Image caption: The distribution of cold gas (blue) and dust (red) in the galaxy ALESS 073.1 at z~5 from ALMA observations with sub-kpc resolution (Lelli et al. 2021, Science).

Abstract: Gas dynamics plays a fundamental role in understanding the formation and evolution of galaxies. At z=0 gas dynamics has been well studied using a variety of tracers, such as the emission lines of atomic gas, molecular gas, and ionized gas. At higher z, the study of gas dynamics has mostly been restricted to warm ionized gas using H-alpha and [OIII] spectroscopy, leading to a general picture in which high-z disks have large gas clumps and are more turbulent than local ones. Over the past years, the ALMA telescope opened a new window to study galaxy dynamics at z>1 using cold neutral gas, thanks to high-J CO transitions, the [CI] lines of atomic carbon, and the [CII] line of ionized carbon. I will present in-depth studies of several galaxies at z=1-5 with high-resolution (0.1"-0.5") ALMA data of CO, [CI], and [CII] lines, depending on the redshift. The ALMA observations paint a new picture of high-z galaxies: the cold gas has a relatively smooth distribution and forms a low-turbulence rotation-supported disk. The ratios of rotation velocity to velocity dispersion are around 10, comparable to those of spiral galaxies at z=0. Surprisingly, in most cases, the galaxy rotation curves require the presence of a central stellar bulge, which is not self-evident from the available photometry. The presence of rotation-supported gas disks and stellar bulges indicate that these galaxies must have formed and evolved surprisingly fast during the first billion years of the Universe's life, reaching a dynamical state similar to that of local galaxies.

Brief CV of Dr. Federico Lelli:

He is a research staff at the Arcetri Astrophysical Observatory. He got his Ph.D. in 2013 from the University of Groningen with a thesis entitled "Starburst and gas dynamics in low-mass galaxies". Subsequently, he worked at Case Western Reserve University (USA), ESO (Germany) and Cardiff University (UK). His research interests include galaxy dynamics, dark matter, and alternative gravitational theories.