A Radio-Bright Local Little Red Dot Analog

Luis F. Rodriguez, I. FElix Mirabel, Rosa A. Gonzalez-Lopezlira, Laurent Loinard

First listed 2026-08-18 | Last updated 2026-08-17

Abstract

The James Webb Space Telescope revealed the existence in the early Universe ($z >$ 4) of large populations of little red dots (LRDs), compact red luminous sources that host rapidly growing supermassive black holes (SMBHs) surrounded by coeval nuclear starbursts. LRDs have defining properties, one of which is the absence of radio detections. LRDs could be radio-undetected because of their large distances. A way to investigate the radio properties of LRDs is to search for radio emission in their local analogs, the Local Little Red Dot (LLRD) galaxies at $z <$ 1 with analogous properties to LRDs. We report the radio continuum detection of the LLRD analog J204837.26${-}$002437.2 ($z$ = 0.4332, hereinafter J2048). This adds to the previous radio detection of two other LLRDs. However, with a flux density of 3.0$\pm$0.2 mJy at 3.0 GHz, J2048 is two orders of magnitude more radio luminous than the previous detections. The spectral index of $α$ = -0.39$\pm$0.04 is consistent with moderately optically-thick synchrotron emission. The radio luminosity of J2048 is $1.2 \times 10^{41}~ \mathrm{erg ~s^{-1}}$, in the lower end of the range defined by radio-loud giant elliptical galaxies and quasars of $L_R$ = $10^{41-46} ~\mathrm{erg ~s^{-1}}$. The expected radio luminosity of the SMBH associated with J2048 is estimated to be about an order of magnitude larger, suggesting that its radio luminosity could potentially be strongly dimmed. A cosmological ($z >$ 4) LRD with radio luminosity similar to that of J2048 would be detectable using the VLA with moderately long integrations.

Short digest

Rodríguez et al. report a 3.0 GHz detection of the z=0.4332 local little red dot analog J204837.26−002437.2 (J2048), linking JWST-era LRD phenomenology to a nearby compact-red-continuum system with a broad-line AGN and intense starburst. At 3.0±0.2 mJy, J2048 is roughly two orders of magnitude more radio luminous than the two previously detected LLRD analogs, with a relatively flat α=−0.39±0.04 spectrum consistent with moderately optically thick synchrotron emission and a radio luminosity of 1.2×10^41 erg s⁻¹. Its unresolved radio core, possible southeast extension, and luminosity near the low end of radio-loud ellipticals and quasars make it a promising laboratory for testing radio feedback in LRD-like nuclei; the authors argue that the black-hole radio output may nevertheless be suppressed by about an order of magnitude. A similarly luminous z>4 LRD should be reachable with moderately deep VLA observations, offering a concrete route to test whether distant LRDs are intrinsically radio weak or merely hard to detect.

Key figures to inspect

• Figure 1. The stacked 3 GHz VLASS map establishes the central observational result: J2048 is radio-bright and largely unresolved at its Gaia optical position. The marginal southeast protuberance is especially important because it may trace a kpc-scale jet or a second component in a merging ULIRG-like system, directly connecting the detection to competing AGN-feedback and starburst interpretations.
• Figure 2. The multi-survey radio spectrum provides the paper’s key physical diagnostic, showing the fitted spectral index α=−0.39±0.04. Its moderately flat, optically thick synchrotron-like slope underpins the argument that J2048 is not simply a faint star-formation radio counterpart but a useful analog for assessing suppressed or obscured black-hole-linked radio emission in LRDs.