Role of Thermal and Non-thermal Processes in the ISM of Magellanic Clouds

Abstract

The radio continuum emission is a dust-unbiased tracer of both the thermal and non-thermal processes in the interstellar medium. We present new maps of the free-free and synchrotron emission in the Magellanic Clouds (MCs) at 0.166, 1.4, and 4.8GHz with no prior assumption about the radio non-thermal spectrum. The maps were constructed using a de-reddened H$\alpha$ map as a template for the thermal radio emission, which we subtract from maps of the total radio continuum emission. To de-redden the H$\alpha$ emission, it is important to know the fraction of dust surface density that attenuates the H$\alpha$ emission along the line-of-sight, $f_{\text{d}}$. This fraction is obtained by comparing the dust opacity obtained through the infrared emission spectrum and the Balmer decrement method. In star-forming regions, the median $f_{\text{d}}$ is about 0.1 which is by a factor of 3 lower than that in diffuse regions. We obtain a global thermal radio fraction, $f_{\text{th}}$, of 30 per cent (35 per cent) in the LMC (SMC) at 1.4GHz. Furthermore, we present maps of the equipartition magnetic field strength with average values of $\simeq 10.1\mu$G in the LMC and $\simeq 5.5\mu$G in the SMC. The magnetic field is proportional to the star formation rate to a power of 0.24 and 0.20 for the LMC and SMC, respectively. This study shows that the non-thermal processes control the interstellar medium in the MCs.

Accepted for publication in MNRAS

References in corpus (27)

• Infrared Emission from Interstellar Dust. IV. The Silicate-Graphite-PAH Model in the Post-Spitzer Era
• A New Electron Density Model for Estimation of Pulsar and FRB Distances
• The MUSE second-generation VLT instrument
• A distance to the Large Magellanic Cloud that is precise to one per cent
• GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey I: A low-frequency extragalactic catalogue
• Revised equipartition & minimum energy formula for magnetic field strength estimates from radio synchrotron observations
• The Vertical Structure of Warm Ionised Gas in the Milky Way
• A distance determination to the Small Magellanic Cloud with an accuracy of better than 2 percent based on late-type eclipsing binary stars
• The Radio Spectral Energy Distribution and Star Formation Rate Calibration in Galaxies
• Direct simulations of a supernova-driven galactic dynamo
• High-resolution radio continuum survey of M33 II. Thermal and nonthermal emission
• A Radio and Optical Polarization Study of the Magnetic Field in the Small Magellanic Cloud
• The Radio Continuum-Star Formation Rate Relation in WSRT SINGS Galaxies
• A multi-resolution analysis of the radio-FIR correlation in the Large Magellanic Cloud
• High-resolution radio continuum survey of M33: III. Magnetic fields
• The Polycyclic Aromatic Hydrocarbon Mass Fraction on a 10 pc scale in the Magellanic Clouds
• The influence of supernova remnants on the interstellar medium in the Large Magellanic Cloud seen at 20--600 $\mu$m wavelengths
• Magnetic fields and gas in the cluster-influenced spiral galaxy NGC 4254 - II. Structures of magnetic fields
• Spitzer Analysis of HII Region Complexes in the Magellanic Clouds: Determining a Suitable Monochromatic Obscured Star Formation Indicator
• Discovery of massive star formation quenching by nonthermal effects in the center of NGC 1097
• Disk of the Small Magellanic Cloud as traced by Cepheids
• ALMA Observations of a Quiescent Molecular Cloud in the Large Magellanic Cloud
• The ASKAP-EMU Early Science Project: 888 MHz Radio Continuum Survey of the Large Magellanic Cloud
• The ASKAP-EMU Early Science Project:Radio Continuum Survey of the Small Magellanic Cloud
• [Fe XIV] and [Fe XI] reveal the forward shock in SNR 1E0102.2-7219
• Magnetic fields and star formation in low-mass Magellanic-type and peculiar galaxies
• Radio Continuum Sources behind the Large Magellanic Cloud

Cited by in corpus (3)

• Low frequency radio continuum imaging and SED modeling of 11 LIRGs: radio-only and FUV to radio bands
• Gamma-ray emission toward supergiant shells in the Large Magellanic Cloud
• The signature of large scale turbulence driving on the structure of the interstellar medium