Photodissociation regions in M33

We derive total (atomic + molecular) hydrogen densities in giant molecular clouds (GMCs) in the nearby spiral galaxy M33 using a method that views the atomic hydrogen near...我们采用一种观测……附近中性氢的方法，对邻近旋涡星系M33内的巨分子云（giant molecular clouds, GMCs）的总氢密度（原子氢+分子氢）进行了推导。