MOLINARI, SergioSergioMOLINARIMerello, M.M.MerelloELIA, Davide QuintinoDavide QuintinoELIACESARONI, RiccardoRiccardoCESARONITESTI, LeonardoLeonardoTESTIRobitaille, T.T.Robitaille2020-05-132020-05-1320160004-637Xhttp://hdl.handle.net/20.500.12386/24795The evolutionary classification of massive clumps that are candidate progenitors of high-mass young stars and clusters relies on a variety of independent diagnostics based on observables from the near-infrared to the radio. A promising evolutionary indicator for massive and dense cluster-progenitor clumps is the L/M ratio between the bolometric luminosity and the mass of the clumps. With the aim of providing a quantitative calibration for this indicator, we used SEPIA/APEX to obtain CH<SUB>3</SUB>C<SUB>2</SUB>H(J = 12-11) observations, which is an excellent thermometer molecule probing densities ≥slant {10}<SUP>5</SUP> cm<SUP>-3</SUP>, toward 51 dense clumps with M≥slant 1000 M {}<SUB>☉ </SUB> and uniformly spanning -2 ≲ Log(L/M) [L {}<SUB>☉ </SUB>/M {}<SUB>☉ </SUB>] ≲ 2.3. We identify three distinct ranges of L/M that can be associated to three distinct phases of star formation in massive clumps. For L/M ≤slant 1 no clump is detected in CH<SUB>3</SUB>C<SUB>2</SUB>H, suggesting an inner envelope temperature below ∼30K. For 1 ≲ L/M ≲ 10 we detect 58% of the clumps with a temperature between ∼30 and ∼35 K independently from the exact value of L/M; such clumps are building up luminosity due to the formation of stars, but no star is yet able to significantly heat the inner clump regions. For L/M ≳ 10 we detect all the clumps with a gas temperature rising with Log(L/M), marking the appearance of a qualitatively different heating source within the clumps; such values are found toward clumps with UCH II counterparts, suggesting that the quantitative difference in T versus L/M behavior above L/M ∼ 10 is due to the first appearance of ZAMS stars in the clumps.STAMPAenArticle10.3847/2041-8205/826/1/L82-s2.0-84979284949000380739300008https://iopscience.iop.org/article/10.3847/2041-8205/826/1/L82016ApJ...826L...8MFIS/05 - ASTRONOMIA E ASTROFISICA