STELLAR KINEMATICS IN THE NUCLEUS OF NGC-6240 - A MASSIVE GALAXY REVEALED

We have used the 2.3 mum bandhead of CO to measure the kinematics of t he red stellar population in the nucleus of the luminous galaxy NGC 62 40, the near-infrared spectrum of which is dominated by lines of shock ed gas. With this manifest evidence for dissipative effects in the gas , it is such stellar velocity dispersion that is most unambiguously in dicative of gravitational potential. We find a nuclear velocity disper sion sigma = 350 km s-1 which is considerably larger than that seen in any gaseous component of this galaxy. At least one partner in this me rger must therefore have been very massive, with M(B) approximately -2 3. In view of conventional wisdom that the high luminosity of NGC 6240 derives from star formation, it is surprising that we find M/L to be of order unity. While there seems to be little question that star form ation is taking place in this interacting system, this high M/L calls into question the importance of star formation in the luminosity budge t of the galaxy. In particular, it seems likely that the red starlight in NGC 6240 is produced by giants rather than a population of young r ed supergiants. This brings into question the (now reflexive) associat ion of relatively deep CO bands in galaxies (which are conspicuously s trong in NGC 6240) with recent star formation.