Contribution of Bremsstrahlung Emission from Lyα Clouds to the Microwave Background Fluctuations

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Abstract
I calculate the contribution of bremsstrahlung emission from Lyα 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 ΔT/T = 10-5.5±0.4 J221 1/2 (λ/5 cm)2, which varies over characteristic angular scales ~1''-100'', where λ is the observed wavelength and J221 1/2 is a weighted redshift average of the UV background intensity at the Lyman limit in units of 10-21 ergs 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 J221 1/2 101.3±0.4, unless some of the extended flat-spectrum sources that were detected are Lyα absorption systems.
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