Continuum Emission by Cooling Clouds

The collapse of baryons into the center of a host dark matter halo is accompanied by radiation that may be detectable as compact (≲10 kpc) UV-continuum and Lyα emission with Lyα luminosities as high as ∼10 42 –10 43 erg s −1 in halos of mass M = 10 11 –10 12 M ☉ . We show that the observed equivalent width (EW) of the Lyα line emitted by these cooling clouds is EW ≲ 400 Å (rest frame). These luminosities and EWs are comparable to those detected in narrowband surveys for redshifted Lyα emission. The rest-frame ultraviolet of Lyα-emitting cooling clouds radiation may be dominated by two-photon transitions from 2s → 1s. The resulting spectrum can distinguish cooling clouds from a broad class of young star-forming galaxies.