A Panoramic View of the Magnetized ISM

• Applicant: Thushara Pillai, Ph.D.
• Subject Area: Astrophysics and Astronomy
• Term: from 2014 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 263265753

Magnetic fields pervade galaxies, shaping them from the largest scales to the small cores that are collapsing to form stars within molecular clouds. A firm understanding of their role is crucial to our understanding of the physics of ISM from diffuse structures to dense filaments to star forming cores.This reasoning suggests in particular to study the most cold and dense molecular clouds in the interstellar medium (ISM), which may well dominate the reservoir of cold and dense gas in the Milky Way. Among these objects, it is ideal to focus on objects in which the magnetic field has not yet been disturbed by ongoing star formation. Such cold, massive, and starless regions often manifest as Infrared Dark Clouds (IRDCs), i.e., clouds with a column density high enough to cast a shadow at mid-infrared wavelengths ~8 um. Enormous progress has been made in the last decade towards understanding IRDC properties. The next major step in this field should be to understand magnetic fields. No magnetic field estimate for an IRDC has been published to date. This is presumably largely a consequence of the large integration times needed to observe the emission from these relatively faint targets. This is highly regrettable: current studies of IRDC cloud dynamics indicate that magnetic fields are the dominating agent preventing the collapse of clouds.Here I propose to take advantage of progresses in observatory technology and theory to now tackle this crucial gap in our knowledge. My study will in particular use (i) the PolKa dust emission polarimeter now available on APEX, and (ii) upgrades to the Effelsberg backend system. Association with the MPIfR helps to support the significant time requests needed to complete this work. I am currently finishing a first pilot study, presenting the first magnetic field assessment for any IRDC. At high angular resolution I can draw on my existing polarization maps from the SMA and CARMA interferometers. Via collaboration near-infrared dust extinction polarization data will feed into my study. In combination, this work addresses the next big step in exploring the enigmatic IRDCs, respectively magnetic fields in the dense gas. From an observational perspective, Germany is in a unique position to conduct this research.Many aspects of this work are enabled by the theoretical groundwork laid by German theorists. In particular, numerical simulations from R. Banerjee's group in Hamburg are crucial to unravel observations of the tangled field lines expected in molecular clouds. Conversely, the observational data obtained here will constrain their modelling work.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1573: Physics of the Interstellar Medium