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The MAgnetic field in the GALaxy, using Optical Polarization of Stars

Periodic Reporting for period 2 - MAGALOPS (The MAgnetic field in the GALaxy, using Optical Polarization of Stars)

Reporting period: 2020-03-01 to 2021-08-31

This project aims to understand the magnetic fields in the Milky Way at a more fundamental level.
Our Milky Way consists of billions of stars, but also giant interstellar gas clouds from which these stars form. This gas is threaded by a magnetic field, which acts as an invisible tug or glue to the gas. This means that the magnetic field has a direct influence on motions of the interstellar gas and on the formation of stars. However, the Milky Way's magnetic field also is a disturbing actor on astronomical observations of the Universe beyond the Milky Way, such as external galaxies or the Cosmic Microwave Background. Some of these observations of polarized radiation therefore need accurate knowledge of the Milky Way's magnetic field to subtract its influence, before these data can be used.
In this project, we perform observations of polarized light of stars in the Milky Way, which has an imprint of the strength and structure of the Milky Way's magnetic field in it. From these observations, combined with modeling of this magnetic field, we derive its large-scale morphology and statistical turbulent properties. Currently, many large-scale magnetic field models exist, but there is currenlty no method to quantitatively determine the relative quality of these models.
The final objectives of this project are therefore:
- to characterize the strength and morphology of the large-scale component of the Milky Way's magnetic field
- to determine the statistical properties of the small-scale, turbulent component of this field.
Our conclusions will benefit the astronomical community working on interstellar medium and star formation issues, but also the research fields which see the Milky Way's magnetic field as a contaminating factor that needs to be removed, such as the fields of ultra-high energy cosmic rays or cosmic microwave background polarization.
This project is fundamental research and therefore does not have a direct impact on society. The indirect impact is two-fold:
- it provides training of PhD students and postdocs, and also of bachelor and master students associated with this project. Their training is not only topic-based, but has a general component of complex problem solving and ciritical thinking which are useable throughout society
- science communication and outreach to the general public in the form of lectures, master classes, popular articles, interviews, etc.
WP1 (= data processing and analysis of the Interstellar Polarization Survey and the SOUTHPOL survey): data processing of the Interstellar Polarization Survey (IPS) is completed by PhD student José Versteeg (started Oct 2018). At this moment, Versteeg and second PhD student Yenifer Angarita (started Oct 2019) have added stellar distances to the database and applying appropriate quality flags. Versteeg has finished the data processing and has written a paper to be submitted to the peer-reviewed journal Astronomy & Astrophyiscs. The completed draft is now submitted to the co-authors for comments. Angarita is writing a draft of the first analysis of the polarization efficiency in the Interstellar Polarization Survey. Unfortunately, the SOUTHPOL survey is significantly delayed. The telescope on which our polarimeter was mounted has become unavailable and we are actively pursuing options at the moment to obtain a new telescope. Unfortunately, the fund raising efforts for this have been delayed significantly due to the unavailability of funds from our Brazilian collaborators caused by the COVID-19 pandemic. We are hopeful that we can acquire a telescope in the near future and SOUTHPOL can start, albeit with significant delays. In the worst-case scenario, the IPS survey alone will provide sufficient data to finish both PhD projects, with less data analysed in more detail.
WP2 (= Developing a full 3D dust distribution): In the years since the proposal was written, it had become clear that dust distributions have become available in the literature which can be used.
WP3 (= Galactic magnetic field determination with IMAGINE2.0): In October 2019, postdoc Luiz Rodrigues started on this work package. He has been overhauling the IMAGINE software package since then, making usage of the package much easier for users with different backgrounds, including extensive documentation available at https://imagine-code.readthedocs.io/en/ . Unfortunately, Rodrigues has left the field, but postdoc Sebastian Hutschenreuter (started 1 July 2020) has taken over this important job. The software paper is close to completion and a beta-release of the software is being planned.
Data processing of the complete Interstellar Polarization Survey (IPS) has finished and is now being written up for publication by the first project PhD student. These data are of excellent quality and we are taking the first steps in scientific analysis for both project PhD students.
The IMAGINE software package is receiving a total overhaul to make it more user-friendly, which will enable the whole collaboration (and the whole community) to use it, instead of only experts. This is now at the testing stage.
Map of the sky where our new fields (in red) are indicated over the older data (black lines).