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Demonstration of Magnetic Field Tomography with Starlight Polarization toward a Diffuse Sightline of the ISM

Panopoulou, Georgia V. and Tassis, Konstantinos and Skalidis, Raphael and Blinov, Dmitriy and Liodakis, Ioannis and Pavlidou, Vasiliki and Potter, Stephen B. and Ramaprakash, Anamparambu N. and Readhead, Anthony C. S. and Wehus, Ingunn K. (2019) Demonstration of Magnetic Field Tomography with Starlight Polarization toward a Diffuse Sightline of the ISM. Astrophysical Journal, 872 (1). Art. No. 56. ISSN 1538-4357. doi:10.3847/1538-4357/aafdb2.

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The availability of large data sets with stellar distance and polarization information will enable a tomographic reconstruction of the (plane-of-the-sky-projected) interstellar magnetic field in the near future. We demonstrate the feasibility of such a decomposition within a small region of the diffuse interstellar medium (ISM). We combine measurements of starlight (R-band) linear polarization obtained using the RoboPol polarimeter with stellar distances from the second Gaia data release. The stellar sample is brighter than 17 mag in the R-band and reaches out to several kiloparsecs from the Sun. H i emission spectra reveal the existence of two distinct clouds along the line of sight. We decompose the line-of-sight-integrated stellar polarizations to obtain the mean polarization properties of the two clouds. The two clouds exhibit significant differences in terms of column density and polarization properties. Their mean plane-of-the-sky magnetic field orientation differs by 60°. We show how our tomographic decomposition can be used to constrain our estimates of the polarizing efficiency of the clouds as well as the frequency dependence of the polarization angle of polarized dust emission. We also demonstrate a new method to constrain cloud distances based on this decomposition. Our results represent a preview of the wealth of information that can be obtained from a tomographic map of the ISM magnetic field.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Panopoulou, Georgia V.0000-0001-7482-5759
Tassis, Konstantinos0000-0002-8831-2038
Liodakis, Ioannis0000-0001-9200-4006
Potter, Stephen B.0000-0002-5956-2249
Readhead, Anthony C. S.0000-0001-9152-961X
Additional Information:© 2019 The American Astronomical Society. Received 2018 October 22; revised 2018 December 31; accepted 2019 January 8; published 2019 February 11. We thank A. Brimis, I. Komis, I. Leonidaki, and N. Mandarakas for their help during the observations and T. Ghosh for helping with the analysis of Planck data. We thank N. Kylafis for useful suggestions on the paper. We thank the anonymous reviewer for their helpful comments. A.N.R., G.V.P., and A.C.S.R. acknowledge support from the National Science Foundation, under grant number AST-1611547. This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme under grant agreement No. 771282. This work has made use of data from the European Space Agency (ESA) mission Gaia (, processed by the Gaia Data Processing and Analysis Consortium (DPAC; This research made use of the following Python packages: APLpy (Robitaille & Bressert 2012), Astropy (Astropy Collaboration et al. 2013), and healpy (Górski et al. 2005). Facilities: Skinakas:1.3 m - , Gaia - , Effelsberg - , CDS - , IRSA - , Planck - . Software: Astropy, aplpy, healpy.
Group:Astronomy Department
Funding AgencyGrant Number
European Research Council (ERC)771282
Subject Keywords:ISM: clouds – ISM: magnetic fields – techniques: polarimetric
Issue or Number:1
Record Number:CaltechAUTHORS:20190212-150402789
Persistent URL:
Official Citation:Georgia V. Panopoulou et al 2019 ApJ 872 56
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:92852
Deposited By: Tony Diaz
Deposited On:13 Feb 2019 02:09
Last Modified:16 Nov 2021 03:54

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