Evidence for Hot, Diffuse Gas in the Local Supercluster

Abstract

Using the HEAO1 A2 full sky, 2-10 keV X-ray map evidence is found for the presence of diffuse X-ray emission in the plane of the local supercluster. Fitting this diffuse component with a simple ``pillbox'' model implies a volume X-ray emissivity of 3.0 +- 0.3 x 10**39 (20 Mpc/R) erg/s/Mpc**3 where R is the radius of the supercluster and the error is photon counting noise only. If one considers fluctuations in the X-ray background as an additional component of noise then the significance of the detection is reduced to 2 to 3 sigma. This is consistent with fits of the model to data sets obtained by rotating the original data. The distribution of these rotated fits indicates that the detection is signficant at the 99% confidence level. If the source of the X-ray emission is Bremsstrahlung from a uniformly distributed plasma with temperature T_e then the implied electron number density is N_e = 2.5 x 10**-6 (R/20Mpc)**-1/2 (kT_e /10 keV)**-1/4 cm**-3. This value is about an order of magnitude larger than the average baryon number density implied by nucleosynthesis and is consistent with a collapse factor of 10. A search for similar structure in the COBE 53 GHz microwave background map yielded a marginal 1 sigma detection of -17 microKelvin which is consistent with the Sunyaev-Zel'dovich (SZ) effect expected from 10 keV gas.