SMA Observations of Extended $\mathrm{CO}(\mathrm{J}=2-1)$ Emission in Interacting Galaxy NGC 3627

Abstract

We present moderate ($\sim 5^{\prime \prime }$) and high angular resolution ($\sim 1^{\prime \prime }$) observations of ${}^{12}\mathrm{CO}(\mathrm{J}=2-1)$ emission toward nearby, interacting galaxy NGC 3627 taken with the Submillimeter Array (SMA). These SMA mosaic maps of NGC 3627 reveal a prominent nuclear peak, inter-arm regions, and diffuse, extended emission in the spiral arms. A velocity gradient of $\sim 400$-$450$ km s${}^{-1}$ is seen across the entire galaxy with velocity dispersions ranging from $\lesssim 80$ km s${}^{-1}$ toward the nuclear region to $\lesssim 15$ km s${}^{-1}$ in the spiral arms. We also detect unresolved ${}^{13}\mathrm{CO}(\mathrm{J}=2-1)$ line emission toward the nuclear region, southern bar end, and in a relatively isolated clump in the southern portion of the galaxy, while no ${\mathrm{C}}^{18}\mathrm{O}(\mathrm{J}=2-1)$ line emission is detected at a $3\ddot{I}ƒ$ rms noise level of 42 mJy beam${}^{-1}$ per 20 km s${}^{-1}$ channel. Using RADEX modeling with a large velocity gradient approximation, we derive kinetic temperatures ranging from $\sim 5$-$10$ K (in the spiral arms) to $\sim 25$ K (at the center) and H${}_2$ number densities from $\sim$400-1000 cm${}^{-3}$ (in the spiral arms) to $\sim$12500 cm${}^{-3}$ (at the center). From this density modeling, we find a total H${}_2$ mass of $9.6\times 10^9{M}_{\odot }$, which is $\sim 50\%$ higher than previous estimates made using a constant H${}_2$-CO conversion factor but is largely dependent on the assumed vertical distribution of the CO gas. With the exception of the nuclear region, we also identify a tentative correlation between star formation efficiency and kinetic temperature. We derive a galactic rotation curve, finding a peak velocity of $\sim 207$ km s${}^{-1}$ and estimate a total dynamical mass of $4.94\pm 0.70\times 10^{10}{M}_{\odot }$ at a galactocentric radius of $\sim 6.2$ kpc ($121^{\prime \prime }$).

18 pages, 10 figures, accepted for publication in ApJ