Ripples in the OCEANS: Broad Line Variability of Little Red Dots

Madisyn Brooks, Kelcey Davis, Jonathan R. Trump, Raymond C. Simons, Erini Lambrides, Pablo Arrabal Haro, Bren E. Backhaus, Nikko J. Cleri, Steven L. Finkelstein, Mauro Giavalisco, Norman A. Grogin, Michaela Hirschmann, Dale D. Kocevski, Anton M. Koekemoer, Rebecca L. Larson, Ray A. Lucas, Stephen M. Wilkins, Stijn Wuyts, Jorge A. Zavala

First listed 2026-08-14 | Last updated 2026-08-12

Abstract

Little Red Dots (LRDs) are a unique class of compact, red sources discovered in the JWST extragalactic deep fields. Determining if they are indeed powered by accreting supermassive black holes (SMBHs) is one of the main drivers of the intense study of these objects. Evidence for variability in these objects provides a direct test for the active galactic nucleus (AGN) nature of their central engine. In this study, we present a variability analysis of 6 LRDs observed by the $R \sim 2700$ OCEANS survey and leverage archival $R \sim 1000$ spectroscopic data from the CEERS and RUBIES surveys. We report marginal detections of $\rm Hα$ broad-line (BL) variability in the LRDs OCEANS-100424/RUBIES-42232 (27\% variability at 2.1$σ$ significance) and OCEANS-35829/RUBIES-49140 (GlimmIr/Irony; 50\% variability at 1.5$σ$ significance). The other 4 LRDs in our sample do not show evidence for BL variability, with a 1$σ$ upper limit of $4.8 \% - 30\%$ variability between their epochs of observations. We also find no evidence ($<1σ$) for continuum variability in our LRD sample. We compare our results to a sample of SDSS-RM quasars to determine the probability of our broad $\rm Hα$ variability detections. We find that the probability of reproducing 2 variable and 4 nonvariable quasars is $4.71\%$, corresponding to $\sim 2 σ$ departure from typical quasar variability. The detection of BL $\rm Hα$ variability in 2 LRDs provides some evidence for the AGN nature of these objects as opposed to pure scattering models.

Short digest

Brooks et al. test the AGN interpretation of little red dots through multi-epoch JWST/NIRSpec spectroscopy of six OCEANS-selected LRDs, combining new high-resolution OCEANS data with archival CEERS and RUBIES epochs. After calibrating the spectra with narrow [O III] or [Ne III] emission, they find marginal broad Hα variability in OCEANS-100424/RUBIES-42232 (27% at 2.1σ) and OCEANS-35829/RUBIES-49140, the GlimmIr (50% at 1.5σ), while the other four sources yield only upper limits and none shows continuum variability. Comparison with SDSS-RM quasars indicates that the mixture of two variable and four non-variable objects departs from typical quasar broad-line variability, but the two tentative detections nevertheless favor an accreting AGN contribution over a pure scattering origin for the broad lines. The result emphasizes that repeat spectroscopy can separate genuinely variable LRD subtypes from a population whose broad Balmer profiles may not all trace a standard exposed BLR.

Key figures to inspect

• Figure 1. Shows where the six targets sit within the full OCEANS color-selected LRD population and immediately identifies OCEANS-100424 and the GlimmIr as the two marginally variable sources.
• Figure 4. Presents the calibrated multi-epoch Hα profiles and fitted broad components directly, making the line-flux changes and the non-detections across the six-object sample inspectable source by source.
• Figure 5. Synthesizes the central measurement by placing normalized broad Hα flux against rest-frame epoch separation for all six LRDs, separating the two tentative variables from the four upper-limit cases.
• Figure 6. Provides the conclusion-driving comparison to SDSS-RM quasars in matched rest-frame time bins, framing the observed combination of LRD variability measurements and limits relative to ordinary quasar behavior.