Fermi Gamma-ray Space Telescope

Interstellar models of gas and dust in Taurus-Perseus Clouds with Planck and Fermi data

Quentin REMY
Quentin REMY, Isabelle GRENIER, Douglas MARSHALL, Jean-Marc CASANDJIAN

Abstract:

We are applying recently improved multi-wavelength tracers to study the gas content in the different phases of the interstellar medium. We have used observations of the nearby Taurus and Perseus clouds in gamma rays with the Fermi Large Area Telescope and in thermal dust emission with Planck and IRAS in combination with HI and CO line data to (i) probe the gas tracers and cosmic-ray densities over a large range of hydrogen column densities and dust temperatures, (ii) map the dark neutral medium at the atomic/molecular interface, (iii) measure the CO-to-H_2 conversion factor, X_{CO}, and (iv) follow the evolution of the mean dust properties per gas nucleon as the gas becomes denser. The results show a uniform penetration of the cosmic rays to the dense CO cores, significant variations in grain opacity across the clouds, a X_{CO} value close to the average of the others local clouds, and large quantities of dark neutral gas with a mass equivalent to that of the CO-bright phase.