Near-infrared Variability Detected in the Young Star-forming Dwarf Galaxy SBS 0335-052E

Abstract SBS 0335-052E is a young star-forming dwarf galaxy with a total stellar mass of M * ≲ 10 8 M ⊙ and an extremely low metallicity ( Z ∼ 1/40 Z ⊙ ), which has long been considered to be devoid of an active galactic nucleus (AGN). Here, we report the detection of temporal flux variability of SBS 0335-052E in near-infrared (NIR) 3–4 μ m bands on timescales of several years, showing dimming and brightening of up to 50% over 14 yr, based on archival data from the Wide-field Infrared Survey Explorer. Our spectral energy distribution (SED) fitting of archival ultraviolet (UV)-NIR photometry, including AGN SED models, indicates that the variable NIR emission arises from an edge-on AGN dust torus. The UV-optical emission from the accretion disk is obscured and does not reach us, leading to the dominance of the host galaxy’s young stellar population in the UV-optical wavelengths. This analysis favors the presence of a Compton-thick, heavily obscured AGN in SBS 0335-052E, consistent with its observed X-ray weakness. From the SED fitting, we estimate an AGN bolometric luminosity of L bol = 1.2 × 10 43 erg s −1 , which implies a black hole (BH) mass of M BH ≃ 10 5 M ⊙ if the AGN is accreting at the Eddington limit. If confirmed, SBS 0335-052E would be the least massive galaxy known to host an AGN, likely harboring an intermediate-mass BH.