paper

A Multi-wavelength Study of the X-ray Sources in NGC 5018

arXiv:astro-ph/0502114 · doi:10.1086/428939

Abstract

The E3 giant elliptical galaxy NGC5018 was observed with the Chandra X-ray Observatory on 14 April 2001. Results of analysis of these X-ray data as well as of complementary optical, infrared, and radio data are reported. Seven X-ray point sources, including the nucleus, were detected.If they are intrinsic to NGC5018, then all six non-nuclear sources have luminosities exceeding E+39 ergs/s in the 0.5-8.0 keV energy band; placing them in the class of Ultra-luminous X-ray sources. Comparison of X-ray source positions to archival HST/WFPC2 images reveal four of the six non-nuclear sources are spatially-coincident with bright, absolute-magnitude (V) around -8.6 mag, objects. These four objects have optical magnitudes and (V-I) colors consistent with globular clusters in NGC5018 but they also have X-ray-to-optical flux ratios consistent with background active galactic nuclei. Strong, unpolarized, radio emission has been detected from one of the optically-bright counterparts. Another optically-bright counterpart was observed to vary by one mag in optical observations taken 28 July 1997 and 04 Feb 1999. Extended X-ray emission is detected within a 15"radius of the galaxy center at a luminosity of E+40 ergs/s in the X-ray band. Its thermal X-ray spectrum (kT around 0.4 keV) and its spatial coincidence with strong H_alpha emission are consistent with a hot gas origin. The nucleus itself may be a weak X-ray source, around E+39 ergs/s, that displays a radio spectrum typical of AGN.

arXiv commentText with 15 figures and 5 Tables. To appear in the 10 May 2005, issue of The Astrophysical Journal

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