A comparative study of dust grain polarization efficiencies in the interstellar and intracluster mediums towards anticentre galaxy

Abstract

Dust polarization observations at optical wavelengths help understand the dust grain properties and trace the plane-of-the-sky component of the magnetic field. In this study, we make use of published optical polarization data acquired with AIMPOL along with distances (d) and extinction (AV) data. We study the variation of polarization efficiency (P/AV) as a function of AV in the diffuse interstellar medium (ISM) and intracluster mediums (ICM) using the already published polarization data of six clusters. Among these clusters, NGC 2281, NGC 1664, and NGC 1960 are old; while Stock 8, NGC 1931, and NGC 1893 are young. We categorize stars towards each cluster into foreground, background, and cluster members by employing two clustering algorithms GMM and DBSCAN. Thus, classified field stars and cluster members are used to reveal the polarization properties of ISM and ICM dust, respectively. We find that the dust grains located in the diffuse ISM show higher polarization efficiencies when compared to those located in the ICM of younger clusters.