Contribution of Bremsstrahlung Emission from Lyman-alpha Clouds to the Microwave Background Fluctuations
Abstract
I calculate the contribution of Bremsstrahlung emission from Lyman-alpha absorption clouds to the brightness of the microwave sky. The calculation is based only on the assumption that the clouds below the Lyman-limit are in photoionization equilibrium with a UV background radiation, and avoids any uncertainty about the clumpiness of the gas. I predict a minimum fluctuation amplitude in the Rayleigh-Jeans regime of DeltaT/T = 10-5.5+-0.4*J21*(L/5cm)2, which varies over characteristic angular scales of 1-100'', where L is the observed wavelength and J21 is a weighted redshift average of the UV background intensity at the Lyman-limit in units of 10-21 erg cm-2 s-1 Hz-1 sr-1. Detection of this signal can be used to map the intergalactic hydrogen distribution and to calibrate the UV background at high redshifts. Existing VLA observations constrain J21<101.3+-0.4, unless some of the extended flat-spectrum sources which were detected are Lyman-alpha absorption systems.
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