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  1. OA@INAF
  2. PRODOTTI RICERCA INAF
  3. 1 CONTRIBUTI IN RIVISTE (Journal articles)
  4. 1.01 Articoli in rivista
Please use this identifier to cite or link to this item: http://hdl.handle.net/20.500.12386/29170
Title: X-ray emission of z > 2.5 active galactic nuclei can be obscured by their host galaxies
Authors: Circosta, C.
Vignali, C.
GILLI, Roberto 
Feltre, A.
Vito, F.
Calura, F.
Mainieri, V.
MASSARDI, MARCELLA 
Norman, C.
Issue Date: 2019
Journal: ASTRONOMY & ASTROPHYSICS 
Number: 623
First Page: A172
Abstract: We present a multiwavelength study of seven active galactic nuclei (AGN) at spectroscopic redshift >2.5 in the 7 Ms Chandra Deep Field South that were selected for their good far-infrared (FIR) and submillimeter (submm) detections. Our aim is to investigate the possibility that the obscuration observed in the X-rays can be produced by the interstellar medium (ISM) of the host galaxy. Based on the 7 Ms Chandra spectra, we measured obscuring column densities N<SUB>H, X</SUB> in excess of 7 × 10<SUP>22</SUP> cm<SUP>-2</SUP> and intrinsic X-ray luminosities L<SUB>X</SUB> > 10<SUP>44</SUP> erg s<SUP>-1</SUP> for our targets, as well as equivalent widths for the Fe Kα emission line EW<SUB>rest</SUB> ≳ 0.5-1 keV. We built the UV-to-FIR spectral energy distributions (SEDs) by using broadband photometry from the CANDELS and Herschel catalogs. By means of an SED decomposition technique, we derived stellar masses (M<SUB>*</SUB> ∼ 10<SUP>11</SUP> M<SUB>☉</SUB>), IR luminosities (L<SUB>IR</SUB> > 10<SUP>12</SUP> L<SUB>☉</SUB>), star formation rates (SFR ∼ 190-1680 M<SUB>☉</SUB> yr<SUP>-1</SUP>) and AGN bolometric luminosities (L<SUB>bol</SUB> ∼ 10<SUP>46</SUP> erg s<SUP>-1</SUP>) for our sample. We used an empirically calibrated relation between gas masses and FIR/submm luminosities and derived M<SUB>gas</SUB> ∼ 0.8-5.4 × 10<SUP>10</SUP> M<SUB>☉</SUB>. High-resolution (0.3-0.7″) ALMA data (when available, CANDELS data otherwise) were used to estimate the galaxy size and hence the volume enclosing most of the ISM under simple geometrical assumptions. These measurements were then combined to derive the column density associated with the ISM of the host, which is on the order of N<SUB>H, ISM</SUB> ∼ 10<SUP>23-24</SUP> cm<SUP>-2</SUP>. The comparison between the ISM column densities and those measured from the X-ray spectral analysis shows that they are similar. This suggests that at least at high redshift, significant absorption on kiloparsec scales by the dense ISM in the host likely adds to or substitutes that produced by circumnuclear gas on parsec scales (i.e., the torus of unified models). The lack of unobscured AGN among our ISM-rich targets supports this scenario.
Acknowledgments: We acknowledge financial contribution from the agreement ASI-INAF n. 2017-14-H.O
URI: http://hdl.handle.net/20.500.12386/29170
URL: https://www.aanda.org/articles/aa/abs/2019/03/aa34426-18/aa34426-18.html
ISSN: 0004-6361
DOI: 10.1051/0004-6361/201834426
Bibcode ADS: 2019A&A...623A.172C
Fulltext: open
Appears in Collections:1.01 Articoli in rivista

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