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arXiv · 2002.04040

ALMA reveals the molecular gas properties of 5 star-forming galaxies across the main sequence at 3 < z < 3.5

Paolo Cassata·Daizhong Liu·Brent Groves·Eva Schinnerer·Eduardo Ibar·Mark Sargent·Alexander Karim·Margherita Talia·Olivier Le Fevre·Lidia Tasca·Brian C. Lemaux·Bruno Ribeiro·Stefano Fiore·Michael Romano·Chiara Mancini·Laura Morselli·Giulia Rodighiero·Lucia Rodriguez-Munoz·Andrea Enia·Vernesa Smolcic
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Abstract

We present the detection of CO(5-4) with S/N> 7 - 13 and a lower CO transition with S/N > 3 (CO(4-3) for 4 galaxies, and CO(3-2) for one) with ALMA in band 3 and 4 in five main sequence star-forming galaxies with stellar masses 3-6x10^10 M/M_sun at 3 < z < 3.5. We find a good correlation between the total far-infrared luminosity LFIR and the luminosity of the CO(5-4) transition L'CO(5-4), where L'CO(5-4) increases with SFR, indicating that CO(5-4) is a good tracer of the obscured SFR in these galaxies. The two galaxies that lie closer to the star-forming main sequence have CO SLED slopes that are comparable to other star-forming populations, such as local SMGs and BzK star-forming galaxies; the three objects with higher specific star formation rates (sSFR) have far steeper CO SLEDs, which possibly indicates a more concentrated episode of star formation. By exploiting the CO SLED slopes to extrapolate the luminosity of the CO(1-0) transition, and using a classical conversion factor for main sequence galaxies of alpha_CO = 3.8 M_sun(K km s^-1 pc^-2)^-1, we find that these galaxies are very gas rich, with molecular gas fractions between 60 and 80%, and quite long depletion times, between 0.2 and 1 Gyr. Finally, we obtain dynamical masses that are comparable with the sum of stellar and gas mass (at least for four out of five galaxies), allowing us to put a first constraint on the alpha_CO parameter for main sequence galaxies at an unprecedented redshift.

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Paolo Cassata, Daizhong Liu, Brent Groves, Eva Schinnerer, Eduardo Ibar, Mark Sargent, Alexander Karim, Margherita Talia, Olivier Le Fevre, Lidia Tasca, Brian C. Lemaux, Bruno Ribeiro, Stefano Fiore, Michael Romano, Chiara Mancini, Laura Morselli, Giulia Rodighiero, Lucia Rodriguez-Munoz, Andrea Enia, Vernesa Smolcic. 2020-02-10. ALMA reveals the molecular gas properties of 5 star-forming galaxies across the main sequence at 3 < z < 3.5. https://doi.org/10.3847/1538-4357%2Fab7452

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