Tracing the magnetic field morphology of the LDN 1172/1174 cloud complex

Abstract

Context. The LDN 1172/1174 cloud complex in the Cepheus Flare region presents a hub-filament structure with the reflection nebula, NGC 7023, illuminated by a Herbig Be star, HD 200775, which consists of the hub with a ~5 pc long narrow filament attached to it. Formation of a sparse cluster of low- and intermediate-mass stars is presently taking place in the hub.

Aims. The aim of this work is to map the magnetic field geometry of LDN 1172/1174 to understand the role played by the field lines in the formation of the molecular cloud.

Methods. Unpolarized background stars can be used to measure dichroically polarized light produced by the magnetically aligned grains present in molecular clouds. As these dust grains get aligned with their minor axes parallel to the ambient magnetic field, the polarization measurements can provide the plane-of-sky component of the magnetic field. We made R-band polarization measurements of 249 stars projected on the entire LDN 1172/1174 cloud complex to map the geometry of the magnetic field of this region.

Results. The magnetic field geometry constructed from our R-band polarization measurements is found to be parallel to the elongated structure inferred from the column density distribution of the cloud produced using the Herschel images. Our R-band polarization measurements are found to be in good agreement with those obtained from Planck. There is evidence of a possible distortion of the magnetic fields toward the northwestern part of the cloud by HD 200775. The magnetic field strength is estimated as ~30 μG. The estimated star formation rate (SFR)/mass of 2.0 ± 1.3% Myr−1 and 0.4 ± 0.3% Myr−1 for LDN 1172/1174 and the neighboring cloud complex, LDN 1147/1158, respectively, are found to be consistent with the mean SFR/mass found for the clouds with magnetic field orientations parallel and perpendicular to their elongated structures, respectively. These results support earlier findings that the clouds with magnetic field lines parallel to their long axes seem to have higher SFRs compared to those with the magnetic field orientation perpendicular to the cloud elongation.