A z ~ 0.4 Galaxy Reflecting the high-redshift Little Red Dots: An Extended Starburst with an Overmassive Black Hole

Xiaoyang Chen, Kohei Ichikawa, Masayuki Akiyama, Kohei Inayoshi, Akio K. Inoue, Masafusa Onoue, Yoshiki Toba, Jorge A. Zavala, Tom J. Bakx, Toshihiro Kawaguchi, Kianhong Lee, Naoki Matsumoto, Bovornpratch Vijarnwannaluk

First listed 2025-10-03 | Last updated 2026-01-07

Abstract

One of the most remarkable discoveries of JWST is a population of compact, red sources at z > 4, commonly referred to as Little Red Dots (LRDs). Spectroscopic identifications reported that most LRDs are active galactic nuclei (AGNs), which are preferentially found around z ~ 6 and could imply a key phase in the formation and growth of black holes (BHs) in the early universe. Photometric surveys at lower redshift have recently been carried out to trace their evolution across cosmic time, and a small number of LRD-like galaxies have been spectroscopically identified at both Cosmic Noon and in the local universe. Here we report the discovery of one of the lowest-z LRD-like galaxies, J204837.26-002437.2 (hereafter J2048) at z = 0.4330, using new Gemini-N/GMOS IFU observations combined with archival multi-band photometric SED data. The GMOS data reveal extended blue emission from starburst with a star formation rate of 400 solar mass per year, together with an extended, highly fast ionized outflow. This is the first spectroscopic confirmation of extended host emission and outflow in an LRD-like galaxy, providing a unique laboratory for understanding the nature of their high-redshift counterparts. Moreover, J2048 would host an extremely overmassive BH with a BH-to-stellar mass ratio of ~ 60%, with the BH mass and host stellar mass estimated to be 10^10.2 and 10^10.4 solar masses, respectively. We discuss the origin and evolutionary fate of J2048, and the implications that such low-z analogs have for interpreting the properties of high-z LRDs.

Short digest

Gemini-N/GMOS IFU plus multi-band SEDs reveal J2048 (z = 0.4330) as a rare low‑z analog of the JWST Little Red Dots. The IFU resolves an extended blue continuum from a powerful starburst (SFR ≈ 400 M⊙ yr⁻1) alongside spatially extended, very fast ionized outflows, while the nucleus shows BLR Hα atop a compact red continuum. Joint spectrum+SED fitting implies an extreme BH-to-stellar mass ratio of ~60% (MBH ≈ 10^10.2 M⊙ vs M⋆ ≈ 10^10.4 M⊙), i.e., an overmassive black hole. As one of the lowest‑z LRD-like systems with spectroscopically confirmed host emission and outflows, J2048 offers a nearby laboratory for testing the v‑shaped SED, feedback, and early BH growth scenarios inferred at high z.

Key figures to inspect

• Figure 1: Use the tri-color IFU map and radial profiles to compare the spatial extents of young stars (3500–4000 Å), narrow Hα, and [O III] outflow versus the PSF (0.65″), quantifying how far the blue starburst and ionized wind extend beyond the unresolved BLR.
• Figure 2: Inspect the line decomposition around Hβ–[O III] and Hα–[N II] to identify the two blueshifted outflow components, measure their velocity offsets/widths, and verify the BLR Hα profile used for the black-hole mass estimate against the stellar and AGN continuum fits.
• Figure 3: Check the simultaneous spectrum+SED fit (0.2–20 μm) for constraints on the weak/absent torus emission, the large starburst contribution and dust attenuation, and the reported upper limit on any old stellar population; use the residual panels to gauge calibration/systematic uncertainties.
• Figure 4: Examine the unresolved-core SED (after subtracting outskirts) and its UV/optical power-law slopes against JADES and COSMOS-Web LRD stacks to validate the v-shaped SED similarity between J2048’s nucleus and high‑z LRDs.