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

Abstract

We present the analysis of ∼100 pc scale compact radio continuum sources detected in 63 local (ultra)luminous infrared galaxies (U/LIRGs; L IR ≥ 1011 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 (ΣSFR) are measured for “SF” and “SBnuc” using both the total 33 GHz continuum emission (SFR ∼ 0.14–13 M ⊙ yr−1, ΣSFR ∼ 13–1600 M ⊙ yr−1 kpc−2) and the thermal free–free emission from H ii regions (median SFRth ∼ 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.

GOALS-JWST: Pulling Back the Curtain on the AGN and Star Formation in VV 114

“…We extract spectra from 10 regions of interest within the channel 1 FOV to investigate IR-bright sources resolved in the MIRI imaging as well as diffuse emission surrounding those sources and in the eastern nucleus (Figure 1). We chose five locations coincident with the two brightest IR sources, the NE and SW cores ((a), (c)), and several bright clumps identified in the MIRI imaging data and in both the submillimeter and radio ((d), (e), and (f)) (Saito et al 2018;Evans et al 2022;Song et al 2022). We also chose five regions intended to capture diffuse emission between (b) and around ((g), (h), (i), and (j)) the bright clumps coincident with some tidal and shock features previously identified using ALMA (Saito et al 2017(Saito et al , 2018.…”

Where are the Eddington-limited starbursts? Gravitational lensing provides a way forward for sub-kiloparsec views of star formation

“…The canonical and well-studied ULIRG Arp 220, for example, has regions forming stars at surface densities of Σ SFR ∼ 10 4.1±0.1 M yr −1 kpc −2 (Barcos- Muñoz et al 2015). On the other hand, Song et al (2022) found predominantly sub-Eddington star formation in a broader sample of local luminous infrared galaxies (LIRGs; L IR = 10 11−12 L ) and ULIRGs. If the extreme hyper-luminous IR galaxies (HyLIRGs; L IR > 10 13 L ) seen at high-z like the PASSAGES objects are in fact sub-Eddington, it might suggest simply that their orderof-magnitude increase in IR luminosity over ULIRGs is accompanied by a comparable ∼ 0.5 dex increase in radius.…”

PASSAGES: The Wide-ranging, Extreme Intrinsic Properties of Planck-selected, Lensed Dusty Star-forming Galaxies

“…However, angular resolution plays a critical role in this measurement, as it may be possible for objects to be sub-Eddington on global, galaxy-integrated scales but super-Eddington in local regions of dense star formation, as suggested by Simpson et al (2015a) and Barcos-Muñoz et al (2017). For example, for local ULIRGs, Song et al (2022) found radio continuum clumps smaller than 100 pc with large surface densities up to Σ SFR ≈ 1600 M e yr −1 kpc −2 .…”