Lighting The Dark Molecular Gas Using The Mid Infrared H2 Rotational Lines

The knowledge of molecular gas distribution is necessary to understand star formation in galaxies\footnote{Bigiel, F., Leroy, A., Walter, F., et al.\ 2008, The Astronomical Journal, 136, 2846 (2008) }. The molecular gas content of galaxies must be inferred using indirect tracers since H$_{2}$ which forms a major component of molecular gas in galaxies is not observable under typical conditions of interstellar medium\footnote{Solomon, P. M., Rivolo, A. R., Barett, J., and Yahil, A. The Astrophysical Journal, 319, 730 (1987)}. Physical processes causing enhancement and reduction of these tracers can cause misleading estimates of the molecular gas content in galaxies. We have devised a new method to measure molecular gas mass using quadrupole rotational lines of H$_{2}$ found in the mid infrared spectra of various types of galaxies. We apply our model to derive the amount of molecular gas even in low metallicity galaxies where indirect tracers are unable to estimate the dark molecular gas mass\footnote{Wolfire, M. G., Hollenbach, D., and McKee, C. F. The Astrophysical Journal, 716, 1191 (2010)}