Sub-arcsecond LOFAR imaging of Arp 299 at 150 MHz: Tracing the nuclear and diffuse extended emission of a bright LIRG
Journal article, 2022

Context. Arp 299 is the brightest luminous infrared galaxy (LIRG) within 50 Mpc, with IR luminosity log(LIR/L⊙) = 11.9. It provides a unique laboratory for testing physical processes in merging galaxies. Aims. We study for the first time the low-frequency (∼150 MHz) radio brightness distribution of Arp 299 at subarcsecond resolution, tracing in both compact and extended emission regions the local spectral energy distribution (SED) in order to characterize the dominant emission and absorption processes. Methods. We analysed the spatially resolved emission of Arp 299 revealed by 150 MHz international baseline Low-Frequency Array (LOFAR) and 1.4, 5.0, and 8.4 GHz Very Large Array (VLA) observations. Results. We present the first subarcsecond (0.4″ ×100 pc) image of the whole Arp 299 system at 150 MHz. The high surface brightness sensitivity of our LOFAR observations (∼100 μJy beam-1) allowed us to detect all of the nuclear components detected at higher frequencies, as well as the extended steep-spectrum emission surrounding the nuclei. We obtained spatially resolved, two-point spectral index maps for the whole galaxy: the compact nuclei show relatively flat spectra, while the extended, diffuse component shows a steep spectrum. We fitted the radio SED of the nuclear regions using two different models: a continuous free-free medium model and a clumpy model. The continuous model can explain the SED of the nuclei assuming a population of relativistic electrons subjected to synchrotron, bremsstrahlung, and ionization losses. The clumpy model fits assuming relativistic electrons with negligible energy losses, and thermal fractions that are more typical of star-forming galaxies than those required for the continuous model. Conclusions. Our results confirm the usefulness of combining spatially resolved radio imaging at both MHz and GHz frequencies to characterize in detail the radio emission properties of LIRGs from the central 100 pc out to the kiloparsec galaxy-wide scales.

Galaxies: star formation

Radio continuum: galaxies

ISM: magnetic fields

HII regions

ISM: jets and outflows

Instrumentation: high angular resolution


Naim Ramirez-Olivencia

Institute of Astrophysics of Andalusia (IAA)

Eskil Varenius

Chalmers, Space, Earth and Environment, Geoscience and Remote Sensing

M.A. Pérez-Torres

Institute of Astrophysics of Andalusia (IAA)

Antxon Alberdi

Institute of Astrophysics of Andalusia (IAA)

John Conway

Chalmers, Space, Earth and Environment, Onsala Space Observatory

A. Alonso-Herrero

Centro de Astrobiologia (CAB)

M. Pereira-Santaella

Centro de Astrobiologia (CAB)

R. Herrero-Illana

Institute of Space Sciences (ICE) - CSIC

European Southern Observatory Santiago

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 658 A4

Subject Categories

Astronomy, Astrophysics and Cosmology

Atom and Molecular Physics and Optics

Other Physics Topics



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