V. Catán | Searcharxiv

arXiv2026

The Extended Mapping Obscuration to Reionization with ALMA (Ex-MORA) Survey: A Molecular Gas Line Search

Current investigations of cold gas in the interstellar medium face selection biases, as optical/near-infrared surveys favor massive, low-obscuration galaxies and miss gas-rich passive or inefficient star-forming systems. Overcoming this requires large-volume line surveys selected by molecular gas rather than stellar luminosity. We present a molecular gas census across $0.5 < z < 5$ using ALMA Band 4 observations from the Extended Mapping of Obscuration to Reionization Survey (Ex-MORA), covering 577 arcmin$^2$. Combining an unbiased search for bright emitters with a targeted search using spectroscopic redshift priors, we detect 52 galaxies in CO or \ci transitions (two showing two lines). Physical properties were derived via \texttt{CIGALE} with non-parametric star-formation histories, and gas masses were estimated using metallicity-dependent conversion factors. The sample is dominated by main-sequence (MS) galaxies with high stellar masses (median $\log M_*/\text{M}_{\odot} = 10.83$) and large gas reservoirs ($>10^{10}\,\text{M}_{\odot}$). Gas fraction ($μ_{\text{gas}}$) increases with redshift for active populations, though high-redshift trends are influenced by a gas-rich protocluster at $z \approx 2.4$. Conversely, an overdensity at $z \approx 0.73$ mirrors the field population. Five Green Valley (GV) galaxies exhibit a $μ_{\text{gas}}$ peak at cosmic noon, suggesting stellar feedback may suppress star formation by heating gas rather than rapidly depleting it in at least some transitional systems. Resolved kinematics show a prevalence of rotating disks. These results demonstrate that wide-area line searches effectively recover massive gas reservoirs across diverse evolutionary stages

astro-ph.GA↗

arXiv2024

Molecular gas budget of strongly magnified low-mass star-forming galaxies at cosmic noon

This study aims to investigate the molecular gas content of strongly magnified low-mass star-forming galaxies around the cosmic noon period ($z\sim2$) through observations of CO emission lines and dust continuum emission, both of which serve as tracers for molecular gas. We observed twelve strongly lensed galaxies with the Atacama Compact Array to detect CO mid-j rotational transitions and dust continuum. Thanks to the strong lensing, we were able to probe the low-mass regime, previously understudied. With a compiled set of observations, we recalibrate empirical relations between star formation rate density and the CO line ratios. Using SED fitting, we derived galaxy properties and performed galaxy stacking to combine the faint signals. In all cases, molecular gas masses were estimated using both tracers. We detected CO emission in three out of 12 galaxies and dust continuum emission in three of them. The obtained molecular gas masses indicate that most of these galaxies ($\rm{M}_* < 10^{10.7}$ $\rm{M}_\odot$) have lower molecular gas fractions and shorter depletion times compared to the expectations from established scaling relations at these redshifts. Several possible explanations for this gas deficit were explored, including uncertainties in mass estimates, effects of low metallicity environments, larger atomic gas reservoirs in low-mass systems, and the possibility that these represent low-mass analogs of "main sequence starburst" galaxies, which are undergoing sustained star formation due to gas compaction despite low overall gas fractions. We conclude that there is a molecular gas deficit at these mass and metallicity regimes. Our results suggest that this deficit is likely due to a significant amount of atomic gas, which our stacking indicates is about 91% of the total gas. However, this estimation might be an upper limit in the case of our galaxies containing CO-dark gas.

astro-ph.GA↗