Large-scale magnetic fields in Bok globules

Abstract

Context. The role of magnetic fields in the star formation process is a contentious matter of debate. In particular, no clear observational proof exists of a general influence by magnetic fields during the initial collapse of molecular clouds. Aims. Our aim is to examine magnetic fields and their influence on a wide range of spatial scales in low-mass star-forming regions. Methods. We trace the large-scale magnetic field structure on scales of 10 3 −10 5 AU in the local environment of Bok globules through optical and near-infrared polarimetry and combine these measurements with existing submillimeter measurements, thereby characterizing the small-scale magnetic field structure on scales of 10 2 −10 3 AU. Results. For the first time, we present polarimetric observations in the optical and near-infrared of the three Bok globules B335, CB68, and CB54, combined with archival observations in the submillimeter and the optical. We find a significant polarization signal (P 2%, P/σ P > 3) in the optical and near-infrared for all three globules. Additionally, we detect a connection between the structure on scales of 10 2 −10 3 AU to 10 3 −10 4 AU for both B335 and CB68. Furthermore, for CB54, we trace ordered polarization vectors on scales of ∼10 5 AU. We determine a magnetic field orientation that is aligned with the CO outflow in the case of CB54, but nearly perpendicular to the CO outflow for CB68. For B335 we find a change in the magnetic field oriented toward the outflow direction, from the inner core to the outer regions. Conclusions. We find strongly aligned polarization vectors that indicate dominant magnetic fields on a wide range of spatial scales.

Magnetic field geometry of the large globule CB 34

“…In the case of globules B335, CB230 and CB68, the outflows are oriented almost perpendicular to the inner magnetic field (Wolf et al 2003;Bertrang et al 2014). Bertrang et al (2014) also reported that the magnetic field orientation of CB54 is aligned with CO outflow.…”

“…They commented that in those sources the fields have been wrapped up toroidally by envelope rotation. Many observations have been reported to study the correlation between magnetic field and CO outflow of the Bok globules (e.g., Cohen et al (1984); Vrba et al (1986); Jones & Amini (2003); Wolf et al (2003); Hull et al (2013);Bertrang et al (2014); Soam et al (2015)). Some study shows a good alignment of globule's magnetic field with outflow axis (e.g., Cohen et al (1984); Vrba et al (1986); Jones & Amini (2003)), whereas misalignment of magnetic field direction and outflow axis have been also reported (e.g.…”

“…Hull et al (2014) found that the outflows are randomly aligned with B-fields, but sources with low polarization fractions showed hints of outflows being preferentially perpendicular to smallscale B-fields. Bertrang et al (2014) reported a magnetic field orientation parallel to the CO outflow in cloud CB54, while cloud B335 shows a change in the magnetic field orientation toward the outflow axis from the inner core to the envelope regions. In CB68, they found a magnetic field orientation almost perpendicular to the CO outflow.…”

“…Complementary to this, the thermal reemission of aligned grains located in the high-density central region of molecular clouds is linearly polarized perpendicular to the magnetic field direction and can thus be studied through submillimeter polarimetric measurement. Numerous studies have been made on molecular clouds through optical and submillimeter polarimetry (Kane et al 1995;Wolf et al 2003;Alves et al 2008;Ward-Thompson et al 2009;Franco et al 2010;Paul et al 2012;Chakraborty et al 2014;Bertrang et al 2014;Chakraborty & Das 2016).…”

Magnetic field geometry of an unusual cometary cloud Gal 110-13

“…The polarization measurements in optical (e.g., Vrba et al 1976;Goodman et al 1990;Alves et al 2008;Soam et al 2013;Alves et al 2014), near-infrared (e.g., Goodman et al 1995;Chapman et al 2011;Sugitani et al 2011;Clemens 2012;Cashman & Clemens 2014;Bertrang et al 2014;Kusune et al 2015;Alves et al 2014) and submillimeter-millimeter wavelengths (e.g., Rao et al 1998;Dotson et al 2000Dotson et al , 2010Vaillancourt & Matthews 2012;Hull et al 2014;Alves et al 2014) are used to map the magnetic field geometry of molecular clouds. Optical polarization position angles trace the plane of the sky orientation of the ambient magnetic field at the periphery of the molecular clouds (with A V ∼ 1-2 mag; Goodman et al 1995;Goodman 1996).…”