Researchers Discover Different Magnetic Field Structures of NGC 4217 Galaxy

The NGC 4217 galaxy, a Milky Way-like galaxy, boasts different shapes, such as giant loops, superbubbles, and X-shaped magnetic field structures. A new study offers insights into how such structures are formed.

The spiral galaxy NGC 4217 has a huge magnetic field that is shown here as green lines. The data for this visualization was recorded with the radio telescope Karl G. Jansky Very Large Array (VLA) of the National Science Foundation. The image of the galaxy shown from the side is taken from data from the Sloan Digital Sky Survey and Kitt Peak National Observatory. Image Credit: Composite image by Yelena Stein of the Centre de Données astronomiques de Strasbourg (CDS) with the support of Jayanne English (University of Manitoba). VLA radio data from Yelena Stein and Ralf-Jürgen Dettmar (Ruhr University Bochum). The observations are part of the project Continuum Halos in Nearby Galaxies – an EVLA Survey (CHANG-ES) led by Judith Irwin (Queen’s University, Canada). The optical data are from the Sloan Digital Sky Survey. The ionized hydrogen data (red) are from the 0.9 m telescope of the Kitt Peak National Observatory, collected by Richard J. Rand of the University of New Mexico. The software code for tracing the magnetic field lines was adapted from the Linear Integral Convolution code provided by Arpad Miskolczi of Ruhr University.

Spiral galaxies such as the Milky Way can contain sprawling magnetic fields. Although different theories about their formation exist, until now, the process has not been understood so well.

At present, an international team of researchers has performed an in-depth analysis of the magnetic field of the NGC 4217 galaxy based on radio astronomical observations, discovering the so-far mysterious magnetic field structures. The data indicates that formation and explosions of stars, or supernovae, cause these visible structures.

Headed by Dr Yelena Stein from Ruhr-Universität Bochum, the Centre de Données astronomiques de Strasbourg, and the Max Planck Institute for Radio Astronomy in Bonn along with US-American and Canadian collaborators, the researchers published the study findings in the Astronomy and Astrophysics journal, online on July 21st, 2020.

The analyzed data had been collected in the project titled “Continuum Halos in Nearby Galaxies,” which involved the use of radio waves to measure 35 galaxies. “Galaxy NGC 4217 is of particular interest to us,” noted Yelena Stein, who started the study at the Chair of Astronomy at Ruhr-Universität Bochum under Professor Ralf-Jürgen Dettmar.

Dr Stein currently works at the Centre de Données astronomiques de Strasbourg.

NGC 4217 is similar to the Milky Way and located just about 67 million light-years away, implying that it is much closer to it, in the Ursa Major constellation. Hence, the team believes some of the study findings can be successfully applied to the Milky Way galaxy.

Magnetic Fields and Origins of Star Formation

Evaluation of the data from NGC 4217 revealed a number of remarkable structures. Similar to observations in other galaxies, this galaxy also has an X-shaped magnetic field structure that extends far outward from the disk of the galaxy, for more than 20,000 light-years.

Apart from the X-shape, the researchers discovered two large bubble structures, also called superbubbles, as well as a helix structure. The bubble structures are caused when several massive stars explode as supernovae, and also originate from regions stars are formed, emitting stellar winds in the process. Therefore, the researchers guess there could be a link between these phenomena.

It is fascinating that we discover unexpected phenomena in every galaxy whenever we use radio polarisation measurements. Here in NGC 4217, it is huge magnetic gas bubbles and a helix magnetic field that spirals upwards into the galaxy’s halo.

Dr Rainer Beck, Study Author, Max Planck Institute for Radio Astronomy

Furthermore, the analysis unraveled extensive loop structures in the magnetic fields along the whole galaxy.

This has never been observed before. We suspect that the structures are caused by star formation, because at these points matter is ejected outward.

Dr Yelena Stein, Centre de Données astronomiques de Strasbourg, University of Strasbourg

Image Shows Magnetic Field Structures

As part of the analysis, the team integrated different techniques that allowed them to visualize the galaxy’s chaotic and ordered magnetic fields both along the line of sight and perpendicular to it. The outcome was an extensive image of the structures.

Dr Stein optimized the results by combining the data assessed through radio astronomy with an image of NGC 4217 captured in the visible light range.

Visualising the data was important to me. Because when you think about galaxies, magnetic fields is not the first thing that comes to mind, although they can be gigantic and display unique structures. The image is supposed to shift the magnetic fields more into focus.

Dr Yelena Stein, Centre de Données astronomiques de Strasbourg, University of Strasbourg

This study was financially supported by the Hans Böckler Foundation and the German Research Foundation (DFG Research Unit 1254).

Data were offered by the Sloan Digital Sky Survey III—funded by the Alfred P. Sloan Foundation and participating institutions, the National Science Foundation, and the U.S. Department of Energy Office of Science—and by the Wide-field Infrared Survey Explorer, which is funded by the National Aeronautics and Space Administration.

Journal Reference:

Stein, Y., et al. (2020) CHANG-ES XXI. Transport processes and the X-shaped magnetic field of NGC 4217: off-center superbubble structure. Astronomy & Astrophysics.

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