A Statistical Study Of Clumps In The M16 Giant Molecular Cloud

Stars form in molecular clumps whose properties play key roles in star formation.To study properties of clumps,12CO(J=1-0),13CO(J=1-0)and C18O(J=1-0)emission lines are observed simultaneously by DLH-13.7m radio telescope towards M16 giant molecular cloud.We introduce briefly the basic performance of telescope,OTF observation method and MWISP project.After removing the bad channels,calibrating the temperature with the main beam efficiency,data are re-gridded and mosaiked to FITS cube using the GILDAS software package.Basic information of M16 is obtained from three CO emission lines and then molecular clumps are extracted in 13CO(J=1-0)and C18O(J=1-0)lines.Four methods of clumps identification are tested,including GAUSSCLUMPS,CLUMPFIND,REINHOLD and FELLWALKER.And the GAUSSCLUMPS algorithm in GILDAS is used to extract the clumps in M16 because of shorter run time and accuracy of extracting clumps.After obtaining the emission line parameters and clump samples,the properties are calculated under local thermodynamic equilibrium(LTE)assumption,including line-width,radius,excitation temperature,optical depth,column density and clump mass.In order to evaluate whether clumps are bound or unbound,the virial mass and virial parameter are calculated.As a result,the majority of 13 CO clumps and all of C18 O clumps are bound,which suggest that those clumps may form stars in the future.By investigating dynamic state of clumps,it is found that 13 CO clumps are turbulently supported and thermal and turbulence play equal roles against gravity for C18 O clumps.In clumps column density probability function,it can be fitted by power-law distribution above star formation column density threshold.And those clumps in power-law region are may forming massive stars.For mass-radius relationship,both 13 CO and C18 O clumps are fitted bykRM μ,where κ is approximate to 2.Moreover,it is found that κ increases with virial parameter decreasing,which suggest that the existence of M-R relationship evolution sequence with cloud evolution.In this paper,the shapes of both 13 CO and C18 O clumps CMF are similar to IMF,whose power indexes are 2.21 and 2.18,respectively.Assuming that the clump surface density is constant,velocity dispersion-size relationship,so called Larson’s first relationship,is very weak even does not exist.However,theresult is different when clump surface density is added to size,which presents a tighter relationship.This suggest that Larson’s scaling relationship systematically varies with the surface density.Finally,according to channel map and the distribution of clump light-of-sight velocities,we find that M16 consists of two smaller molecular cloud.