H[TINF]2[/TINF] Emission from the Inner 400 Parsecs of the Galaxy

Abstract

We have mapped the H2 v = 1 → 0 S(1) (λ = 2.1215 μm) emission line along a 400 pc-long strip and in a 50 pc region in the Galactic center. There is H2 emission throughout the surveyed region. The typical dereddened (AK = 2.5 mag) H2 v = 1 → 0 S(1) surface brightness, ~3 × 10-5 ergs s-1 cm-2 sr-1, is similar to the surface brightness in large-scale photon-dominated regions in the Galactic disk. We investigate two possible excitation mechanisms for the H2 emission, UV excitation by photons from OB stars and shock waves, and conclude that UV excitation is more likely. The total H2 v = 1 → 0 S(1) luminosity in the inner 400 pc region of the Galaxy is 8000 L☉. The ratio of the H2 to far-IR luminosity in the inner 400 pc of the Galaxy agrees with that in starburst galaxies and ultraluminous IR-bright galaxies.