Discovery of the first heavily obscured QSO candidate at <i>z</i> &gt; 6 in a close galaxy pair

Vito, F.; Brandt, W. N.; Bauer, F. E.; Gilli, R.; Luo, B.; Zamorani, G.; Calura, F.; Comastri, A.; Mazzucchelli, Chiara; Mignoli, M.; Nanni, Riccardo; Shemmer, Ohad; Vignali, C.; Brusa, M.; Cappelluti, N.; Civano, F.; Volonteri, Marta

doi:10.1051/0004-6361/201935924

Cited by 46 publications

(48 citation statements)

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“…Both quasars have [C II] bright companions (Decarli et al 2017;Willott et al 2017) reminiscent of ongoing mergers, and these are the only systems at redshifts z > 6 with companions detected in [C II] and in rest-frame UV Mazzucchelli et al 2019;Neeleman et al 2019). While here we report that PJ308−21 is X-ray luminous and its companion may host a heavily-obscured X-ray source, in an analysis of PSOJ167−13 (z = 6.5) Vito et al (2019a) report a detection of only one source, which also appears to be heavily-obscured. That these two quasars beyond z > 6 have both rest-frame UV-bright companions and heavily obscured quasar candidates may be in keeping with the prediction of Circosta et al (2019) that the host's interstellar medium is capable of producing significant column densities of n H around high-redshift quasars.…”

Section: Discussionmentioning

confidence: 47%

“…Nevertheless, studies of individual quasars are still highly fruitful at characterizing mechanisms for early SMBH growth. For example, Bañados et al (2018) showed that AGN are already X-ray luminous at z = 7.5, Vito et al (2019a) identified a heavily obscured quasar candidate in a z = 6.5 quasar/galaxy pair, and Nanni et al (2018) found potential evidence of AGN variability and of jets from a z = 6.3 quasar.…”

Section: Introductionmentioning

confidence: 99%

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X-Ray Observations of a z ∼ 6.2 Quasar/Galaxy Merger

Connor¹,

Bañados²,

Stern³

et al. 2019

ApJ

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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 +9.6 −8.6 net counts, we find that PSO J308.0416−21.2339 is powerful (L X = 2.31 +1.14 −0.76 × 10 45 erg s −1 cm −2 in rest frame 2.0 − 10.0 keV) yet soft (spectral power-law index Γ = 2.39 +0.37 −0.36 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 represent a 2.4σ detection. 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 AGN.

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Section: Discussionmentioning

confidence: 47%

Section: Introductionmentioning

confidence: 99%

X-Ray Observations of a z ∼ 6.2 Quasar/Galaxy Merger

Connor¹,

Bañados²,

Stern³

et al. 2019

ApJ

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“…The offset between the Xray centroid and the [C II] position of this galaxy is only ≈ 0.15 arcsec. A thorough investigation and discussion of this system has been presented separately (Vito et al 2019).…”

Section: Psoj167-13mentioning

confidence: 99%

The X-ray properties of z > 6 quasars: no evident evolution of accretion physics in the first Gyr of the Universe

