High-Mass Star Formation in the Outer Scutum-Centaurus Arm
  The Outer Scutum-Centaurus (OSC) spiral arm is the most distant molecular
spiral arm in the Milky Way, but until recently little was known about this
structure. Discovered by Dame and Thaddeus (2011), the OSC lies $\sim$15 kpc
from the Galactic Center. Due to the Galactic warp, it rises to nearly
4$^{\circ}$ above the Galactic Plane in the first Galactic quadrant, leaving it
unsampled by most Galactic plane surveys. Here we observe HII region candidates
spatially coincident with the OSC using the Very Large Array to image radio
continuum emission from 65 targets and the Green Bank Telescope to search for
ammonia and water maser emission from 75 targets. This sample, drawn from the
WISE Catalog of Galactic HII Regions, represents every HII region candidate
near the longitude-latitude (l,v) locus of the OSC. Coupled with their
characteristic mid-infrared morphologies, detection of radio continuum emission
strongly suggests that a target is a bona fide HII region. Detections of
associated ammonia or water maser emission allow us to derive a kinematic
distance and determine if the velocity of the region is consistent with that of
the OSC. Nearly 60% of the observed sources were detected in radio continuum,
and over 20% have ammonia or water maser detections. The velocities of these
sources mainly place them beyond the Solar orbit. These very distant high-mass
stars have stellar spectral types as early as O4. We associate high-mass star
formation at 2 new locations with the OSC, increasing the total number of
detected HII regions in the OSC to 12.
