Tentative Detection of Neutral Gas in a Little Red Dot at z = 4.46

Abstract JWST has revealed a population of broad-line active galactic nuclei at z > 4 with remarkably red colors, so-called “Little Red Dots” (LRDs). Ubiquitous Balmer breaks suggest that they harbor old stellar populations in massive, compact host galaxies. We present Atacama Large Millimeter/submillimeter Array observations of three LRDs at z = 3.10, 4.46, and 7.04, targeting molecular and neutral gas via CO(7–6) and [C i ](2–1), respectively. We do not detect CO in any target, placing conservative limits on the host molecular gas mass of ≲(1–5) × 10 10 M ⊙ . We report the tentative (∼3.5 σ ) detection of the [C i ](2–1) line in A2744-45924 ( z = 4.46), one of the brightest known LRDs. The [C i ] line is narrow (FWHM ∼ 80 km s −1 ), implying a dynamical mass ≲10 10 M ⊙ , adopting conservative limits for the size of the galaxy. The dynamical mass limit is significantly lower than expected from the local M BH – M dyn relation, and is an order of magnitude below the stellar mass derived from spectral energy distribution fitting, potentially supporting a nonstellar origin of the Balmer break. These results, while tentative, paint a picture of LRDs that is markedly different than typical high- z quasars, which live in massive, gas-rich, and actively star-forming host galaxies.