Vol 22, No 7

## The Relative Orientation between Local Magnetic Field and Galactic Plane in Low Latitude Dark Clouds

#### Gulafsha B. Choudhury, Himadri S. Das, B. J. Medhi, J. C. Pandey, S. Wolf et al.

Abstract

In this work, we study the magnetic field morphology of selected star-forming clouds spread over the galactic latitude (b) range −10° to 10°. The polarimetric observations of clouds CB24, CB27 and CB188 are conducted to study the magnetic field geometry of those clouds using the 104 cm Sampurnanand Telescope (ST) located at ARIES, Manora Peak, Nainital, India. These observations are combined with those of 14 further low latitude clouds available in the literature. Most of these clouds are located within a distance range 140–500 pc except for CB3 (2500 pc), CB34 (1500 pc), CB39 (1500 pc) and CB60 (1500 pc). Analyzing the polarimetric data of 17 clouds, we find that the alignment between the envelope magnetic field ($$\theta_{B}^{\rm env}$$) and galactic plane (GP) ($$\theta_{\rm GP}$$) of the low-latitude clouds varies with their galactic longitudes (l). We observe a strong correlation between the longitude (l) and the offset ($$\theta_{\rm off}=|\theta_{B}^{\rm env} -\theta_{\rm GP} |$$) which shows that $$\theta_{B}^{\rm env}$$ is parallel to the GP when the clouds are situated in the region 115° < l < 250°. However, B env q has its own local deflection irrespective of the orientation of θGP when the clouds are at l < 100° and l > 250°. To check the consistency of our results, the stellar polarization data available in the Heiles catalog are overlaid on the DSS image of the clouds having mean polarization vector of field stars. The results are almost consistent with the Heiles data. A systematic discussion is presented in the paper. The effect of turbulence in the cloud is also studied which may play an important role in causing the misalignment phenomenon observed between $$\theta_{B}^{\rm env}$$ and $$\theta_{\rm GP}$$. We have used Herschel (Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.) SPIRE 500 μm and SCUBA 850 μm dust continuum emission maps in our work to understand the density structure of the clouds.

Keywords

polarization – (ISM:) dust – extinction – ISM: magnetic fields – galaxies: magnetic fields

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