We have mapped the entire region of ≈ 1° × 1.5° of Heiles' Cloud 2 (HCL2) in Taurus Molecular Cloud Complex using the optically thin C18O J=1-0 emission. The FWHM beam size was 17″ and the map covers the spatial scales from 0.03 pc to 3 pc.
It is found that HCL2 consists of six filaments with a mean size of 1.17 pc × 0.35 pc. All the filaments are perpendicular to the local magnetic field. This fact suggests the magnetic field probably determines the orientation of the filaments.
Non-thermal motions are dominant in the filaments. Within the six filaments, we found the difference of the C18O line widths between the filaments associated with and without YSOs. The C18O spectra in the filaments with YSOs show broader line widths than those in the starless filaments. These broad lines are not associated with YSOs themselves, but are concentrated in strong line intensity regions. The lines in these regions seem to have several peaks. These facts suggest the presence of several small fragments along a line of sight, and the crowdedness of the fragments would determine the line widths. The concentrations of the fragments might trigger the star formation within the filaments.
In 1981, Larson found the size-line width relation toward various molecular clouds, so called “Larsons's Laws” (Larson 1981). After his investigation, many investigators reported the same relation from large scales (molecular clouds) to small scales (dense cores).