Small Protoplanetary Disks in the Orion Nebula Cluster and OMC1 with
  ALMA
  The Orion Nebula Cluster (ONC) is the nearest dense star-forming region at
$\sim$400 pc away, making it an ideal target to study the impact of high
stellar density and proximity to massive stars (the Trapezium) on
protoplanetary disk evolution. 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 ALMA at three wavelengths with resolutions of
0.095\arcsec (3 mm; Band 3), 0.048\arcsec (1.3 mm; Band 6), and 0.030\arcsec
(0.85 mm; 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 3 mm, with sizes from $\sim$8 - 100 AU. 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 (>75 AU) disks in both our samples compared to
other nearby star-forming regions, indicating that environmental disk
truncation processes are significant. While photoevaporation from nearby
massive Trapezium stars may account for the smaller disks in the ONC, the
embedded sources in OMC1 are hidden from this radiation and thus must truncated
by some other mechanism, possibly dynamical truncation or accretion-driven
contraction.
