Several studies of nearby active galactic nuclei (AGN) have shown that the
soft X-ray emission presents a size and morphology that resembles that of the
narrow-line region (NLR) traced by [O III]. Since the NLR is mainly constituted
by gas photoionised by the AGN, it seems logical to assume that this is also
the primary source of the soft X-ray emission. However, these results are based
on individual sources or small samples, particularly focused on type-2 Seyfert
galaxies. Very little has been said concerning other types of AGN. The purpose
of this work is to compare the circumnuclear morphologies of soft X-ray and [O
III] images to test whether they match in different optical classes of AGN. Our
sample is composed of 27 AGN: nine type-1 Seyferts, 10 type-2 Seyferts, and
eight low ionisation nuclear emission-line regions (LINERs). We find a good
match in 100% of the type-2 Seyferts in our sample. This correspondence is less
frequent in type-1 Seyferts (22%) and it is not seen in LINERs. The good
resemblance in type-2 Seyferts constitutes an evidence for a common physical
origin. We argue that the lack of correspondence in type-1 Seyferts might be
due to the line of sight perpendicular to the accretion disk. Based on the
morphologies of the eight LINERs in our sample, we discard a common origin for
the soft X-ray and [O III] emissions in these objects. Regarding the X-ray
properties, both high column density and hard X-ray luminosity are associated
with matched morphologies.Comment: Accepted by MNRAS. 20 pages, 9 figure
