A DEEP SEARCH FOR MOLECULAR GAS IN TWO MASSIVE LYMAN BREAK GALAXIES AT z = 3 AND 4: VANISHING CO-EMISSION DUE TO LOW METALLICITY?
- Purple Mountain Observatory and Key Laboratory for Radio Astronomy, Chinese Academy of Sciences, Nanjing 210008 (China)
- CEA Saclay, DSM/Irfu/Service d'Astrophysique, Orme des Merisiers, F-91191 Gif-sur-Yvette Cedex (France)
- Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH (United Kingdom)
- Max-Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany)
- National Radio Astronomy Observatory, P.O. Box O, Socorro, NM 87801 (United States)
- Institut für Astronomie, Universität Wien, Türkenschanzstrasse 17, A-1160 Wien (Austria)
- National Optical Astronomical Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States)
- Institute for Astronomy, University of Hawaii, Honolulu, HI 96822 (United States)
We present deep IRAM Plateau de Bure Interferometer observations, searching for CO-emission toward two massive, non-lensed Lyman break galaxies at z = 3.216 and 4.058. With one low significance CO detection (3.5σ) 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{sub 2} conversion factor, i.e., weaker CO-emission for a given molecular (H{sub 2}) mass. The required metallicities at z > 3 are lower than predicted by the fundamental metallicity relation 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.
- OSTI ID:
- 22215421
- Journal Information:
- Astrophysical Journal Letters, Vol. 776, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 2041-8205
- Country of Publication:
- United States
- Language:
- English
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