Submillimeter Array Observations of Extended CO (J = 2 − 1) Emission in the Interacting Galaxy NGC 3627

Abstract

Abstract We present moderate (∼5″) and high angular resolution (∼1″) observations of 12CO (J = 2 − 1) emission toward the 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 ∼400–450 km s−1 is seen across the entire galaxy with velocity dispersions ranging from ≲80 km s−1 toward the nuclear region to ≲15 km s−1 in the spiral arms. We also detect unresolved 13CO (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 C18O(J = 2 − 1) line emission is detected at a 3σ 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 ∼5 to 10 K (in the spiral arms) to ∼25 K (at the center) and H2 number densities from ∼400 to 1000 cm−3 (in the spiral arms) to ∼12,500 cm−3 (at the center). From this density modeling, we find a total H2 mass of 9.6 × 109 M ⊙, which is ∼50% higher than previous estimates made using a constant H2–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 ∼207 km s−1 and estimate a total dynamical mass of 4.94 ± 0.70 × 1010 M ⊙ at a galactocentric radius of ∼6.2 kpc (121″).