The host galaxy/AGN connection in nearby early-type galaxies. Sample selection and hosts brightness profiles

TL;DR

This study investigates the relationship between radio and optical properties of nearby early-type galaxies, focusing on their brightness profiles and nuclear activity, revealing that bright radio sources are linked to core galaxies, while fainter sources are found in both core and power-law types.

Contribution

It introduces a new classification of early-type galaxies based on brightness profile slopes and analyzes their radio-optical properties, expanding understanding of AGN-host connections.

Findings

Bright radio sources are associated with core galaxies.

Below a certain radio luminosity, core and power-law galaxies show similar properties.

Optically nucleated galaxies are more common in the sample.

Abstract

This is the first of a series of three papers exploring the connection between the multiwavelength properties of AGNs in nearby early-type galaxies and the characteristics of their hosts. We selected two samples, both with high resolution 5 GHz VLA observations available and providing measurements down to 1 mJy level, reaching radio-luminosities as low as 10^19 W/Hz. We focus on the 116 radio-detected galaxies as to boost the fraction of AGN with respect to a purely optically selected sample. Here we present the analysis of the optical brightness profiles based on archival HST images, available for 65 objects. We separate early-type galaxies on the basis of the slope of their nuclear brightness profiles, into core and power-law galaxies following the Nuker's scheme, rather than on the traditional morphological classification (i.e. into E and S0 galaxies). Our sample of AGN candidates is indistinguishable, when their brightness profiles are concerned, from galaxies of similar optical luminosity but hosting weaker (or no) radio-sources. We confirm previous findings that relatively bright radio-sources (L_r > 10^(21.5) W/Hz) are uniquely associated to core galaxies. However, below this threshold in radio-luminosity core and power-law galaxies coexist and they do not show any apparent difference in their radio-properties. Not surprisingly, since our sample is deliberately biased to favour the inclusion of active galaxies, we found a higher fraction of optically nucleated galaxies. Addressing the multiwavelength properties of these nuclei will be the aim of the two forthcoming papers.