Vito

Brandt

Bauer

et al. 2019

A&A

Self Cite

106

150

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Context. X-ray emission from quasars (QSOs) has been used to assess supermassive black hole (SMBH) accretion properties up to z ≈ 6. However, at z > 6 only ≈ 15 QSOs are covered by sensitive X-ray observations, preventing a statistically significant investigation of the X-ray properties of the QSO population in the first Gyr of the Universe. Aims. We present new Chandra observations of a sample of 10 z > 6 QSOs, selected to have virial black-hole mass estimates from Mg II line spectroscopy (log M BH M = 8.5 − 9.6). Adding archival X-ray data for an additional 15 z > 6 QSOs, we investigate the X-ray properties of the QSO population in the first Gyr of the Universe, focusing in particular on the L UV − L X relation, which is traced by the α ox parameter, and the shape of their X-ray spectra. Methods. We performed photometric analyses to derive estimates of the X-ray luminosities of our z > 6 QSOs, and thus their α ox values and bolometric corrections (K bol = L bol /L X ). We compared the resulting α ox and K bol distributions with the results found for QSO samples at lower redshift, and ran several statistical tests to check for a possible evolution of the L UV − L X relation. Finally, we performed a basic X-ray spectral analysis of the brightest z > 6 QSOs to derive their individual photon indices, and joint spectral analysis of the whole sample to estimate the average photon index. Results. We detected seven of the new Chandra targets in at least one standard energy band, while two more are detected discarding energies E > 5 keV, where background dominates. We confirm a lack of significant evolution of α ox with redshift, extending the results from previous works up to z > 6 with a statistically significant QSO sample, and the trend of an increasing bolometric correction with increasing luminosity found for QSOs at lower redshifts. The average power-law photon index of our sample ( Γ = 2.20 +0.39 −0.34 and Γ = 2.13 +0.13 −0.13 for sources with < 30 and > 30 net counts, respectively) is slightly steeper than, but still consistent with, typical QSOs at z = 1 − 6. Conclusions. All these results point toward a lack of substantial evolution of the inner accretion-disk/hot-corona structure in QSOs from low redshift to z > 6. Our data hint at generally high Eddington ratios at z > 6.

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“…X-ray observations are extremely valuable to search for binary SMBH systems, as they can also unveil highly dustobscured AGN, which are not necessarily radio-loud (e.g. Vito et al 2019). The occurrence of SMBH binaries is crucial to our understanding of galaxy formation, as they directly indicate that galaxies evolve through mergers (e.g.…”

Section: Tracing the Evolution Of Active Galaxies Using Large Samplesmentioning

confidence: 99%

Constraining VLBI−optical offsets in high redshift galaxies using strong gravitational lensing

Spingola

Barnacka

2020

Monthly Notices of the Royal Astronomical Society

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We present a multi-wavelength analysis of two highly magnified strong gravitationally lensed galaxies, CLASS B0712+472 and CLASS B1608+656, at redshifts 1.34 and 1.394, respectively, using new VLBI and archival HST observations. We reconstruct the positions of the radio and optical emissions with their uncertainties using Monte Carlo sampling. We find that in CLASS B0712+472 the optical and radio emissions are co-spatial within 2 ± 5 mas (17 ± 42 pc at redshift of 1.34). But, in CLASS B1608+656, we reconstruct an optical-radio offset of 25 ± 16 mas (214 ± 137 pc at redshift of 1.394), the smallest offset measured for an AGN at such high redshift. The spectral features indicate that CLASS B1608+656 is a post-merger galaxy, which, in combination with the optical-VLBI offset reported here, makes CLASS B1608+656 a promising candidate for a high-z offset-AGN. Furthermore, the milliarcsecond angular resolution of the VLBI observations combined with the precise lens models allow us to spatially locate the radio emission at 0.05 mas precision (0.4 pc) in CLASS B0712+472, and 0.009 mas precision (0.08 pc) in CLASS B1608+656. The search for optical-radio offsets in high redshift galaxies will be eased by the upcoming synoptic all-sky surveys, including E-ELT and SKA, which are expected to find ∼ 10 5 strongly lensed galaxies, opening an era of large strong lensing samples observed at high angular resolution.

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Discovery of the first heavily obscured QSO candidate at z > 6 in a close galaxy pair

Cited by 46 publications

References 46 publications

X-Ray Observations of a z ∼ 6.2 Quasar/Galaxy Merger

X-Ray Observations of a z ∼ 6.2 Quasar/Galaxy Merger

The X-ray properties of z > 6 quasars: no evident evolution of accretion physics in the first Gyr of the Universe

Constraining VLBI−optical offsets in high redshift galaxies using strong gravitational lensing

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