From Max Planck Institute for Radio Astronomy: “Giant magnetic ropes in the outskirts of a spiral galaxy”


From Max Planck Institute for Radio Astronomy

November 26, 2019

Dr. Marita Krause
Phone:+49 228 525-312
mkrause@mpifr-bonn.mpg.de

Max-Planck-Institut für Radioastronomie, Bonn
Dr. Norbert Junkes
Press and Public Outreach
Phone:+49 228 525-399
njunkes@mpifr-bonn.mpg.de

First detection of regular magnetic field reversals in the halo of NGC 4631.

An international consortium led by scientists from the Max Planck Institute for Radio Astronomy in Bonn, Germany, investigated polarized radio emission from the galaxy NGC 4631 at the VLA radio telescope with a broad-band receiver in a number of spectral windows.

NRAO/Karl V Jansky Expanded Very Large Array, on the Plains of San Agustin fifty miles west of Socorro, NM, USA, at an elevation of 6970 ft (2124 m)

They detected for the first time a regular magnetic field over scales of several thousands of light years in the halo of NGC 4631. Moreover, they discovered reversals in the large-scale magnetic field, which they call giant magnetic ropes. This discovery will strengthen the impact of large-scale dynamo theories for spiral galaxies. Further, the regular halo fields may be regarded as a link to intergalactic magnetic fields and will help to understand their origin which is a mystery so far.

The results are reported in the current issue of the journal Astronomy & Astrophysics.

1
The spiral galaxy NGC 4631 is seen edge-on, with its disk of stars shown in pink. The observed magnetic field pattern is displayed by the hair-like structure in green and blue. It extends beyond the disk into the galaxy’s extended halo. Green indicates magnetic fields pointing roughly toward us and blue fields pointing away from us. This phenomenon, with the field alternating in direction, has never before been seen in the halo of a galaxy.

© Composite image by Jayanne English (Univ. of Manitoba). Radio data: Jansky-VLA (Silvia Carolina Mora-Partiarroyo et al. 2019). Optical data: Mayall 4-meter telescope (Maria Patterson and Rene Walterbos, New Mexico State Univ.). Software code for tracing the magnetic field lines: Arpad Miskolczi (Ruhr-Univ. Bochum).


NOAO/Mayall 4 m telescope at Kitt Peak, Arizona, USA, Altitude 2,120 m (6,960 ft)

NGC 4631, the “Whale Galaxy”, located 25 million light-years from Earth in the constellation Canes Venatici, is about 80 thousand light-years across, slightly smaller than our own Milky Way. It was discovered by the famous German-born British astronomer Sir William Herschel in 1787. This galaxy has a companion, NGC 4627, a small elliptical galaxy.

Observations of the polarized radio emission of NGC 4631, performed with the Karl G. Jansky Very Large Array (VLA), reveal regular magnetic fields protruding above and below the galaxy’s disk (see Fig. 1).

“This is the first time that we have clearly detected what astronomers call large-scale, coherent, magnetic fields far in the halo of a spiral galaxy, with the field lines aligned in the same direction over distances of a thousand light-years. We even see a regular pattern of this organized field changing direction,” said Marita Krause, scientist at the Max-Planck Institute for Radioastronomy (MPIfR) in Bonn, Germany, and corresponding author of the publication.

The strength of 4 microGauss for the regular magnetic field is surprisingly high for a halo, comparable with the regular magnetic field strength in the disks of spiral galaxies.

An international team of astronomers who are part of a project called the Continuum HAlos in Nearby Galaxies — an EVLA Survey (CHANG-ES), said the image indicates a large-scale, coherent magnetic field that is generated by dynamo action within the galaxy and spirals far outward in the form of giant magnetic ropes perpendicular to the disk. The CHANG-ES project is led by Judith Irwin of Queen’s University in Ontario, Canada, a co-author of the paper.

“At the moment, I’m afraid that we are a little bit like the blind men and the elephant, since each time we sample the magnetic field in a different way we reach a different conclusion about its nature! However, our models suggest this field includes smaller, twisting cones emanating from the spiral arms,” said Richard Henriksen, also of Queen’s University.

The results were achieved by combining data from multiple observations with the VLA’s giant dish antennas arranged in different configurations to show both large structures and finer details within NGC 4631. The naturally-emitted radio waves from that galaxy were analyzed to reveal the magnetic fields, including their directions.

The scientists said the techniques used to determine the direction of the magnetic field lines can now be used on other galaxies to answer important questions about whether coherent magnetic fields are common in galactic halos and what their shapes are.

