Radio Emission from non-Radio Emitting Galaxies

Details Radio Emission from non-Radio Emitting Galaxies Radio Emission from non-Radio Emitting Galaxies

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...211.9526h&link_type=abstract

American Astronomical Society, AAS Meeting #211, #95.26; Bulletin of the American Astronomical Society, Vol. 39, p.898

Astronomy and Astrophysics

Astronomy

Scientific paper

We investigate the radio emission of 185,000 quiescent galaxies selected from the Sloan Digital Sky Survey. By median-stacking FIRST cutouts centered on the optically-selected sources, we are able to reach very low levels of 1.4 GHz flux density. The quiescent galaxy sample is composed of two subgroups inhabiting vastly different regimes: those targeted for the MAIN Galaxy Sample ( 55%), and those targeted for the Luminous Red Galaxy (LRG) Sample ( 45%). We find the behavior of the MAIN galaxy sample to be similar to that of the star forming sample, which we use to calibrate a radio-SFR conversion. We confirm a tight power-law dependence for the star forming sample, where LR (SFR)1.37. For the MAIN sample quiescent galaxies, this translates into SFRs of up to 10 solar masses/yr, yet they lie clearly below the sensitivity range of traditional optical emission-line diagnostics at a given absolute magnitude of the host galaxy. The total range of SFR predicted for the MAIN sample by the radio is greater than that calculated using the D4000 spectral index, though the two indicators agree around an SFR of 1 solar masses/yr. We also find that the radio-derived SFRs are significantly higher than SFRs estimated for similar populations of galaxies using analysis of UV emission. For the LRGs, the radio emission is considerably strong. However, we find the emission to be independent of SFR as derived from the D4000 spectral index, implying that a strong AGN component dominates the radio emission of these quiescent LRGs.

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