Host galaxy of low-luminosity compact sources

Abstract

The term `active galactic nuclei' (AGN) is applied to a huge variety of objects, classified on the basis of their properties at different wavelengths. Peaked sources (PSs) represent a class of AGN at the first stage of evolution, characterised by a peaked radio spectrum. Among these radio sources, low-luminosity compact (LLC) sources can be identified as PSs accreting with a high Eddington rate, harbouring low-power jets, and hosting low-mass black holes. These properties are also shared by narrow-line Seyfert 1 galaxies (NLS1s). In 2016, LLCs were hypothesised to be the parent population of NLS1s with a flat radio spectrum (F-NLS1s), suggesting that the former may be the same objects as the latter but, instead, seen at a higher inclination. Based on radio luminosity functions and optical spectra analysis, ten LLCs were identified as valid F-NLS1s candidates. To account for the missing piece to the puzzle and verifying whether these LLCs could be hosted in late-type galaxies as NLS1s, we performed a photometric decomposition of their Pan-STARRS1 images in all five filters. We used the 2D fitting algorithm GALFIT for the single-band analysis and its extension GALFITM for the multi-band analysis. Considering that the morphological type and the structural parameters of the host may be dependent on the wavelength, we found six out of ten LLCs hosted in late-type galaxies, probably with pseudo-bulges, along with three point-like sources and one object of an uncertain classification. Although this study is based on a small sample, it represents the first morphological analysis of LLC host galaxies. These results confirm the trend observed in NLS1s, indicating late-type and disc-like host galaxies for LLCs and supporting the validity of the parent population scenario.