Interstellar Polarization Survey. III. Relation between Optical Polarization and Reddening in the General Interstellar Medium

Author(s)

Angarita, Y. ; Versteeg, M. J. F. ; Haverkorn, M. ; Rodrigues, C. V. ; Magalhaes, A. M. ; Santos-Lima, R. ; Kawabata, Koji S.

• Document type: Journal article
• Source: ASTRONOMICAL JOURNAL; v. 166, n. 1, p. 19-pg., 2023-07-01.

Abstract

Optical starlight can be partially polarized while propagating through the dusty, magnetized interstellar medium (ISM). The polarization efficiency describes the polarization intensity fraction per reddening unit, P-V/E(B - V), related to the interstellar dust grains and magnetic field properties. The maximum value observed, [P-V/E(B - V)](max), is thus achieved under optimal polarizing conditions of the ISM. Therefore, the analysis of polarization efficiency observations across the Galaxy contributes to the study of magnetic field topology, small-scale magnetic fluctuations, grain-alignment efficiency, and composition. Infrared observations from Planck satellite have set [P-V/E(B - V)](max) to 13% mag(-1). However, recent optical polarization observations in Planck's highly polarized regions showed polarization efficiency values between 13.6% mag(-1) and 18.2% mag(-1) (depending on the extinction map used), indicating that [P-V/E(B - V)] max is not well constrained yet. We used V-band polarimetry of the Interstellar Polarization Survey ( consisting of similar to 10,500 high-quality observations distributed in 34 fields of 0 degrees. 3 x 0 degrees. 3) to accurately estimate the polarization efficiency in the ISM. We estimated the upper limit of PV/E(B - V) with the weighted 99th percentile of the field. In five regions, the polarization efficiency upper limit is above 13% mag-1. Furthermore, we found [P-V/E(B - V)](max) = 15.8(-0.9)(+1.3) mag(-1) using diffuse intermediate-latitude (|b| > 7 degrees. 5) regions with apparently strong regular Galactic magnetic field in the plane-of-sky. We studied the variations of P-V/E(B - V) across the sky and tested toy models of polarization efficiency with Galactic longitude that showed some correspondence with a uniform spiral magnetic field. (AU)

• FAPESP's process: 10/19694-4 - SOUTH POL: revealing the polarized Southern Sky
• Grantee: Antônio Mário Magalhães
• Support Opportunities: Regular Research Grants
• FAPESP's process: 01/12589-1 - Stars, the interstellar medium and their interrelationships
• Grantee: Antônio Mário Magalhães
• Support Opportunities: Research Projects - Thematic Grants