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Molecular gas in super spiral galaxies

Ute LisenfeldPatrick M. OglePhilip N. AppletonThomas H. JarrettBlanca M. Moncada-Cuadri
Mar 2023
At the highest stellar masses (log(\mstar) $\gtrsim$ 11.5 \msun), only asmall fraction of galaxies are disk-like and actively star-forming objects.These so-called `super spirals' are ideal objects to better understand howgalaxy evolution proceeds and to extend our knowledge about the relationbetween stars and gas to a higher stellar mass regime. We present new CO(1-0)data for a sample of 46 super spirals and for 18 slightly lower-mass(log(\mstar) $>$ 11.0 \msun ) galaxies with broad HI lines -- HI fast-rotators(HI-FRs). We analyze their molecular gas mass, derived from CO, in relation totheir star formation rate (SFR) and stellar mass, and compare the results tovalues and scaling relations derived from lower-mass galaxies. We confirm thatsuper spirals follow the same star-forming main sequence (SFMS) as lower-massgalaxies. We find that they possess abundant molecular gas, which lies abovethe extrapolation of the scaling relation with stellar mass derived fromlower-mass galaxies, but within the relation between \mmol/\mstar and thedistance to the SFMS. The molecular gas depletion time, \taudep = \mmol/SFR, ishigher than for lower-mass galaxies on the SFMS (\taudep = 9.30 $\pm$ 0.03,compared to \taudep = 9.00 $\pm$ 0.02 for the comparison sample) and seems tocontinue an increasing trend with stellar mass. HI-FR galaxies have anatomic-to-molecular gas mass ratio that is in agreement with that of lower-massgalaxies, indicating that the conversion from the atomic to molecular gasproceeds in a similar way. We conclude that the availability of molecular gasis a crucial factor to enable star formation to continue and that, if gas ispresent, quenching is not a necessary destiny for high-mass galaxies. Thedifference in gas depletion time suggests that the properties of the moleculargas at high stellar masses are less favorable for star formation.