Publ. Astron. Soc. Japan (2018) 00(0), 1–33 1 doi: 10.1093/pasj/xxx000 CO Multi-line Imaging of Nearby Galaxies (COMING) IV. Overview of the Project Kazuo SORAI1, 2, 3, 4, 5, Nario KUNO4, 5, Kazuyuki MURAOKA6, Yusuke MIYAMOTO7, 8, Hiroyuki KANEKO7, Hiroyuki NAKANISHI9 , Naomasa NAKAI4, 5, 10, Kazuki YANAGITANI6 , Takahiro TANAKA4, Yuya SATO4, Dragan SALAK10, Michiko UMEI2 , Kana MOROKUMA-MATSUI7, 8, 11, 12, Naoko MATSUMOTO13, 14, Saeko UENO9, Hsi-An PAN15, Yuto NOMA10, Tsutomu, T. TAKEUCHI16 , Moe YODA16, Mayu KURODA6, Atsushi YASUDA4 , Yoshiyuki YAJIMA2 , Nagisa OI17, Shugo SHIBATA2, Masumichi SETA10, Yoshimasa WATANABE4, 5, 18, Shoichiro KITA4, Ryusei KOMATSUZAKI4 , Ayumi KAJIKAWA2, 3, Yu YASHIMA2, 3, Suchetha COORAY16 , Hiroyuki BAJI6 , Yoko SEGAWA2 , Takami TASHIRO2 , Miho TAKEDA6, Nozomi KISHIDA2 , Takuya HATAKEYAMA4 , Yuto TOMIYASU4 and Chey SAITA9 1Department of Physics, Faculty of Science, Hokkaido University, Kita 10 Nishi 8, Kita-ku, Sapporo 060-0810, Japan 2Department of Cosmosciences, Graduate School of Science, Hokkaido University, Kita 10 Nishi 8, Kita-ku, Sapporo 060-0810, Japan 3Department of Physics, School of Science, Hokkaido University, Kita 10 Nishi 8, Kita-ku, Sapporo 060-0810, Japan 4Division of Physics, Faculty of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8571, Japan 5Tomonaga Center for the History of the Universe (TCHoU), University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8571, Japan 6Department of Physical Science, Osaka Prefecture University, Gakuen 1-1, Sakai, Osaka 599-8531, Japan 7Nobeyama Radio Observatory, Minamimaki, Minamisaku, Nagano 384-1305, Japan 8Chile Observatory, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan 9Graduate School of Science and Engineering, Kagoshima University, 1-21-35 Korimoto, Kagoshima, Kagoshima 890-0065, Japan 10 arXiv:1910.03863v1 [astro-ph.GA] 9 Oct 2019 Department of Physics, School of Science and Technology, Kwansei Gakuin University, Gakuen 2-1, Sanda, Hyogo 669-1337, Japan 11Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210, Japan 12Institute of Astronomy, Graduate School of Science, The University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015, Japan 13The Research Institute for Time Studies, Yamaguchi University, Yoshida 1677-1, Yamaguchi, Yamaguchi 753-8511, Japan 14Mizusawa VLBI Observatory, National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan 15Institute of Astronomy and Astrophysics, Academia Sinica, 11F of AS/NTU Astronomy-Mathematics Building, No.1, Sec. 4, Roosevelt Rd, Taipei 10617, Taiwan 16Division of Particle and Astrophysical Science, Nagoya University, Furo-cho, Chikusa-ku, c 2018. Astronomical Society of Japan. 2 Publications of the Astronomical Society of Japan, (2018), Vol. 00, No. 0 Nagoya, Aichi 464-8602, Japan 17Tokyo University of Science, Faculty of Science Division II, Liberal Arts, 1-3, Kagurazaka Shinjuku-ku Tokyo 162-8601 Japan 18College of Engineering, Nihon University, 1 Nakagawara, Tokusada, Tamuramachi, Koriyama, Fukushima 963-8642, Japan ∗E-mail: [email protected] Received 2018 December 17; Accepted 2019 September 18 Abstract Observations of the molecular gas in galaxies are vital to understanding the evolution and star- forming histories of galaxies. However, galaxies with molecular gas maps of their whole discs having sufficient resolution to distinguish galactic structures are severely lacking. Millimeter wavelength studies at a high angular resolution across multiple lines and transitions are par- ticularly needed, severely limiting our ability to infer the universal properties of molecular gas in galaxies. Hence, we conducted a legacy project with the 45 m telescope of the Nobeyama Radio Observatory, called the CO Multi-line Imaging of Nearby Galaxies (COMING), which simultaneously observed 147 galaxies with high far-infrared flux in 12CO, 13CO, and C18O J =1 − 0 lines. The total molecular gas mass was derived using the standard CO–to–H2 con- version factor and found to be positively correlated with the total stellar mass derived from the WISE 3.4µm band data. The fraction of the total molecular gas mass to the total stellar mass in galaxies does not depend on their Hubble types nor the existence of a galactic bar, although when galaxies in individual morphological types are investigated separately, the fraction seems to decrease with the total stellar mass in early-type galaxies and vice versa in late-type galax- ies. No differences in the distribution of the total molecular gas mass, stellar mass, and the total molecular gas to stellar mass ratio was observed between barred and non-barred galax- ies, which is likely the result of our sample selection criteria, in that we prioritized observing FIR bright (and thus molecular gas-rich) galaxies. Key words: galaxies: ISM — galaxies: statistics — atlases — surveys — methods: data analysis 1 Introduction mation is not uniform both within and between different galaxies. Some questions must be answered for us to un- How