Lonely Little Red Dots: Challenges to the AGN-nature of little red dots through their clustering and spectral energy distributions

María Carranza-Escudero, Christopher J. Conselice, Nathan Adams, Thomas Harvey, Duncan Austin, Peter Behroozi, Leonardo Ferreira, Katherine Ormerod, Qiao Duan, James Trussler, Qiong Li, Lewi Westcott, Rogier A. Windhorst, Dan Coe, Seth H. Cohen, Cheng Cheng, Simon P. Driver, Brenda Frye, Lukas J. Furtak, Norman A. Grogin, Nimish P. Hathi, Rolf A. Jansen, Anton M. Koekemoer, Madeline A. Marshall, Rosalia O'Brien, Norbert Pirzkal, Maria Polletta, Aaron Robotham, Michael J. Rutkowski, Jake Summers, Stephen M. Wilkins, Christopher N. A. Willmer, Haojing Yan, Adi Zitrin

First listed 2025-06-04 | Last updated 2025-08-20

Abstract

Observations with the James Webb Space Telescope (JWST) reveal a previously unseen population of compact red objects, known as ``little red dots`` (LRDs). We study a new photometrically selected sample of 124 LRDs in the redshift range $z$ $\sim$ 3 - 10 selected from NIRCam coverage of the CEERS, NEP-TDF, JADES and JEMS surveys. For JADES, the NEP-TDF and CEERS, we compare SED models with and without AGN components and analyse the impact of an AGN component on the goodness of fit using the Bayesian information criterion (BIC). We find that whilst the $χ^{2}$ of the majority of models containing AGN components is improved compared to models without AGN components, we show that the BIC suggests models without AGN are a more appropriate fit to LRD SEDs, especially when MIRI data is available. We also measure LRD clustering in the CEERS field, JADES field, and NEP-TDF, where we compare the spatial distribution of LRDs and galaxies with Kolmogorov-Smirnov tests of equality of distribution. We find that the neighbourhood of LRDs tends to be less dense compared to galaxies at all selections and masses and at similar redshifts. We further measure upper limit estimates for the halo masses of LRDs using abundance matching. Whilst the population of LRDs could be a mixture of several different inherent populations, as a whole it does appear that these systems are mostly hosting compact galaxies or star clusters in formation.

Short digest

Builds a 124-object little red dot sample at z≈3–10 from CEERS, NEP‑TDF, JADES, and JEMS, then tests SED fits with and without AGN components using BIC. Despite lower χ² when adding AGN templates, BIC generally prefers non‑AGN SEDs, especially when MIRI photometry is included. KS tests of projected environments show LRDs occupy sparser neighborhoods than comparison galaxies, and abundance matching yields conservative halo-mass upper limits. Together these point to most LRDs being compact galaxies or forming star clusters rather than AGN‑dominated, while allowing for a mixed population.

Key figures to inspect

• Figure 1 (redshift distribution): Confirms the sample peaks near z≈5; use it to gauge where conclusions about SEDs and environments are best constrained and to compare directly with prior LRD redshift distributions.
• Figure 2 (number density evolution): Track the comoving density versus redshift with Poisson errors; check whether densities around z≈4–6 are consistent with the non‑AGN interpretation and how steep any evolution is.
• Figure 3 (CEERSP2:2580 Hα): A single‑Gaussian Hα with FWHM ≈240 km/s—inspect residuals to see how clean the narrow profile is and how it supports star‑forming/compact galaxy scenarios over broad‑line AGN.
• Figure 4 (CEERSP7:8486 Hα): Broad (≈1980 km/s) plus narrow (≈560 km/s) components—use this to probe the minority broad‑line cases and assess the note that the apparent absorption could be [N II], i.e., how robust the AGN interpretation is.