The resolved star-formation efficiency of early-type galaxies

Williams, Thomas G., Belfiore, Francesco, Bureau, Martin, Barnes, Ashley T., Bigiel, Frank, Choi, Woorak, Chown, Ryan, Colombo, Dario, Dale, Daniel A., Davis, Timothy A. ORCID: https://orcid.org/0000-0003-4932-9379, Elford, Jacob, Gensior, Jindra, Glover, Simon C. O., Groves, Brent, Klessen, Ralf S, Liang, Fu-Heng, Pan, Hsi-An, Ruffa, Ilaria, Saito, Toshiki, Sánchez-Blázquez, Patricia, Sarzi, Marc and Schinnerer, Eva 2025. The resolved star-formation efficiency of early-type galaxies. Monthly Notices of the Royal Astronomical Society 538 (4) , pp. 3219-3246. 10.1093/mnras/staf498

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Abstract

Understanding how and why star formation varies between galaxies is fundamental to our comprehension of galaxy evolution. In particular, the star-formation efficiency (SFE; star-formation rate or SFR per unit cold gas mass) has been shown to vary substantially both across and within galaxies. Early-type galaxies (ETGs) constitute an extreme case, as about a quarter have detectable molecular gas reservoirs but little to no detectable star formation. In this work, we present a spatially resolved view of the SFE in 10 ETGs, combining state-of-the-art Atacama Large Millimeter/submillimeter Array (ALMA) and Multi Unit Spectroscopic Explorer (MUSE) observations. Optical spectroscopic line diagnostics are used to identify the ionized emission regions dominated by star formation, and reject regions where the ionization arises primarily from other sources. We identify very few regions where the ionization is consistent with pure star formation. Using ${\rm H}\alpha$ as our SFR tracer, we find that previous integrated measurements of the star-formation rate based on UV and 22 $\mu$m emission are systematically higher than the SFR measured from ${\rm H}\alpha$. However, for the small number of regions where ionization is primarily associated with star formation, the SFEs are around 0.4 dex higher than those measured in star-forming galaxies at a similar spatial resolution (with depletion times ranging from $10^8$ to $10^{10}$ yr). Whilst the SFE of ETGs is overall low, we find that the SFEs of individual regions within ETGs can be similar to, or higher than, similar sized regions within star-forming galaxies.

Item Type:	Article
Date Type:	Published Online
Status:	Published
Schools:	Schools > Physics and Astronomy
Additional Information:	License information from Publisher: LICENSE 1: URL: https://creativecommons.org/licenses/by/4.0/, Start Date: 2025-03-27
Publisher:	Oxford University Press
ISSN:	0035-8711
Date of First Compliant Deposit:	14 April 2025
Date of Acceptance:	21 March 2025
Last Modified:	14 Apr 2025 09:46
URI:	https://orca.cardiff.ac.uk/id/eprint/177637

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