Ultra-Violet Imaging Telescope Observations of the Star-Forming Ring in NGC7252: Evidence of Possible AGN Feedback Suppressing Central Star Formation

TL;DR

This study uses high-resolution UV imaging to reveal a star-forming ring in NGC7252, suggesting recent star formation activity possibly influenced by past AGN feedback that suppressed central star formation.

Contribution

It provides new high-resolution UV observations of NGC7252, identifying a young star-forming ring and linking it to potential AGN feedback effects on the galaxy's central star formation.

Findings

A blue circumnuclear ring of ~3.2 kpc diameter with young stellar populations.

Presence of younger star-forming clumps within the ring.

Evidence suggesting AGN feedback may have suppressed star formation in the galaxy's core.

Abstract

Some post-merger galaxies are known to undergo a starburst phase that quickly depletes the gas reservoir and turns it into a red-sequence galaxy, though the details are still unclear. Here we explore the pattern of recent star formation in the central region of the post-merger galaxy NGC7252 using high resolution UV images from the UVIT on ASTROSAT. The UVIT images with 1.2 and 1.4 arcsec resolution in the FUV and NUV are used to construct a FUV-NUV colour map of the central region. The FUV-NUV pixel colour map for this canonical post-merger galaxy reveals a blue circumnuclear ring of diameter $\sim$ 10 " (3.2 kpc) with bluer patches located over the ring. Based on a comparison to single stellar population models, we show that the ring is comprised of stellar populations with ages $\lesssim$ 300 Myr, with embedded star-forming clumps of younger age ($\lesssim$ 150Myr). The suppressed star formation in the central region, along with the recent finding of a large amount of ionised gas, leads us to speculate that this ring may be connected to past feedback from a central super-massive black hole that has ionised the hydrogen gas in the central $\sim$ 4" $\sim$ 1.3 kpc.