On the nature of the near-UV extended light in Seyfert galaxies

TL;DR

This study investigates the origin of near-UV extended emission in Seyfert galaxies, finding that ionized gas emission dominates in half, while the rest is mainly from the galactic bulge or possibly scattered AGN light or young stars.

Contribution

It provides a detailed analysis of the components contributing to near-UV emission in Seyfert galaxies using multi-band and high-resolution imaging, clarifying the nature of the extended UV light.

Findings

Ionized gas dominates near-UV emission in half of the sample.

Remaining emission mainly from galactic bulge or scattered AGN light.

Presence of star-forming regions and off-nuclear clusters in some galaxies.

Abstract

We study the nature of the extended near-UV emission in the inner kiloparsec of a sample of 15 Seyfert galaxies which have both near-UV (F330W) and narrow band [OIII] high resolution Hubble images. For the majority of the objects we find a very similar morphology in both bands. From the [OIII] images we construct synthetic images of the nebular continuum plus the emission line contribution expected through the F330W filter, which can be subtracted from the F330W images. We find that the emission of the ionised gas dominates the near-UV extended emission in half of the objects. A further broad band photometric study, in the bands F330W (U), F547M (V) and F160W (H), shows that the remaining emission is dominated by the underlying galactic bulge contribution. We also find a blue component whose nature is not clear in 4 out of 15 objects. This component may be attributed to scattered light from the AGN, to a young stellar population in unresolved star clusters, or to early-disrupted clusters. Star forming regions and/or bright off-nuclear star clusters are observed in 4/15 galaxies of the sample.