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 and on optical data of Local Group morphology. From the predicted X-ray intensities, total Local Group mass, and central cooling time of the halo, we derive 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 typical 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 possess a significant X-ray halo. The prospects for further constraining halo parameters from UV absorption-line observations are considered. We explicitly calculate the ability of the halo to distort the cosmic microwave background (CMB) in terms of the resulting CMB temperature variations and multipole anisotropies.