Far-ultraviolet fluorescent molecular hydrogen emission map of the Milky Way Galaxy
Abstract
We present the far-ultraviolet (FUV) fluorescent molecular hydrogen (H2) emission map of the Milky Way Galaxy obtained with FIMS/SPEAR covering ~76% of the sky. The extinction-corrected intensity of the fluorescent H2 emission has a strong linear correlation with the well-known tracers of the cold interstellar medium (ISM), including color excess E(B-V), neutral hydrogen column density N(H I), and Halpha emission. The all-sky H2 column density map was also obtained using a simple photodissociation region model and interstellar radiation fields derived from UV star catalogs. We estimated the fraction of H2 (fH2) and the gas-to-dust ratio (GDR) of the diffuse ISM. The fH2 gradually increases from <1% at optically thin regions where E(B-V) < 0.1 to ~50% for E(B-V) = 3. The estimated GDR is ~5.1 x 1021 atoms cm-2 mag-1, in agreement with the standard value of 5.8 x 1021 atoms cm-2 mag-1.