Galactic Magnetic Fields. II. Applying the Model to Nearby Galaxies
Many spiral galaxies host magnetic fields with energy densities comparable to those of the turbulent and thermal motions of their interstellar gas. However, quantitative comparison between magnetic field properties inferred from observation and those obtained from theoretical modeling has been lacki...
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IOP Publishing
2025-01-01
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| Series: | The Astrophysical Journal |
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| Online Access: | https://doi.org/10.3847/1538-4357/ade13e |
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| author | Rion Glenn Nazareth Gayathri Santhosh Luke Chamandy |
| author_facet | Rion Glenn Nazareth Gayathri Santhosh Luke Chamandy |
| author_sort | Rion Glenn Nazareth |
| collection | DOAJ |
| description | Many spiral galaxies host magnetic fields with energy densities comparable to those of the turbulent and thermal motions of their interstellar gas. However, quantitative comparison between magnetic field properties inferred from observation and those obtained from theoretical modeling has been lacking. In L. Chamandy et al. (Paper I ), we developed a simple, axisymmetric galactic dynamo model that uses various observational data as input. Here, we apply our model to calculate radial profiles of azimuthally and vertically averaged magnetic field strength and pitch angle, gas velocity dispersion and scale height, turbulent correlation time and length, and the sizes of supernova remnants for the galaxies M31, M33, M51, and NGC 6946, using input data collected from the literature. Scaling factors are introduced to account for a lack of precision in both theory and observation. Despite the simplicity of our model, its outputs agree fairly well with galaxy properties inferred from observation. Additionally, we find that most of the parameter values are similar between galaxies. We extend the model to predict the magnetic field pitch angles arising from a combination of mean-field dynamo action and the winding up of the random small-scale field owing to the large-scale radial shear. We find their magnitudes to be much smaller than those of the pitch angles measured in polarized radio and far-infrared emission. This suggests that effects not included in our model, such as effects associated with spiral arms, are needed to explain the pitch angle values. |
| format | Article |
| id | doaj-art-6e75554ff25e4eef8faf29022af28a3a |
| institution | DOAJ |
| issn | 1538-4357 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
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| series | The Astrophysical Journal |
| spelling | doaj-art-6e75554ff25e4eef8faf29022af28a3a2025-08-20T03:15:31ZengIOP PublishingThe Astrophysical Journal1538-43572025-01-01988219710.3847/1538-4357/ade13eGalactic Magnetic Fields. II. Applying the Model to Nearby GalaxiesRion Glenn Nazareth0https://orcid.org/0009-0008-1859-5029Gayathri Santhosh1https://orcid.org/0009-0008-8628-3537Luke Chamandy2https://orcid.org/0000-0003-4935-5550National Institute of Science Education and Research , An OCC of Homi Bhabha National Institute, Bhubaneswar 752050, Odisha, India ; lchamandy@niser.ac.inNational Institute of Science Education and Research , An OCC of Homi Bhabha National Institute, Bhubaneswar 752050, Odisha, India ; lchamandy@niser.ac.in; Department of Physics and Astronomy, University of Bologna , via Gobetti 93/2, 40129 Bologna, Italy; INAF—Istituto di Radioastronomia , via Gobetti 101, 40129 Bologna, ItalyNational Institute of Science Education and Research , An OCC of Homi Bhabha National Institute, Bhubaneswar 752050, Odisha, India ; lchamandy@niser.ac.inMany spiral galaxies host magnetic fields with energy densities comparable to those of the turbulent and thermal motions of their interstellar gas. However, quantitative comparison between magnetic field properties inferred from observation and those obtained from theoretical modeling has been lacking. In L. Chamandy et al. (Paper I ), we developed a simple, axisymmetric galactic dynamo model that uses various observational data as input. Here, we apply our model to calculate radial profiles of azimuthally and vertically averaged magnetic field strength and pitch angle, gas velocity dispersion and scale height, turbulent correlation time and length, and the sizes of supernova remnants for the galaxies M31, M33, M51, and NGC 6946, using input data collected from the literature. Scaling factors are introduced to account for a lack of precision in both theory and observation. Despite the simplicity of our model, its outputs agree fairly well with galaxy properties inferred from observation. Additionally, we find that most of the parameter values are similar between galaxies. We extend the model to predict the magnetic field pitch angles arising from a combination of mean-field dynamo action and the winding up of the random small-scale field owing to the large-scale radial shear. We find their magnitudes to be much smaller than those of the pitch angles measured in polarized radio and far-infrared emission. This suggests that effects not included in our model, such as effects associated with spiral arms, are needed to explain the pitch angle values.https://doi.org/10.3847/1538-4357/ade13eInterstellar mediumGalaxy magnetic fieldsSupernova remnantsRadio continuum emissionSpiral pitch angleScale height |
| spellingShingle | Rion Glenn Nazareth Gayathri Santhosh Luke Chamandy Galactic Magnetic Fields. II. Applying the Model to Nearby Galaxies The Astrophysical Journal Interstellar medium Galaxy magnetic fields Supernova remnants Radio continuum emission Spiral pitch angle Scale height |
| title | Galactic Magnetic Fields. II. Applying the Model to Nearby Galaxies |
| title_full | Galactic Magnetic Fields. II. Applying the Model to Nearby Galaxies |
| title_fullStr | Galactic Magnetic Fields. II. Applying the Model to Nearby Galaxies |
| title_full_unstemmed | Galactic Magnetic Fields. II. Applying the Model to Nearby Galaxies |
| title_short | Galactic Magnetic Fields. II. Applying the Model to Nearby Galaxies |
| title_sort | galactic magnetic fields ii applying the model to nearby galaxies |
| topic | Interstellar medium Galaxy magnetic fields Supernova remnants Radio continuum emission Spiral pitch angle Scale height |
| url | https://doi.org/10.3847/1538-4357/ade13e |
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