We present a comparative study of physical properties derived from gas and dust emission in a sample of 1068 dense Galactic clumps .
The sources are selected from the crossmatch of the Hi-GAL survey with 16 catalogues of NH _ { 3 } line emission in its lowest inversion ( 1,1 ) and ( 2,2 ) transitions .
The sample covers a large range in masses and bolometric luminosities , with surface densities above \Sigma = 0.1 g cm ^ { -2 } and with low virial parameters \alpha < 1 .
The comparison between dust and gas properties shows an overall agreement between T _ { \textit { kin } } and T _ { \textit { dust } } at volumetric densities n \gtrsim 1.2 \times 10 ^ { 4 } cm ^ { -3 } , and a median fractional abundance \chi ( NH _ { 3 } ) = 1.46 \times 10 ^ { -8 } .
While the protostellar clumps in the sample have small differences between T _ { \textit { kin } } and T _ { \textit { dust } } , prestellar clumps have a median ratio T _ { \textit { kin } } / T _ { \textit { dust } } = 1.24 , suggesting that these sources are thermally decoupled .
A correlation is found between the evolutionary tracer L / M and the parameters T _ { \textit { kin } } / T _ { \textit { dust } } and \chi ( NH _ { 3 } ) in prestellar sources and protostellar clumps with L / M < 1 L _ { \odot } M _ { \odot } ^ { -1 } .
In addition , a weak correlation is found between non-thermal velocity dispersion and the L / M parameter , possibly indicating an increase of turbulence with protostellar evolution in the interior of clumps .
Finally , different processes are discussed to explain the differences between gas and dust temperatures in prestellar candidates , and the origin of non-thermal motions observed in the clumps .