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D. M. Clark, S. S. Eikenberry (University of Florida), B. R. Brandl (Cornell University and Leiden University), J. C. Wilson (Cornell University and University of Virginia), J. C. Carson (Cornell University and University of Florida), C. P. Henderson (Cornell University), T. P. Hayward (Gemini), D. J. Barry, J. R. Houck (Cornell University), A. Ptak, E. Colbert (Johns Hopkins University)
We use deep J (1.25 \mum) and Ks (2.15 \mum) images of the Antennae (NGC 4038/9) obtained with the Wide-field InfraRed Camera on the Palomar 200-inch telescope, together with the Chandra X-ray source list of Zezas et al. (2001), to establish an X-ray/IR astrometric frame tie with ~ 0.5 \arcsec RMS residuals over a ~5 \arcmin field. We find 13 ``strong" IR counterparts <1.0 \arcsec from X-ray sources, and an additional 6 ``possible" IR counterparts between 1.0 \arcsec and 1.5 \arcsec from X-ray sources. Based on detailed study of the surface density of IR sources near the X-ray sources, we expect only ~2 of the ``strong" counterparts and ~3 of the ``possible" counterparts to be chance superpositions of unrelated objects.
Comparing the IR counterparts to our photometric study of ~250 IR clusters in the Antennae, we find that IR counterparts to X-ray sources are \Delta MK ~1.2 mag more luminous than average non-X-ray clusters (>99.9% confidence), and that the X-ray/IR matches are concentrated in the spiral arms and ``bridge" regions of the Antennae. This implies that these X-ray sources lie in the most ``super" of the Antennae's Super Star Clusters, and thus trace the recent massive star formation history here. Based on the NH inferred from the X-ray sources without IR counterparts, we determine that the absence of most of the ``missing" IR counterparts is not due to extinction, but that these sources are intrinsically less luminous in the IR, implying that they trace a different (older?) stellar population. We find no clear correlation between X-ray luminosity classes and IR properties of the sources, though small number statistics hamper this analysis.
Finally, we find a Ks = 16.2 mag counterpart to the Ultra-Luminous X-ray (ULX) source X-37 within <0.5 \arcsec, eliminating the need for the ``runaway binary" hypothesis proposed by previous authors for this object. We discuss some of the implications of this detection for models of ULX emission.
This work is funded by an NSF CAREER grant.
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.