Studies Of The Galactic Magnetic Fields Based On Starlight Polarization And Supernova Remnant

The origin and evolution of magnetic fields is an important and fundamental question in astrophysics,which has not been solved yet.The Milky Way is the clearest galaxy we can observe and study,providing an ideal laboratory for understanding the cosmic magnetic field.The Galactic magnetic field can be measured in a variety of ways,such as the Faraday rotation of pulsars and extragalactic radio sources,the Zeeman effect of spectral lines,the synchrotron radiation of relativistic electrons in the magnetic field,the thermal polarized emission of dust,and the polarization of starlight.Different measurements can reveal the structure of the magnetic field in different interstellar medium(ISM): such radio polarization,mainly reflects the properties of the magnetic field in diffuse ionized gas;the Zeeman effect is mainly used to reveal the magnetic field of very dense local regions in gas clouds,and the stellar polarization reflects the extended magnetic field structure in gas clouds.An accurate model of the Galactic magnetic field needs to be based on observations of the magnetic field of all interstellar medium.But the current observations are so inadequate that they limit our understanding of the magnetic field in the Milky Way.Starlight polarization serves one of the powerful tools to study magnetic fields in the Galactic interstellar medium.Heiles catalogue contains polarization information for9286 stars and is by far the biggest.This catalogue has been extensively used to study magnetic fields.However,the distance parameters of the stars in this catalogue are from photometric observations and very uncertain.We cross match Heiles catalogue with Gaia Data Release 2(DR2),and identify 7613 stars using both angular separation and magnitude as constraints.We then obtain precise distances from Gaia DR2 for these stars.For more than 90% of the stars,the relative errors of the new distances are within 20%.Based on the new catalogue,we demonstrate how starlight polarization can probe Galactic magnetic fields.The magnetic field supernova remnant(SNR)is closely related to the galactic magnetic field,as the radio emission from SNRs originates primarily from synchrotron radiation of relativistic electrons in the presence of compressed magnetic fields.Radio observation is crucial for detecting the magnetic field of SNR and its connection with the galaxy.To further explore the relationship between the magnetic field of the Milky Way and the magnetic field of the supernova remnant,we selected large SNR samples with distinct shell or filamentary structures from the 843 MHz supernova remnant table and observed them using the CSIRO Australia Telescope Compact Array(ATCA).From these observations,we chose the SNR G315.4-2.3 with bilateral symmetry to study its structure,and analyze its relationship with the large-scale magnetic field of the Milky Way from the aspect of radio polarization observations.