Stellar Dynamics and the Implications on the Merger Evolution in NGC 6240

We report near-infrared integral field spectroscopy of the luminous merginggalaxy NGC 6240. Stellar velocities show that the two K-band peaks separated by1.6arcsec are the central parts of inclined, rotating disk galaxies with equalmass bulges. The dynamical masses of the nuclei are much larger than thestellar mass derived from the K-band light, implying that the progenitorgalaxies were galaxies with massive bulges. The K-band light is dominated byred supergiants formed in the two nuclei in starbursts, triggered ~2x10^7 yearsago, possibly by the most recent perigalactic approach. Strong feedback effectsof a superwind and supernovae are responsible for a short duration burst(~5x10^6 years) which is already decaying. The two galaxies form aprograde-retrograde rotating system and from the stellar velocity field itseems that one of the two interacting galaxies is subject to a progradeencounter. Between the stellar nuclei is a prominent peak of molecular gas(H_2, CO). The stellar velocity dispersion peaks there indicating that the gashas formed a local, self-gravitating concentration decoupled from the stellargravitational potential. NGC 6240 has previously been reported to fit theparadigm of an elliptical galaxy formed through the merger of two galaxies.This was based on the near-infrared light distribution which follows ar^1/4-law. Our data cast strong doubt on this conclusion: the system is by farnot relaxed, rotation plays an important role, as does self-gravitating gas,and the near-infrared light is dominated by young stars.Comment: 34 pages, 11 figures, using AASTEX 5.0rc3.1, paper submitted to the Astrophysical Journal, revised versio