- [*] An HST Survey of Intermediate Luminosity X-ray Objects
- Roye E.W., Colbert E.J.M., Heckman T., Ptak R.F.,
van der Marel R.P.
- BAAS, in press, 2003 (HEAD meeting 35, 14.03)
- © 2003. The American Astronomical Society.
All Rights Reserved.
We searched for optical counterparts to 54 Intermediate-luminosity
X-ray Objects (IXOs, a.k.a. ULXs) using HST WFPC2 archive data, and
have uncovered a high yield of intriguing possible correlations. A
total of 124 IXOs were identified from searching all of the Chandra
ACIS archival galaxy data as of July 17, 2002. Archival WFPC2 data
were available for 54 of these IXOs. The optical data utilized in this
study consisted of 121 HST WFPC2 associations (stacked images). We
will discuss the various methods used to register the HST WFPC2 images
with the Chandra X-ray images. Our preliminary analysis indicates that
37 (~70%) of the 54 IXOs have at least one 4 sigma counterpart within
1" of the IXO position, and ~25% have unique counterparts (mostly in
elliptical galaxies). The detection limit of the counterparts was
typically 24-25 magnitudes in B, V, and R. The absolute magnitudes of
many of the found counterparts appeared to correspond roughly to
either the expected magnitudes for globular clusters, or the expected
magnitudes for the brightest stars. Initial results illustrate that of
the 37 IXOs with counterparts, 25 (~70%) were in spiral, irregular,
and merger galaxies, where the counterparts were often diffuse or
clump-like sources. The counterparts found in elliptical galaxies
were primarily single luminous point-sources, most likely globular
clusters. We will discuss the results of color analysis for fields
where counterparts in multiple bands exist, particularly for cases
where a single counterpart is found. A preliminary finding in
elliptical galaxies is that globular clusters associated with IXOs
tend to be red, suggesting that IXOs are not found in metal-poor
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Last modified March 30, 2003.
Roeland van der Marel,