Investigating Little Red Dots with UV Excess: Are They the High-redshift Siblings of Blue Hot Dust-obscured Galaxies?

Abstract Little red dots (LRDs), newly identified compact and dusty galaxies with an unexpectedly high number density observed by JWST, have an unusual “V-shaped” rest-frame UV to near-infrared spectral energy distribution (SED). A group of hyperluminous, obscured quasars with excess blue emission, called blue-excess hot dust-obscured galaxies (BHDs), also exhibit qualitatively similar SEDs to those of LRDs. They represent a rare population of galaxies hosting supermassive black holes (SMBHs) accreting near the Eddington limit at redshifts z ∼ 1–4. In this study, we compare their multiwavelength SEDs to investigate whether LRDs, or a subset of them, could be high-redshift analogs of BHDs. Our analysis reveals that despite their similar “V-shape” SEDs, LRDs appear to be a different population than BHDs. The “V-shape” of BHDs appears at longer wavelengths compared to LRDs due to different selection strategies, suggesting LRDs have much less dust attenuation than typical BHDs. The bluer colors in the rest-frame infrared (continuum) emission of LRDs suggest the absence of hot dust heated by active galactic nuclei (AGN) accretion activities. We also argue that the blue excess in LRDs is unlikely from AGN scattered light. The compact morphologies and lower X-ray detection frequencies of LRDs suggest a distinct formation pathway from BHDs, which are thought to be powered by super-Eddington accretion onto central SMBHs following major galaxy mergers.