Molecular Hydrogen in the Lagoon: H2 Line Emission from Messier 8

Abstract

The 2.12 μm v = 1−0 S(1) line of molecular hydrogen has been imaged in the Hourglass region of M8. The line is emitted from a roughly bipolar region, centred around the O7 star Herschel 36. The peak H₂ 1−0 S(1) line intensity is 8.2 × 10⁻¹⁵ erg s⁻¹ cm⁻²arcsec⁻². The line centre emission velocity varies from −25 kms⁻¹ in the SE lobe to +45 kms⁻¹ in the NW lobe. The distribution is similar to that of the CO J = 3−2 line. The H₂ line appears to be shock-excited when a bipolar outflow from Herschel 36 interacts with the ambient molecular cloud. The total luminosity of all H₂ lines is estimated to be ~16 L_⊙ and the mass of the hot molecular gas ~9 × 10⁻⁴ M_⊙ (without any correction for extinction).