Local Analogs of Little Red Dots: Optical Variability and Evidence for an Active Galactic Nucleus Origin

Le résumé fourni par la source

Abstract Little red dots (LRDs) draw extensive attention because of their unique observational characteristics and apparent overabundance in the early Universe, raising new insights into early black hole formation and growth. Early studies show that LRDs exhibit weak variability in photometry and emission-line fluxes, suggesting a preference for super-Eddington accretion or disfavoring an active galactic nucleus (AGN) origin. However, the current data are limited, preventing us from placing strong constraints on their variability. Based on Zwicky Transient Facility (ZTF) light curves with a baseline of ∼6 yr, we here study the optical variability of seven previously reported local analogs of LRDs at z ∼ 0.3, offering an insight into LRDs from a low-redshift sample. Three out of seven local analogs show excess variances on all three bands of their light curves, and two of them can be fitted with the damping random walk model, supporting their AGN origins for the variability. The remaining sources show weak variance in at least one band, but no detectable variability, exhibiting SF ∞ upper limits consistent with estimates from high-redshift LRDs. Their nondetection of variability is likely due to the large photometric uncertainty. As an implication, by simulating long baseline light curves with the variability amplitude of local analogs and adopting JWST observation cadence, we investigate the limitation of the variability amplitude estimate for LRDs. Our mock observations imply that the current constraints on LRDs’ variability are probably underestimated. This underestimation might be induced by the short temporal baseline of observations, as well as the intrinsic scatter of the empirical M BH – τ relation.

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