AChandraObservation of the Nearby Lenticular Galaxy NGC 5102: Where Are the X‐Ray Binaries?

We present results from a 34 ks Chandra/ACIS-S observation of the nearby(d=3.1 Mpc) lenticular galaxy NGC 5102, previously shown to have an unusuallylow X-ray luminosity. We detect eleven X-ray point sources within the the$D_{25}$ optical boundary of the galaxy (93% of the light), one third to onehalf of which are likely to be background AGN. One source is coincident withthe optical nucleus and may be a low-luminosity AGN. Only two sources with anX-ray luminosity greater than 10$^{37}$ ergs s$^{-1}$ in the 0.5-5.0 keV bandwere detected, one of which is statistically likely to be a background AGN. Weexpected to detect 6 such luminous sources if the XRB population scaleslinearly with optical magnitude of the host galaxy. NGC 5102 has an unusuallylow number of XRBs. NGC 5102 is unusually blue for its morphological type, andhas undergone at least two recent bursts of star formation. We present theresults of optical/UV spectral synthesis analysis and demonstrate that asignificant fraction ($>$50%) of the stars in this galaxy are comparativelyyoung ($<3\times10^9$ years old). If the lack of X-ray binaries is related tothe relative youth of most of the stars, this would support models of LMXBformation and evolution that require wide binaries to shed angular momentum ona timescale of Gyrs. We find that NGC 5102 has an unusually low specificfrequency of globular clusters ($S_N\sim$0.4), which could also explain thelack of LMXBs. We also detect diffuse X-ray emission in the central $\sim$1 kpcof the galaxy. This hot gas is most likely a superbubble created by multiplesupernovae of massive stars born during the most recent star burst, and isdriving the shock into the ISM which was inferred from optical observations.Comment: 33 pages, 7 figures, 6 tables - Accepted for publication in the Astrophysical Journa