Characterizing Compact 15–33 GHz Radio Continuum Sources in Local U/LIRGs

• Published in: The Astrophysical journal 2022-11, Vol.940 (1), p.52
• Main Authors: Song, Y., Linden, S. T., Evans, A. S., Barcos-Muñoz, L., Murphy, E. J., Momjian, E., Díaz-Santos, T., Larson, K. L., Privon, G. C., Huang, X., Armus, L., Mazzarella, J. M., U, V., Inami, H., Charmandaris, V., Ricci, C., Emig, K. L., McKinney, J., Yoon, I., Kunneriath, D., Lai, T. S.-Y., Rodas-Quito, E. E., Saravia, A., Gao, T., Meynardie, W., Sanders, D. B.
• Format: Article
• Language: English
• Subjects: Active galactic nuclei; Astrophysics; Clumps; Continuum radiation; Emissions; Galaxies; Galaxy nuclei; H II regions; Infrared astronomy; Interstellar matter; Interstellar medium; Luminous infrared galaxies; Radio continuum emission; Radio sources (astronomy); Star & galaxy formation; Star formation; Star forming regions; Starbursts; Stars; Supernovae; Very Large Array
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ac923b

We present the analysis of ∼100 pc scale compact radio continuum sources detected in 63 local (ultra)luminous infrared galaxies (U/LIRGs; L IR ≥ 10 11 L ⊙ ), using FWHM ≲ 0.″1–0.″2 resolution 15 and 33 GHz observations with the Karl G. Jansky Very Large Array. We identify a total of 133 compact radio sources with effective radii of 8–170 pc, which are classified into four main categories—“AGN” (active galactic nuclei), “AGN/SBnuc” (AGN-starburst composite nucleus), “SBnuc” (starburst nucleus), and “SF” (star-forming clumps)—based on ancillary data sets and the literature. We find that “AGN” and “AGN/SBnuc” more frequently occur in late-stage mergers and have up to 3 dex higher 33 GHz luminosities and surface densities compared with “SBnuc” and “SF,” which may be attributed to extreme nuclear starburst and/or AGN activity in the former. Star formation rates (SFRs) and surface densities (Σ SFR ) are measured for “SF” and “SBnuc” using both the total 33 GHz continuum emission (SFR ∼ 0.14–13 M ⊙ yr −1 , Σ SFR ∼ 13–1600 M ⊙ yr −1 kpc −2 ) and the thermal free–free emission from H ii regions (median SFR th ∼ 0.4 M ⊙ yr −1 , Σ SFR th ∼ 44 M ⊙ yr −1 kpc −2 ). These values are 1–2 dex higher than those measured for similar-sized clumps in nearby normal (non-U/LIRGs). The latter also have a much flatter median 15–33 GHz spectral index (∼−0.08) compared with “SBnuc” and “SF” (∼−0.46), which may reflect higher nonthermal contribution from supernovae and/or interstellar medium densities in local U/LIRGs that directly result from and/or lead to their extreme star-forming activities on 100 pc scales.