Context : Observationalidentificationofasolidevolutionarysequenceforhigh-massstar-formingregionsisstillmissing.Spectroscopicobservationsgivetheopportunitytotestpossibleschemesandconnectthephasesidentifiedtophysicalprocesses .

Aims : Weaimtousetheprogressiveheatingofthegascausedbythefeedbackofhigh-massyoungstellarobjectstoprovethestatisticalvalidityofthemostcommonschemesusedtoobservationallydefineanevolutionarysequenceforhigh-massclumps , andcharacterisethesensitivityofdifferenttracerstothisprocess .

Methods : Fromthespectroscopicfollow-upscarriedouttowardssubmillimetercontinuum ( dust ) emission-selectedmassiveclumps ( theATLASGALTOP100sample ) withtheIRAM30 m , Mopra , andAPEXtelescopesbetween 84 \usk \giga \hertz and 365 \usk \giga \hertz , weselectedseveralmultipletsofCH _ { 3 } CN , CH _ { 3 } CCH , andCH _ { 3 } OH emissionlinestoderiveandcomparethephysicalpropertiesofthegasintheclumpsalongtheevolutionarysequence , fittingsimultaneouslythelargenumberoflinesthatthesemoleculeshaveintheobservedband.OurfindingsarecomparedwithresultsobtainedfromopticallythinCOisotopologues , dust , andammoniafrompreviousstudiesonthesamesample .

Results : Thechemicalpropertiesofeachspecieshaveamajorroleonthemeasuredphysicalproperties.Lowtemperaturesaretracedbyammonia , methanol , andCO ( intheearlyphases ) , thewarmanddenseenvelopecanbeprobedwithCH _ { 3 } CN , CH _ { 3 } CCH , and , inevolvedsourceswhereCOisabundantinthegasphase , viaitsopticallythinisotopologues.CH _ { 3 } OH andCH _ { 3 } CN arealsoabundantinthehotcores , andwesuggestthattheirhigh-excitationtransitionsaregoodtoolstostudythekinematicsinthehotgasassociatedwiththeinnerenvelopesurroundingtheyoungstellarobjectsthattheseclumpsarehosting.Alltracersshow , todifferentdegreesaccordingtotheirproperties , progressivewarmingwithevolution.Therelationbetweengastemperatureandtheluminosity-to-mass ( L / M ) ratioisreproducedbyasimpletoymodelofaspherical , internallyheatedclump .

Conclusions : Theevolutionarysequencedefinedfortheclumpsisstatisticallyvalidandwecouldidentifythephysicalprocessesdominatingindifferentintervalsof L / M .For L / M \lesssim 2 \usk \mathrm { L _ { \odot } } \usk \mathrm { M _ { \odot } } ^ { -1 } alargequantityofthegasisstillaccumulatedandcompressedatthebottomofthepotentialwell.Between 2 \usk \mathrm { L _ { \odot } } \usk \mathrm { M _ { \odot } } ^ { -1 } \lesssim L / M \lesssim 40 \usk% \mathrm { L _ { \odot } } \usk \mathrm { M _ { \odot } } ^ { -1 } theyoungstellarobjectsgainmassandincreaseinluminosity ; thefirsthotcoreshostingintermediate-orhigh-massZAMSstarsappeararound L / M \sim 10 \usk \mathrm { L _ { \odot } } \usk \mathrm { M _ { \odot } } ^ { -1 } .Finally , for L / M \gtrsim 40 \usk \mathrm { L _ { \odot } } \usk \mathrm { M _ { \odot } } ^ { -1 } H ii regionsbecomecommon , showingthatdissipationoftheparentalclumpdominates .