Shanghai Astronomical Observatory Astrophysics Colloquium

Title：Evolution of Cold Gas Fraction, Depletion Time and Kinematics of High-redshift Galaxies

Speaker：Daizhong Liu (刘岱钟) (Purple Mountain Observatory )

Time：3:00 pm June 20th (Thursday)

Tencent Meeting：42915400486 password: 6360

Location: Lecture Hall, 3rd floor

Abstract：

Cold gas is the raw material that collapses and forms new stars in galaxies, thus it plays a crucial role in galaxy evolution. Understanding what drives the amount of cold gas (cold gas fraction), the consuming time of cold gas (depletion time), and how gas kinematics change with cosmic time are fundamental quests for a complete view of galaxy evolution. I will first highlight our work named the Automated Mining of the ALMA Archive in COSMOS (A3COSMOS) project, where we utilize hundreds of hours of public ALMA (sub)millimeter archival observations to obtain statistical knowledge of galaxy evolution. The A3COSMOS project has led to the constraining of cold gas fraction and depletion time ‘scaling relations’ and cosmic molecular gas density evolution from redshift z~0–6, and it has become a useful resource for the community. I will also highlight recent studies of cold and ionized gas kinematics in high-redshift galaxies, including our recent high-resolution (sub)millimeter interferometry and near-infrared integral field unit (IFU) studies of strongly lensed ultraluminous and hyperluminous galaxies at z~2, which show surprisingly regular rotation and massive turbulent gas-rich disks. I will discuss the ‘paradigm’ of star-forming galaxy evolution established based on two decades of rest-frame optical imaging and IFU studies at z~1–3, and how the recent (sub)millimeter interferometric studies of z~4–5 starbursts show worrisome controversial results. I will summarize the talk with the current understanding of the ‘paradigm’ of massive main-sequence galaxy evolution, which has been established over the last two decades but is facing new challenges, and the future of galaxy evolution with next-generation telescopes.

CV：Daizhong Liu (刘岱钟) is currently a researcher at the Purple Mountain Observatory (PMO). He obtained the B.S. degree from the astronomy department of Nanjing University in 2010, and the PhD from PMO in 2016. From 2016 to 2020, he conducted post-doctoral research at the Max Planck Institute for Astronomy (MPIA) in Heidelberg. Then, from 2020 to 2024, he did post-doctoral research at the Max Planck Institute for Extraterrestrial Physics (MPE) in Garching bei Munich. His research interest includes submillimeter galaxies, molecular gas, star formation in galaxies, ISM, kinematics, and galaxy evolution. He is part of the Physics at High Angular resolution in Nearby GalaxieS (PHANGS), the Cosmic Evolution Survey (COSMOS), and the Atacama Large Aperture Submillimeter Telescope (AtLAST) projects. His recent works include gas fraction and depletion time scaling relations, atomic carbon (CI) and CO excitation in nearby galaxies, high-resolution cold and ionized gas imaging in high-z starbursts, kinematics of high-z galaxies, and participating in submillimeter experiments at the PMO.

 Koushare link to the recorded presentation