ALMA obs. of protoplanetary disks in ONC & OMC1

The OMC1 molecular cloud is a region of high extinction situated behind the Trapezium in which actively forming stars are shielded from the Trapezium's strong radiation. In this work, we survey disks at high resolution with Atacama Large Millimeter/submillimeter Array at three wavelengths with resolutions of 0.095 (3mm; Band 3), 0.048 (1.3mm; Band 6), and 0.030 (0.85mm; Band 7) centered on radio Source I. We detect 127 sources, including 15 new sources that have not previously been detected at any wavelength. 72 sources are spatially resolved at 3mm, with sizes from ~8-100au.

We classify 76 infrared-detected sources as foreground ONC disks and the remainder as embedded OMC1 disks. The two samples have similar disk sizes, but the OMC1 sources have a dense and centrally concentrated spatial distribution, indicating they may constitute a spatially distinct subcluster. We find smaller disk sizes and a lack of large (>75au) disks in both our samples compared to other nearby star-forming regions, indicating that environmental disk truncation processes are significant.