"The Cosmic Evolution of Star Formation and Molecular Gas from Redshift 0 to 6 from A3COSMOS"
Daizhong Liu
Our understanding of galaxy evolution has been revolutionized in the last decade. The evolution of galaxies’ stellar mass functions and the cosmic star formation rate (SFR) density have been reasonably well constrained out to redshift z~6. However, the evolution of the cold gas reservoir, which sets the SFR of a galaxy, has been largely unconstrained until recently.Observing molecular gas in a large sample of galaxies is challenging even with the currently most sensitive Atacama Large Millimeter/submillimeter Array (ALMA) interferometers. Recent studies of galaxies’ cold gas evolution explored redshifts up to about z~3 reporting some differed trends. As several studies have calibrated the (sub-)millimetre dust continuum as a tracer of molecular gas, we have initiated our A3COSMOS project to mine all the public ALMA archive data in the 2 sq. degree COSMOS field in a systematic way to obtain coherent dust continuum imaging. This resulted in ~2000 ALMA images covering ~230 sq. arc min with over 1500 high-confidence ALMA detections. This large sample enabled a detailed study of molecular gas fraction and depletion time in ~1663 galaxies and their evolution from today’s universe out to z~6. We find a tight scaling relation in the high-dimensional space of redshift(or cosmic time), stellar mass and SFR for these galaxies and use it to constrain the cosmic molecular gas density across time. I will further present how our result impacts our current understanding of galaxy evolution, and what breakthroughs can be expected from future studies of gas evolution with (sub-)millimeter/radio telescopes like ALMA and next generation Very Large Array (ngVLA).
"Molecular Clouds in the Nearby (Ultra-)luminous Infrared Galaxies"
Toshiki Saito
(Ultra-)luminous infrared galaxies (LIRGs and ULIRGs) form stars 10-100 times more efficiently than nearby typical spiral galaxies, which is attributed to nearby (U)LIRGs being gas-rich merging galaxies. Numerical simulations and sub-kpc observations clearly show that tidal interaction between gas-rich progenitors is condensing gas and triggering subsequent starburst activity in the nuclear region and throughout the extended disk. However, it is unclear if the properties of GMCs - the sites for star formation - in (U)LIRGs differ as well from those in spiral galaxies potentially implying important changes to current theories. In this talk,I would like to present initial results from an ongoing ALMA project aiming at providing an unprecedented, significant number of > 3,000 GMCs in (U)LIRGs.