TY - JOUR
T1 - Chandra and Magellan /FIRE follow-up observations of PSO167-13
T2 - An X-ray weak QSO at z = 6.515
AU - Vito, F.
AU - Brandt, W. N.
AU - Ricci, F.
AU - Congiu, E.
AU - Connor, T.
AU - Bañados, E.
AU - Bauer, F. E.
AU - Gilli, R.
AU - Luo, B.
AU - Mazzucchelli, C.
AU - Mignoli, M.
AU - Shemmer, O.
AU - Vignali, C.
AU - Calura, F.
AU - Comastri, A.
AU - Decarli, R.
AU - Gallerani, S.
AU - Nanni, R.
AU - Brusa, M.
AU - Cappelluti, N.
AU - Civano, F.
AU - Zamorani, G.
N1 - Funding Information:
Acknowledgements. We thank the referee, Belinda Wilkes, for her useful comments and suggestions. We thank Marcel Neeleman, Bram Venemans, Estelle Pons, and Weimin Yi for useful discussions, and Marianne Vestergaard for providing the iron UV emission template of Vestergaard & Wilkes (2001). We acknowledge support from CXC grants GO0-21078D (W. N. B.) and GO0-21078C (O. S.), from ANID grants CATA-Basal AFB-170002 (F. E. B., E. C.), FONDECYT Regular 1190818 (F. E. B.) and 1200495 (F. E. B.), Millennium Science Initiative ICN12_009 (F. E. B.), the NSFC grant 11991053 and National Key R&D Program of China grant 2016YFA0400702 (B. L.), from ASI-INAF n. 2018-31-HH.0 grant and PRIN-MIUR 2017 (S. G.), and from the agreement ASI-INAF n. 2017-14-H.O. The work of T. C. was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. This research has made use of data obtained from the Chandra Data Archive (Proposal IDs 19700183 and 21700027), and software provided by the Chandra X-ray Center (CXC) in the application packages CIAO. This paper includes data gathered with the 6.5 meter Magellan Telescopes located at Las Campanas Observatory, Chile (CNTAC proposal ID CN2020A-22). This research made use of SAO Image DS9 Joye & Mandel (2003) and Astropy, (http://www.astropy.org) a community-developed core Python package for Astronomy (Astropy Collaboration 2013, 2018).
Publisher Copyright:
© ESO 2021.
PY - 2021/5/1
Y1 - 2021/5/1
N2 - Context. The discovery of hundreds of quasi-stellar objects (QSOs) in the first gigayear of the Universe powered by already grown supermassive black holes (SMBHs) challenges our knowledge of SMBH formation. In particular, investigations of z > 6 QSOs that present notable properties can provide unique information on the physics of fast SMBH growth in the early Universe. Aims. We present the results of follow-up observations of the z = 6.515 radio-quiet QSO PSO167-13, which is interacting with a close companion galaxy. The PSO167-13 system has recently been proposed to host the first heavily obscured X-ray source at high redshift. The goals of these new observations are to confirm the existence of the X-ray source and to investigate the rest-frame UV properties of the QSO. Methods. We observed the PSO167-13 system with Chandra/ACIS-S (177 ks) and obtained new spectroscopic observations (7.2 h) with Magellan/FIRE. Results. No significant X-ray emission is detected from the PSO167-13 system, suggesting that the obscured X-ray source previously tentatively detected was either due to a strong background fluctuation or is highly variable. The upper limit (90% confidence level) on the X-ray emission of PSO167-13 (L2-10 keV < 8.3 × 1043 erg s-1) is the lowest available for a z > 6 QSO. The ratio between the X-ray and UV luminosity of αox < -1.95 makes PSO167-13 a strong outlier from the αox - LUV and LX - Lbol relations. In particular, its X-ray emission is more than six times weaker than the expectation based on its UV luminosity. The new Magellan/FIRE spectrum of PSO167-13 is strongly affected by unfavorable sky conditions, but the tentatively detected C IV and Mg II emission lines appear strongly blueshifted. Conclusions. The most plausible explanations for the X-ray weakness of PSO167-13 are intrinsic weakness or small-scale absorption by Compton-thick material. The possible strong blueshift of its emission lines hints at the presence of nuclear winds, which could be related to its X-ray weakness.
AB - Context. The discovery of hundreds of quasi-stellar objects (QSOs) in the first gigayear of the Universe powered by already grown supermassive black holes (SMBHs) challenges our knowledge of SMBH formation. In particular, investigations of z > 6 QSOs that present notable properties can provide unique information on the physics of fast SMBH growth in the early Universe. Aims. We present the results of follow-up observations of the z = 6.515 radio-quiet QSO PSO167-13, which is interacting with a close companion galaxy. The PSO167-13 system has recently been proposed to host the first heavily obscured X-ray source at high redshift. The goals of these new observations are to confirm the existence of the X-ray source and to investigate the rest-frame UV properties of the QSO. Methods. We observed the PSO167-13 system with Chandra/ACIS-S (177 ks) and obtained new spectroscopic observations (7.2 h) with Magellan/FIRE. Results. No significant X-ray emission is detected from the PSO167-13 system, suggesting that the obscured X-ray source previously tentatively detected was either due to a strong background fluctuation or is highly variable. The upper limit (90% confidence level) on the X-ray emission of PSO167-13 (L2-10 keV < 8.3 × 1043 erg s-1) is the lowest available for a z > 6 QSO. The ratio between the X-ray and UV luminosity of αox < -1.95 makes PSO167-13 a strong outlier from the αox - LUV and LX - Lbol relations. In particular, its X-ray emission is more than six times weaker than the expectation based on its UV luminosity. The new Magellan/FIRE spectrum of PSO167-13 is strongly affected by unfavorable sky conditions, but the tentatively detected C IV and Mg II emission lines appear strongly blueshifted. Conclusions. The most plausible explanations for the X-ray weakness of PSO167-13 are intrinsic weakness or small-scale absorption by Compton-thick material. The possible strong blueshift of its emission lines hints at the presence of nuclear winds, which could be related to its X-ray weakness.
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U2 - 10.1051/0004-6361/202140399
DO - 10.1051/0004-6361/202140399
M3 - Article
AN - SCOPUS:85107079327
SN - 0004-6361
VL - 649
JO - Astronomy and Astrophysics
JF - Astronomy and Astrophysics
M1 - A122
ER -