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Missing molecular gas in low mass star-forming galaxies at cosmic noon

Presentation #310.07 in the session Evolution of Galaxies V.

Published onJun 29, 2022
Missing molecular gas in low mass star-forming galaxies at cosmic noon

The molecular gas content of galaxies is deeply connected to the rates and timescales of star formation. Understanding this connection is particularly important at z~2-3, where the cosmic star formation rate density was at its peak. However, most of what we know about molecular gas in high-z galaxies is limited to the brightest and most massive objects. In order to get a more complete picture, we have conducted a pilot survey of molecular gas in low mass (M* <1010 Msun) strongly-lensed galaxies with the Atacama Compact Array. Taking advantage of the flux magnification provided by gravitational lensing, we measured (or put upper limits on) the molecular gas fraction of four “normal” star forming galaxies at z~2-3. Using three independent tracers (CO, CI and dust), we find that these galaxies seem to have 0.5-1.0 dex less gas than expected from standard scaling relations, adding evidence to a trend that was already hinted by previous studies. Our results open the possibility of a fundamentally different mode of star formation taking place in these lower mass galaxies, but also stress the need of larger samples and the reduction of systematics in tracer-to-gas mass calibrations.

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