UVIT Survey of AGN host Galaxies – I: Star Formation Scenarios
arxiv(2024)
Abstract
Circumnuclear star formation (SF) is generally seen in galaxies hosting
active galactic nuclei (AGN); however, the connection between the AGN activity
and SF in them is less well understood. To explore this connection on scales of
a few tens of parsec to a few tens of kiloparsec and larger, we carried out an
investigation of SF in seven Seyfert type AGN and one LINER galaxy, using
observations with the Ultra-Violet Imaging Telescope (UVIT) on board AstroSat in the near ultra-Violet (NUV; 2000-3000 Å) and far ultra-Violet
(FUV; 2000-3000 Å) bands. A total of 1742 star-forming regions were
identified, having size scales of 0.010 to 63.642 kpc^2. Considering all the
galaxies, we found a positive correlation between their total surface density
of SF (Σ_SFR) and extinction. For five galaxies, namely NGC 1365, NGC
4051, NGC 4321, NGC 5033 and NGC 6814, we found a gradual decrease of both
extinction and Σ_SFR from the centre to the outer regions. Four
sources are found to lie in the main sequence (MS) of star-forming galaxies,
and the other four are away from MS. We found the ratio of the star formation
rate (SFR) in the nuclear region to the total SFR to be positively correlated
with the Eddington ratio. This points to the influence of AGN on enhancing the
SF characteristics of the hosts. However, the impact is dominant only in the
central nuclear region with no significant effect on the larger scales probed
in this work.
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