Periodic Reporting for period 5 - MAGALOPS (The MAgnetic field in the GALaxy, using Optical Polarization of Stars)
Reporting period: 2024-09-01 to 2025-08-31
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, a fingerprint of the Big Bang. 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 currently 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.
Using a large data set called the Interstellar Polarization survey, we obtained new information on both the large-scale and the small-scale components of the Milky Way's magnetic field. New large-scale magnetic field strengths in interstellar clouds were derived, inclusing 3D spatial information, and depolarization by turbulent fields was investigated. In addition, these observations provide novel ways to study the properties and distribution of interstellar dust. We also developed a large-scale magnetic field modeling engine called IMAGINE and used inversion methods to determine the Galactic Faraday rotation sky and magnetic field distributions.
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 critical thinking which are usable in any career that these students may choose.
- science communication and outreach to the general public in the form of lectures, master classes, popular articles, interviews, etc.
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, a fingerprint of the Big Bang. 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 currently 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.
Using a large data set called the Interstellar Polarization survey, we obtained new information on both the large-scale and the small-scale components of the Milky Way's magnetic field. New large-scale magnetic field strengths in interstellar clouds were derived, inclusing 3D spatial information, and depolarization by turbulent fields was investigated. In addition, these observations provide novel ways to study the properties and distribution of interstellar dust. We also developed a large-scale magnetic field modeling engine called IMAGINE and used inversion methods to determine the Galactic Faraday rotation sky and magnetic field distributions.
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 critical thinking which are usable in any career that these students may choose.
- 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) was executed by the first PhD student (PhD1), who started Oct 2018. Next, two PhD students (PhD2 started Oct 2019) have added stellar distances to the database, applying appropriate quality flags. PhD1 published the first paper on the survey data in the peer-reviewed journal Astronomical Journal in 2023, after which she wrote a paper on the scientific interpretation of the data in one particular region (the Southern Coalsack cloud). A third paper, on interpretation of polarization statistics, is finished but awaits submission until after the IPS Survey paper is submitted. PhD2 published the first analysis of the polarization efficiency in the Interstellar Polarization Survey in 2023, followed by papers on determinations of magnetic field strength in clouds in 2024, and full magnetic field tomography in 2025. Both PhD candidates defended their PhD theses successfully in Feb 2025. A third PhD student collaborated on a small part of the project, identifying Galactic magnetic fields in two particular regions in the Southern sky, resulting in an acknowledgment and a co-authorship in two separate papers.
The SOUTH POL survey was significantly delayed due to several independent reasons. The telescope on which the project's polarimeter was mounted became unavailable before the start of the project. Several options were pursued to obtain a new telescope. In 2020 and 2021, the fund raising efforts for this were delayed significantly due to the unavailability of funds from our Brazilian collaborators caused by the COVID-19 pandemic. Discussions and preparations for the refurbishment of an existing telescope at the Cerro Tololo Inter-American Observatory in Chile had proceeded to a fairly advanced state, when a better option occurred in the form of a newly to be built telescope at the Pico dos Dios observatory in Brazil, where our polarimeter will be the main instrument.
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, a first postdoc started on this work package. He had 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/(opens in new window) . A second postdoc (started 1 July 2020) followed up on this important job. This resulted in a beta-release of the software, a publicly available magnetic field model library, and several related science papers in 2022 and 2024.
Overview of results:
* 6 science papers in peer-reviewed journals where project members are first author (one to be submitted) on the starlight polarization survey (WP1)
* 2 science papers in peer-reviewed journals where project members are first author on modeling of the Galactic magnetic field (WP3)
* publication of IMAGINE magnetic field modeling software and the Galactic magnetic field model library (both including documentation) (WP3)
* contributions from authors paid by the project to 34 papers in peer-reviewed journals
These papers have accrued a total of 1308 citations (23 Oct 2025).
The SOUTH POL survey was significantly delayed due to several independent reasons. The telescope on which the project's polarimeter was mounted became unavailable before the start of the project. Several options were pursued to obtain a new telescope. In 2020 and 2021, the fund raising efforts for this were delayed significantly due to the unavailability of funds from our Brazilian collaborators caused by the COVID-19 pandemic. Discussions and preparations for the refurbishment of an existing telescope at the Cerro Tololo Inter-American Observatory in Chile had proceeded to a fairly advanced state, when a better option occurred in the form of a newly to be built telescope at the Pico dos Dios observatory in Brazil, where our polarimeter will be the main instrument.
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, a first postdoc started on this work package. He had 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/(opens in new window) . A second postdoc (started 1 July 2020) followed up on this important job. This resulted in a beta-release of the software, a publicly available magnetic field model library, and several related science papers in 2022 and 2024.
Overview of results:
* 6 science papers in peer-reviewed journals where project members are first author (one to be submitted) on the starlight polarization survey (WP1)
* 2 science papers in peer-reviewed journals where project members are first author on modeling of the Galactic magnetic field (WP3)
* publication of IMAGINE magnetic field modeling software and the Galactic magnetic field model library (both including documentation) (WP3)
* contributions from authors paid by the project to 34 papers in peer-reviewed journals
These papers have accrued a total of 1308 citations (23 Oct 2025).
Despite the delay in the SOUTH POL survey, excellent science results have been obtained with its pilot Interstellar Polarization Survey (IPS), resulting in 6 published papers in peer-reviewed journals and one awaiting submission.
In addition to the science goals on galactic magnetic field, papers have been published on dust distribution and properties as well. For details, see above.
In addition to the science goals on galactic magnetic field, papers have been published on dust distribution and properties as well. For details, see above.