Oral Presentation

Vz-GAL Cold Molecular Gas Survey of High-redshift Dusty Galaxies as a demonstrator for the power of ALMA Band 1

Author(s): Prachi Prajapati (1. University of Cologne, 2. MPIfR), Dominik Riechers (University of Cologne), Bethany Jones (University of Cologne), Tom Bakx (Chalmers University of Technology), Pierre Cox (Institut d'Astrophysique de Paris), Stefano Berta (IRAM), Kristy Butler (University of Leiden), Asantha Cooray (University of California), Andrew Harris (University of Maryland), Rob Ivison (ESO), Matthew Lehnert (Universität Lyon), Roberto Neri (IRAM), Axel Weiss (MPIfR), Chentao Yang (Chalmers University of Technology)

Presenter: Prachi Prajapati (1. University of Cologne,
2. Max Planck Institute for Radio Astronomy, Germany)

The galaxies and star formation we observe today are shaped by a long history of galaxy evolution.
High-redshift dusty star-forming galaxies (DSFGs) are important for studying obscured star
formation through their cold molecular gas, which fuels star formation and reveals the total gas
distribution and morphology. I will present the status of the Vz-GAL large program using the NSF's
Karl G. Jansky Very Large Array (VLA) to observe CO(1-0) emission in 135 Herschel-selected
DSFGs (1 < z < 6), about half of which are completed, with the remaining observations scheduled
in Spring 2025. The main scientific goals are to uncover trends in gas depletion timescales, CO-line
ratios, and scaling relations with statistical significance, which are crucial for understanding galaxy
evolution. While the VLA observations provide key constraints, our study is limited to northern and
equatorial survey fields, and thus misses all DSFGs in the southern Herschel fields for which we
have successfully obtained high-J CO-based redshifts. I will outline how ALMA Band 1 will allow
us to overcome this critical limitation, to significantly improve our understanding of galaxy
formation in the early universe on a broader scale. The Band 1 (35–51 GHz) offers a unique
opportunity for detecting CO(1-0) and underlying dust continuum in galaxies at 1.3 < z < 2.3 with
enhanced sensitivity and higher resolution. Furthermore, CO(2-1) can also be probed for galaxies
lying even farther, i.e., 3.6 < z < 5.6. Therefore, future ALMA observations at these frequencies
could significantly improve our ability to probe cold gas reservoirs and free-free emission in such
DSFGs lying around the peak of cosmic star formation history and beyond.