Star formation efficiency in galaxy bulges: observational results of 6 galaxies with <100 pc resolution data from ALMA and SITELLE

Anan Lu ( Université McGill )

Star formation efficiency has been shown to vary across different environments, particularly within galactic starbursts and deep within the bulges of galaxies. The bulges of galaxies share similar environments with elliptical galaxies, with rich molecular gas reservoirs but scarce star formation (SF). With the capabilities of ALMA, we can now spatially resolve the fundamental SF units, giant molecular clouds (GMCs, with size of ~10 pc), in bulges and elliptical galaxies up to ~80 Mpc away. We also measure the spatially resolved star formation rate at comparable resolution, using SITELLE at CFHT. In this talk, I will present a sample of 6 elliptical or bulge-dominated galaxies, which are observed with ALMA and SITELLE and reveal suppressed SF. I will offer two detailed case studies: (1) We find that within the central kpc of NGC 3169, the molecular gas surface densities and depletion times increase with decreasing radius, as a result of AGN feedback and bulge morphology (Lu et al. 2022). (2) In NGC 524 we measure a similar radial profile but with strong shear forces that lead to diffuse ionized gas and GMCs with low surface brightness and high virial parameters (Lu et al., submitted). I will place these results in the context of the larger sample and discuss the spatially-resolved star formation efficiencies of these galaxies, their radial profiles, as well as the lifecycle and properties of GMCs and HII regions that regulate their SF.