Follow-up ALMA studies of HLWAS sources

Roman’s High Latitude Wide Area Survey will provide a key piece for our understanding of the distant universe, building a deep and wide census of high-z sources, including AGN hosting galaxies and quasars at very high z. As demonstrated by an accelerating rate of publications in the field (e.g., Endsley et al., 2022, Harikane et al., 2022), ALMA is a powerhouse for pointed characterization of high-z sources, and specifically for z>3, can provide information inaccessible solely from Roman’s observations. 'In particular, access to the redshifted atomic and molecular hydride lines of C, O and possibly N is crucial to obtain accurate spectroscopic redshifts, and to evaluate the state of the cold gas component. Photometry in the submm regime is a key SED point for dusty, star-forming galaxies. The recent installation of the new ALMA Band 1 (35-50 GHz) also opens up the ability to search for 'redshifted low-J CO lines, which are a good diagnostic for estimating the mass of the molecular gas reservoir. At the time of Roman’s mission, ALMA’s Wideband Sensitivity Upgrade (WSU) will be underway, improving the line sensitivity by a factor ~1.5, and providing much more efficient spectral scanning for redshift surveys. Using recent results as examples, this poster reviews possible ALMA follow-up studies of sources identified through the HLWA survey, and quantify how the WSU will deepen the reach of ALMA studies in this field.