The evolution of temperature and density structures of OB
  cluster-forming molecular clumps
  OB star clusters originate from parsec-scale massive molecular clumps. We aim
to understand the evolution of temperature and density structures on the
intermediate-scale ($\lesssim$0.1-1 pc) extended gas of massive clumps. We
performed $\sim$0.1 pc resolution observations (SMA+APEX) of multiple molecular
line tracers (e.g., CH$_{3}$CCH, H$_{2}$CS, CH$_{3}$CN, CH$_{3}$OH) which cover
a wide range of excitation conditions, towards a sample of eight massive
clumps. Based on various radiative transfer models, we constrain the gas
temperature and density structures and establish an evolutionary picture, aided
by a spatially-dependent virial analysis and abundance ratios of multiple
species. We determine temperature radial profiles varying between 30-200 K over
a continuous scale, from the center of the clumps out to 0.3-0.4 pc radii. The
clumps' radial gas density profiles, described by radial power-laws with slopes
between -0.6 and $\sim$-1.5, are steeper for more evolved sources, as suggested
by results based on both dust continuum, representing the bulk of the gas
($\sim$10$^{4}$ cm$^{-3}$), and CH$_{3}$OH lines probing the dense gas
($\gtrsim$10$^{6}$-10$^{8}$ cm$^{-3}$) regime. The density contrast between the
dense gas and the bulk gas increases with evolution, and may be indicative of
spatially and temporally varying star formation efficiencies. The radial
profiles of the virial parameter show a global variation towards a sub-virial
state as the clump evolves. The line-widths decline with increasing radius
around the central core region and increase in the outer envelope, with a slope
shallower than the case of the supersonic turbulence ($\,\propto\,$$r^{0.5}$)
and the subsonic Kolmogorov scaling ($\,\propto\,$$r^{0.33}$). In the context
of clump evolution, we also find that the abundance ratios of
[CCH]/[CH$_{3}$OH] and [CH$_{3}$CN]/[CH$_{3}$OH] show correlations with clump
$L/M$.
