Enhanced UV emission knot in the giant radio galaxy NGC 315: Hint of patchy star formation?

TL;DR

High-resolution UV observations of NGC 315 reveal a UV-emitting knot likely due to ongoing star formation, potentially triggered by AGN feedback or minor mergers, with dust filaments supporting gas inflow scenarios.

Contribution

This study presents the first high-resolution UV imaging of a star-forming knot in NGC 315, linking UV emission to possible AGN or merger-driven star formation mechanisms.

Findings

UV knot has a star formation rate of 0.23±0.10 M☉/yr.

Dust filaments suggest gas inflow possibly from minor mergers or AGN activity.

No significant UV emission detected elsewhere along the dust filaments.

Abstract

High-resolution AstroSat-UltraViolet Imaging Telescope (UVIT) observations revealed a knot of UV emission, $\sim 1.7$ kpc away from the centre of NGC 315, a nearby elliptical galaxy hosting a giant (Mpc scale) radio source with a jet. We suggest that this patchy and spatially extended UV emission is likely due to ongoing star formation (SF) in the galaxy. The estimated SF rate (SFR) averaged over 100 Myr for the UV knot ($0.23\pm0.10$ M$_{\odot}$ yr$^{-1}$) is significantly higher compared to a typical elliptical galaxy. As the galaxy does not show the signatures of recent major mergers, the possible mechanisms for the triggered SF include AGN feedback or minor mergers. Hubble Space Telescope} (HST) observations reveal dust filaments that extend through a UV knot. The origin of dusty filaments, though not clear, could be associated with gas clouds as a result of a minor merger, cooled gas falling into the central BCG and/or condensing of the gas uplifted by AGN jet. No significant clumpy UV emission is observed in other regions along the dust filament. We speculate that mechanical feedback from the AGN jet could be playing a role in triggering SF in the UV knot.