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Heavily reddened type 1 quasars at z > 2 – I. Evidence for significant obscured black hole growth at the highest quasar luminosities

Heavily reddened type 1 quasars at z > 2 – I. Evidence for significant obscured black hole growth at the highest quasar luminosities
Heavily reddened type 1 quasars at z > 2 – I. Evidence for significant obscured black hole growth at the highest quasar luminosities
We present a new population of z > 2 dust-reddened, type 1 quasars with 0.5 ≲ E(B − V) ≲ 1.5, selected using near-infrared (NIR) imaging data from the UKIDSS-LAS (Large Area Survey), ESO-VHS (European Southern Observatory-VISTA Hemisphere Survey) and WISE surveys. NIR spectra obtained using the Very Large Telescope for 24 new objects bring our total sample of spectroscopically confirmed hyperluminous (>1013 L⊙), high-redshift dusty quasars to 38. There is no evidence for reddened quasars having significantly different Hα equivalent widths relative to unobscured quasars. The average black hole masses (∼109–1010 M⊙) and bolometric luminosities (∼1047 erg s−1) are comparable to the most luminous unobscured quasars at the same redshift, but with a tail extending to very high luminosities of ∼1048 erg s−1. 66 per cent of the reddened quasars are detected at >3σ at 22 μm by WISE. The average 6-μm rest-frame luminosity is log10(L6 μm/ erg s−1) = 47.1 ± 0.4, making the objects among the mid-infrared brightest active galactic nuclei (AGN) currently known. The extinction-corrected space density estimate now extends over three magnitudes (−30 < Mi < −27) and demonstrates that the reddened quasar luminosity function is significantly flatter than that of the unobscured quasar population at z = 2–3. At the brightest magnitudes, Mi ≲ −29, the space density of our dust-reddened population exceeds that of unobscured quasars. A model where the probability that a quasar becomes dust reddened increases at high luminosity is consistent with the observations and such a dependence could be explained by an increase in luminosity and extinction during AGN-fuelling phases. The properties of our obscured type 1 quasars are distinct from the heavily obscured, Compton-thick AGN that have been identified at much fainter luminosities and we conclude that they likely correspond to a brief evolutionary phase in massive galaxy formation.
0035-8711
3368-3389
Banerji, Manda
ce0a04bf-70a4-4b64-9027-b1a01def7325
Alaghband-Zadeh, S.
7d36b464-4547-4900-8739-06bb1c759932
Hewett, Paul C.
a4763f70-9f9a-4a4e-85ed-10694a66e5c9
Mcmahon, Richard G.
43b8802d-36da-4b74-a7e4-66155c0e1a87
Banerji, Manda
ce0a04bf-70a4-4b64-9027-b1a01def7325
Alaghband-Zadeh, S.
7d36b464-4547-4900-8739-06bb1c759932
Hewett, Paul C.
a4763f70-9f9a-4a4e-85ed-10694a66e5c9
Mcmahon, Richard G.
43b8802d-36da-4b74-a7e4-66155c0e1a87

Banerji, Manda, Alaghband-Zadeh, S., Hewett, Paul C. and Mcmahon, Richard G. (2015) Heavily reddened type 1 quasars at z > 2 – I. Evidence for significant obscured black hole growth at the highest quasar luminosities. Monthly Notices of the Royal Astronomical Society, 447 (4), 3368-3389. (doi:10.1093/mnras/stu2649).

Record type: Article

Abstract

We present a new population of z > 2 dust-reddened, type 1 quasars with 0.5 ≲ E(B − V) ≲ 1.5, selected using near-infrared (NIR) imaging data from the UKIDSS-LAS (Large Area Survey), ESO-VHS (European Southern Observatory-VISTA Hemisphere Survey) and WISE surveys. NIR spectra obtained using the Very Large Telescope for 24 new objects bring our total sample of spectroscopically confirmed hyperluminous (>1013 L⊙), high-redshift dusty quasars to 38. There is no evidence for reddened quasars having significantly different Hα equivalent widths relative to unobscured quasars. The average black hole masses (∼109–1010 M⊙) and bolometric luminosities (∼1047 erg s−1) are comparable to the most luminous unobscured quasars at the same redshift, but with a tail extending to very high luminosities of ∼1048 erg s−1. 66 per cent of the reddened quasars are detected at >3σ at 22 μm by WISE. The average 6-μm rest-frame luminosity is log10(L6 μm/ erg s−1) = 47.1 ± 0.4, making the objects among the mid-infrared brightest active galactic nuclei (AGN) currently known. The extinction-corrected space density estimate now extends over three magnitudes (−30 < Mi < −27) and demonstrates that the reddened quasar luminosity function is significantly flatter than that of the unobscured quasar population at z = 2–3. At the brightest magnitudes, Mi ≲ −29, the space density of our dust-reddened population exceeds that of unobscured quasars. A model where the probability that a quasar becomes dust reddened increases at high luminosity is consistent with the observations and such a dependence could be explained by an increase in luminosity and extinction during AGN-fuelling phases. The properties of our obscured type 1 quasars are distinct from the heavily obscured, Compton-thick AGN that have been identified at much fainter luminosities and we conclude that they likely correspond to a brief evolutionary phase in massive galaxy formation.

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Heavily reddened type 1 quasars at z 2 I Evidence for significant obscured black-hole growth at the highest quasar luminosities - Accepted Manuscript
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Accepted/In Press date: 11 December 2014
e-pub ahead of print date: 27 January 2015
Published date: 11 March 2015
Additional Information: arxiv is am

Identifiers

Local EPrints ID: 443889
URI: http://eprints.soton.ac.uk/id/eprint/443889
ISSN: 0035-8711
PURE UUID: 848eeb5b-274d-49fb-a34a-3479671ca2ee

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Date deposited: 16 Sep 2020 16:34
Last modified: 25 Nov 2021 23:06

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Contributors

Author: Manda Banerji
Author: S. Alaghband-Zadeh
Author: Paul C. Hewett
Author: Richard G. Mcmahon

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