The Core of NGC 6240 from Keck Adaptive Optics andHubble Space TelescopeNICMOS Observations

We present results of near infrared imaging of the disk-galaxy-merger NGC6240 using adaptive optics on the Keck II Telescope and reprocessed archivaldata from NICMOS on the Hubble Space Telescope. Both the North and South nucleiof NGC 6240 are clearly elongated, with considerable sub-structure within eachnucleus. In K' band there are at least two point-sources within the Northnucleus; we tentatively identify the south-western point-source within theNorth nucleus as the position of one of the two AGNs. Within the South nucleus,the northern sub-nucleus is more highly reddened. Based upon the nuclearseparation measured at 5 GHz, we suggest that the AGN in the South nucleus isstill enshrouded in dust at K' band, and is located slightly to the north ofthe brightest point in K' band. Within the South nucleus there is strong H2 1-0S(1) line emission from the northern sub-nucleus, contrary to the conclusionsof previous seeing-limited observations. Narrowband H2 emission-line imagesshow that a streamer or ribbon of excited molecular hydrogen connects the Northand South nuclei. We suggest that this linear feature corresponds to a bridgeof gas connecting the two nuclei, as seen in computer simulations of mergers.Many point-like regions are seen around the two nuclei. These are mostprominent at 1.1 microns with NICMOS, and in K'-band with Keck adaptive optics.We suggest that these point-sources represent young star clusters formed in thecourse of the merger.Comment: 50 pages, 13 figures. To be published in the Astrophysical Journal, March 10, 200