THE TWO-COMPONENT RADIO LUMINOSITY FUNCTION OF QUASI-STELLAR OBJECTS: STAR FORMATION AND ACTIVE GALACTIC NUCLEUS
- National Radio Astronomy Observatory, 520 Edgemont Rd., Charlottesville, VA 22903 (United States)
- Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States)
Despite decades of study, it remains unclear whether there are distinct radio-loud and radio-quiet populations of quasi-stellar objects (QSOs). Early studies were limited by inhomogeneous QSO samples, inadequate sensitivity to probe the radio-quiet population, and degeneracy between redshift and luminosity for flux-density-limited samples. Our new 6 GHz Expanded Very Large Array (EVLA) observations allow us for the first time to obtain nearly complete (97%) radio detections in a volume-limited color-selected sample of 179 QSOs more luminous than M{sub i} = -23 from the Sloan Digital Sky Survey (SDSS) Data Release Seven in the narrow redshift range 0.2 < z < 0.3. The dramatic improvement in radio continuum sensitivity made possible with the new EVLA allows us, in 35 minutes of integration, to detect sources as faint as 20 {mu}Jy, or log [L{sub 6GHz}(W Hz{sup -1})] {approx} 21.5 at z = 0.25, well below the radio luminosity, log [L{sub 6}(W Hz{sup -1})] {approx} 22.5, that separates star-forming galaxies from radio-loud active galactic nuclei (AGNs) driven by accretion onto a supermassive black hole. We calculate the radio luminosity function (RLF) for these QSOs using three constraints: (1) EVLA 6 GHz observations for log [L{sub 6}(W Hz{sup -1})] < 23.5, (2) NRAO-VLA Sky Survey observations for log [L{sub 6}(W Hz{sup -1})] > 23.5, and (3) the total number of SDSS QSOs in our volume-limited sample. We show that the RLF can be explained as a superposition of two populations, dominated by AGNs at the bright end and star formation in the QSO host galaxies at the faint end.
- OSTI ID:
- 21565463
- Journal Information:
- Astrophysical Journal Letters, Vol. 739, Issue 1; Other Information: DOI: 10.1088/2041-8205/739/1/L29; ISSN 2041-8205
- Country of Publication:
- United States
- Language:
- English
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