Chandra and ROSAT Observations of NGC 5044: Profile of Dark Halos in Galaxy Groups

Abstract

Abstract We combined spatially resolved Chandra data with the ROSAT data to constrain the dark-matter distribution in the galaxy group NGC 5044. Within $250 \, h^{-1}_{50} \,\mathrm{kpc}$, the total mass is found to be $\sim 1.6 \times10^{13} \,{{{M}_{\odot}}}$, 12% of which constitutes baryonic mass. Within the inner central regions, the total mass profile exhibits a double structure, typical for groups containing a cD galaxy. Following previous studies of mostly rich galaxy clusters, we studied in detail the nature of such a double structure, whereby we inferred likely interface between the cD galaxy and the surrounding galaxies. For this interesting group, we determined for the first time the galaxy-group interface, which is around 7.5 kpc from the peak of the X-ray emission. The total mass internal to this interface radius is found to be ${\sim 7.1 \times10^{10} \,{{{M}_{\odot}}}}$. Beyond this radius, the total mass profile becomes DM-dominated and the corresponding DM profile is reasonably fitted with the NFW model, yielding results consistent with the observed scatter expected for CDM halos. A power-law fit to the DM mass profile gives $\alpha = 1.88 \pm 0.32$, a slope that is within the observed range, but is significantly larger than that of low surface brightness galaxies and self-interacting DM halos.