文章基本信息

标题：X-ray emission of z > 2.5 active galactic nuclei can be obscured by their host galaxies
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作者：C. Circosta ; C. Vignali ; R. Gilli 等
期刊名称：Astronomy & Astrophysics
印刷版ISSN：0004-6361
电子版ISSN：1432-0746
出版年度：2019
卷号：623
DOI：10.1051/0004-6361/201834426
语种：English
出版社：EDP Sciences
摘要：We present a multiwavelength study of seven active galactic nuclei (AGN) at spectroscopic redshift >2.5 in the 7 MsChandraDeep Field South that were selected for their good far-infrared (FIR) and submillimeter (submm) detections. Our aim is to investigate the possibility that the obscuration observed in the X-rays can be produced by the interstellar medium (ISM) of the host galaxy. Based on the 7 MsChandraspectra, we measured obscuring column densitiesNH, Xin excess of 7 × 1022cm−2and intrinsic X-ray luminositiesLX > 1044erg s−1for our targets, as well as equivalent widths for the Fe Kαemission line EWrest ≳ 0.5−1 keV. We built the UV-to-FIR spectral energy distributions (SEDs) by using broadband photometry from the CANDELS andHerschelcatalogs. By means of an SED decomposition technique, we derived stellar masses (M* ∼ 1011M⊙), IR luminosities (LIR > 1012L⊙), star formation rates (SFR ∼ 190−1680M⊙yr−1) and AGN bolometric luminosities (Lbol ∼ 1046erg s−1) for our sample. We used an empirically calibrated relation between gas masses and FIR/submm luminosities and derivedMgas ∼ 0.8−5.4 × 1010 M⊙. High-resolution (0.3−0.7″) ALMA data (when available, CANDELS data otherwise) were used to estimate the galaxy size and hence the volume enclosing most of the ISM under simple geometrical assumptions. These measurements were then combined to derive the column density associated with the ISM of the host, which is on the order ofNH, ISM ∼ 1023−24cm−2. The comparison between the ISM column densities and those measured from the X-ray spectral analysis shows that they are similar. This suggests that at least at high redshift, significant absorption on kiloparsec scales by the dense ISM in the host likely adds to or substitutes that produced by circumnuclear gas on parsec scales (i.e., the torus of unified models). The lack of unobscured AGN among our ISM-rich targets supports this scenario.
关键词：engalaxies: activegalaxies: evolutiongalaxies: star formationquasars: generalsurveysX-rays: galaxies