The regular halo fields may also be regarded as a link to intergalactic magnetic fields and will help to understand their origin which is a mystery up to now.

CHANG-ES, the “Continuum Halos in Nearby Galaxies, an EVLA Survey” project, brings together scientists from all over the globe in order to investigate the occurrence and origin of galaxy halos by means of radio observations.

The extended spherical area around the disk of a spiral galaxy is called halo. It forms the interface between the well-studied disks of galaxies and the intergalactic medium.

The National Radio Astronomy Observatory (NRAO) is a facility of the National Science Foundation (NSF), operated under cooperative agreement by Associated Universities, Inc. The Karl G. Jansky Very Large Array (VLA) interferometer near Socorro (New Mexico, USA) is operated by NRAO.

Authors of the original paper comprise Silvia Carolina Mora-Partiarroyo, Marita Krause, Aritra Basu, Rainer Beck, Theresa Wiegert, Judith Irwin, Richard Henriksen, Yelena Stein, Carlos J. Vargas, Volker Heesen, René A. M. Walterbos, Richard J. Rand, George Heald, Jiangtao Li, Patrick Kamieneski, and Jayanne English. The first four authors are all affiliated with the MPIfR in Bonn, Germany.

The results are based on the doctoral thesis of Silvia Carolina Mora-Partiarroyo, the first author, at MPIfR and Bonn University. The thesis was supervised by Marita Krause.

A theoretical model is described in Woodfinden et al. 2019 MNRAS, 487, 1498.

See the full article here .

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MPIFR/Effelsberg Radio Telescope, Germany

The Max Planck Institute for Radio Astronomy (German: Max-Planck-Institut für Radioastronomie) is located in Bonn, Germany. It is one of 80 institutes in the Max Planck Society (German: Max-Planck-Gesellschaft).

By combining the already existing radio astronomy faculty of the University of Bonn led by Otto Hachenberg with the new Max Planck institute the Max Planck Institute for Radio Astronomy was formed. In 1972 the 100-m radio telescope in Effelsberg was opened. The institute building was enlarged in 1983 and 2002.

The institute was founded in 1966 by the Max-Planck-Gesellschaft as the “Max-Planck-Institut für Radioastronomie” (MPIfR).

The foundation of the institute was closely linked to plans in the German astronomical community to construct a competitive large radio telescope in (then) West Germany. In 1964, Professors Friedrich Becker, Wolfgang Priester and Otto Hachenberg of the Astronomische Institute der Universität Bonn submitted a proposal to the Stiftung Volkswagenwerk for the construction of a large fully steerable radio telescope.

In the same year the Stiftung Volkswagenwerk approved the funding of the telescope project but with the condition that an organization should be found, which would guarantee the operations. It was clear that the operation of such a large instrument was well beyond the possibilities of a single university institute.

Already in 1965 the Max-Planck-Gesellschaft (MPG) decided in principle to found the Max-Planck-Institut für Radioastronomie. Eventually, after a series of discussions, the institute was officially founded in 1966.

The Max Planck Society for the Advancement of Science (German: Max-Planck-Gesellschaft zur Förderung der Wissenschaften e. V.; abbreviated MPG) is a formally independent non-governmental and non-profit association of German research institutes founded in 1911 as the Kaiser Wilhelm Society and renamed the Max Planck Society in 1948 in honor of its former president, theoretical physicist Max Planck. The society is funded by the federal and state governments of Germany as well as other sources.

According to its primary goal, the Max Planck Society supports fundamental research in the natural, life and social sciences, the arts and humanities in its 83 (as of January 2014)[2] Max Planck Institutes. The society has a total staff of approximately 17,000 permanent employees, including 5,470 scientists, plus around 4,600 non-tenured scientists and guests. Society budget for 2015 was about €1.7 billion.

The Max Planck Institutes focus on excellence in research. The Max Planck Society has a world-leading reputation as a science and technology research organization, with 33 Nobel Prizes awarded to their scientists, and is generally regarded as the foremost basic research organization in Europe and the world. In 2013, the Nature Publishing Index placed the Max Planck institutes fifth worldwide in terms of research published in Nature journals (after Harvard, MIT, Stanford and the US NIH). In terms of total research volume (unweighted by citations or impact), the Max Planck Society is only outranked by the Chinese Academy of Sciences, the Russian Academy of Sciences and Harvard University. The Thomson Reuters-Science Watch website placed the Max Planck Society as the second leading research organization worldwide following Harvard University, in terms of the impact of the produced research over science fields.