  Using images from the Spitzer GLIMPSE Legacy survey, we have identified more
than 300 extended 4.5 micron sources (abbreviated EGO, Extended Green Object,
for the common coding of the [4.5] band as green in 3-color composite IRAC
images). We present a catalog of these EGOs, including integrated flux density
measurements at 3.6, 4.5, 5.8, 8.0, and 24 microns from the GLIMPSE and MIPSGAL
surveys. The average angular separation between a source in our sample and the
nearest IRAS point source is >1 arcminute. The majority of EGOs are associated
with infrared dark clouds (IRDCs), and where high-resolution 6.7 GHz methanol
maser surveys overlap the GLIMPSE coverage, EGOs and 6.7 GHz methanol masers
are strongly correlated. Extended 4.5 micron emission is thought to trace
shocked molecular gas in protostellar outflows; the association of EGOs with
IRDCs and 6.7 GHz methanol masers suggests that extended 4.5 micron emission
may pinpoint outflows specifically from massive protostars. The mid-infrared
colors of EGOs lie in regions of color-color space occupied by young protostars
still embedded in infalling envelopes.
