| Title: |
Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) XXII. Chandra observations of narrow-line quasar candidates at z>6 |
| Authors: |
Iwasawa, Kazushi; Gilli, Roberto; Vito, Fabio; Matsuoka, Yoshiki; Onoue, Masafusa; Strauss, Michael A.; Kashikawa, Nobunari; Toba, Yoshiki; Shimasaku, K.; Inayoshi, K.; Nagao, Tohru; Kawanaka, N.; Silverman, John D.; Izumi, Takuma; Kohno, Kotaro; Ueda, Y. |
| Contributors: |
NASA; Agencia Estatal de Investigación (España); Ministerio de Ciencia e Innovación (España); European Commission; Japan Society for the Promotion of Science; Istituto Nazionale di Astrofisica; Iwasawa, Kazushi; Gilli, Roberto; Vito, Fabio; Matsuoka, Yoshiki |
| Publisher Information: |
EDP Sciences |
| Publication Year: |
2026 |
| Collection: |
Digital.CSIC (Consejo Superior de Investigaciones Científicas / Spanish National Research Council) |
| Subject Terms: |
Galaxies: active; Galaxies: high-redshift; X-rays: galaxies |
| Description: |
We report on Chandra X-ray observations of four narrow-line quasar candidates at z~6, selected from the SHELLQs project, based on the Subaru Hyper Suprime-Cam survey. These objects are characterised by narrow (FWHM1e44 erg/s) Lya and faint UV continuum (M_1450 = -22 - -21), prompting us to examine whether they are obscured luminous AGN at the epoch of reionization. However, none of these objects were detected by Chandra, giving an upper limit to their rest-frame 2-10 keV luminosity (Lx) of 2e44 erg/s (2 sigma), assuming a spectral slope Gamma=2. Subsequent rest-frame optical spectroscopy of these objects by the JWST-NIRSpec, presented in a companion paper, show weak broad Balmer emission at the base of narrow cores. With the scaling relation for low-redshift AGN, the observed strong [OIII]5007 flux of these sources would predict Lx to be around 1e45 erg/s, which is well above the Chandra upper limits. These optical spectra and X-ray quietness are reminiscent of JWST-selected broad-line AGN. We attribute the weak broad Balmer emission to the broad-line regions hidden partially by optically-thick obscuring matter which also hides the optical and X-ray continuum emission from the accretion disc. Compton-thick obscuration, which would strongly suppress X-ray emission, could be due to a dense inter-stellar medium that is often present in galaxies at high redshifts. Alternatively, the same effect could be obtained from an inflated disc at the innermost radii in a supercritical accretion flow, when the disc is viewed at inclined angles. ; We thank Shin Mineshige, Livia Vallini, Roberto Decarli for useful discussion, and Guido Risaliti for providing us with the data used for Fig. 7. This paper employs a list of Chandra datasets, obtained by the Chandra X-ray Observatory, contained in the Chandra Data Collection (CDC) 396 DOI:10.25574/cdc.396 and made use of software provided by the Chandra X-ray Center (CXC). This work is based in part on observations made with the NASA/ESA/CSA James Webb ... |
| Document Type: |
article in journal/newspaper |
| File Description: |
application/pdf |
| Language: |
English |
| Relation: |
#PLACEHOLDER_PARENT_METADATA_VALUE#; info:eu-repo/grantAgreement/AEI/Plan Estatal de Investigación Científica y Técnica y de Innovación 2021-2023/PID2022-136828NB-C44/ES/ESTUDIO DE EYECCIONES DE FUENTES DE ALTA ENERGIA: OBSERVACIONES DE FUENTES EXTRAGALACCTICAS/; https://doi.org/10.1051/0004-6361/202555410; Sí; Astronomy & Astrophysics 706: A305 (2026); https://hdl.handle.net/10261/426104; http://arxiv.org/abs/2505.04826v3 |
| DOI: |
10.1051/0004-6361/202555410 |
| Availability: |
https://hdl.handle.net/10261/426104; https://doi.org/10.1051/0004-6361/202555410; http://arxiv.org/abs/2505.04826v3 |
| Rights: |
info:eu-repo/semantics/openAccess |
| Accession Number: |
edsbas.11ED5C5A |
| Database: |
BASE |