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

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, 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 integral field unit observations combined with archival multiband photometric spectral energy distribution data. The GMOS data reveal extended blue emission from starburst with a star formation rate of 400 M ⊙ yr −1 , 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 M ⊙ , 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.