Kavli Affiliate: Luis C. Ho
| First 5 Authors: Shuying Zhou, Shuying Zhou, , ,
| Summary:
The high-redshift ($z>4$) compact sources with “V-shaped" spectral energy
distributions (SEDs), known as Little Red Dots (LRDs), are discovered by the
James Webb Space Telescope and provide valuable clues to the physics of active
galactic nuclei (AGNs) in the early universe. The nature of LRDs is
controversial. Recently, several studies have investigated LRDs through
variability, a characteristic feature of AGNs. These studies explore LRD
variability by extrapolating empirical relationships from local quasars. Here,
we adopt the Corona-heated Accretion-disk Reprocessing (CHAR) model, which is
motivated by accretion physics and applicable to reproduce AGN conventional
variability, to study the variability of $22$ LRDs in citetTee2025. Our
results indicate that the observed variability in LRDs is dominated by
measurement uncertainties. Within the CHAR model, the lack of variability in
LRDs can be explained by two scenarios: either AGNs contribute $lesssim30%$
of the observed luminosities, or they are intrinsically luminous AGNs. We use
simulations to demonstrate the observational requirements to effectively
investigate LRDs via variability: first, a sample of about $200$ LRDs; second,
each LRD has two observations separated by at least two years in the observed
frame; third, the photometric uncertainty is $leq 0.07$ mag. If the LRDs still
lack variability under these conditions, the time-domain study would provide
independent evidence that the accretion mode of LRDs differs significantly from
low-redshift quasars.
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