What you see is what you get: empirically measured bolometric luminosities of Little Red Dots

Jenny E. Greene, David J. Setton, Lukas J. Furtak, Rohan P. Naidu, Marta Volonteri, Pratika Dayal, Ivo Labbe, Pieter van Dokkum, Rachel Bezanson, Gabriel Brammer, Sam E. Cutler, Karl Glazebrook, Anna de Graaff, Michaela Hirschmann, Raphael E. Hviding, Vasily Kokorev, Joel Leja, Hanpu Liu, Yilun Ma, Jorryt Matthee, Themiya Nanayakkara, Pascal A. Oesch, Richard Pan, Sedona H. Price, Justin S. Spilker, Bingjie Wang, John R. Weaver, Katherine E. Whitaker, Christina C. Williams, Adi Zitrin

First listed 2025-09-05 | Last updated 2025-09-05

Abstract

New populations of red active galactic nuclei (known as ``Little Red Dots'') discovered by JWST exhibit remarkable spectral energy distributions. Leveraging X-ray through far-infrared observations of two of the most luminous known Little Red Dots, we directly their bolometric luminosities. We find evidence that more than half of the bolometric luminosity likely emerges in the rest-frame optical, with $L_{\rm bol}/L_{5100} = 5$, roughly half the value for ``standard'' Active Galactic Nuclei. Meanwhile, the X-ray emitting corona, UV-emitting black-body, and reprocessed mid to far-infrared emission are all considerably sub-dominant, assuming that the far-infrared luminosity is well below current measured limits. We present new bolometric corrections that dramatically lower inferred bolometric luminosities by a factor of ten compared to published values in the literature. These bolometric corrections are in accord with expectations from models in which gas absorption and reprocessing are responsible for the red rest-frame optical colors of Little Red Dots. We discuss how this lowered luminosity scale suggests a lower mass scale for the population by at least an order of magnitude {\bf (e.g., $\sim 10^5-10^7~{\rm M_{\odot}}$ black holes, and $\sim 10^8~{\rm M_{\odot}}$ galaxies)}, alleviating tensions with clustering, overmassive black holes, and the integrated black hole mass density in the Universe.

Short digest

Empirically integrating X-ray–to–far-IR SEDs for two of the most luminous Little Red Dots (A2744-45924 and RUBIES-BLAGN-1), the authors directly measure bolometric luminosities rather than adopting standard AGN corrections. They find that over half of Lbol emerges in the rest-frame optical with Lbol/L5100≈5, while X-ray, UV, and reprocessed mid/far-IR components are sub-dominant, and deep ALMA/MIRI limits rule out a standard dust-reddened AGN SED. New bolometric corrections lower previously inferred luminosities by ~10×, implying BH masses of ~10^5–10^7 Msun (and ~10^8 Msun hosts) if radiating near Eddington and easing tensions with clustering and BH mass density. A key assumption is that far-IR luminosities lie well below current observational limits.

Key figures to inspect

• Figure 1: Compare the integrated panchromatic SEDs of A2744-45924 and RUBIES-BLAGN-1 across the shaded X-ray/UV/optical/NIR/IR bands to see that the optical dominates Lbol and that ALMA/MIRI limits exclude a standard Eddington AGN SED scaled to prior assumptions.
• Figure 2: Inspect the shift from H-based (and reddening-corrected) Lbol to the new empirical values—an order-of-magnitude drop—and read off the implied BH masses at the Eddington line (~10^5–10^7 Msun).
• Figure 3: Look at the updated bolometric luminosity function versus models (DELPHI; Volonteri et al.) and the “maximum” halo line to see how the downward Lbol revision brings LRDs below theoretical ceilings and alleviates prior tensions.