Description of source "g7" from Chambers et al. (2011)


Green excess sources g6 through g10 are located in close proximity to one another in a large IRDC complex. This IRDC is part of the dust ridge, and is adjacent to Sgr B2, one of the most massive star-forming regions in the Galaxy. The green sources are near the southern edge of the IRDC, just north of the bright Sgr B2 HII regions, suggestive that star formation is progressing from south to north in this cloud (Y-Z09). We assign the Galactic center distance to each of these green sources. Source g6, at 29.9 ± 8.2 the most massive of our sources, appears reddish in Figure 8, and is coincident with bright 24 µm emission. We do not associate g6 with any CH3OH maser emission, but we do detect a 6.7 GHz maser emission to its north. This maser site, which displays multiple velocity features, is not associated with any obvious IRAC emission, but is coincident with faint 24 µm emission. Sources g7, g8, and g9 are shown in Figure 9. Bright green in color in the IRAC image, g7 also displays bright 24 µm. It has a mass of 9.4 ± 1.2 M_0 and is not associated with any CH3OH maser. Sources g8 and g9 are reddish in color, and the region immediately surrounding them harbors seven 6.7 GHz masers (within ~1 arcmin), along with several sites of 44 GHz maser emission (within ~1 arcmin). The velocities of the 6.7 GHz masers fall in the range of ~48-73 km s-1, and the 44 GHz masers fall in the range of ~46-78 km s-1, both of which are consistent with the measured velocity of ionized gas seen toward this region. The large number of maser sites, along with their spread in velocity, indicates a high rate of star formation in this area. Source g9 has a mass of 21 ± 7 M_0, but due to a poorly constrained fit, g8 has no derived mass. Both g8 and g9 are located in a region of bright 24 µm emission. Source g10 (9.5 ± 0.7) displays extended 4.5 µm emission, and is not coincident with 24 µm emission (Figure 10). We detect three 6.7 GHz masers in the g10 field, but none are close enough to be associated with the green source. Two of these masers display a single velocity feature, while the other shows two components. None of the masersites are coincident with bright IRAC or 24 µm emission.