623 net counts in the 2–12 keV rest-frame band). We have taken the effects of combining spectra from sources at different redshifts and from both EPIC-pn and EPIC-MOS cameras into account, as well as their spectral resolution; we checked our results using thorough simulations. We explored the iron line components of distant AGN focusing on the narrow core which arises from material far from the central BH and on the putative relativistic component emitted in the accretion disk.
Results. The average spectrum shows a highly significant iron feature. Estimating its equivalent width (EW) with a model-independent method suggests a higher EW in a broader range. The line, modelled as an unresolved Gaussian, is significant at 6.8σ and has an EW = 95 ± 22 eV for the full sample. We find that our current data can be fitted equally welladding a relativistic profile to the narrow component (in the full sample, EW = 140 ± 120 eV and 67 ± 28 eV respectively for the relativistic and narrow lines).
Conclusions. Thanks to the high quality of the XMM CDFS spectra and to the detailed modelling of the continuum and instrumental effects, we have shown that the most distant AGN exhibit a highly significant iron emission feature. It can be modelled both with narrow and broad lines which suggest that the EW becomes higher when a broader energy range around the line centroid is considered, provides tantalising evidence for reflection by material both very close and far away from the central engine. The EW of both features are similar to those observed in individual nearby AGN, hence they must be a widespread characteristic of AGN, since otherwise the average values would be smaller than observed.
Key words: galaxies: active / X-rays: galaxies
Based on observations by XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA member states and NASA.
Tables 3–5 are available in electronic form at http://www.aanda.org
© ESO, 2013
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.