Compact Radio Cores and Nuclear Activity in Seyfert Galaxies

Abstract

Using recent high-resolution (<0.1") radio observations of a large sample of Seyfert galaxies (Roy et al., 1994), we analyze the relations between their compact radio core emission and several nuclear and host galaxy properties (galaxy morphology, optical, infrared, X-ray, extended radio emissions, interaction parameters, and some emission line properties). We apply survival analysis techniques in order to exploit the information contained in the numerous "censored" data (upper limits on fluxes).We find that Seyfert nuclei hosted in early-type galaxies are, on average, characterized by stronger radio core emission than the norm for Seyfert galaxies. Galaxies with a nearby companion display enhanced radio core emission with respect to objects without companions. Furthermore, we confirm that Seyfert types 2 host more powerful compact radio cores than types 1.Remarkably, radio core emission appears to be unrelated to optical, near-infrared, and far-infrared radiations, but shows some correlation with total radio emission and with tracers of nuclear activity such as the IRAS 12 and 25 µm band, hard X-ray and narrow-line emissions. This favours the view that Seyfert radio cores are typically powered by AGN rather than by radio supernovae.A link between radio core strength and bolometric luminosity is suggested, in analogy to what is observed in the cores of radio-quiet QSOs.

Seyfert galaxies and the radio--far-infrared correlation

“…Both Kendall's tau and Spearman's rho correlation tests returned a probability of < 0.01 per cent that the core and total luminosities are not correlated. This is consistent with similar results by Giuricin, Fadda & Mezzetti (1996) and others.…”

Nuclear Luminosities and Radio Loudness of Seyfert Nuclei

“…Moreover, with our deÐ-nition of the radio loudness parameter, each of two radio classes plausibly follows its own correlation. Of the three radio-optical correlations for Seyfert galaxies, the best known is that involving the [O III] luminosity (de Bruyn & Wilson 1978 ;Whittle 1985Whittle , 1992bGiuricin, Fadda, & Mezzetti 1996). Our results improve on the previous studies in several respects.…”

“…Second, its scatter is considerably reduced, most likely because of the high detection rate, the homogeneity of our sample, and the fact that we have restricted ourselves only to type 1 sources. Third, we (as do Giuricin et al 1996) explicitly account for distance e †ects. And fourth, we expand on the dynamic range of the luminosities, not only toward weaker sources but also connecting with the quasar domain.…”

“…The integrated optical luminosities do correlate with radio power (Isobe, Feigelson, & Nelson 1986 ;Edelson 1987 ;Giuricin et al 1990), but evidently not when distance e †ects are considered (Giuricin et al 1996). Giuricin et al (1996) collected groundbased nuclear magnitudes for a heterogeneous sample of Seyfert 1 nuclei, and these, too, were found to be intrinsically decoupled from the radio powers. Our sample, on the contrary, shows a strong, intrinsic correlation between P 6 cm and (Fig.…”

The relationship between radio power at 22 and 43 GHz and black hole properties of AGN in elliptical galaxies

“…There is a relationship between the radio power and luminosity of optical emission lines in active galaxies such as Seyfert (de Bruyn & Wilson 1978;Whittle 1985Whittle , 1992Giuricin et al 1996) and powerful radio galaxies (Baum & Heckman 1989 which suggests that the [OIII] emission line can be used to estimate the strength of AGN activity (Mulchaey et al 1994). We discussed the relationship between radio and [OIII] λ5007 emission line luminosity and investigated whether radio emission by AGN is relevant to optical AGN activity.…”