WISDOM project - XXIII. Star-formation efficiencies of eight early-type galaxies and bulges observed with SITELLE and ALMA

Lu, Anan, Haggard, Daryl, Bureau, Martin, Gensior, Jindra, Robert, Carmelle, Williams, Thomas G., Liang, Fu-Heng, Choi, Woorak, Davis, Timothy A. ORCID: https://orcid.org/0000-0003-4932-9379, Ruffa, Ilaria, Babic, Sara, Boyce, Hope, Cappellari, Michele, Cheung, Benjamin, Drissen, Laurent, Elford, Jacob S., Martin, Thomas, Rhea, Carter, Rousseau-Nepton, Laurie, Sarzi, Marc and Zhang, Hengyue 2025. WISDOM project - XXIII. Star-formation efficiencies of eight early-type galaxies and bulges observed with SITELLE and ALMA. Monthly Notices of the Royal Astronomical Society 540 (1) , 71–89. 10.1093/mnras/staf675

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Abstract

Early-type galaxies (ETGs) are known to harbour dense spheroids of stars with scarce star formation (SF). Approximately a quarter of these galaxies have rich molecular gas reservoirs yet do not form stars efficiently. These gas-rich ETGs have properties similar to those of bulges at the centres of spiral galaxies. We use spatially resolved observations (⁠ pc resolution) of warm ionized-gas emission lines (H  ⁠, [O iii], [N ii], H  ⁠, and [S ii]) from the imaging Fourier transform spectrograph SITELLE at the Canada–France–Hawaii Telescope and cold molecular gas [12CO(2–1) or 12CO(3–2)] from the Atacama Large Millimeter/submillimeter Array to study the SF properties of eight ETGs and bulges. We use the ionized-gas emission lines to classify the ionization mechanisms and demonstrate a complete absence of regions dominated by SF ionization in these ETGs and bulges, despite abundant cold molecular gas. The ionization classifications also show that our ETGs and bulges are dominated by old stellar populations. We use the molecular gas surface densities and H  -derived SF rates (in spiral galaxies outside of the bulges) or upper limits (in ETGs and bulges) to constrain the depletion times (inverse of the SF efficiencies), suggesting again suppressed SF in our ETGs and bulges. Finally, we use the molecular gas velocity fields to measure the gas kinematics, and show that bulge dynamics, particularly the strong shear due to the deep and steep gravitational potential wells, is an important SF regulation mechanism for at least half of our sample galaxies.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Schools > Physics and Astronomy
Publisher:	Oxford University Press
ISSN:	0035-8711
Date of First Compliant Deposit:	15 May 2025
Date of Acceptance:	11 April 2025
Last Modified:	27 May 2025 10:00
URI:	https://orca.cardiff.ac.uk/id/eprint/178307

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