Based on archival Chandra observations with a total exposure of 1.3 Ms , we study X-ray point sources in the Fornax cluster of galaxies , with the primary aim of searching for intra-cluster X-ray source populations .
We detect 1177 point sources out to a projected radius of \sim 30 arcmin ( \sim 180 kpc ) from the cluster center and down to a limiting 0.5–8 keV luminosity of \sim 3 \times 10 ^ { 37 } { ~ { } erg~ { } s ^ { -1 } } .
We construct source surface density profile , after excluding sources associated with foreground stars , known globular clusters , ultra-compact dwarfs and galactic nuclei .
From this profile we statistically identify \sim 183 excess sources that are not associated with the bulk stellar content of the individual member galaxies of Fornax , nor with the cosmic X-ray background .
Taking into account Poisson error and cosmic variance , the cumulative significance of this excess is at \gtrsim 2 \sigma level ( with a maximum of 3.6 \sigma ) outside three effective radii of the central giant elliptical , NGC 1399 .
The luminosity function of the excess sources is found to be significantly steeper than that of the GC-hosting sources ( presumably low-mass X-ray binaries [ LMXBs ] ) , disfavoring the possibility that unidentified GCs are primarily responsible for the excess .
We show that a large fraction of the excess can be related to the extended stellar halo of NGC 1399 and/or the diffuse intra-cluster light , thus providing strong evidence for the presence of intra-cluster X-ray sources in Fornax , the second unambiguous case for a galaxy cluster after Virgo .
Other possible origins of the excess , including supernova-kicked LMXBs and stripped nucleated dwarf galaxies are discussed .