Circumnuclear Star Clusters in the Galaxy Merger Ngc 6240, Observed with Keck Adaptive Optics and the Hubble Space Telescope

Q1 We discuss images of the central 10 kpc (in projection) of the galaxy merger NGC 6240 at H and K 0 bands, taken with the NIRC2 narrow camera on Keck II using natural guide star adaptive optics. We detect 28 star clusters in the NIRC2 images, of which only 7 can be seen in the similar spatial resolution, archival WFPC2 Planetary Camera data at either B or I band. Combining the NIRC2 narrow camera pointings with wider NICMOSNIC2 images taken with the F110W, F160W, and F222Mfilters, we identify a total of 32 clusters that are detected in at least one of these five infrared (kc > 1 m) bandpasses. By comparing to instantaneous burst, stellar population synthesis models (Bruzual & Charlot) Q2 , we estimate that most of the clusters are consistent with being 15Myr old and have photometric masses ranging from 7 ; 10 to 4 ; 10 M . The total contribution to the star formation rate (SFR) from these clusters is approximately 10M yr , or 10% of the total SFR in the nuclear region. We use these newly discovered clusters to estimate the extinction towardNGC6240’s double nuclei and find values of AV as high as 14mag along some sight lines, with an average extinction of AV 7 mag toward sight lines within 300 of the double nuclei. Subject headinggs: galaxies: individual (NGC 6240) — galaxies: interactions — galaxies: starburst — galaxies: star clusters — instrumentation: adaptive optics