Abstract
I SUGGEST here that the disk of the Galaxy is surrounded by a shell of gas at a temperature intermediate between the 102–104 K of the disk and the 106 K of the corona1, and that this “chromosphere” may be detectable. This suggestion is related to the hypothesis2,3 that the Galaxy is accreting hot gas from the intergalactic space of the Local Group. According to the calculations of Hunt4, if accretion is occurring the rate of mass influx ∼2n−4/T6 M⊙ per year, where n−4 and T6 are the unenhanced density and temperature of the intergalactic gas in units of 10−4 atoms cm−3 and millions of degrees respectively, and the mass and velocity of the Galaxy are taken to be 1.7 × 1011 M⊙ and less than ∼100 km s−1. We shall adopt as representative values n−4∼3 and T6∼2 (for further discussion and references, see ref. 3) which lead to an accretion rate ∼3 M⊙ per year. This rate is compatible with dynamical considerations concerning the motion of interstellar gas in the disk of the Galaxy, and with the age of the Galaxy, the present density of this gas and estimates5 of the rate of star formation.
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SCIAMA, D. On a Possible Interstellar Galactic Chromosphere. Nature 240, 456–457 (1972). https://doi.org/10.1038/240456a0
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DOI: https://doi.org/10.1038/240456a0
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