Description of source "G18.67+0.03" from Towner et al. (2017)


We detect two sources of 1.3 cm continuum emission in the VLA FOV (Figure 1). CM1 is weak, unresolved, and coincident with the EGO, a compact MIPSGAL 24 μm source, and 6.7 GHz Class II CH3OH maser emission (Cyganowski et al. 2009; Green et al. 2010; see also Cyganowski et al. 2012). The measured peak intensity of CM1 (0.18 mJy beam−1, Table 4) is consistent with this source being undetected by Cyganowski et al. (2011a; 4σ upper limit of 0.94 mJy beam −1 at 1.3 cm). We also detect strong, resolved 1.3 cm continuum emission ~13² W of the EGO, from the source designated “UCHII” by Cyganowski et al. (2012; F G18.67+0.03-CM1 in Cyganowski et al. 2011a).

The only 25 GHz CH3OH detection in the field is thermal, and is coincident with CM1 and 6.7 GHz CH3OH maser emission. Unusually, CH3OH emission is detected in the 52 and 82 lines, but not 32. The brightness temperature Tb = 15 K, with the optically thin LTE calculations suggesting a temper-ature range of 40–50 K. The detection of thermal CH3OH at 25 GHz is consistent with the presence of strong hot core molecular line emission from the EGO in SMA observations by Cyganowski et al. (2012), who find a CH3CN temperature of 175 K. Notably, though both the EGO and the UC H II region to the west are associated with 44 GHz Class I CH3OH masers (Cyganowski et al. 2009, 2012), no 25 GHz CH3OH maser emission is detected within the VLA FOV.