[Astro] Lunch Talk - 5/6/25

[Joseph Butler]

Hi everyone,

This week’s lunch talk will be given by Guillaume, at 1pm Thursday in A113. Title and abstract are below.

Title: No hidden monsters: Probing recently-quenched galaxies for obscured AGN with JWST

Abstract: This talk presents a mid-infrared study of recently-quenched galaxies with JWST, with the aim of searching for obscured AGN activity. We focus on the transition class of post-starburst galaxies (PSBs) which provide insight into the intermediate stage of galaxy evolution between star-forming and quiescent, a necessity for understanding what drives quenching and galaxy bimodality. For massive galaxies (M* > 10^10), quenching models frequently invoke AGN feedback, and PSBs often exhibit strong outflows, consistent with this scenario. However, recent studies of massive PSBs have found no evidence of excess AGN activity from their X-ray and optical properties. This lack of activity indicates either AGN are not the main quenching mechanism, are short-lived and do not linger into the PSB phase, or are heavily obscured. If dust obscured, the presence of AGN activity could still be detected through the infrared (IR) emission of this hot dust. To test this, we use a sample of ∼150 photometrically-selected PSBs within the PRIMER-UDS field at 0.5 < z < 3.0, and utilise the 7.7 μm and 18 μm JWST/MIRI photometry (as well as an additional eight NIRCam and three HST wavebands) to probe the IR dust emission of these galaxies. We find interesting differences between low and high-mass PSBs, and interestingly no excess dust emission within the high-mass galaxies. This indicates there are no hidden AGN, or indeed residual star-formation within these galaxies. I will discuss the implications of these results on the current understanding of what quenches massive galaxies at these redshifts.

Thanks,
Joe
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