2024/06/03 by Anan Lu, Daryl Haggard, Lu, Anan +37 · 1 citation
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Astrophysical Phenomena and Observations
paper · pdf · doi:10.48550/arxiv.2406.01291
Early-type galaxies (ETGs) are known to harbour dense spheroids of stars but scarce star formation (SF). Approximately a quarter of these galaxies have rich molecular gas reservoirs yet do not form stars efficiently. We study here the ETG NGC~524, with strong shear suspected to result in a smooth molecular gas disc and low star-formation efficiency (SFE). We present new spatially-resolved observations of the \textsuperscript12CO(2-1)-emitting cold molecular gas from the Atacama Large Millimeter/sub-millimeter Array (ALMA) and of the warm ionised-gas emission lines from SITELLE at the Canada-France-Hawaii Telescope. Although constrained by the resolution of the ALMA observations (≈37~pc), we identify only 52 GMCs with radii ranging from 30 to 140~pc, a low mean molecular gas mass surface density ⟨Σ\rm gas⟩≈125~M_\odot~pc-2 and a high mean virial parameter ⟨α\rm obs,vir⟩≈5.3. We measure spatially-resolved molecular gas depletion times (τ\rm dep≡1/\rm SFE) with a spatial resolution of ≈100~pc within a galactocentric distance of 1.5~kpc. The global depletion time is ≈2.0~Gyr but τ\rm dep increases toward the galaxy centre, with a maximum τ\rm dep,max≈5.2~Gyr. However, no pure \ionHII region is identified in NGC~524 using ionised-gas emission-line ratio diagnostics, so the τ\rm dep inferred are in fact lower limits. Measuring the GMC properties and dynamical states, we conclude that shear is the dominant mechanism shaping the molecular gas properties and regulating SF in NGC~524. This is supported by analogous analyses of the GMCs in a simulated ETG similar to NGC~524.