* Astronomy

Title: Infrared Counterparts to Chandra X-Ray Sources in the Antennae
Authors: D.M. Clark, S.S. Eikenberry, B.R. Brandl, J.C. Wilson, J.C. Carson, C.P. Henderson, T. L. Hayward, D.J. Barry, A.F. Ptak, E.J.M. Colbert

We use deep J and Ks images of the Antennae (NGC 4038/9) obtained with WIRC on the Palomar 200-inch telescope, together with the Chandra X-ray source list of Zezas et al. (2002a), to search for IR counterparts to X-ray point sources. We establish an X-ray/IR astrometric frame tie with 0.5" rms residuals over a \~4.3' field. We find 13 ''strong'' IR counterparts brighter than Ks = 17.8 mag and < 1.0" from X-ray sources, and an additional 6 "possible'' IR counterparts between 1.0" and 1.5" from X-ray sources. The surface density of IR sources near the X-ray sources suggests only ~2 of the "strong'' counterparts and ~3 of the "possible'' counterparts are chance superpositions of unrelated objects.
Comparing both strong and possible IR counterparts to our photometric study of ~220 Antennae, IR clusters, we find the IR counterparts to X-ray sources are \~1.2 mag more luminous in Ks than average non-X-ray clusters. We also note that the X-ray/IR matches are concentrated in the spiral arms and ''overlap'' 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 N_H inferred from the X-ray sources without IR counterparts, we determine that the absence of most of the ''missing'' IR counterparts is because they are intrinsically less luminous in the IR, implying that they trace a different (possibly older) stellar population.

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A new Hubble image of the Antennae galaxies is the sharpest yet of this merging pair of galaxies. As the two galaxies smash together, thousand of millions of stars are born, mostly in groups and clusters of stars.


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Credit NASA

The Universe is an all-action arena for some of the largest, most slowly evolving and surprising processes known to mankind. A new picture taken by the Advanced Camera for Surveys (ACS), onboard the NASA/ESA Hubble Space Telescope, shows the best ever view of the Antennae galaxies - seemingly a violent clash between a pair of once isolated galaxies, but in reality a fertile marriage.

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