title: Carbon monoxide in an extremely metal-poor galaxy.
abstract: Extremely metal-poor galaxies with metallicity below 10% of the solar value in the local universe are the best analogues to investigating the interstellar medium at a quasi-primitive environment in the early universe. In spite of the ongoing formation of stars in these galaxies, the presence of molecular gas (which is known to provide the material reservoir for star formation in galaxies such as our Milky Way) remains unclear. Here we report the detection of carbon monoxide (CO), the primary tracer of molecular gas, in a galaxy with 7% solar metallicity, with additional detections in two galaxies at higher metallicities. Such detections offer direct evidence for the existence of molecular gas in these galaxies that contain few metals. Using archived infrared data, it is shown that the molecular gas mass per CO luminosity at extremely low metallicity is approximately one-thousand times the Milky Way value.
authors.affiliation: School of Astronomy and Space Science, Nanjing University, Nanjing 210093, China.|Key Laboratory of Modern Astronomy and Astrophysics (Nanjing University), Ministry of Education, Nanjing 210093, China.|Collaborative Innovation Center of Modern Astronomy and Space Exploration, Nanjing 210093, China.
authors.forename: Yong
authors.initials: Y
authors.lastname: Shi
authors.affiliation: Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030, China.|Key Laboratory of Radio Astronomy, Chinese Academy of Sciences, Nanjing 210008, China.
authors.forename: Junzhi
authors.initials: J
authors.lastname: Wang
authors.affiliation: Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK.|ESO, Karl-Schwarzschild-Strasse 2, Garching 85748, Germany.
authors.forename: Zhi-Yu
authors.initials: ZY
authors.lastname: Zhang
authors.affiliation: Key Laboratory of Radio Astronomy, Chinese Academy of Sciences, Nanjing 210008, China.|Purple Mountain Observatory, Chinese Academy of Sciences, 2 West Beijing Road, Nanjing 210008, China.
authors.forename: Yu
authors.identifier: 0000-0003-0007-2197
authors.initials: Y
authors.lastname: Gao
authors.affiliation: Tianjin Astrophysics Center, Tianjin Normal University, Tianjin 300387, China.
authors.forename: Cai-Na
authors.initials: CN
authors.lastname: Hao
authors.affiliation: Tianjin Astrophysics Center, Tianjin Normal University, Tianjin 300387, China.
authors.forename: Xiao-Yang
authors.initials: XY
authors.lastname: Xia
authors.affiliation: School of Astronomy and Space Science, Nanjing University, Nanjing 210093, China.|Key Laboratory of Modern Astronomy and Astrophysics (Nanjing University), Ministry of Education, Nanjing 210093, China.|Collaborative Innovation Center of Modern Astronomy and Space Exploration, Nanjing 210093, China.
authors.forename: Qiusheng
authors.initials: Q
authors.lastname: Gu