A Mini Survey of Methyl Cyanide toward Extended Green Objects.

We present results of a survey of methyl cyanide (CH₃CN) J = 12–11 toward 56 sources, including 35 Extended Green Objects (EGOs) and 21 nearby AKARI counterparts, with the Submillimeter Telescope (SMT) in order to characterize the nature of EGOs. CH₃CN, a tracer of hot core emission, is detected in 19 EGOs (∼54%) and five AKARI bright sources (∼24%). By analyzing the observed CH₃CN features, we find an average line width of 6.5 km s⁻¹. For the sources detected with CH₃CN, we derive CH₃CN column densities log₁₀(N [cm⁻²]) = 14–17 with gas temperatures in the range 40–300 K. The small filling factors (10⁻²–10⁻⁴) may reflect the rather compact CH₃CN emitting regions, which correspond to linear sizes of ∼0.01–0.08 pc. We also estimate the virial masses and gas masses of these sources. Our derived gas masses are lower than the virial masses, possibly because CH₃CN traces more energetic motions such as outflows and shocks. Alternatively, we cannot rule out that the virial masses are overestimated due to the presence of unresolved CH₃CN kinetic components, such as the rotation structures observed around the young stellar objects. [ABSTRACT FROM AUTHOR]