Seeking the epoch of maximum luminosity for dusty quasars
- Department of Theoretical Physics, Faculty of Physics, Yerevan State University, Yerevan, 0025 (Armenia)
- Center for Radiophysics and Space Research, Cornell University, Ithaca, NY 14853 (United States)
Infrared luminosities νL{sub ν}(7.8 μm) arising from dust reradiation are determined for Sloan Digital Sky Survey (SDSS) quasars with 1.4 < 5 using detections at 22 μm by the Wide-Field Infrared Survey Explorer. Infrared luminosity does not show a maximum at any redshift z < 5, reaching a plateau for z ≳ 3 with maximum luminosity νL{sub ν}(7.8 μm) ≳ 10{sup 47} erg s{sup –1}; luminosity functions show one quasar Gpc{sup –3} having νL{sub ν}(7.8 μm) > 10{sup 46.6} erg s{sup –1} for all 2 < 5. We conclude that the epoch when quasars first reached their maximum luminosity has not yet been identified at any redshift below 5. The most ultraviolet luminous quasars, defined by rest frame νL{sub ν}(0.25 μm), have the largest values of the ratio νL{sub ν}(0.25 μm)/νL{sub ν}(7.8 μm) with a maximum ratio at z = 2.9. From these results, we conclude that the quasars most luminous in the ultraviolet have the smallest dust content and appear luminous primarily because of lessened extinction. Observed ultraviolet/infrared luminosity ratios are used to define 'obscured' quasars as those having >5 mag of ultraviolet extinction. We present a new summary of obscured quasars discovered with the Spitzer Infrared Spectrograph and determine the infrared luminosity function of these obscured quasars at z ∼ 2.1. This is compared with infrared luminosity functions of optically discovered, unobscured quasars in the SDSS and in the AGN and Galaxy Evolution Survey. The comparison indicates comparable numbers of obscured and unobscured quasars at z ∼ 2.1 with a possible excess of obscured quasars at fainter luminosities.
- OSTI ID:
- 22365541
- Journal Information:
- Astrophysical Journal, Vol. 790, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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