Molecular Clouds Resolved at the Onset of Cosmic Noon

TL;DR

This paper reports the discovery and spectroscopic resolution of molecular clouds in a high-redshift radio galaxy, providing insights into early universe star formation processes.

Contribution

It presents the first spectrally resolved molecular clouds at Cosmic Noon, revealing their properties and environment in a distant galaxy.

Findings

Molecular clouds detected as CO(0-1) absorption at z=3.4

Cloud velocity dispersions similar to local universe clouds

Clouds located within a 30 kpc stellar nebula

Abstract

We present the discovery of seven molecular clouds in the radio galaxy B2 0902+34 at redshift z=3.4. These clouds are detected as CO(0-1) absorption features against the bright radio continuum, and spectrally resolved using the Karl G. Jansky Very Large Array (VLA). The velocity dispersion of the individual absorption components ranges from 3-7 km/s, which is similar to values observed for molecular clouds in the Milky Way and nearby galaxies, and imply cloud radii of R~10$^{1-2}$ pc. The absorbing clouds are found in a region of high obscuration inside a 30 kpc wide stellar nebula, as revealed by rest-frame near-ultraviolet imaging performed with the Hubble Space Telescope (HST). The fact that we spectrally resolve molecular clouds at the onset of Cosmic Noon opens prospects for studying cloud chemistry and physics that drive the formation of stars in the Early Universe.