The final data release of ALLSMOG: a survey of CO in typical local low-M_∗ star-forming galaxies

¹ INAF–Osservatorio Astronomico di Brera, via Brera 28, 20121 Milan, Italy
e-mail: claudia.cicone@brera.inaf.it
² Institute for Astronomy, Department of Physics, ETH Zurich, Wolfgang-Pauli-Strasse 27, 8093 Zurich, Switzerland
³ Cavendish Laboratory, University of Cambridge, 19 J. J. Thomson Ave, Cambridge CB3 0HE, UK
⁴ Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
⁵ Square Kilometre Array Organisation, Lower Withington, Cheshire, SK11 9DL, UK
⁶ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
⁷ Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
⁸ European Southern Observatory, 3107 Alonso de Córdova, Vitacura, Santiago, Chile
⁹ Joint ALMA Observatory, 3107 Alonso de Córdova, Vitacura, Santiago, Chile
¹⁰ Núcleo de Astronomía, Facultad de Ingeniería, Universidad Diego Portales, Av. Ejército 441, 3107 Santiago, Chile
¹¹ National Astronomical Observatory of Japan (NAOJ), 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
¹² Department of Astronomical Science, The Graduate University for Advanced Studies (SOKENDAI), 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
¹³ Kavli Institute for Astronomy and Astrophysics, Peking University, 100871 Beijing, PR China
¹⁴ Jodrell Bank Centre for Astrophysics, School of Physics & Astronomy, The University of Manchester, Oxford Road, Manchester M13 9PL, UK
¹⁵ Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
¹⁶ Department of Astronomy, Cornell University, 220 Space Sciences Building, Ithaca, NY 14853, USA

Received: 13 February 2017
Accepted: 3 May 2017

Abstract

We present the final data release of the APEX low-redshift legacy survey for molecular gas (ALLSMOG), comprising CO(2–1) emission line observations of 88 nearby, low-mass (10^8.5<M_∗ [M_⊙] < 10¹⁰) star-forming galaxies carried out with the 230 GHz APEX-1 receiver on the APEX telescope. The main goal of ALLSMOG is to probe the molecular gas content of more typical and lower stellar mass galaxies than have been studied by previous CO surveys. We also present IRAM 30 m observations of the CO(1–0) and CO(2–1) emission lines in nine galaxies aimed at increasing the M_∗< 10⁹M_⊙ sample size. In this paper we describe the observations, data reduction and analysis methods and we present the final CO spectra together with archival Hi 21 cm line observations for the entire sample of 97 galaxies. At the sensitivity limit of ALLSMOG, we register a total CO detection rate of 47%. Galaxies with higher M_∗, SFR, nebular extinction (A_V), gas-phase metallicity (O/H), and Hi gas mass have systematically higher CO detection rates. In particular, the parameter according to which CO detections and non-detections show the strongest statistical differences is the gas-phase metallicity, for any of the five metallicity calibrations examined in this work. We investigate scaling relations between the CO(1–0) line luminosity (L'_CO(1-0)) and galaxy-averaged properties using ALLSMOG and a sub-sample of COLD GASS for a total of 185 sources that probe the local main sequence (MS) of star-forming galaxies and its ± 0.3 dex intrinsic scatter from M_∗ = 10^8.5M_⊙ to M_∗ = 10¹¹M_⊙. L'_CO(1-0) is most strongly correlated with the SFR, but the correlation with M_∗ is closer to linear and almost comparably tight. The relation between L'_CO(1-0) and metallicity is the steepest one, although deeper CO observations of galaxies with A_V< 0.5 mag may reveal an as much steep correlation with A_V. Our results suggest that star-forming galaxies across more than two orders of magnitude in M_∗ obey similar scaling relations between CO luminosity and the galaxy properties examined in this work. Besides SFR, the CO luminosity is likely most fundamentally linked to M_∗, although we note that stellar mass alone cannot explain all of the variation in CO emission observed as a function of O/H and M_HI.