The EDGE-CALIFA survey: Variations in the Molecular Gas Depletion Time in Local Galaxies

Abstract

We present results from the EDGE survey, a spatially resolved CO(1-0) follow-up to CALIFA, an optical Integral Field Unit (IFU) survey of local galaxies. By combining the data products of EDGE and CALIFA, we study the variation in molecular gas depletion time ($\ddot{I}{„}_{\mathrm{dep}}$) on kiloparsec scales in 52 galaxies. We divide each galaxy into two parts: the center, defined as the region within $0.1R_{25}$, and the disk, defined as the region between $0.1$ and $0.7R_{25}$. We find that 14 galaxies show a shorter $\ddot{I}{„}_{\mathrm{dep}}$ ($\sim 1$ Gyr) in the center relative to that in the disk ($\ddot{I}{„}_{\mathrm{dep}}\sim 2.4$ Gyrs), which means the central region in those galaxies is more efficient at forming stars per unit molecular gas mass. This finding implies that the centers with shorter $\ddot{I}{„}_{\mathrm{dep}}$ resemble the intermediate regime between galactic disks and starburst galaxies. Furthermore, the central drop in $\ddot{I}{„}_{\mathrm{dep}}$ is correlated with a central increase in the stellar surface density, suggesting that a shorter $\ddot{I}{„}_{\mathrm{dep}}$ is associated with molecular gas compression by the stellar gravitational potential. We argue that varying the CO-to-H${}_2$ conversion factor only exaggerates the central drop of $\ddot{I}{„}_{\mathrm{dep}}$.

17 pages, accepted in ApJ on Aug 24, 2017