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Carbon monoxide in clouds at low metallicity in the dwarf irregular galaxy WLM

Elmegreen, Bruce G. and Rubio, Monica and Hunter, Deidre A. and Verdugo, Celia and Brinks, Elias and Schruba, Andreas (2013) Carbon monoxide in clouds at low metallicity in the dwarf irregular galaxy WLM. Nature, 495 (7442). pp. 487-489. ISSN 0028-0836. doi:10.1038/nature11933.

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Carbon monoxide (CO) is the primary tracer for interstellar clouds where stars form, but it has never been detected in galaxies in which the oxygen abundance relative to hydrogen is less than 20 per cent of that of the Sun, even though such ‘low-metallicity’ galaxies often form stars. This raises the question of whether stars can form in dense gas without molecules, cooling to the required near-zero temperatures by atomic transitions and dust radiation rather than by molecular line emission; and it highlights uncertainties about star formation in the early Universe, when the metallicity was generally low. Here we report the detection of CO in two regions of a local dwarf irregular galaxy, WLM, where the metallicity is 13 per cent of the solar value. We use new submillimetre observations and archival far-infrared observations to estimate the cloud masses, which are both slightly greater than 100,000 solar masses. The clouds have produced stars at a rate per molecule equal to 10 per cent of that in the local Orion nebula cloud. The CO fraction of the molecular gas is also low, about 3 per cent of the Milky Way value. These results suggest that in small galaxies both star-forming cores and CO molecules become increasingly rare in molecular hydrogen clouds as the metallicity decreases.

Item Type:Article
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URLURL TypeDescription
Elmegreen, Bruce G.0000-0002-1723-6330
Hunter, Deidre A.0000-0002-3322-9798
Brinks, Elias0000-0002-7758-9699
Additional Information:© 2013 Macmillan Publishers Limited. Received 24 October 2012. Accepted 23 January 2013. Published online 27 March 2013. This work was funded in part by the US National Science Foundation through grants AST-0707563 and AST-0707426 to D.A.H. and B.G.E. M.R. and C.V. wish to acknowledge support from CONICYT (FONDECYT grant no. 1080335). M.R. was also supported by the Chilean Center for Astrophysics FONDAP grant no. 15010003. A.S. was supported by the Deutsche Forschungsgemeinschaft Priority Program 1177. We are grateful to M. Albrecht for help with the LABOCA data reduction and to L. Hill for making Fig. 1a. The National Radio Astronomy Observatory is a facility of the US National Science Foundation operated under cooperative agreement by Associated Universities, Inc. Author Contributions: B.G.E. coordinated the observational team, did the calculations for Table 2 and wrote the manuscript; M.R. was principal investigator for Chilean observing time on the APEX telescope and, with C.V., observed the galaxy in CO and at 870mm, reduced the relevant data in Table 1 and did relevant calculations for Table 2; D.A.H. determined the observational strategy, selected WLM for study, chose the observing coordinates, extracted the HI spectra from the LITTLE THINGS data and prepared Fig. 1. E.B. was principal investigator on the APEX proposal using European time through ESO and coordinated the work on data uncertainties and background noise. A.S. made the WLMHI data cube from Jansky Very Large Array observations. All authors discussed the results and commented on the manuscript.
Funding AgencyGrant Number
Chilean Center for Astrophysics FONDAP15010003
Deutsche Forschungsgemeinschaft (DFG)1177
Issue or Number:7442
Record Number:CaltechAUTHORS:20130429-083322792
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Official Citation:Carbon monoxide in clouds at low metallicity in the dwarf irregular galaxy WLM Bruce G. Elmegreen, Monica Rubio, Deidre A. Hunter, Celia Verdugo, Elias Brinks + et al. pp.487-489
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:38145
Deposited By: Ruth Sustaita
Deposited On:29 Apr 2013 15:58
Last Modified:09 Nov 2021 23:33

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