A Chandra Observation of the Nearby Lenticular Galaxy NGC 5102: Where Are the X-Ray Binaries?

• Published in: The Astrophysical journal 2005-06, Vol.625 (2), p.785-795
• Main Authors: Kraft, R. P, Nolan, L. A, Ponman, T. J, Jones, C, Raychaudhury, S
• Format: Article
• Language: English
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1086/429982

We present results from a 34 ks Chandra ACIS-S observation of the low-mass X-ray binary (LMXB) population and the hot interstellar medium (ISM) in the nearby (d = 3.1 Mpc) lenticular galaxy NGC 5102, previously shown to have an unusually low X-ray luminosity. We detect 11 X-ray point sources within the D sub(25) optical boundary of the galaxy (93% of the light), one-third to one-half of which are likely to be background active galactic nuclei (AGNs). One of the X-ray sources is coincident with the optical nucleus and may be a low-luminosity AGN. Only two sources with an X-ray luminosity greater than 10 super(37) ergs s super(-1) in the 0.5-5.0 keV band were detected, one of which is statistically likely to be a background AGN. We expected to detect seven or five such luminous sources if the X-ray binary (XRB) population scales linearly with the B-band or J-band magnitudes, respectively, of the host galaxy. By this measure, NGC 5102 has an unusually low number of XRBs. The deficit of LMXBs is even more striking, because some of these sources may in fact be high-mass X-ray binaries (HMXBs). NGC 5102 is unusually blue for its morphological type and has undergone at least two recent bursts of star formation only similar to 1.5 x 10 super(7) and similar to 3 x 10 super(8) yr ago. We present the results of optical/UV spectral synthesis analysis and demonstrate that a significant fraction (>50%) of the stars in this galaxy are comparatively young (