Analysis of Multi-epoch JWST Images of $\sim 300$ Little Red Dots: Tentative Detection of Variability in a Minority of Sources

TL;DR

This study analyzes multi-epoch JWST images of approximately 300 Little Red Dots, likely AGNs at high redshift, finding most do not show strong variability, but identifying eight highly variable candidates, advancing understanding of early universe black hole activity.

Contribution

It provides the first comprehensive variability analysis of Little Red Dots using multi-epoch JWST data, revealing their generally low variability and identifying rare highly variable sources.

Findings

Most LRDs do not show strong variability.

Eight LRD candidates exhibit significant variability.

Variability patterns are consistent with super-Eddington accretion or galaxy dominance.

Abstract

James Webb Space Telescope (JWST) has revealed a population of red and compact sources at $z \gtrsim 5$ known as ``Little Red Dots'' (LRDs) that are likely active galactic nuclei (AGNs). Here we present a comprehensive study of the variability of 314 LRDs with multi-epoch JWST observations in five deep fields: UDS, GOODS-S, GOODS-N, Abell 2744, and COSMOS. Our analyses use all publicly available JWST NIRCam imaging data in these fields, together with multi-epoch JWST MIRI images available. We measure the significance (signal-to-noise ratio or ${\rm SNR}_{\rm var}$) of the variabilities for all LRDs and statistically evaluate their variabilities using the ${\rm SNR}_{\rm var}$ distributions. We pay particular attention to the systematic offsets of photometric zero points among different epochs that seem to commonly exist. The derived ${\rm SNR}_{\rm var}$ distributions of the LRDs, including those with broad H$\alpha$/H$\beta$ emission lines, follow the standard Gaussian distribution, and are generally consistent with those of the comparison samples of objects detected in the same images. This finding suggests that the LRD population on average does not show strong variability, which can be explained by super-Eddington accretion of the black holes in AGNs. Alternatively, many of them may be dominated by galaxies. We also find eight strongly variable LRD candidates with variability amplitudes of 0.24 -- 0.82 mag. The rest-frame optical SEDs of these variable LRDs should have significant AGN contribution. Future JWST observations will provide more variability information of LRDs.