and where stars form in galaxies are clues to under- derstand the causes of a variety of star formations within standing galaxy evolution, and require information about a galaxy and among galaxies. the distribution, dynamics, and physical properties of their Many studies have observed the distribution and dy- molecular gas content. H II regions and massive stars namics of molecular gas in galaxies. Molecular gas in spi- are found in spiral arms (Lynds 1980; Garc´ıa G´omez & ral galaxy M 51 is primarily concentrated along the two Athanassoula 1993; Thilker et al. 2002; Oey et al. 2003; grand-design spiral arms, but also detected in the interarm Bresolin et al. 2005), while only a few are found in the regions (Garc´ıa-Burillo et al. 1993; Nakai et al. 1994). The bar of some barred spiral galaxies (Koopmann et al. 2001; velocity of molecular gas qualitatively changes at the spiral James et al. 2004; Hernandez et al. 2005; Erroz-Ferrer arm in accordance with density wave theory, and the esti- et al. 2015). Interacting and merging galaxies often dis- mated elliptical motion can explain the surface density con- play an abundance of star-forming regions in both their trast of the molecular gas between the spiral arms and the interface regions, especially compared to their spiral arms interarm regions (Kuno & Nakai 1997). Flocculent galax- (Koopmann et al. 2001; Wang et al. 2004; Torres-Flores ies also display molecular gas concentrations along their et al. 2014), while little new stars form even in the spiral spiral arms, such as in NGC 5055 (Kuno et al. 1997). On- arms of some galaxies (van den Bergh 1976; Kennicutt & the-fly (OTF) observations of the barred spiral galaxy M 83 Edgar 1986; Masters et al. 2010; Fraser-McKelvie et al. showed that the CO disc has a sharp edge, while the H I 2016). These observational results indicate that star for- disc more gradually extends to larger radii (Crosthwaite Publications of the Astronomical Society of Japan, (2018), Vol. 00, No. 0 3 et al. 2002). sure in cluster environments (Nakanishi et al. 2006). A In the recent years, CO observations with high spatial total of 28 Virgo cluster spirals were also mapped with resolution have resolved giant molecular clouds (GMCs) in the Five College Radio Astronomy Observatory (FCRAO) galaxies. Giant molecular cloud associations (GMAs) are 14 m telescope (Chung et al. 2009b); however, some galax- dominant in the spiral arms and broken up into GMCs in ies overlap with one another. The total number of mapped the interarm regions in M 51 (Koda et al. 2009). In the galaxies in these three surveys was 74. barred spiral galaxy NGC 4303, the molecular gas in the Many mapping observations of molecular gas, whose bar has a lower star formation efficiency (SFE) than that sample size numbers were 10 or fewer, and surveys with in the spiral arms, where the SFE is the star formation interferometers covering only the central regions have also rate (SFR) divided by the molecular gas mass (Momose been made [Sakamoto et al. 1999; Sofue et al. 2003; et al. 2010). The SFE depends on the environment at sub- CARMA STING (Survey Toward Infrared-bright Nearby kpc scales, and increases with the surface density of the Galaxies), Rahman et al. 2012]. However, combining such molecular gas (Momose et al. 2013). Meanwhile, in the data is not necessarily suitable for comparing many galax- local spiral galaxy M 33, the molecular gas fractions are ies because spatial resolutions and instrument sensitivity loosely correlated with the neutral gas fraction observed can wildly differ between surveys. In addition, observa- at the GMC scales, with particular variations in the inner tions with interferometers alone miss extended emission disc (Tosaki et al. 2011). A CARMA (Combined Array (i.e., are “resolved out”); hence, there are concerns that for Research in Millimeter Astronomy interferometer) and such observations underestimate the total molecular gas Nobeyama Nearby galaxies (CANON) survey resolved ap- mass of the target galaxies. If mapping does not extend proximately 200 GMCs in the inner discs of five galaxies across the entirety of the galactic disc, then correct infor- and revealed that they are similar to those in the Milky mation on the molecular gas and star formation in outer Way (Donovan Meyer et al. 2013). PAWS (Plateau de Bure regions, particularly in interacting galaxies, are impossible Interferometer Arcsecond Whirlpool Survey, Schinnerer to obtain. et al. 2013) observed M 51 at 40 pc resolution and Surveys targeting higher-J transitions have also been ∼ found that the dynamical environment of the GMCs sig- conducted, although they carry added caveats for estimat- nificantly influences their star-forming capability (Meidt ing the total molecular gas masses of the target galax- et al. 2013), and that feedback from massive stars affects ies. HERACLES (HEterodyne Receiver Array CO Line the dependency of the GMC properties on the environ- Extragalactic Survey, Leroy et al.