Extragalactic Magnetism with SOFIA (SALSA Legacy Program): The Magnetic Fields in the Multiphase Interstellar Medium of the Antennae Galaxies*

Abstract

Mergers are thought to be a fundamental channel for galaxy growth, perturbing the gas dynamics and the magnetic fields (B-fields) in the interstellar medium (ISM). However, the mechanisms that amplify and dissipate B-fields during a merger remain unclear. We characterize the morphology of the ordered B-fields in the multiphase ISM of the closest merger of two spiral galaxies, the Antennae galaxies. We compare the inferred B-fields using 154 μm thermal dust and 11 cm radio synchrotron emission polarimetric observations. We find that the 154 μm B-fields are more ordered across the Antennae galaxies than the 11 cm B-fields. The turbulent-to-ordered 154 μm B-field increases at the galaxy cores and star-forming regions. The relic spiral arm has an ordered spiral 154 μm B-field, while the 11 cm B-field is radial. The 154 μm B-field may be dominated by turbulent dynamos with high 12CO(1–0) velocity dispersion driven by star-forming regions, while the 11 cm B-field is cospatial with high H i velocity dispersion driven by galaxy interaction. This result shows the dissociation between the warm gas mainly disturbed by the merger, and the dense gas still following the dynamics of the relic spiral arm. We find a ∼8.9 kpc scale ordered B-field connecting the two galaxies. The base of the tidal tail is cospatial with the H i and 12CO(1–0) emission and has compressed and/or sheared 154 μm and 11 cm B-fields driven by the merger. We suggest that amplified B-fields, with respect to the rest of the system and other spiral galaxies, may be supporting the gas flow between both galaxies and the tidal tail.

Extragalactic Magnetism with SOFIA (SALSA Legacy Program). V. First Results on the Magnetic Field Orientation of Galaxies

“…Flocculent spirals (i.e., NGC 253, NGC 6946) would be less affected by the spiral density arm shear compression, and as a consequence, they might present less ordered spiral magnetic fields, or lower alignment with their morphological counterparts (see NGC 6946). Similar results should apply to starburst galaxies (e.g., M82), while active galactic nucleus (AGN) dominated (e.g., Circinus), interacting, or recent merger galaxies (like the Antennae galaxies or Centaurus A; Chyży & Beck 2004;Lopez-Rodriguez 2021;Lopez-Rodriguez et al 2023) may, in addition, present shock or AGN-induced aligned magnetic fields (Lopez-Rodriguez et al 2021b).…”

“…Diffuse atomic gas also responds collisionally, but its scale height is significantly higher, and its structure is more affected by supernova explosions and galaxy-scale processes, such as tidal interactions, bar, or spiral formation. Observational effects compatible with these hypotheses have been measured in several galaxies: in the outskirts of M51 (SALSA I; Borlaff et al 2021), due to the interaction with M51b; in the central starburst of NGC 1097 (SALSA II; Lopez-Rodriguez et al 2021a), where the radio B-field has a spiral shape following the diffuse gas and the FIR B-field is cospatial with a galactic shock at the boundaries of the bar and the starburst ring; and, finally, in the relic spiral arm of the Antennae galaxies (SALSA VI; Lopez-Rodriguez et al 2023), where the radio Bfield is radial and cospatial with the H I gas dynamics and the FIR B-field is spiral and cospatial with the dense and molecular ISM.…”

“…This result may be due to the different thermodynamical properties between the warm diffuse ISM and the cold dust filaments associated with star-forming regions and molecular clouds. In the closest merger of two spiral galaxies (the Antennae galaxies), the FIR B-field closely follows the relic spiral arm, while the radio B-field is mostly radial (Lopez-Rodriguez et al 2023;SALSA VI). This result suggests that the FIR B-field may be cospatial with the molecular gas in the midplane of the relic spiral arm, while the radio B-field seems to be more aligned with the dynamics of the H I gas on an extraplanar layer above the disk affected by the merger activity.…”

The Structure of Magnetic Fields in Spiral Galaxies: A Radio and Far-infrared Polarimetric Analysis

“…Large-scale spiral magnetic field (B-field) structures are frequently observed in spiral galaxies (e.g., Beck et al 2019;Lopez-Rodriguez et al 2023). These B-fields are thought to be generated via a mean-field dynamo driven by differential rotation of the galactic disk and turbulent helical motions (Shukurov & Subramanian 2021).…”

Polarized thermal emission from dust in a galaxy at redshift 2.6

“… Magnetic fields are fundamental to the evolution of galaxies, playing a key role in the astrophysics of the interstellar medium and star formation. Large-scale ordered magnetic fields have been mapped in the Milky Way and nearby galaxies 1 , 2 , but it is not known how early in the Universe such structures formed 3 . Here we report the detection of linearly polarized thermal emission from dust grains in a strongly lensed, intrinsically luminous galaxy that is forming stars at a rate more than 1,000 times that of the Milky Way at redshift 2.6, within 2.5 Gyr of the Big Bang 4 , 5 .…”