The magnetic field and dust filaments in the Polaris Flare

Abstract

In diffuse molecular clouds, possible precursors of star-forming clouds, the effect of the magnetic field is unclear. In this work we compare the orientations of filamentary structures in the Polaris Flare, as seen through dust emission by Herschel, to the planeof-the-sky magnetic field orientation (B pos ) as revealed by stellar optical polarimetry with RoboPol. Dust structures in this translucent cloud show a strong preference for alignment with B pos . 70% of field orientations are consistent with those of the filaments (within 30• ). We explore the spatial variation of the relative orientations and find it to be uncorrelated with the dust emission intensity and correlated to the dispersion of polarization angles. Concentrating in the area around the highest column density filament, and in the region with the most uniform field, we infer the B pos strength to be 24 − 120 µG. Assuming that the magnetic field can be decomposed into a turbulent and an ordered component, we find a turbulent-to-ordered ratio of 0.2 − 0.8, implying that the magnetic field is dynamically important, at least in these two areas. We discuss implications on the 3D field properties, as well as on the distance estimate of the cloud.

First Results from BISTRO: A SCUBA-2 Polarimeter Survey of the Gould Belt

“…Figure 5 shows that the B-field lies roughly parallel to this subfilament, again as seen in Taurus (Palmeirim et al 2013). Similar behavior is also seen in the low-density striations in the Polaris Flare region (Ward- Thompson et al 2010;Panopoulou et al 2016).…”

Striations in molecular clouds: streamers or MHD waves?

“…Likewise, using the same method and the results presented in Chapman et al (2011) it is found that in the northwest part of the Taurus molecular cloud the ratio of the turbulent to the ordered component of the magnetic field is ∼ 11%. In general, the ratio of the ordered to turbulent component in molecular clouds can be up to ∼ 75% (Houde et al 2016) and, within uncertainties, it can also be up to 40% in regions where striations appear (Panopoulou et al 2016b). For the strength of the magnetic field in the striations region in the Polaris flare, Panopoulou et al (2016b) reported values that ranged up to ∼ 80 µG.…”

“…In general, the ratio of the ordered to turbulent component in molecular clouds can be up to ∼ 75% (Houde et al 2016) and, within uncertainties, it can also be up to 40% in regions where striations appear (Panopoulou et al 2016b). For the strength of the magnetic field in the striations region in the Polaris flare, Panopoulou et al (2016b) reported values that ranged up to ∼ 80 µG. Since striations appear in regions of well ordered magnetic field our reference value for the amplitude of the perturbation is 15% the background value of each perturbed quantity.…”

“…Using the Rolling Hough Transform (RHT) algo-rithm (Clark et al 2014) they concluded that striations were in excellent alignment with the magnetic field. Panopoulou et al (2016b) also used RHT to compare the orientation of the plane-of-the-sky (POS) magnetic field with linear structures in the Polaris flare and reported that the majority of striations were aligned with the projected magnetic field. The alignment between these structures and the magnetic field has also been pointed out in all clouds by all relevant studies in the literature (Goldsmith et al 2008;Chapman et al 2011;Hennemann et al 2012;Palmeirim et al 2013;Alves de Oliveira et al 2014).…”

Probing the cold magnetised Universe with SPICA-POL (B-BOP)

“…XXXV, 2016, see Figs. 1b & 1c), a trend also seen in optical and near-IR polarization observations (Chapman et al, 2011;Palmeirim et al, 2013;Panopoulou et al, 2016;Soler et al, 2016). There is also a hint from Planck polarization observations of the nearest clouds that the direction of the magnetic field may change within dense filaments from nearly perpendicular in the ambient cloud to more parallel in the filament interior (cf.…”