CENSUS AND ANALYSIS OF GALACTIC MOLECULAR CLOUDS

Abstract

In this project, all available databases of molecular and gas-dust clouds in the Galaxy were cross-identi ed by taking into account available properties, including position, angular dimensions, velocity,density, temperature and mass. An initial list of about 7000 entries was condensed into a cross-identi edall-sky catalogue containing molecular and gas-dust clouds. Some relationships were studied between themain physical features of clouds. Finally, we prepared a complex observing program and address futurework for lling in the gaps.Key words: Galaxy: structure{Galaxy: disk { Galaxy: kinematics and dynamics - ISM: structure {ISM: clouds - radio lines: ISM - Catalogs1. INTRODUCTIONAt the present time the rapid progress both in in-strumentation and observing technology creates con-ditions for in-depth study of the interstellar medium(ISM) in the Galaxy as well as in other galaxies such asLMC, SMC, M31, M33, M51, M77, M83, M110, IC10,NGC185, NGC1569, NGC2976, NGC3077, NGC4038/9,NGC4214, NGC4449, NGC4605, etc. A signi cant frac-tion of the baryon mass of the ISM in the Galaxy andobserved galaxies is concentrated in the form of nebulaor clouds with molecular content in the densest parts(see, e.g., Draine 2011). Naturally, the molecular clouds(MoC) should be closely related to cold dust-gas clouds,particularly HI ones. They have to play a key-role inthe star forming processes as well as in the kinematicsand dynamics of the Galaxy on the whole. The abovereasons prove the importance of the census, systematicstudy and survey of MoC populations.2. CENSUS AND CATALOGTo attempt to nd solutions for at least some issues re-garding the physics and evolution of the MoC systemin our Galaxy and their impact on the dynamics andevolution of the Galaxy generally, and to extend theresults to MoC systems in other galaxies, we drafteda consolidated and uni ed composite all-sky catalog ofmolecular and dust-gas clouds that are observable fromthe Earth based on recent data. The preliminary re-sults were reported in Hojaev et al. (2013). Electronicdata bases and webservices such as VizieR, SIMBAD atCDS, 2MASS (Ks Atlas) and DSS as well as originalhttp://pkas.kas.orgpapers, reports and other publications were used. Thegeneral catalog has been divided into 3 sub-catalogs: 1)large and giant MoCs; 2) MoCs with moderate massesand sizes; 3) small MoCs including clumps and cores.All main catalogs and subcatalogs contain the coordi-nates, sizes, distances, masses and other physical pa-rameters (such as density, temperature, radial velocity,etc.) that are available for the di erent clouds. In ourGalaxy there are about 200 large and giant molecularclouds, more than 2500 smaller cold dark clouds (includ-ing clumps and cores this value exceeds approximately6000 objects) observed in the Solar vicinity and neigh-borhood up to 11 kpc away.3. ANALYSIS AND DISCUSSIONBased on the data in the combined catalog, we analysedphysical conditions in the MoCs and searched for re-lations between the physical parameters of the MoCsobserved. Due to the space limitations, we restrictourselves to discussing only a few. In Figure 1, wepresent a plot of the column density of molecular hy-drogen as a function of the cloud virial mass. The lin-ear t to the data is: N(H