A Higher Efficiency of Converting Gas to Stars Pushes Galaxies at z ˜ 1.6 Well Above the Star-forming Main Sequence

Sargent, M, Silverman, J D, Daddi, E, Rodighiero, G, Rujopakarn, W, Sargent, M, Renzini, A, Liu, D, Feruglio, C, Kashino, D, Sanders, D, Kartaltepe, J, Nagao, T, Arimoto, N, Berta, S, Bethermin, M, Koekemoer, A, Lutz, D, Magdis, G, Mancini, C, Onodera, M and Zamorani, G (2015) A Higher Efficiency of Converting Gas to Stars Pushes Galaxies at z ˜ 1.6 Well Above the Star-forming Main Sequence. The Astrophysical Journal, 812 (2). ISSN 0004-637X

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Local starbursts have a higher efficiency of converting gas into stars, as compared to typical star-forming galaxies at a given stellar mass, possibly indicative of different modes of star formation. With the peak epoch of galaxy formation occurring at z > 1, it remains to be established whether such an efficient mode of star formation is occurring at high redshift. To address this issue, we measure the molecular gas content of seven high-redshift (z ˜ 1.6) starburst galaxies with the Atacama Large Millimeter/submillimeter Array and IRAM/Plateau de Bure Interferometer. Our targets are selected from the sample of Herschel far-infrared-detected galaxies having star formation rates (˜300-800 M⊙ yr-1) elevated (≳4×) above the star-forming main sequence (MS) and included in the FMOS-COSMOS near-infrared spectroscopic survey of star-forming galaxies at z ˜ 1.6 with Subaru. We detect CO emission in all cases at high levels of significance, indicative of high gas fractions (˜30%-50%). Even more compelling, we firmly establish with a clean and systematic selection that starbursts, identified as MS outliers, at high redshift generally have a lower ratio of CO to total infrared luminosity as compared to typical MS star-forming galaxies, although with a smaller offset than expected based on past studies of local starbursts. We put forward a hypothesis that there exists a continuous increase in star formation efficiency with elevation from the MS with galaxy mergers as a possible physical driver. Along with a heightened star formation efficiency, our high-redshift sample is similar in other respects to local starbursts, such as being metal rich and having a higher ionization state of the interstellar medium.

Item Type: Article
Schools and Departments: School of Mathematical and Physical Sciences > Physics and Astronomy
Subjects: Q Science > QB Astronomy
Depositing User: Mark Sargent
Date Deposited: 09 Feb 2016 09:26
Last Modified: 08 Mar 2017 05:39
URI: http://srodev.sussex.ac.uk/id/eprint/59584

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