UVIT Survey of AGN host Galaxies -- I: Star Formation Scenarios

TL;DR

This study uses UVIT observations to analyze star formation in seven Seyfert AGN and one LINER galaxy, revealing correlations between star formation, extinction, and AGN activity, with effects mainly confined to nuclear regions.

Contribution

First UVIT-based survey of star formation in AGN host galaxies across multiple scales, highlighting the localized influence of AGN on star formation.

Findings

Positive correlation between star formation surface density and extinction.

Gradual decrease of extinction and star formation rate from center to outskirts in some galaxies.

AGN activity influences nuclear star formation but has limited impact on larger scales.

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 {\it AstroSat} in the near ultra-Violet (NUV; 2000-3000 \AA) and far ultra-Violet (FUV; 2000-3000 \AA) 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 ($\Sigma_{SFR}$) 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 $\Sigma_{SFR}$ 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.