The resolved star-formation efficiency of early-type galaxies

Thomas G. Williams; Francesco Belfiore; Martin Bureau; Ashley T. Barnes; Frank Bigiel; Woorak Choi; Ryan Chown; Dario Colombo; Daniel A. Dale; Timothy A. Davis; Jacob Elford; Jindra Gensior; Simon C. O. Glover; Brent Groves; Ralf S. Klessen; Fu-Heng Liang; Hsi-An Pan; Ilaria Ruffa; Toshiki Saito; Patricia Sánchez-Blázquez; Marc Sarzi; Eva Schinnerer

arXiv · 2503.17440

The resolved star-formation efficiency of early-type galaxies

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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 ten 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.

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Thomas G. Williams, Francesco Belfiore, Martin Bureau, Ashley T. Barnes, Frank Bigiel, Woorak Choi, Ryan Chown, Dario Colombo, Daniel A. Dale, Timothy A. Davis, Jacob Elford, Jindra Gensior, Simon C. O. Glover, Brent Groves, Ralf S. Klessen, Fu-Heng Liang, Hsi-An Pan, Ilaria Ruffa, Toshiki Saito, Patricia Sánchez-Blázquez, Marc Sarzi, Eva Schinnerer. 2025-03-21. The resolved star-formation efficiency of early-type galaxies. https://arxiv.org/abs/2503.17440

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