Constraints on a Local Group X-ray halo

A simple model for a hot Local Group halo is constructed using the standard beta -model for the halo density and by choosing model parameters based on all available observations of X-ray emission in other groups of galaxies a nd on optical data of Local Group morphology. From the predicted X-ray inte nsities, total Local Group mass, and central cooling time of the halo, we d erive very conservative upper limits on the central halo density and global temperature T of N-o = 5 x 10(-4) cm(-3) and kT = 0.5 keV, irrespective of realistic values of the density profile parameters r(c) and beta. A typica l poor group value of beta = 0.5 requires kT = 0.15 keV and N-o < 10(-4) cm (-3), from which it is concluded that the Local Group is very unlikely to p ossess a significant X-ray halo. The prospects for further constraining hal o parameters from UV absorption-line observations are considered. We explic itly calculate the ability of the halo to distort the cosmic microwave back ground (CMB) in terms of the resulting CMB temperature variations and multi pole anisotropies.