The magnetic fields of the Milky Way, often called the Galactic magnetic fields, can be revealed through several approaches, see Han (2017, ARA&A 55, pp.111-157) for a review.

We have worked on this topic for more than 30 years. The earliest paper is presented by Han & Qiao (1994, A &A 288, 759-772). We have made much progress on the measurements of the magnetic fields in the Galactic disk by pulsar rotation measures (RMs) and the RMs of the polarized radio sources behind the Milky Way, such as Han et al. (1999, MNRAS 306, 371); and Han et al. (2006, ApJ 642, 868). The two most recent measurements are Han J.L. et al. (2018, ApJS, 234, 11) and Xu & Han (2022, SCPMA 65, 129704). The most updated model for the magnetic fields in the Galactic disk is in Han J.L. et al. (2018, ApJS, 234, 11).

For the magnetic fields in the Galactic halo, we first identified the antisymmetry of the RM distribution of radio sources at high Galactic latitudes (|b|>8°) in the sky with respect to the Galactic coordinates, and the results are presented in Han et al. (1997, A &A 322, 98-102), which has been interpreted as evidence fo r the magnetic tories in the Galactic halo with field directions reversed above and below the Galactic plane. Such an antisymmetric distribution of the RM sky now has been confirmed by more and more RM data, and the field structure was re-emphasized by Han et al. (1999, MNRAS 306, 371), and now it has been included in almost all models for the Galactic magnetic fields though the above original papers sometimes are not included in the references. The most updated development in the halo magnetic fields is the measurements of the radius range of the magnetic torius by Xu J. & Han J.L. (2024, ApJ, submitted) from the local-subtracted RM distribution.

Note that in addition to the large-scale magnetic fields, the fields exist on almost all scales. The magnetic field energy on different scales is difficult to measure. Such a spatial energy spectrum is fundamental for the machanism for the magnetic field developmemts in the interstellar medium, such as dynamo processes. Han et al. (2004, ApJ 610, 820-826) have got it measured on the galactic scales. For convenience of the usage of the best models of the large-scale magnetic field, we assemble the magnetic field models in the Galactic disk obtained by Han et al. (2018, ApJS, 234, 11) and the halo toroidal field by Xu & Han (2024, ApJ) here. We provide the C code for calculating the magnetic fields at any point in our Milky Way according to these models. Inside the package, both the Cartesian coordinates (x, y, z) and Galactocentric cylindrical coordinates (R, φ, z) are used. The x - y plane coincides to the Galactic plane with x paralleling to l=90° and y to l=180°. The Sun is located at (x, y, z)=(0, 8.3, 0). R=√(x²+y²) is the Galactocentric radius, φ is the azimuth angle starting from x-axis and increasing in the counterclockwise direction, z is the distance to the Galactic plane. A user can input the Galactic longitude and latitude and also the distance (in kpc) from the Sun, the package return three magnetic field components: Br, Bφ and Bz in the Galactocentric cylindrical coordinates for the disk magnetic fields, the halo magnetic fields and the total magnetic fields, respectively. To compile and execute the package:

1. Download the C-code;

2. Compile it easily by "gcc GMFcal.c -o GMFcal -lm";

3. Run it as: "./GMFcal [-l] GL [-b] GB [-d] Dist". Here GL is Galactic longitude in degree, GB is Galactic latitude in degree and Dist is distance in kpc.

If you found this code is useful for your research work, please please cite by Han (et al. 2018, ApJS, 234, 11) and Xu J. & Han J.L. (2024, ApJ, submitted)

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Contact: xujun(at)nao.cas.cn or hjl(at)nao.cas.cn
Last Modified: 1-April-2024.