Year: 2026
Type: article
Abstract: Several local ( z ≲ 0.2) metal-poor dwarf active galactic nuclei (AGNs) have remarkably similar properties to those of high-redshift little red dots (LRDs), and are proposed to be local analogs of LRDs. We use long-term photometric and spectroscopic observations of three local LRDs spanning ∼20 yr to measure variability in their rest-frame optical continua and broad H α emission lines. Using Zwicky Transient Facility light curves over a rest-frame ∼5 yr baseline, the r -band intrinsic rms variability is ( 9 × 1 0 − 5 ) − 9 × 10 - 5 + 0.014 mag (J1022+0841), 0.025 ± 0.004 mag (J1025+1402) and 0.020 ± 0.005 mag (J1047+0739), indicating low intrinsic variability (<3%–4% at 3 σ ). These variability amplitudes are much lower than those for dwarf AGNs and more massive quasars. We constrain the broad H α variability to be less than a few percent, without significant profile changes, over a rest-frame baseline of ∼15 yr in J1025+1402 and J1047+0739, respectively. Local LRDs have exceptionally large H α equivalent widths and H α /H β ratios that far exceed the Case B recombination value, in contrast with normal broad-line AGNs. In the context of recent theoretical models of LRDs as dense gas-enshrouded massive black holes with super-Eddington accretion, our results suggest that the photosphere emission is long-term stable and the broad Balmer lines do not arise primarily by photoionization. This scenario is consistent with the lack of variability, large H α /H β ratios, little dust extinction, and expected high gas density. Virial black hole mass estimates using broad H α assuming photoionization are therefore highly questionable for LRDs.
Source: The Astrophysical Journal
Authors: Colin J. Burke, Zachary Stone, Yue Shen, Yan-Fei 燕飞 Jiang 姜
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $4,499
OpenAlex ID: W4416550230