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ABSTRACT From near-infrared spectroscopic measurements of the Mg ii emission line doublet, we estimate the black hole (BH) mass of the quasar, SMSS J215728.21–360215.1, as being (3.4 ± 0.6) × 1010 M⊙ and refine the redshift of the quasar to be z = 4.692. SMSS J2157 is the most luminous known quasar, with a 3000 Å luminosity of (4.7 ± 0.5) × 1047 erg s−1 and an estimated bolometric luminosity of 1.6 × 1048 erg s−1, yet its Eddington ratio is only ∼0.4. Thus, the high luminosity of this quasar is a consequence of its extremely large BH – one of the most massive BHs at z > 4.
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Discovery of the most luminous quasar of the last 9 Gyr
Abstract We report the discovery of a bright ( $g = 14.5$ mag (AB), $K = 11.9$ mag (Vega)) quasar at redshift $z=0.83$ — the optically brightest (unbeamed) quasar at $z>0.4$ . SMSS J114447.77-430859.3, at a Galactic latitude of $$b=+18.1^{\circ}$$ , was identified by its optical colours from the SkyMapper Southern Survey (SMSS) during a search for symbiotic binary stars. Optical and near-infrared spectroscopy reveals broad Mg ii , H $$\unicode{x03B2}$$ , H $$\unicode{x03B1}$$ , and Pa $$\unicode{x03B2}$$ emission lines, from which we measure a black hole mass of $$\log_{10}\! (M_{\mathrm{BH}}/\mathrm{M}_{\odot}) = 9.4 \pm 0.5$$ . With its high luminosity, $$L_{\mathrm{bol}} = (4.7\pm1.0)\times10^{47}\,\mathrm{erg\,s}^{-1}$$ or $$M_{i}(z=2) = -29.74$$ mag (AB), we estimate an Eddington ratio of $$\approx1.4$$ . As the most luminous quasar known over the last $${\sim}$$ 9 Gyr of cosmic history, having a luminosity $$8\times$$ greater than 3C 273, the source offers a range of potential follow-up opportunities.
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- Award ID(s):
- 1908284
- PAR ID:
- 10381322
- Date Published:
- Journal Name:
- Publications of the Astronomical Society of Australia
- Volume:
- 39
- ISSN:
- 1323-3580
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1017/pasa.2022.36
