SPECTRAL APPEARANCE OF NONUNIFORM GAS AT HIGH-Z

The spectrum of non-uniform gas emitting line radiation in an expanding universe displays frequency structure on scale fJvjv 10-3 if the scale of lumpiness is 1o-3 cH-1, but the detailed spectral structure is correspondingly uncorrelated on angular scales larger than 10-3 rad (4 arcmin). Thus, lumpy high-redshift gas may appear as a distinctive signature in the variation of the spectrum of background radiation across the sky, even if the bulk of the background comes from other sources. 21-cm emission or absorption might be visible with present techniques out to 1+z 10 (150 MHz), Ly-a emission out to 1+z 5 (6000 A). These observations would be a valuable probe of cosmic structure at early times. © Royal Astronomical Society • Provided by the NASA Astrophysics Data System.