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Astronomy

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    $\begingroup$ I didn't have the knowledge to answer the primary question. i do have the google fu to answer the side question. References to that word are easy to find if one gives google a helping hand. Here are four such references: 1, 2, 3, 4. There are several others. $\endgroup$
    – David Hammen
    Commented Jan 28 at 13:02
  • $\begingroup$ For a 21 cm radio image of an ordinary galaxy, see nrao.edu/pr/2001/m33gas $\endgroup$
    – John Doty
    Commented Jan 29 at 1:03
  • $\begingroup$ baryonic mass of a cloud/galaxy - For a galaxy with stars, it wouldn't be counting mass of hydrogen inside stars, right? Because they'd be plasma, not atoms with electrons. Are we just talking about "dark galaxies" here, or is most of the hydrogen in a typical galaxy not in stars? (Or you meant to write something else, or I'm missing something...) $\endgroup$
    – Peter Cordes
    Commented Jan 29 at 18:52
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    $\begingroup$ @PeterCordes indeed. Only the baryonic mass in the form of neutral hydrogen. $\endgroup$
    – ProfRob
    Commented Jan 29 at 18:57