TRACING HIGH-DENSITY GAS IN M82 AND NGC 4038

We present the first detection of CS in the Antennae galaxies toward the NGC 4038 nucleus, as well as the first detections of two high-J (5-4 and 7-6) CS lines in the center of M82. The CS(7-6) line in M82 shows a profile that is surprisingly different from those of other low-J CS transitions we observed. This implies the presence of a separate, denser and warmer molecular gas component. The derived physical properties and the likely location of the CS(7-6) emission suggest an association with the supershell in the center of M82. © 2008. The American Astronomical Society. All rights reserved. Printed in U.S.A