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Paper: Where Are the Missing Baryons and Metals?
Volume: 390, Pathways Through an Eclectic Universe
Page: 483
Authors: Pagel, B.E.J.
Abstract: The question of missing baryons arises because the smoothed-out density of baryons in the Universe is known from WMAP and primordial deuterium to be close to ΩB = 0.04, whereas the corresponding figure for stars, based on the luminosity density from galaxy redshift surveys, is only 1/10 of this, or less, giving rise to the concept of “baryonic dark matter”.

A clue to the nature of the missing baryons comes from the statistics of the Lyman-α forest at redshifts of 2 to 3, where the abundance of the corresponding ionized gas is estimated to be virtually equal to ΩB. Most of that gas is probably still there, partly in the form of remaining Lyman-α forest and partly in the form of still more highly ionized intra-cluster and warm–hot intergalactic gas (WHIM). Most of the “metals” seem to be about equally shared between the WHIM and stars.

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