Please use this identifier to cite or link to this item:
logo share SHARE logo core CORE BASE
Visualizar otros formatos: MARC | Dublin Core | RDF | ORE | MODS | METS | DIDL | DATACITE

Exploring the active galactic nuclei population with extreme X-ray-to-optical flux ratios (fx/fo > 50)

AuthorsDella Ceca, R.; Carrera, Francisco J. CSIC ORCID CVN ; Caccianiga, A.; Severgnini, P.; Ballo, Lucía CSIC ORCID; Braito, V.; Corral, Amalia CSIC ORCID ; Moro, A. del; Mateos, Silvia CSIC ORCID ; Ruiz Camuñas, A. CSIC ORCID; Watson, M. G.
KeywordsX-ray galaxies
Quasars: general
Galaxies: active
BL Lacertae objects: general
Galaxies: nuclei
Issue Date2015
PublisherOxford University Press
CitationMonthly Notices of the Royal Astronomical Society 447(4): 3227-3242 (2015)
AbstractThe cosmic history of the growth of supermassive black holes in galactic centres parallels that of star formation in the Universe. However, an important fraction of this growth occurs inconspicuously in obscured objects, where ultraviolet/optical/near-infrared emission is heavily obscured by dust. Since the X-ray flux is less attenuated, a high X-ray-to-optical flux ratio (fx/fo) is expected to be an efficient tool to find out these obscured accreting sources. We explore here via optical spectroscopy, X-ray spectroscopy and infrared photometry the most extreme cases of this population (those with fx/fo > 50, EXO50 sources hereafter), using a well-defined sample of seven X-ray sources extracted from the 2XMM catalogue. Five EXO50 sources (∼70 per cent of the sample) in the bright flux regime explored by our survey (f(2−10 keV) ≥ 1.5 × 10−13 erg cm−2 s−1) are associated with obscured AGN (NH > 1022 cm−2), spanning a redshift range between 0.75 and 1 and characterized by 2–10 keV intrinsic luminosities in the QSO regime (e.g. well in excess to 1044 erg s−1). We did not find compelling evidence of Compton thick active galacic nuclei (AGN). Overall, the EXO50 type 2 QSOs do not seem to be different from standard X-ray-selected type 2 QSOs in terms of nuclear absorption; a very high AGN/host galaxy ratio seems to play a major role in explaining their extreme properties. Interestingly, three out of five EXO50 type 2 QSO objects can be classified as extreme dust-obscured galaxies (EDOGs, f24 μm/fR ≥ 2000), suggesting that a very high AGN/host ratios (along with the large amount of dust absorption) could be the natural explanation also for a part of the EDOG population. The remaining two EXO50 sources are classified as BL Lac objects, having rather extreme properties, and which are good candidates for TeV emission.
Publisher version (URL)htpps://
Identifiersdoi: 10.1093/mnras/stu2665
e-issn: 1365-2966
issn: 0035-8711
Appears in Collections:(IFCA) Artículos

Files in This Item:
File Description SizeFormat
X-ray-to-optical.pdf2,23 MBUnknownView/Open
Show full item record
Review this work


checked on Sep 25, 2023


checked on Sep 26, 2023

Page view(s)

checked on Sep 28, 2023


checked on Sep 28, 2023

Google ScholarTM




WARNING: Items in Digital.CSIC are protected by copyright, with all rights reserved, unless otherwise indicated.