Open AccessThe complex radio and X‐ray structure in the nuclear regions of the active galaxy NGC 1365
Author(s) -
Stevens Ian R.,
Forbes Duncan A.,
Norris Ray P.
Publication year - 1999
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.1999.02543.x
Subject(s) - physics , astrophysics , rosat , astronomy , active galactic nucleus , x shaped radio galaxy , galaxy , radio galaxy , supernova
We present a multiwavelength analysis of the prominent active galaxy NGC 1365, in particular looking at the radio and X‐ray properties of the central regions of the galaxy. We analyse ROSAT (PSPC and HRI) observations of NGC 1365, and discuss recent ASCA results. In addition to a number of point sources in the vicinity of NGC 1365, we find a region of extended X‐ray emission extending along the central bar of the galaxy, combined with an emission peak near the centre of the galaxy. This central X‐ray emission is centred on the optical/radio nucleus, but is spatially extended. The X‐ray spectrum can be well fitted by a thermal plasma model, with a temperature of kT =0.6–0.8 keV and a very low local absorbing column. The thermal spectrum is suggestive of starburst emission rather than emission from a central black hole. The ATCA radio observations show a number of hotspots, located in a ring around a weak radio nucleus. Synchrotron emission from electrons accelerated by supernovae and supernova remnants (SNRs) is the likely origin of these hotspots. The radio nucleus has a steep spectrum, indicative perhaps of an active galactic nucleus (AGN) or SNRs. The evidence for a jet emanating from the nucleus (as has been previously claimed) is at best marginal. The extent of the radio ring is comparable to that of the extended central X‐ray source. We discuss the nature of the central activity in NGC 1365 in the light of these observations. The extended X‐ray emission and the thermal spectra strongly suggest that at soft X‐ray energies we are not seeing emission predominantly from a central black hole, although the presence of Fe K line emission at higher energies does suggest the presence of an AGN. Consequently, a black hole is probably not the dominant contributor to the energetics of the central regions of NGC 1365 at radio, optical or soft X‐ray wavelengths. Activity associated with a starburst is likely the dominant explanation for the observed properties of NGC 1365.