分子氢

• Mid-infrared molecular hydrogen (H2) emission is a powerful cooling agent in galaxy mergers and in radio galaxies; （ rotational transition）[1]
• Table 1. H2 Rotational Transitionsa

• Notation b Transition c Rest λµm d Eu=k [K] e A [10−7 s−1] f g (J) g
• S(0) J = 2 - 0 28.219 510 0.00029 5
• S(1) J = 3 - 1 17.035 1015 0.00476 21
• S(2) J = 4 - 2 12.279 1682 0.0276 9
• S(3) J = 5 - 3 9.665 2504 0.0984 33
• S(4) J = 6 - 4 8.025 3474 0.264 13
• S(5) J = 7 - 5 6.910 4586 0.588 45
• S(6) J = 8 - 6 6.109 5829 1.14 17
• S(7) J = 9 - 7 5.511 7197 2.00 57

• The [C II] 158um emission

correlates with galaxies' molecular gas mass, with a mean absolute deviation of 0.2 dex and without evident systematics:

the [C II]-to-H2 conversion factor (alpha_[C II] ~ 30 Msun/Lsun) is largely independent of galaxies' depletion time, metallicity, and redshift.