A CLASS I AND CLASS II CH₃OH MASER SURVEY OF EGOs FROM THE GLIMPSE SURVEY

TLDR

Extended green objects (EGOs) are massive young stellar object outflow candidates identified by extended 4.5 µm emission in Spitzer Galactic Legacy Infrared Mid‑Plane Survey images. The study aims to characterize EGOs by conducting high‑resolution VLA observations of Class I 44 GHz and Class II 6.7 GHz CH₃OH masers and complementary JCMT single‑pointing surveys of HCO⁺(3–2) and SiO(5–4) line emission. Using the VLA, the authors mapped ∼20 EGOs at.

Abstract

We present the results of a high angular resolution Very Large Array (VLA) Class I 44 GHz and Class II 6.7 GHz CH3OH maser survey of a sample of ∼20 massive young stellar object (MYSO) outflow candidates selected on the basis of extended 4.5 μm emission in Spitzer Galactic Legacy Infrared Mid-Plane Survey Extraordinaire images. These 4.5 μm selected candidates are referred to as extended green objects (EGOs), for the common coding of this band as green in three-color Infrared Array Camera images. The detection rate of 6.7 GHz Class II CH3OH masers, which are associated exclusively with massive YSOs, toward EGOs is ≳64%—nearly double the detection rate of surveys using other MYSO selection criteria. The detection rate of Class I 44 GHz CH3OH masers, which trace molecular outflows, is ∼89% toward EGOs associated with 6.7 GHz CH3OH masers. The two types of CH3OH masers exhibit different spatial distributions: 6.7 GHz masers are centrally concentrated and usually coincide with 24 μm emission, while 44 GHz masers are widely distributed and generally trace diffuse 4.5 μm features. We also present results of a complementary James Clerk Maxwell Telescope (JCMT) single-pointing molecular line survey of EGOs in the outflow tracers HCO+(3–2) and SiO(5–4). The HCO+ line profiles and high SiO detection rate (90%) are indicative of the presence of active outflows. No 44 GHz continuum emission is detected at the 5 mJy beam−1 (5σ) level toward 95% of EGOs surveyed, excluding bright ultracompact H ii regions as powering sources for the 4.5 μm outflows. The results of our surveys constitute strong evidence that EGOs are young, massive YSOs, with active outflows, presumably powered by ongoing accretion.