BASS-CO: A Legacy Survey of Molecular Gas in Powerful Nearby AGN

BASS-CO is the largest survey of molecular gas in AGN host galaxies and aims to investigate the specific role of AGN in galaxy evolution including the potential impact of AGN feedback on the gas content of galaxies and the processes governing the fueling of the AGN. It is now known that the molecular gas fraction is one of the most important properties driving the transition of massive galaxies from blue and star-forming to red and quenched and energy input from AGN through jets and/or outflows is thought to strongly influence this process. Further, molecular gas is also the main fuel for AGN and thus an inventory of its availability can highlight under which global conditions are optimal for igniting the AGN.

The full survey is the combination of two large programs at the IRAM-30m and APEX telescopes as well as a smaller program at the JCMT. The targeted sample stems from the 70 month Swift/BAT catalog that provided a large sample of very hard X-ray (14-195 keV) detected AGN that is unbiased against host galaxy properties or AGN obscuration. The BAT AGN Spectroscopic Survey (BASS) has been extensively following up these AGN with a coordinated multiwavelength effort and with this BASS-CO survey, we observed 133 northern hemisphere nearby (z < 0.05) BAT AGN using IRAM-30m, 165 southern hemisphere BAT AGN using APEX, and 35 with JCMT.

CO 1-0, CO 2-1 spectra, and optical imaging for 3 BASS-CO AGN with increasing S/N. Red and blue circles on the optical images mark the IRAM-30m beam at 115 and 230 GHz respectively.

Key scientific goals of the survey include answering 1) Do AGN host galaxies contain the same amount of molecular gas as similar inactive galaxies? 2) Do AGN host galaxies follow the same established molecular gas scaling relations? 3) Is star formation more or less efficient in the presence of an AGN? 4) Is there a threshold molecular gas mass or fraction for an AGN to ignite? Our sample and observations are uniquely positioned to answer these questions given the mostly unbiased selection of our sample and the wealth of multiwavelength ancillary data available including Herschel far-infrared photometry that is crucial for measuring accurate star formation rates in AGN hosts. We also can combine our survey with another IRAM-30m legacy survey, xCOLDGASS, that probes the full nearby galaxy population and provides an important “control” sample to test for effects of the AGN.

The official repository for BASS-CO will be at the BASS website and the data for the IRAM 30-m portion is provided at IRAM. In this first data release, we provide reduced IRAM 30-m CO 1-0 and CO 2-1 spectra at the native frequency spacing. Catalogs of CO flux measurements, molecular gas masses, and CO linewidths as well as complementary host galaxy (e.g. stellar masses, SFRs, morphology, etc) and AGN properties (e.g. black hole masses, luminosities, Eddington ratios, etc) will be made available after the completion of the survey publications.

a) Distribution of AGN bolometric luminosity for BASS-CO showing the large range of our sample. b) and c) Distribution of stellar mass and distribution of redshift for BASS-CO and xCOLD GASS samples showing the overlap in important properties and allowing for accurate comparison between the molecular gas properties of AGN and inactive galaxies.

Please contact Taro Shimizu to inquire about the data.

Last update : June 2020