Abstract: 

As most of the molecular clouds are filamentary and elongated, the magnetic fields (B-fields) in these clouds are found either parallel or perpendicular to the main axes. In the talk, I will present the B-fields mapped in IRDC G34.43+0.24 using 850 micron polarized dust emission observed with the POL-2 instrument at JCMT. We examine the magnetic field geometries and strengths in the northern, central, and southern regions of the filament. The overall field geometry is ordered and aligned closely perpendicular to the filament's main axis, particularly in regions containing the central clumps MM1 and MM2, whereas MM3 in the north has field orientations aligned with its major axis. The overall field orientations are uniform at large (POL-2 at 14” and SHARP at 10”) to small scales (TADPOL at 2.5” and SMA at 1.5”) in the MM1 and MM2 regions. The SHARP/CSO observations in MM3 at 350 micron from Tang et al. show a similar trend as seen in our POL-2 observations. TADPOL observations demonstrate a well-defined field geometry in MM1/MM2 consistent with MHD simulations of accreting filaments. We obtained a plane-of-sky magnetic field strength of 470+/-190 micG, 100+/-40 micG, and 60+/-34 micG in the central, northern and southern regions of G34, respectively, using the updated Davis-Chandrasekhar-Fermi relation. The estimated value of field strength, combined with column density and velocity dispersion values available in the literature, suggests G34 to be marginally critical with criticality parameter values 0.8+/-0.4, 1.1+/-0.8, and 0.9+/-0.5 in the central, northern, and southern regions, respectively. The turbulent motions in G34 are sub-Alfvénic with Alfvénic Mach numbers of 0.34+/-0.13, 0.53+/-0.30, and 0.49+/-0.26 in the three regions. The observed aligned B-fields in G34.43+0.24 are consistent with theoretical models suggesting that B-fields play an important role in guiding the contraction of the cloud driven by gravity. I will also discuss some of my ongoing projects where I am investigating the dust grain characteristics such as heating, radiative alignment, and collisional disalignment of grains.