Most work on high-mass star formation has focused on observations of young massive stars in protoclusters .
Very little is known about the preceding stage .
Here , we present a new high-resolution study of pre-protocluster regions in tracers exclusively probing the coldest and dense gas ( NH _ { 2 } D ) .
The two target regions G29.96 $ - $ 0.02 and G35.20 $ - $ 1.74 ( W48 ) are drawn from the SCAMPS project , which searches for pre-protoclusters near known ultracompact H ii regions .
We used our data to constrain the chemical , thermal , kinematic , and physical conditions ( i.e. , densities ) in G29.96e and G35.20w . \mathrm { NH _ { 3 } } , \mathrm { NH _ { 2 } D } , and continuum emission were mapped using the VLA , and PdBI .
In particular , \mathrm { NH _ { 2 } D } is a unique tracer of cold , precluster gas at high densities , while \mathrm { NH _ { 3 } } traces both the cold and warm gas of modest-to-high densities .
In G29.96e , Spitzer images reveal two massive filaments , one of them in extinction ( infrared dark cloud ) .
Dust and line observations reveal fragmentation into multiple massive cores strung along filamentary structures .
Most of these are cold ( < 20 ~ { } K ) , dense ( > 10 ^ { 5 } ~ { } cm ^ { -3 } ) and highly deuterated ( [ \mathrm { NH _ { 2 } D } / \mathrm { NH _ { 3 } } ] > 6 \% ) .
In particular , we observe very low line widths in \mathrm { NH _ { 2 } D } ( FWHM \lesssim 1 ~ { } km s ^ { -1 } ) .
These are very narrow lines that are unexpected towards a region forming massive stars .
Only one core in the center of each filament appears to be forming massive stars ( identified by the presence of masers and massive outflows ) ; however , it appears that only a few such stars are currently forming ( i.e. , just a single Spitzer source per region ) .
These multi-wavelength , high-resolution observations of high-mass pre-protocluster regions show that the target regions are characterized by ( i ) turbulent Jeans fragmentation of massive clumps into cores ( from a Jeans analysis ) ; ( ii ) cores and clumps that are “ over-bound/subvirial ” , i.e .
turbulence is too weak to support them against collapse , meaning that ( iii ) some models of monolithic cloud collapse are quantitatively inconsistent with data ; ( iv ) accretion from the core onto a massive star , which can ( for observed core sizes and velocities ) be sustained by accretion of envelope material onto the core , suggesting that ( similar to competitive accretion scenarios ) the mass reservoir for star formation is not necessarily limited to the natal core ; ( v ) high deuteration ratios ( [ \mathrm { NH _ { 2 } D } / \mathrm { NH _ { 3 } } ] > 6 \% ) , which make the above discoveries possible ; ( vi ) and the destruction of \mathrm { NH _ { 2 } D } toward embedded stars .