Direct spectroscopic identification of the origin of "green fuzzy" emission in star-forming regions

Abstract

"Green fuzzies" or "extended green objects" were discovered in the recent Spitzer GLIMPSE survey data. These extended sources have enhanced emission in the 4.5 μm IRAC channel images (which are generally assigned to be green when making three-color RGB images from Spitzer data). Green fuzzies are frequently found in the vicinities of massive young stellar objects (MYSO), and it has been established that they are in some cases associated with outflows. Nevertheless, the spectral carrier(s) of this enhanced emission is (are) still uncertain. Although it has been suggested that Br α, H2, [Fe II], and/or broad CO emission may be contributing to and enhancing the 4.5 μm flux from these objects, to date there have been no direct observations of the 4-5 μm spectra of these objects. Here we report on the first direct spectroscopic identification of the origin of the green fuzzy emission. We obtained spatially resolved L- and M-band spectra for two green fuzzy sources using NIRI on the Gemini North telescope. In the case of one source, G19.88 - 0.53, we detect three individual knots of green fuzzy emission around the source. The knots exhibit a pure molecular hydrogen line emission spectrum, with the 4.695 μm ν = 0-0 S(9) line dominating the emission in the 4-5 μm wavelength range, and no detected continuum component. Our data for G19.88 - 0.53 prove that green fuzzy emission can be due primarily to emission lines of molecular hydrogen within the bandpass of the IRAC 4.5 μm channel. However, the other target observed, G49.27 - 0.34, does not exhibit any line emission and appears to be an embedded MYSO with a cometary UC H II region. We suggest that the effects of extinction in the 3-8 μm wavelength range and an exaggeration in the color stretch of the 4.5 μm filter in IRAC RGB images could lead to embedded sources such as this one falsely appearing "green." © 2010. The American Astronomical Society. All rights reserved..