Affiliation: Department of Astrophysics, Univ. of Vienna

Contribution: Oral

Title: Quenching of high redshift cluster galaxies and properties of z>3 HST-dark galaxies revealed by JWST

Abstract: First I will discuss galaxy evolution of high-redshift cluster galaxies. Using spectroscopic redshifts of these z>1.5 cluster galaxies I computed the location of these galaxies in the projected velocity-versus-position phase-space to separate the cluster sample into a virialized region of objects accreted longer ago and a region of infalling galaxies. I used near-infrared spectroscopy of Hα, [NII], [OIII] and Hβ of galaxies covering a region that corresponds to about one virial radius, and found the computed metallicities of these high-redshift cluster galaxies inside half R200 to be enhanced compared to infalling galaxies and field galaxies at similar redshifts and of similar masses. This indicates that the density of the intracluster medium in this massive cluster environment becomes high enough toward the cluster center such that the ram pressure exceeds the restoring pressure of the hot gas reservoir of cluster galaxies. This can remove the gas reservoir stopping the inflow of diluting gas thereby enhancing gas metallicities and initiating quenching. Although the galaxies continue to form stars, albeit at slightly lower rates, using the available cold gas in the disk which is not stripped: Molecular gas masses derived from ALMA CO(2-1) for several cluster galaxies suggest that the main component of the stripped gas is the neutral gas reservoir, while the molecular gas is relatively much less affected by the ram pressure, such that the galaxies continue to form stars from the molecular gas. I will also present first results from our new JWST spectroscopic program for galaxies at redshifts between 3 and 7, which are not detected at optical wavelengths, due to significant dust obscuration (“HST-dark galaxies”). We measured [OIII], Hβ, Hα and [NII] emission lines for these enigmatic galaxies, enabling us to quantify their physical properties like gas metallicities, star formation rates and contribution of active galactic nuclei (AGN), aiming to clarify their nature.

This contribution can be found here (pdf).