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Circumgalactic and Intergalactic Media
One of the triumphs of the Big Bang Nucleosynthesis (BBN) theory is that its predicted
abundances of primordial isotopes agree with the measured values. Moreover, the predicted
baryonic mass seems to be accounted for at high redshifts (z > 2-3) observationally.
Going towards lower redshifts, however, only about two thirds of the BBN baryons are
detected; this is the "missing baryon problem". The common wisdom is that those baryons
are not actually missing, but are hidden in some warm-hot gas of very low density, which
makes it difficult to detect; cosmological hydrodynamic simulations support this view.
Such gas may be "seen" through the emission or absorption lines of its highly ionized
constituents. For that, an X-ray spectrometer of high throughput and high resolution
would likely be required. We are developing cryogenic microcalorimeters for a
spectroscopic satellite mission that is being conceptualized to significantly advance
the study of circumgalactic and intergalactic media (and thus the formation and evolution