  Using infrared to (sub)millimeter data from Spitzer, Herschel, the James
Clerk Maxwell Telescope, and the IRAM 30-m telescope, we conducted an unbiased
survey of the massive dense cores (MDCs) in the Cygnus X molecular cloud
complex, aimed at characterizing the physical conditions of high-mass star
formation (HMSF) at ~0.1 pc scales. We created 5 deg times 6 deg images of the
70-1200 um dust continuum, gas column density, and dust temperature of Cygnus
X. A spatial relation between the dense regions (Av > 15) and the developed HII
regions was found, indicating the impact of the latter on the global structures
of Cygnus X. With a 35-Msun mass threshold implied by HMSF signposts, we
identified 151 MDCs with sizes of ~0.1 pc, masses of 35-1762 Msun, and
temperatures of 8-35 K. Our MDC sample is statistically complete in Cygnus X
and is three times larger than that in Motte et al. (2007). The MDCs were
classified into IR-bright/IR-quiet ones based on their mid-infrared fluxes and
a large "IR-quiet" proportion (90%) was found in our sample. Two possible
scenarios were proposed to interpret this: accelerated HMSF and the
incapability of HMSF of the IR-quiet MDCs. We also found 26 starless MDCs by
their lack of compact emissions at 21-70 um wavelengths, of which the most
massive ones are probably the best candidates of initial HMSF sites in Cygnus
X.
