Sub-arcsecond LOFAR imaging of Arp 299 at 150 MHz

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