The Disk-Halo Connection and Where Has All The Gas Gone - Astrophysics > Cosmology and Nongalactic AstrophysicsReportar como inadecuado

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Abstract: The wealth of data in the past decades, and especially in the past 15 yearshas transformed our picture of the gas around the Milky Way and other spiralgalaxies. There is good evidence for extraplanar gas that is a few kpc inheight and is seen in all gaseous phases: neutral; warm atomic; and hot, X-rayemitting gas. This medium is seen not only around the Milky Way, but otherspiral galaxies and it is related to the star formation rate, so it is likelyproduced by the activity in the disk through a galactic fountain. More extendedexamples of halo gas are seen, such as the HVC around the Milky Way and aroundM31. This gas is typically 10-20 kpc from the galaxy and is not seen beyond 50kpc. This gas is most likely being accreted. A hot dilute halo 1E6 K ispresent with a similar size, although its size is poorly determined. An ongoingcontroversy surrounds the relative amounts of outflow from the disk andaccretion onto galaxies such as the Milky Way. There is good evidence foraccretion of cold material onto the Milky Way and other galaxies, but it is notclear if there is enough to modify the gas content and star formationproperties in the disk. The reservoir of accretion material is as yetunidentified. Some of these findings may be related to the issue that galaxiesare baryon-poor: their baryon to dark matter ratio is well below thecosmological value. The absence of baryons may be due to extremely violentoutflow events in the early stages of galaxy formation. We may be able tounderstand this stage of galaxy evolution by applying our deepeningunderstanding of our local disk-halo environment.

Autor: Joel N. Bregman


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