A Cluster of 1.3 cm Continuum Sources in OMC1 South

Abstract

We present sensitive 1.3 cm radio continuum observations of the region OMC1 South (OMC-1S) in Orion using the Very Large Array in its B configuration. We detect eleven radio sources clustered in a $30{}^{\prime \prime }\times 30{}^{\prime \prime }$ region, of which only three had been detected previously at radio wavelengths in deep 3.6 cm observations. The eight new radio sources are compact (${\theta }_s\le 0\text{.}{}^{\prime \prime }1$) and we set lower limits to their spectral indices, $\alpha >0.8\pm 0.3$ (with $S_{\nu }\propto {\nu }^{\alpha }$), that suggest that they may be optically-thick H II regions. However, one of the new sources exhibits significant circular polarization, indicating that gyrosynchrotron emission with large positive spectral indices may be an alternative explanation. Furthermore, we find that four other sources are associated with infrared sources of low bolometric luminosity that cannot drive an H II region. Finally, two of the sources previously detected at 3.6-cm are angularly resolved in the 1.3 cm image and their major axes have position angles that align well with large scale outflows emanating from OMC-1S. The radio source 143-353 has a major axis with a position angle consistent with those of the HH 202 and HH 528 flows, while the radio source 134-411 has a major axis with a position angle consistent with that of the low-velocity molecular outflow associated with the far-infrared source FIR~4.

arXiv comment13 pages, 3 figures

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