Lord of LRDs: Insights into a "Little Red Dot" with a low-ionization spectrum at z = 0.1

TL;DR

This paper reports the discovery and detailed analysis of a low-ionization spectrum galaxy at low redshift that exhibits features similar to high-redshift 'Little Red Dots', providing insights into their nature and environment.

Contribution

It presents the first detailed study of a local LRD with multi-wavelength observations, revealing complex gaseous environments and spectral features comparable to high-redshift LRDs, challenging existing models.

Findings

Discovery of a local LRD at z=0.1 with unique spectral features.

Identification of low-ionization lines and deep Balmer absorption.

Confirmation of extreme X-ray weakness suggesting Compton-thick obscuration.

Abstract

Recent observations by the James Webb Space Telescope (JWST) have revealed a puzzling population of optically red and compact galaxies with peculiar "V"-shaped spectra at high redshift, known as "Little Red Dots" (LRDs). Until now, most spectroscopically confirmed LRDs are found at $z>4$ and it has been speculated that LRDs are tracing the early stages of black hole evolution. We report an independent rediscovery of a broad-line active galactic nucleus (AGN), SDSS J102530.29+140207.3, at $z=0.1$, which shows spectral features matching those of LRDs seen in the early Universe, including the V-shaped spectrum, broad Balmer lines (with widths of 1000-2000 km/s), and deep Balmer absorption. We present a new GTC observation of this LRD, which reveals an optical continuum similar to those of G-to-K giant stars including an unambiguous G-band absorption originating from the CH molecule. In addition, this local LRD shows a series of absorption lines potentially related to low-ionization ions or atoms but are deeper than what is observed in empirical stellar templates. We further identify a series of [FeII] emission lines indicative of low-ionization gas, which we find also present in a JWST-selected LRD at $z=2.26$. We find small but statistically significant variability in the H$\alpha$ of SDSS J102530.29+140207.3 consistent with previous findings. Finally, we report new observations with NuSTAR. We confirm the extreme X-ray weakness of this LRD, which might imply Compton-thick gas obscuration with $N_{\rm H}>10^{24}~{\rm cm^{-2}}$. All evidence suggests SDSS J102530.29+140207.3 has a complex gaseous environment and the strong ionic, atomic, and molecular absorptions are hard to explain with typical stellar and AGN models.