MOLECULAR GAS and STAR-FORMATION PROPERTIES in the CENTRAL and BAR REGIONS of NGC 6946

In this work, we investigate the molecular gas and star-formationroperties in the barred spiral galaxy NGC 6946 using multiple molecular lines and star-formation tracers. A high-resolution image (100c) of ¹³CO (1-0) is created for the inner 2 kpc disk by the single-dish Nobeyama Radio Observatory 45 m telescope and interferometer Combined Array for Research in Millimeter-wave Astronomy, including the central region (nuclear ring and bar) and the offset ridges of therimary bar. Single-dish HCN (1-0) observations were also made to constrain the amount of dense gas. Thehysicalroperties of molecular gas are inferred from (1) the large velocity gradient calculations using our observations and archival ¹²CO (1-0), ¹²CO(2-1) data, (2) the dense gas fraction suggested by the luminosity ratio of HCN to ¹²CO (1-0), and (3) the infrared color. The results show that the molecular gas in the central region is warmer and denser than that of the offset ridges. The dense gas fraction of the central region is similar to that of luminous infrared galaxies/ultraluminous infrared galaxies, whereas the offset ridges are close to the global average of normal galaxies. The coolest and least-dense region is found in a spiral-like structure, which was misunderstood to beart of the southernrimary bar inrevious low-resolution observations. The star-formation efficiency (SFE) changes by about five times in the inner disk. The variation of SFE agrees with therediction in terms of star formation regulated by the galactic bar. We find a consistency between the star-forming region and the temperature inferred by the infrared color, suggesting that the distribution of subkiloparsec-scale temperature is driven by star formation.