Abstract
The magnetic field in the local interstellar medium does not follow the large-scale Galactic magnetic field. The local magnetic field has probably been distorted by the Local Bubble, a cavity of hot ionized gas extending all around the Sun and surrounded by a shell of cold neutral gas and dust. However, so far no conclusive association between the local magnetic field and the Local Bubble has been established. Here we develop an analytical model for the magnetic field in the shell of the Local Bubble, which we represent as an inclined spheroid, off-centred from the Sun. We fit the model to Planck dust polarized emission observations within 30° of the Galactic poles. We find a solution that is consistent with a highly deformed magnetic field, with significantly different directions towards the north and south Galactic poles. This work sets a methodological framework for modelling the three-dimensional (3D) structure of the magnetic field in the local interstellar medium, which is a most awaited input for large-scale Galactic magnetic field models.
Highlights
The interstellar medium (ISM) of our Galaxy is threaded by a pervasive magnetic field that plays an important role in many astrophysical processes
The observations include several local structures, which appear large on the sky because of their proximity, but are not part of the large-scale magnetic field. The most important such structure is the Local Bubble, an interstellar bubble located around the Sun and extending out to ∼60 pc towards the Galactic centre and 250 pc towards the north and south Galactic poles (Puspitarini et al 2014)
The Local Bubble is thought to be the result of supernova explosions, which swept out a cavity of hot ionized gas and pushed most of the evacuated matter, together with the frozen-in magnetic field, into a dense shell of cold neutral gas and dust (Cox & Reynolds 1987; Shelton 1998; Fuchs et al 2006; Lallement et al 2014)
Summary
The interstellar medium (ISM) of our Galaxy is threaded by a pervasive magnetic field that plays an important role in many astrophysical processes (see e.g. Ferrière 2001; Heiles & Haverkorn 2012). Han et al 2006; Sun & Reich 2010; Jansson & Farrar 2012; Jaffe et al 2013; Terral & Ferrière 2017) These aim at describing the large-scale structure of the magnetic field, commonly divided into disk and halo components. B denote Galactic longitude and latitude, respectively These departures from the large-scale magnetic field were related to the Local Bubble shell by Leroy (1999), who, based on stellar polarization observations, found coherent magnetic field orientations over the distance range 60–150 pc. Planck Collaboration Int. XLIV (2016) analysed the Planck maps of dust polarized emission towards the southern Galactic cap (b < −60◦), and found that these could be represented by a uniform magnetic field pointing in the direction ( , b) = (70◦, 24◦), with a significant vertical component. Such a model will contribute to our understanding of the large-scale Galactic magnetic field and will lead to a more accurate modelling of the Galactic polarized foreground emission, which contaminates observations of the B modes of the cosmic microwave background (BICEP2/Keck Collaboration et al 2015) and of HI emission from the epoch of reionization (Jelicet al. 2010)
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