The EDGE-CALIFA Survey: Spatially Resolved ¹³CO(1–0) Observations and Variations in ¹²CO(1–0)/¹³CO(1–0) in Nearby Galaxies on Kiloparsec Scales

Abstract We present 13CO(J = 1 → 0) observations for the EDGE-CALIFA survey, which is a mapping survey of 126 nearby galaxies at a typical spatial resolution of 1.5 kpc. Using detected 12CO emission as a prior, we detect 13CO in 41 galaxies via integrated line flux over the entire galaxy and in 30 galaxies via integrated line intensity in resolved synthesized beams. Incorporating our CO observations and optical IFU spectroscopy, we perform a systematic comparison between the line ratio  12 / 13 ≡ I [ 12 CO ( J = 1 → 0 ) ] / I [ 13 CO ( J = 1 → 0 ) ] and the properties of the stars and ionized gas. Higher  12 / 13 values are found in interacting galaxies compared to those in noninteracting galaxies. The global  12 / 13 slightly increases with infrared color F 60/F 100 but appears insensitive to other host-galaxy properties such as morphology, stellar mass, or galaxy size. We also present azimuthally averaged  12 / 13 profiles for our sample up to a galactocentric radius of 0.4r 25 (∼6 kpc), taking into account the 13CO nondetections by spectral stacking. The radial profiles of  12 / 13 are quite flat across our sample. Within galactocentric distances of 0.2r 25, the azimuthally averaged  12 / 13 increases with the star formation rate. However, Spearman rank correlation tests show the azimuthally averaged  12 / 13 does not strongly correlate with any other gas or stellar properties in general, especially beyond 0.2r 25 from the galaxy centers. Our findings suggest that in the complex environments in galaxy disks,  12 / 13 is not a sensitive tracer for ISM properties. Dynamical disturbances, like galaxy interactions or the presence of a bar, also have an overall impact on  12 / 13 , which further complicates the interpretations of  12 / 13 variations.