Description of source "g11" from Chambers et al. (2011)


Foreground green excess sources g11-g15 are associated with the Sharpless 20 (Sh20; Sharpless 1959; Dutra et al. 2003) star formation region, which is centered at l = 0.5, b = -0.3 (Marsalkova 1974). Source g11 (5.2 ± 2.5 M_0) displays bright, compact 4.5 µm emission, but no correlated 24 µm emission (Figure 11). It is located within an IRDC, adjacent to a bright loop of 8 µm emission that is likely part of Sh20. We did not detect any CH3OH maser toward g11. Green source g12, which has a mass of 2.1 ± 1.2 M_0, shows faint, extended 4.5 µm emission along with coincident 24 µm emission (Figure 12). The IRDC that harbors g12 is adjacent to Sh20. We detect two 44 GHz CH3OH masers associated with g12, with single velocity features at 15 and 17 km s-1. One of the maser sites resides within the extent of the 4.5 µm emission, while the other is ~10" away. The 4.5 µm and 24 µm emission from g13 are bright and extended (Figure 13). This source is located just south of Sh20, embedded withinan IRDC. It has a mass of 9.9± 1.7 M_0, and we detect a single 44 GHz CH3OH maser toward it. This maser has a single velocity feature at 13 km s-1 that is located on a knot of 4.5 µm emission 19" away from the center of the green source. Located just south of g13, g14 displays two knots of 4.5 µm emission, both of which are coincident with 24 µm emission (Figure 14). This 7.4 ± 1.7 M_0 source displays no CH3OH maser emission and is found within an IRDC. Green source g15 (Figure 15) shows extended 4.5 µm emission coincident with 24 µm emission. This source, with a mass of 14.3 ± 4.2 M_0, is not associated with a 44 GHz maser. The 4.5 µm emission from g15 is positionally coincident with a 6.7 GHz maser that has a single velocity feature at 26 km s-1. It is also surrounded by a bright ring of 8 and 24 µm emission, so it is unclear if g15 is embedded in an IRDC, or if the region in which it sits is only dark at 8 µm relative to the bright ringof emission.