2014A&A...567A..10L

The process of gravitational fragmentation in the L1482 molecular filament of the California molecular cloud is studied by combining several complementary observations and physical estimates. We investigate the kinematic and dynamical states of this molecular filament and physical properties of several dozens of dense molecular clumps embedded therein. We present and compare molecular line emission observations of the J=2-1 and J=3-2 transitions of ¹²CO in this molecular complex, using the Koelner Observatorium fuer Sub-Millimeter Astronomie (KOSMA) 3-m telescope. These observations are complemented with archival data observations and analyses of the ¹³CO J=1-0 emission obtained at the Purple Mountain Observatory (PMO) 13.7-m radio telescope at Delingha Station in QingHai Province of west China, as well as infrared emission maps from the Herschel Space Telescope online archive, obtained with the SPIRE and PACS cameras. Comparison of these complementary datasets allows for a comprehensive multiwavelength analysis of the L1482 molecular filament. We have identified 23 clumps along the molecular filament L1482 in the California molecular cloud. For these molecular clumps, we were able to estimate column and number densities, masses, and radii. The masses of these clumps range from ∼6.8 to 62.8M_☉ with an average value of 24.7_–16.2^+31.1M_☉. Eleven of the identified molecular clumps appear to be associated with protostars and are thus referred to as protostellar clumps. Protostellar clumps and the remaining starless clumps of our sample appear to have similar temperatures and linewidths, yet on average, the protostellar clumps appear to be slightly more massive than the latter. All these molecular clumps show supersonic nonthermal gas motions. While surprisingly similar in mass and size to the much better known Orion molecular cloud, the formation rate of high-mass stars appears to be suppressed in the California molecular cloud compared with that in the Orion molecular cloud based on the mass-radius threshold derived from the static Bonnor-Ebert sphere. The largely uniform ¹²CO J=2-1 line-of-sight velocities along the L1482 molecular cloud shows that it is a generally coherent filamentary structure. Since the NGC1579 stellar cluster is at the junction of two molecular filaments, the origin of the NGC1579 stellar cluster might be merging molecular filaments fed by converging inflows. Our analysis suggests that these molecular filaments are thermally supercritical and molecular clumps may form by gravitational fragmentation along the filament. Instead of being static, these molecular clumps are most likely in processes of dynamic evolution.