The role of molecular gas in galaxy transition in compact groups ^⋆

¹ Departamento de Física Teórica y del CosmosUniversidad de Granada, Spain and Instituto Carlos I de Física Téorica y Computacional, Facultad de Ciencias, 18071 Granada, Spain
e-mail: ute@ugr.es
² Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101, USA
³ Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA
⁴ NASA Herschel Science Center, IPAC, Caltech, Pasadena, CA 91125, USA
⁵ Department of Physics and Astronomy, University of Western Ontario, London, ON N6A 3K7, Canada
⁶ Centre for Planetary and Space Exploration, University of Western Ontario, London, ON N6A 3K7, Canada
⁷ Institut d’Astrophysique de Paris, CNRS, UMR 7095, 98bis boulevard Arago, 75014 Paris, France
⁸ Sorbonne Universités, UPMC Université Paris 06, 4 place Jussieu, 75005 Paris, France
⁹ Department of Astronomy, University of Virginia, PO Box 400325, Charlottesville, VA 22904-4325, USA

Received: 30 March 2017
Accepted: 2 August 2017

Abstract

Compact groups (CGs) provide an environment in which interactions between galaxies and with the intra-group medium enable and accelerate galaxy transitions from actively star forming to quiescent. Galaxies in transition from active to quiescent can be selected, by their infrared (IR) colors, as canyon or infrared transition zone (IRTZ) galaxies. We used a sample of CG galaxies with IR data from the Wide Field Infrared Survey Explorer (WISE) allowing us to calculate the stellar mass and star formation rate (SFR) for each galaxy. Furthermore, we present new CO(1−0) data for 27 galaxies and collect data from the literature to calculate the molecular gas mass for a total sample of 130 galaxies. This data set allows us to study the difference in the molecular gas fraction (M_mol/M_∗) and star formation efficiency (SFE = SFR/M_mol) between active, quiescent, and transitioning (i.e., canyon and IRTZ) galaxies. We find that transitioning galaxies have a mean molecular gas fraction and a mean SFE that are significantly lower than those of actively star-forming galaxies. The molecular gas fraction is higher than that of quiescent galaxies, whereas the SFE is similar. These results indicate that the transition from actively star-forming to quiescent in CG galaxies goes along with a loss of molecular gas, possibly due to tidal forces exerted from the neighboring galaxies or a decrease in the gas density. In addition, the remaining molecular gas loses its ability to form stars efficiently, possibly owing to turbulence perturbing the gas,as seen in other, well-studied examples such as Stephan’s Quintet and HCG 57. Thus, the amount and properties of molecular gas play a crucial role in the environmentally driven transition of galaxies from actively star forming to quiescent.