Events at Physics |
for a tiny fraction of the ordinary matter in the universe, and astronomers have been intensively searching for the missing baryons for more than a decade, with some palpable (but frustratingly slow) progress. It is likely that the missing baryons are hiding out in very low-density plasmas in galaxy halos and the intergalactic medium.<br>
It is difficult to detect emission from those shady plasmas; ultraviolet and X-ray absorption spectroscopy will provide the main tools for surveillance of most of the baryons for the foreseeable future. UV spectroscopy provides a particularly potent combination of high spectral resolution (R = 20,000 to >>>100,000), rich diagnostics of physical conditions, access to a large number of metals, and many bright background continuum sources. Detection of the missing baryons is a consistency check of CDM cosmology and how large-scale structures grow, but it is also much more. Galaxy-halo-IGM interactions via inflows and outflows must play a major role in galaxy evolution, but again the baryons in the flows are dark, and the flow physics are poorly understood due to missing observational constraints, e.g., of cooling gas at T > 100,000 K.
With the recent deployment of the UV Cosmic Origins Spectrograph on HST, we are on the verge of a major observational bust of the dark baryons. Using data from UV spectrographs on HST and FUSE, this talk will demonstrate the power of the technique and anticipate upcoming breakthroughs. Examples will include insights on galaxy transformation via ram-pressure stripping (or something) and gas consumption, dusty and multiphase galactic fountains, and a new signature of galactic flows. Within 5 years, COS will provide strong statistical constraints on the quantity and physical state of baryons in halos and the IGM.