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sixty - three high mass star forming cores selected from the study of plume et al .
( 1997 ; @xmath1k ) were mapped in cs j@xmath0 at the cso between september 1996 and july 1999 .
nearly all of the cores observed lie in the first and second galactic quadrants .
the cores were mapped using the on - the - fly technique with a square grid in ra - dec coordinates oversampled at 10@xmath2 resolution .
the maps were extended until the cs emission was negligible ( @xmath3 for the average map ) .
the size of each core was determined by deconvolving the telescope main beam fwhm from the observed fwhm of the core .
fifty - seven cores had clearly defined fwhm with an average size of @xmath4 pc .
six cores contained multiple peaks within the core fwhm and were not included in the average .
thirty - three cores had deconvolved sizes that are larger than the cso beamsize indicating that the majority of cores were resolved .
the distribution of core sizes ( figure 1a ) is peaked about the mean ; however , we are biased against small cores sizes due to the resolution of the cso beam and the large distance of high mass star forming regions ( @xmath5 kpc ) .
a size - linewidth relationship can be determined from gaussian fits to the linewidth of the convolved map of the source ( @xmath6 km / s ) .
the size - linewidth relationship shows a weak correlation ( @xmath7 ; figure 1b ) with a least squares fit of @xmath8 and robust estimation fit of @xmath9 .
all of the linewidths are significantly higher than the size - linewidth relationship determined by caselli & myers ( 1995 ) for massive cores in orion indicating that the average high mass star forming core linewidth associated with a water maser is very turbulent .
the mean virial mass of a core was calculated using the cs linewidth and core fwhm size to be @xmath10 m@xmath11 which translates into an average surface density of @xmath12 g @xmath13 .
the corresponding mass spectrum is well fit by a power law ( figure 1c ) , @xmath14 to @xmath15 using least squares and robust estimation .
since we are biased against detecting small core masses ( @xmath16 m@xmath11 ) , the power laws fit to the mass spectrum is restricted to masses larger than 10@xmath17 solar masses .
the virial mass was derived assuming a constant density envelope and that the cs line was optically thin .
preliminary results from dust modeling of 350 @xmath18 emission ( @xmath19 , @xmath20 for 28 cores ; mueller et al . these proceedings ) and c@xmath21s observations ( @xmath22cs@xmath23c@xmath21s@xmath24 for 10 cores ) indicate that the average virial mass and surface density are reduced by a factor of 0.43 when these effects are included .
this cs mapping survey provides a more unbiased look at the statistical properties of high mass star forming cores associated with water masers .
combined with studies of dust continuum emission ( mueller et al .
these proceedings ) and monte carlo modeling of multiple cs transitions ( knez et .
these proceedings ) , a more definitive picture of the density and temperature structure of the envelopes of high mass star forming cores is emerging .
caselli , p. , & myers , p. c. 1995 , , 446 , 665 plume r. , jaffe , d. t. , evans , n. j. e. 1992 , apjs , 78 , 505 plume r. , jaffe , d. t. , evans , n. j. e. , martin - pintado , j. , & gomez - gonzalez , j. 1997 , apj , 476 , 730
in this survey we have systematically mapped 63 cloud cores in the cs j@xmath0 line towards a sample of high mass star forming cores with water masers ( plume et al . 
 1992 , plume et al . 
 1997 ) using the cso . from the cs spectra and maps we determine cloud core sizes , virial masses , a mass spectrum , and a size - linewidth relationship