HIGH-RESOLUTION ~(13)CO AND C~(18)O J = 1-0 OBSERVATIONS OF NGC 1068: MOLECULAR GAS PROPERTIES AND A HIGH C~(18)O/~(13)CO INTENSITY RATIO

摘要

We present high-resolution (～5″-6″) aperture synthesis observations of ~(13)CO and C~(18)O J = 1-0 lines in the prototypical Seyfert 2 galaxy NGC 1068. The line ratio S_v(~(12)CO)/S_v(~(13)CO) varies significantly along the ring, indicating optical depth variations. We also find a high average line ratio < R > = < S_v(C~(18)O)/S_v(~(13)CO) > = 0.3, which is almost twice the highest value in our own galaxy. This is also one of the highest values reported to date for an extragalactic source and the first such measurement for Seyfert galaxies. We argue that such a high value could be the result of optical depth effects and/or an intrinsically high [C~(18)O/~(13)CO] abundance.