X-Ray Observations of a z ∼ 6.2 Quasar/Galaxy Merger
Abstract
Quasars at early redshifts (z > 6) with companion galaxies offer unique insights into the growth and evolution of the first supermassive black holes. Here, we report on a 150 ks Chandra observation of PSO J308.0416-21.2339, a z = 6.23 quasar with a merging companion galaxy identified in [C II] and rest-frame UV emission. With {72.3}-8.6+9.6 net counts, we find that PSO J308.0416-21.2339 is powerful ({L}X={2.31}-0.76+1.14× {10}45 {erg} {{{s}}}-1 {cm}}-2 in rest-frame 2.0-10.0 keV) yet soft (spectral power-law index {{Γ }}={2.39}-0.36+0.37 and optical-to-X-ray slope α OX = -1.41 ± 0.11). In addition, we detect three hard-energy photons 2.″0 to the west of the main quasar, cospatial with the brightest UV emission of the merging companion. As no soft-energy photons are detected in the same area, this is potentially indicative of a highly obscured source. With conservative assumptions, and accounting for both background fluctuations and the extended wings of the quasar’s emission, these photons only have a probability P = 0.021 of happening by chance. If confirmed by deeper observations, this system is the first high-redshift quasar and companion individually detected in X-rays and is likely a dual active galactic nucleus.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- December 2019
- DOI:
- 10.3847/1538-4357/ab5585
- arXiv:
- arXiv:1909.08619
- Bibcode:
- 2019ApJ...887..171C
- Keywords:
-
- Quasar-galaxy pairs;
- Quasars;
- Galaxy mergers;
- Double quasars;
- X-ray astronomy;
- X-ray quasars;
- 1316;
- 1319;
- 608;
- 406;
- 1810;
- 1821;
- Astrophysics - Astrophysics of Galaxies;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 8 pages, 4 figures, published in the Astrophysical Journal. Revised to reflect accepted version