Molecular Gas Distribution in Barred and Nonbarred Galaxies along the Hubble Sequence

We present results from a survey of ¹²CO (J = 1–0) spectra obtained for the central regions of 68 nearby galaxies at an angular resolution of 16'' using the Nobeyama Radio Observatory 45 m telescope, aimed at characterizing the properties of star-forming molecular gas. Combined with observations of similar resolution in the literature, the compiled sample set of 166 galaxies span a wide range of galactic properties. NGC 4380, which was previously undetected in CO, was detected. This initial paper of a series will focus on the data and the gaseous properties of the samples, and particularly on the degree of central concentration of molecular gas in a range of morphological types, from early (S0/Sa) to late (Sd/Sm) galaxies with and without bars. The degree of molecular central concentration in the central kiloparsec, compared with the central several kiloparsecs of galaxies, is found to vary smoothly with Hubble type, so that early-type galaxies show larger central concentration. The comparison of barred and nonbarred galaxies within early- and late-type galaxies suggest that difference in Hubble type, representing the effect of bulges, is the more important factor in concentrating gas into the central regions than bars.