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arXiv · 1810.01596

The molecular gas content and fuel efficiency of starbursts at z ~ 1.6 with ALMA

J. Silverman·W. Rujopakarn·E. Daddi·A. Renzini·G. Rodighiero·D. Liu·A. Puglisi·M. Sargent·C. Mancini·J. Kartaltepe·D. Kashino·A. Koekemoer·N. Arimoto·M. Bethermin·S. Jin·G. Magdis·T. Nagao·M. Onodera·D. Sanders·F. Valentino
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Abstract

We present an analysis of the molecular gas properties, based on CO(2 - 1) emission, of twelve starburst galaxies at z~1.6 selected by having a boost (>~4x) in their star formation rate (SFR) above the average star-forming galaxy at an equivalent stellar mass. ALMA observations are acquired of six additional galaxies than previously reported through our effort. As a result of the larger statistical sample, we significantly detect, for the first time at high-z, a systematically lower L'_CO/L_IR ratio in galaxies lying above the star-forming `main sequence' (MS). Based on an estimate of alpha_CO (i.e., the ratio of molecular gas mass to L'_CO(1-0)), we convert the observational quantities (e.g., L'_CO/L_IR) to physical units (M_gas/SFR) that represent the gas depletion time or its inverse, the star formation efficiency. We interpret the results as indicative of the star formation efficiency increasing in a continuous fashion from the MS to the starburst regime, whereas the gas fractions remain comparable to those of MS galaxies. Although, the balance between an increase in star-formation efficiency or gas fraction depends on the adopted value of alpha_CO as discussed.

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J. Silverman, W. Rujopakarn, E. Daddi, A. Renzini, G. Rodighiero, D. Liu, A. Puglisi, M. Sargent, C. Mancini, J. Kartaltepe, D. Kashino, A. Koekemoer, N. Arimoto, M. Bethermin, S. Jin, G. Magdis, T. Nagao, M. Onodera, D. Sanders, F. Valentino. 2018-10-03. The molecular gas content and fuel efficiency of starbursts at z ~ 1.6 with ALMA. https://doi.org/10.3847/1538-4357/aae25e

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