Search

Context. Dense molecular filaments are central to the star formation process, but the detailed manner in which they fragment into prestellar cores is not well understood yet. Aims. Here, we investigate the fragmentation properties and dynamical state of several star-forming filaments in the X-shaped nebula region of the California molecular cloud in an effort to shed some light on this issue. Methods. We used multiwavelength far-infrared images from Herschel as well as the getsources and getfilaments extraction methods to identify dense cores and filaments in the region and derive their basic properties. We also used a map of 13CO(2−1) emission from the Arizona 10m Submillimeter Telescope (SMT) to constrain the dynamical state of the filaments. Results. We identified ten filaments with aspect ratios of AR > 4 and column density contrasts of C > 0.5, as well as 57 dense cores, including two protostellar cores, 20 robust prestellar cores, 11 candidate prestellar cores, and 24 unbound starless cores. All ten filaments have roughly the same deconvolved full width at half maximum (FWHM), with a median value of 0.12 ± 0.03 pc, which is independent of their column densities ranging from <1021 cm−2 to >1022 cm−2. Two star-forming filaments (# 8 and # 10) stand out since they harbor quasi-periodic chains of dense cores with a typical projected core spacing of ~0.15 pc. These two filaments have thermally supercritical line masses and are not static. Filament 8 exhibits a prominent transverse velocity gradient, suggesting that it is accreting gas from the parent cloud gas reservoir at an estimated rate of ~40 ± 10 M⊙ Myr−1 pc−1. Filament 10 includes two embedded protostars with outflows and it is likely at a somewhat later evolutionary stage than filament 8. In both cases, the observed (projected) core spacing is similar to the filament width and significantly shorter than the canonical separation of ~4 times the filament width predicted by classical cylinder fragmentation theory. It is unlikely that projection effects can explain this discrepancy. We suggest that the continuous accretion of gas onto the two star-forming filaments, as well as the geometrical bending of the filaments, may account for the observed core spacing. Conclusions. Our findings suggest that the characteristic fragmentation lengthscale of molecular filaments is quite sensitive to external perturbations from the parent cloud, such as the gravitational accretion of ambient material. [ABSTRACT FROM AUTHOR]

Aims. 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. Methods. 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 Kölner Observatorium für 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. Results. 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 62.8 M⊙ with an average value of 24.7-16.2+31.1 M⊙. 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 NGC 1579 stellar cluster is at the junction of two molecular filaments, the origin of the NGC 1579 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. [ABSTRACT FROM AUTHOR]