BACKGROUND X-RAY-EMISSION FROM HOT GAS IN CDM AND CDM- SPECTRAL SIGNATURES(LAMBDA UNIVERSES )

We present a new treatment of two popular models for the growth of str ucture, examining the X-ray emission from hot gas with allowance for s pectral line emission from various atomic species, primarily ''metals. '' The X-ray emission from bright cluster sources is not significantly different from that found in prior work and, as noted earlier, shows that the CDM+A model is consistent but the standard, COBE-normalized m odel is inconsistent with existing observations-after allowance for th e still considerable numerical modeling uncertainties. But we find one important new result. Radiation in the softer band 0.5-1.0 keV is pre dominantly emitted by gas far from cluster centers (hence ''background ''). This background emission dominates the cluster emission below 1 k eV, and observations of it should show clear spectral signatures indic ating its origin. In particular, the ''iron blend'' should be seen pro minently in this spectral bin from cosmic background hot gas at high g alactic latitudes and should show shadowing against the SMC indicating its extragalactic origin. Certain O VII lines also provide a signatur e of this gas which emits a spectrum characteristic of 10(6.6+/-0.6) K gas. Recent Advanced Satellite for Cosmology and Astrophysics observa tions of the X-ray background tentatively indicate the presence of com ponents with exactly the spectral features we predict here.