Filament L1482 in the California molecular cloud

Abstract

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 12 CO 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 13 CO 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 +31.1 −16.2 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 12 CO 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.

The impact of turbulence and magnetic field orientation on star-forming filaments

“…The gas is isothermal at a temperature of 15 K, which agrees well with temperatures observed in a number of filaments (e.g. André et al 2010;Arzoumanian et al 2011;Li et al 2014). The mean molecular weight is set to µ mol = 2.3 typical for molecular gas.…”

“…Observations of star-forming filaments reveal nonthermal line widths, which indicate an additional turbulent velocity field with typical Mach numbers between 1 and 3 (Arzoumanian et al 2013;Hacar et al 2013;Furuya et al 2014;Henshaw et al 2014;Jiménez-Serra et al 2014;Li et al 2014). For this reason, we apply a transonic or supersonic turbulent velocity field.…”

“…Furthermore, line emission observations of e.g. C 18 O or N2H + towards star forming filaments (Arzoumanian et al 2013;Hacar et al 2013;Furuya et al 2014;Henshaw et al 2014;Jiménez-Serra et al 2014;Li et al 2014) report non-thermal line broadening, which points to an additional trans-to supersonic turbulent velocity field. Temperatures in filaments are typically in the seifried@ph1.uni-koeln.de range of ∼ 10 to 15 K, which is particularly important for calculating the critical mass per unit length of a filament (Ostriker 1964).…”

Observations of Magnetic Fields Surrounding LkHα 101 Taken by the BISTRO Survey with JCMT-POL-2

“…The non-thermal velocity dispersion along the lineof-sight has been measured by the Purple Mountain Observatory (PMO) 13.7-m radio telescope using the 13 CO(1−0) transition (Li et al 2014). The results are σ V = 0.52 km s −1 (meaning ∆V = 2.355σ V = 1.22 km s −1 ) for Clump 10 and σ V = 0.64 km s −1 (meaning ∆V = 2.355σ V = 1.52 km s −1 ) for Clump 12.…”

“…Since the redshifted parts of the cloud trace well the 850 µm polarized emission from the region we use their velocity dispersion to calculate the B-field strength in the next section. However, we conservatively use uncertainties on velocity dispersion estimated from the combination of the three independent measurements added in quadrature: 13 CO(1−0) emission (Li et al 2014), HARP blueshifted, and HARP red-shifted spectra instead of using only the uncertainties from the fits to the HARP red-shifted spectra. The final velocity dispersion retained for further analysis are 1.32 ± 0.40 km s −1 and 1.86 ± 0.19 km s −1 for the central region and dust lane, respectively.…”