A Mini Survey of Methyl Cyanide toward Extended Green Objects

Abstract

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.