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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/20.500.12386/29167
Title: Discovery of the first heavily obscured QSO candidate at z > 6 in a close galaxy pair
Authors: Vito, F.
Brandt, W. N.
Bauer, F. E.
GILLI, Roberto 
Luo, B.
Zamorani, G.
CALURA, Francesco 
COMASTRI, Andrea 
Mazzucchelli, C.
Mignoli, M.
Nanni, R.
Shemmer, O.
Vignali, C.
Brusa, M.
Cappelluti, N.
Civano, F.
Volonteri, M.
Issue Date: 2019
Journal: ASTRONOMY & ASTROPHYSICS 
Number: 628
First Page: L6
Abstract: While theoretical arguments predict that most of the early growth of supermassive black holes (SMBHs) happened during heavily obscured phases of accretion, current methods used for selecting z > 6 quasars (QSOs) are strongly biased against obscured QSOs, thus considerably limiting our understanding of accreting SMBHs during the first gigayear of the Universe from an observational point of view. We report the Chandra discovery of the first heavily obscured QSO candidate in the early universe, hosted by a close (≈5 kpc) galaxy pair at z = 6.515. One of the members is an optically classified type-1 QSO, PSO167-13. The companion galaxy was first detected as a [C II] emitter by Atacama large millimeter array (ALMA). An X-ray source is significantly (P = 0.9996) detected by Chandra in the 2-5 keV band, with < 1.14 net counts in the 0.5-2 keV band, although the current positional uncertainty does not allow a conclusive association with either PSO167-13 or its companion galaxy. From X-ray photometry and hardness-ratio arguments, we estimated an obscuring column density of N<SUB>H</SUB> > 2 × 10<SUP>24</SUP> cm<SUP>-2</SUP> and N<SUB>H</SUB> > 6 × 10<SUP>23</SUP> cm<SUP>-2</SUP> at 68% and 90% confidence levels, respectively. Thus, regardless of which of the two galaxies is associated with the X-ray emission, this source is the first heavily obscured QSO candidate at z > 6.
Acknowledgments: We acknowledge financial contribution from the agreement ASI-INAF n. 2017-14-H.O
URI: http://hdl.handle.net/20.500.12386/29167
URL: https://www.aanda.org/articles/aa/abs/2019/08/aa35924-19/aa35924-19.html
ISSN: 0004-6361
DOI: 10.1051/0004-6361/201935924
Bibcode ADS: 2019A&A...628L...6V
Fulltext: open
Appears in Collections:1.01 Articoli in rivista

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