Star-Formation in Low Radio Luminosity AGN from the Sloan Digital Sky Survey

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We investigate faint radio emission from low- to high-luminosity Active Galactic Nuclei (AGN) selected from the Sloan Digital Sky Survey (SDSS). Their radio properties are inferred by coadding large ensembles of radio image cut-outs from the FIRST survey, as almost all of the sources are individually undetected. We correlate the median radio flux densities against a range of other sample properties, including median values for redshift, [O III] luminosity, emission line ratios, and the strength of the 4000{angstrom} break. We detect a strong trend for sources that are actively undergoing star-formation to have excess radio emission beyond the {approx} 10{sup ... continued below

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de Vries, W H; Hodge, J A; Becker, R H; White, R L & Helfand, D J April 18, 2007.

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We investigate faint radio emission from low- to high-luminosity Active Galactic Nuclei (AGN) selected from the Sloan Digital Sky Survey (SDSS). Their radio properties are inferred by coadding large ensembles of radio image cut-outs from the FIRST survey, as almost all of the sources are individually undetected. We correlate the median radio flux densities against a range of other sample properties, including median values for redshift, [O III] luminosity, emission line ratios, and the strength of the 4000{angstrom} break. We detect a strong trend for sources that are actively undergoing star-formation to have excess radio emission beyond the {approx} 10{sup 28} ergs s{sup -1} Hz{sup -1} level found for sources without any discernible star-formation. Furthermore, this additional radio emission correlates well with the strength of the 4000{angstrom} break in the optical spectrum, and may be used to assess the age of the star-forming component. We examine two subsamples, one containing the systems with emission line ratios most like star-forming systems, and one with the sources that have characteristic AGN ratios. This division also separates the mechanism responsible for the radio emission (star-formation vs. AGN). For both cases we find a strong, almost identical, correlation between [O III] and radio luminosity, with the AGN sample extending toward lower, and the star-formation sample toward higher luminosities. A clearer separation between the two subsamples is seen as function of the central velocity dispersion {sigma} of the host galaxy. For systems at similar redshifts and values of {sigma}, the star-formation subsample is brighter than the AGN in the radio by an order of magnitude. This underlines the notion that the radio emission in star-forming systems can dominate the emission associated with the AGN.

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PDF-file: 17 pages; size: 0.7 Mbytes

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  • Journal Name: Astronomical Journal, vol. 134, N/A, August 1, 2007, pp. 457-465; Journal Volume: 134

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  • Report No.: UCRL-JRNL-230492
  • Grant Number: W-7405-ENG-48
  • Office of Scientific & Technical Information Report Number: 940897
  • Archival Resource Key: ark:/67531/metadc899784

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  • April 18, 2007

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  • Sept. 27, 2016, 1:39 a.m.

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  • Dec. 2, 2016, 12:36 p.m.

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de Vries, W H; Hodge, J A; Becker, R H; White, R L & Helfand, D J. Star-Formation in Low Radio Luminosity AGN from the Sloan Digital Sky Survey, article, April 18, 2007; Livermore, California. (digital.library.unt.edu/ark:/67531/metadc899784/: accessed November 17, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.