| Surveys at multi-wavelength have revealed that filamentary structures are ubiquitous in cold Galactic interstellar medium(ISM).On a large scale,the filamentary structures exceeding 100 pc play a role as the "skeleton" of spiral arms,supporting the entire Milky Way.On a small scale,the dense filamentary structures connect the collapse of molecular clouds to their fragmentation to eventual form dense cores.Therefore,filamentary molecular cloud is a hot topic in the current astrophysical research.In this thesis,we present a detailed dynamics analysis of several filamentary molecular clouds in the second quadrant of the Milky Way,using the "MWISP" CO survey data from the 13.7 m millimeter-wave telescope of the Purple Mountain Observatory(PMO).In chapter 2,we present the survey of 12CO/13CO/C18O(J=1-0)toward the California molecular cloud within the region of 161.75°≤l≤167.75°,-9.5°≤b≤-7.5°,using the Purple Mountain Observatory 13.7 m millimeter telescope.Adopting a distance of 470 pc,the mass of the observed molecular cloud estimated from 12CO,13CO,and C18O is about 2.59 × 104,1.12 × 104,and 0.09 × 104M⊙,respectively.A large-scale continuous filament extending about 72 pc with a width of about 0.6 pc is revealed from the 13CO images.A systematic velocity gradient perpendicular to the major axis appears and is measured to be～0.82 km s-1 pc-1.The kinematics along the filament shows an oscillation pattern with a fragmentation wavelength of～2.3 pc and a velocity amplitude of～0.92 km s-1,which may be related with core-forming flows.Furthermore,assuming an inclination angle to the plane of the sky of 45°,the estimated average accretion rate is～101M⊙Myr-1 for the cluster Lk Hα101 and～21M⊙Myr-1 for the other regions.In the C18O observations,the large-scale filament could be resolved into multiple substructures and their dynamics are consistent with the scenario of filament formation from converging flows.Approximately 225 C18O cores are extracted,of which 181 are starless cores.Roughly 37%(67/181)of the starless cores have αvir less than 1.Twenty outflow candidates are identified along the filament.Our results indicate active early-phase star formation along the large-scale filament in the California molecular cloud region.In chapter 3,we present observations of J=1-0 transition lines of 12CO,13CO,and C18O towards the Galactic region of 153.6°≤l≤156.5°,1.85°≤b ≤3.5°,using the Purple Mountain Observatory(PMO)13.7 m millimeter telescope.Based on the 13CO data,one main filament and five sub-filaments are found together as a network structure in the velocity interval of[-42.5,-30.0]km s-1.The kinematic distance of this molecular cloud(MC)is estimated to be～4.8 kpc.The median length,width,excitation temperature,line mass of these filaments are～53 pc,～3.4pc,～8.9 K,and～33 M⊙pc-1,respectively.The velocity structures along these filaments exhibit oscillatory patterns,which are likely caused by the fragmentation or accretion process along these filaments.The maximum accretion rate is estimated to be as high as～500 M⊙pc-1.A total of 162 13CO clumps and 246 young stellar objects(YSOs)are identified in this region.Most of the clumps are in gravitationally bound states.Three HII regions(G 154.359+2.606,Sh2-211,Sh2-212)are found to be located in the apexes of the filaments,among which G 154.359+2.606 can be regarded as a candidate for starburst cluster.The observed results may help us to better understand the link between filaments and massive star formation.In chapter 4,we construct a millimeter observation of 12CO/13CO/C18O(J=1-0)towards the region of 115.25°≤l≤118.25°,-0.75°≤b≤2.25°,using the PMO 13.7 m millimeter telescope.This region covers two identified supernova remnants(SNRs)G116.5+1.1 and G116.9+0.2.Signs of interaction between the SNRs and CO molecular cloud are investigated.For G116.5+1.1,Several broad 12CO line profiles are found at the boundary of the SNRs at both velocity intervals of[-12,2]km s-1 and[-55,-35]km s-1.The molecular clouds at[-12,2]km s-1 show morphological agreement with the radio shell.For G116.9+0.2,the broad 12CO line profiles are found at the velocity interval of[-55,-35]k ms-1.A filamentary molecular cloud in the southeast seems to be distorted by the SNR.Using the the Bayesian distance calculator,we put the two SNRs at a distance of～2.8 kpc.Filamentary structures are ubiquitous in the Milky way,and their formation and evolution are affected by a variety of dynamic processes.The regions studied in this thesis contain different types of molecular clouds,including:the California giant molecular cloud with active early-phase star formation in the G160 region,the network-like giant molecular cloud with intense star formation activity in the G155 region,and the molecular clouds that may be associated with supernova remnants in the G116 region.In the California giant molecular cloud,we find a large-scale filamentary structure whose dynamic structure can be explained by converging flow.The varying accretion rates in the local regions can explain the disparities in star formation activity.Within the filamentary structure,starless cores account for 80%of the identified dense cores,indicating that the region is in the early stage of star formation.The dynamic structure is less affected by the feedback of star formation activities,which is helpful for studying the effect of filamentary structure on star formation activities.In the giant molecular cloud in the G155 region,we found 1 main filamentary structure and 5 secondary filamentary structures,which interweave to form a network-like morphology.The high rate of material accretion in the local region explains the region’s strong star formation activity.Three HII regions,in particular,are found near the filament apexes,which aids comprehension of the link between filamentary structures and massive star formation.The molecular cloud in the G116 region can be used to investigate the parent molecular dynamics that link star death and star formation.Supernova explosions inject mass and compress the surrounding gas,resulting in or affecting molecular clouds of various shapes,including filamentary molecular clouds.We find a filamentary cloud in this region,which may be distorted by the presence of remnants. |
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