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

We present a new treatment of two popular models for the growth of structure, examining the X-ray emission from hot gas with allowance for spectral 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 model is inconsistent with existing observations-after allowance for the still considerable numerical modeling uncertainties. But we find one important new result. Radiation in the softer band 0.5-1.0 keV is predominantly emitted by gas far from cluster centers (hence ''background''). This background emission dominates the cluster emission below 1 keV, and observations of it should show clear spectral signatures indicating its origin. In particular, the ''iron blend'' should be seen prominently in this spectral bin from cosmic background hot gas at high galactic latitudes and should show shadowing against the SMC indicating its extragalactic origin. Certain O VII lines also provide a signature of this gas which emits a spectrum characteristic of 10(6.6+/-0.6) K gas. Recent Advanced Satellite for Cosmology and Astrophysics observations of the X-ray background tentatively indicate the presence of components with exactly the spectral features we predict here.