2013ApJS..208...23L

We discuss 94 Extended Green Objects (EGOs) in the northern Galactic plane cataloged by Cyganowski et al., based on near-infrared narrow H₂ (2.122 µm) and continuum observations from the United Kingdom Infrared Telescope. This data set is three times larger than the one in our previous study and is unbiased by preselection. As discussed in the previous paper, the morphologies of the 4.5 µm emission generally resemble those of the near-infrared continuum, but are different from those of the H₂emission. Of our sample, only 28% of EGOs with H₂ emission show similar morphologies between 4.5 µm and H₂emission. These results suggest that the 4.5 µm emission mainly comes from scattered continuum from the embedded young stellar objects, and partially from H₂emission. About half of EGOs are associated with H₂outflows, if the H₂ outflow incompleteness is considered. The H₂ outflow detection rate for EGOs with K-band detections (61%) is significantly higher than for those without K-band detections (36%). This difference may be due to the fact that both H₂ and K-band emissions are associated with outflows, i.e., H₂ emission and K-band continuum are associated with shocks and outflow cavities, respectively. We also compared the correlation between the H₂ outflows and Class I 44 GHz methanol masers from the literature. The methanol masers can be located upstream or downstream of the H₂outflows and some bright H₂ spots or outflows are not associated with methanol masers, suggesting that methanol masers and H₂ emission trace different excitation conditions.