Molecular outflows and extended cold gas in and around high-redshift galaxies

The flow of baryons in and out of galaxies is the primary driver for the evolution of galaxies – inflows bring fresh gas to galaxies to form stars and outflows entrain processed gas outside of galaxies. Outflows thus may enrich the circumgalactic medium (CGM) of galaxies, which can further impact the next stages of gas accretion. If outflows are indeed capable of enriching the CGM of galaxies, we should be able to observe metal-enrich gas beyond the stellar disk of galaxies. So far the community has focused on [CII] observations or CO observations but around extreme galaxies, such as AGN-host galaxies, thereby preventing us to interpret the results in a simple and straightforward way as other factors than outflows might play a role in producing such results. In this work, we aim to search for cold molecular gas in the CGM of typical main-sequence (MS) star-forming galaxies at Cosmic Noon, where we might expect outflows to be particularly prominent. Using ALMA Band 3 CO(2–1) observations, we study the extent of the cold molecular gas of a sample of 26 SFGs on (and above) the MS, via stacking techniques. Also via stacking techniques, we search for broad wings in the stacked spectrum of our sample, that can be indicative of ongoing outflows. We find that the cold molecular gas extends out to scales of ≳ 12 kpc, suggestive of CGM scales. But we do not find evidence for high velocity gas in the stacked CO spectrum that could be indicative of ongoing outflows.