Year: 2026
Type: preprint
Abstract: A major question about JWST's little red dots (LRDs) at $z\sim4-8$ is the origin of their apparent X-ray weakness. Even deep Chandra stacks yield only tentative detections or broad-band limits and cannot distinguish among super-Eddington accretion, intrinsic X-ray weakness, and Compton-thick (CT) obscuration. Local analogs offer a powerful complementary route. At $z\sim0.3$, similarly luminous sources require $\sim10^{3-4}$ less exposure for comparable signal-to-noise, suffer less source confusion, and directly probe the diagnostic rest-frame soft X-rays. Here we present a pilot Einstein Probe/FXT study of six "local little red dots" (LLRDs), V-shaped broad-line green pea galaxies selected as low-redshift counterparts of LRDs. These sources show X-ray diversity: "X-normal" LLRDs resemble type 1 AGNs in X-ray luminosity and optical variability, whereas the "X-weak" stack lies $\sim0.5-0.7$ dex below standard unobscured-quasar scaling relations while remaining compatible with the representative LRD stack and 95% of published individual limits. The X-weak LLRDs also lack detected optical variability and have redder optical continua than X-normal LLRDs, making their V-shaped SEDs closer to those of high-redshift LRDs. The detection of the X-weak stack at $\sim3.3σ$ with the soft-X-ray-sensitive EP-FXT provides rest-frame $\sim2-3$ keV constraints difficult to reconcile with a typical unobscured super-Eddington model or a local-AGN-like CT geometry examined here, although modified variants remain possible. The simplest alternative is a mildly X-ray-weak corona ($Δα_{\mathrm{ox}}\sim-0.1$ to $-0.2$) with Compton-thin absorption ($N_{\mathrm{H}}\sim10^{22-23}$ cm$^{-2}$), consistent with the independent Balmer decrement/break diagnostics. Together with growing samples of local LRD analogs, our results offer a practical path for testing the physical nature of LRD X-ray weakness.
Source: arXiv (Cornell University)
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funders: Smithsonian Institution, U.S. Department of Energy, National Aeronautics and Space Administration, Alfred P. Sloan Foundation, Carnegie Institution of Washington, Ohio State University, California Institute of Technology, Johns Hopkins University, Carnegie Mellon University, University of Notre Dame, New Mexico State University, Space Telescope Science Institute, European Space Agency, York University, University of Oxford, National Natural Science Foundation of China, Ministério da Ciência, Tecnologia e Inovação, Universidad Nacional Autónoma de México, Leibniz-Institut für Astrophysik Potsdam, Max-Planck-Institut für Astrophysik, Max-Planck-Institut für Astronomie, Instituto de Astrofísica de Canarias, Office of Science, Jet Propulsion Laboratory, University of California, Los Angeles, University of Colorado Boulder, Leibniz-Gemeinschaft, Lawrence Berkeley National Laboratory
OpenAlex ID: W7223683723