A deep search for molecular gas in two massive Lyman break galaxies at z=3 and 4: vanishing CO-emission due to low metallicity

Tan, Q, Daddi, E, Sargent, M, Magdis, G, Hodge, J, Béthermin, M, Bournaud, F, Carilli, C, Dannerbauer, H, Dickinson, M, Elbaz, D, Gao, Y, Morrison, G, Owen, F, Pannella, M, Riechers, D and Walter, F (2013) A deep search for molecular gas in two massive Lyman break galaxies at z=3 and 4: vanishing CO-emission due to low metallicity. Astrophysical Journal Letters, 776 (2). L24. ISSN 2041-8205

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Abstract

We present deep IRAM Plateau de Bure Interferometer (PdBI) observations, searching for CO-emission toward two massive, non-lensed Lyman break galaxies (LBGs) at z=3.216 and 4.058. With one low significance CO detection (3.5 sigma) and one sensitive upper limit, we find that the CO lines are >~ 3-4 times weaker than expected based on the relation between IR and CO luminosities followed by similarly, massive galaxies at z=0-2.5. This is consistent with a scenario in which these galaxies have low metallicity, causing an increased CO-to-H_2 conversion factor, i.e., weaker CO-emission for a given molecular (H_2) mass. The required metallicities at z>3 are lower than predicted by the fundamental metallicity relation (FMR) at these redshifts, consistent with independent evidence. Unless our galaxies are atypical in this respect, detecting molecular gas in normal galaxies at z>3 may thus remain challenging even with ALMA.

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: 21 May 2014 14:27
Last Modified: 11 Mar 2017 02:58
URI: http://sro.sussex.ac.uk/id/eprint/48772

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