Cloud motion and magnetic fields: Four clouds in the Cepheus Flare region

Abstract

Context. The Cepheus Flare region consists of a group of dark cloud complexes that are currently active in star formation.

Aims. The aim of this work is to estimate the motions of four clouds, namely L1147/1158, L1172/1174, L1228, and L1251, located at relatively high Galactic latitude (b > 14°) in the Cepheus Flare region. We study the relationship between the motions of the clouds with respect to the magnetic field and the clump orientations with respect to both the magnetic field and the motion.

Methods. We estimated the motions of the molecular clouds using the proper motion and distance estimates of the young stellar objects (YSOs) associated with them using the Gaia EDR3 data. By assuming that the YSOs are associated with the clouds and share the same velocity, the projected directions of motion are estimated for the clouds. We measured the projected geometry of the magnetic field towards the direction of each cloud by combining the Planck polarization measurements.

Results. We estimated a distance of 371 ± 22 pc for L1228 and 340 ± 7 pc for L1251, implying that all four complexes are located at almost the same distance. Assuming that both the clouds and YSOs are kinematically coupled, we estimated the projected direction of motion of the clouds using the proper motions of the YSOs. The directions of motion of all the clouds are offset by ~30° with respect to the ambient magnetic fields, except in L1172/1174 where the offset is ~45°. In L1147/1158, the starless clumps are found to be oriented predominantly parallel to the magnetic fields while prestellar clumps show a random distribution. In L1172/1174, L1228, and L1251, the clumps are oriented randomly with respect to the magnetic field. With respect to the motion of the clouds, there is a marginal trend that the starless clumps are oriented more parallel in L1147/1158 and L1172/1174. In L1228, the major axes of the clumps are oriented more randomly. In L1251, we find a bimodal trend in the case of starless clumps. We do not find any overall specific correlation between the core orientation and the global/local magnetic fields for the clouds in Cepheus. Also, we conclude that the local small-scale dynamics of the cloud with respect to the magnetic field direction could be responsible for the final orientation of the cores.