Journal Article

A new radio loudness diagnostic for active galaxies: a radio-to-mid-infrared parameter

M. Meléndez, S. B. Kraemer and H. R. Schmitt

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 406, issue 1, pages 493-504
Published in print July 2010 | ISSN: 0035-8711
Published online July 2010 | e-ISSN: 1365-2966 | DOI:
A new radio loudness diagnostic for active galaxies: a radio-to-mid-infrared parameter

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We have studied the relationship between the nuclear (high-resolution) radio emission, at 8.4 GHz (3.6 cm) and 1.4 GHz (20 cm), the [O iv]λ25.89 μm, [Ne iii]λ15.56 μm and [Ne ii]λ12.81 μm emission lines and the black hole mass accretion rate for a sample of Seyfert galaxies. In order to characterize the radio contribution for the Seyfert nuclei we used the 8.4 GHz/[O iv] ratio, assuming that [O iv] scales with the luminosity of the active galactic nuclei (AGN). From this we find that Seyfert 1s (i.e. Seyfert 1.0s, 1.2s and 1.5s) and Seyfert 2s (i.e. Seyfert 1.8s, 1.9s and 2.0s) have similar radio contributions, relative to the AGN. On the other hand, sources in which the [Ne ii] emission is dominated either by the AGN or star formation have statistically different radio contributions, with star formation dominated sources more ‘radio loud’, by a factor of ∼2.8 on average, than AGN dominated sources. We show that star formation dominated sources with relatively larger radio contribution have smaller mass accretion rates. Overall, we suggest that 8.4 GHz/[O iv], or alternatively, 1.4 GHz/[O iv] ratios, can be used to characterize the radio contribution, relative to the AGN, without the limitation of previous methods that rely on optical observables.

Keywords: Galaxy: stellar content; galaxies: Seyfert; infrared: galaxies

Journal Article.  6938 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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