Near and mid-infrared images obtained with sub-arcsec spatial resolution of the star forming complex G35.20-1.74 are presented. From our analysis of the infrared images, and from the comparison with similar resolution radio data, the main results are the following:
1) A young embedded stellar cluster has been detected from the near-IR images, on the east side of the cometary-shaped UC HII region. The cluster contains at least 21 members all within the boundary of the diffuse emission observed at 2.2 and 11.2 ( 20 in radius). The majority of these members have infrared excesses and spectral types between B2-B3, assuming =23.
2) Six sources have been found at 11.2 . The brightest of these (MIR3) has an extension of approximately 8 , and coincides with the UC HII region. The sources MIR4,5, and 6 are located inside the cluster area. While the energy distribution of MIR4, and 5 indicates the presence of a circumstellar dust envelope around these sources, the infrared colors of MIR6 are consistent with the presence of a reddened early type star without IR excess.
3) At the position of the H2 O maser, distant about 20 from the UC HII, a very red source was found, detected only at 2.2 and 11.2 . At K the source (MIR1) shows a cometary-like morphology similar to that observed in several candidate protostars. In addition, the lack of the radio continuum and the very steep infrared spectrum indicate that MIR1 is an YSO in a very early phase. The association of this source with the H2 O maser confirms that water vapor masers can trace the youngest evolutionary stages of massive protostellar objects.
4) Finally, comparing the submillimeter and C18 O maps with our infrared images, we can conclude that in G35.20-1.74 star formation has occurred independently (in time and space) in several places of the same large scale molecular clouds.
© European Southern Observatory (ESO) 1997
Online publication: April 8, 1998