ATLASGAL-selected massive clumps in the inner Galaxy: V. Temperature
  structure and evolution
  (Abridged) Aims: We aim to use the progressive heating of the gas caused by
the feedback of high-mass young stellar objects (YSOs) to prove the statistical
validity of the most common schemes used to define an evolutionary sequence for
high-mass clumps, and characterise the sensitivity of different tracers to this
process. Methods: From the spectroscopic follow-ups of the ATLASGAL TOP100
sample, we selected several multiplets of CH3CN, CH3CCH, and CH3OH emission
lines to derive and compare the physical properties of the gas in the clumps
along the evolutionary sequence. Our findings are compared with results
obtained from CO isotopologues, dust, and NH3 from previous studies on the same
sample. Results: The chemical properties of each species have a major role on
the measured physical properties. Low temperatures are traced by NH3, CH3OH,
and CO (in the early phases), the warm and dense envelope can be probed with
CH3CN, CH3CCH, and, in evolved sources via CO isotopologues. CH3OH and CH3CN
are also abundant in the hot cores, and their high-excitation transitions may
be good tools to study the kinematics in the hot gas surrounding the YSOs that
these clumps are hosting. All tracers show, to different degrees, progressive
warming with evolution. The relation between gas temperature and L/M is
reproduced by a toy model of a spherical, internally heated clump. Conclusions:
The evolutionary sequence defined for the clumps is statistically valid and we
could identify the processes dominating in different intervals of L/M. For
L/M<2Lsun/Msun a large quantity of gas is still being accumulated and
compressed at the bottom of the potential well. Between
2Lsun/Msun<L/M<40Lsun/Msun the YSOs gain mass and increase in L; the first hot
cores appear around L/M=10Lsun/Msun. Finally, for L/M>40Lsun/Msun HII regions
become common, showing that dissipation of the parental clump dominates.
