Astrophysical maser radiation from a turbulent medium: Application to 25 GHz methanol masers

Spectral and spatial distributions are calculated for astrophysical maser radiation that emerges from a turbulent medium. Turbulent-velocity fields are created by sampling from Kolmogorov-like distributions. The maps of maser emission created in a turbulent medium appear as if the emission results from a collection of isolated clumps moving with different velocities, even though the physical quantities (other than velocity) are constant within the medium. A detailed comparison is made with observational data about the 25 GHz methanol masers in OMC-1. There is evidence that key simplifications for the calculations-unsaturated masing and uniform excitation-are applicable for these masers. For the actual Kolmogorov distribution, the images are smaller and more numerous than are observed. The spectra also do not exhibit the observed irregularities. Velocity distributions that are somewhat steeper than the Kolmogorov power law lead to calculated images and spectra that reproduce characteristic features of the observations.