The host galaxy/AGN connection*
Brightness profiles of early-type galaxies hosting Seyfert nuclei
INAF - Osservatorio Astronomico di Torino, Strada Osservatorio 20, 10025 Pino Torinese, Italy e-mail: [capetti;balmaverde]@oato.inaf.it
Accepted: 15 March 2007
We recently presented evidence of a connection between the brightness profiles of nearby early-type galaxies and the properties of the AGN they host. The radio loudness of the AGN appears to be univocally related to the host's brightness profile: radio-loud nuclei are only hosted by “core” galaxies while radio-quiet AGN are only found in “power-law” galaxies. We extend our analysis here to a sample of 42 nearby ( 7000 km s-1) Seyfert galaxies hosted by early-type galaxies. From the nuclear point of view, they show a large deficit of radio emission (at a given X-ray or narrow line luminosity) with respect to radio-loud AGN, conforming with their identification as radio-quiet AGN. We used the available HST images to study their brightness profiles. Having excluded complex and highly nucleated galaxies, in the remaining 16 objects the brightness profiles can be successfully modeled with a Nuker law with a steep nuclear cusp characteristic of “power-law” galaxies (with logarithmic slope γ = 0.51-1.07). This result is what is expected for these radio-quiet AGN based on our previous findings, thus extending the validity of the connection between brightness profile and radio loudness to AGN of a far higher luminosity. We explored the robustness of this result against a different choice of the analytic form for the brightness profiles, using a Sérsic law. In no object could we find evidence of a central light deficit with respect to a pure Sérsic model, the defining feature of “core” galaxies in this modeling framework. We conclude that, regardless of the modeling strategy, the dichotomy of AGN radio loudness can be univocally related to the host's brightness profile. Our general results can be re-phrased as “radio-loud nuclei are hosted by core galaxies, while radio-quiet AGN are found in non-core galaxies”.
Key words: galaxies: active / galaxies: Seyfert / galaxies: bulges / galaxies: nuclei / galaxies: elliptical and lenticular, cD
© ESO, 2007