The Stellar Origin of “V-shaped” Spectral Energy Distributions in Ly α -emitting Little Red Dots Revealed by JWST/MIRI

Abstract Understanding the nature of the high-redshift “V-shaped” little red dots (LRDs) recently uncovered by the James Webb Space Telescope (JWST) is crucial for constraining the early coevolution of galaxies and supermassive black holes (SMBHs). Leveraging deep JWST multiband imaging in the GOODS-S field, we photometrically identify six LRDs from a parent sample of MUSE-selected Ly α emitters (LAEs). Their Ly α line profiles are asymmetric, with suppressed blue wings and narrow widths (FWHM < 300 km s −1 ). Spectral energy distribution (SED) modeling suggests that, in the absence of MIRI photometry ( λ rest > 1 μ m), an active galactic nucleus (AGN) could contribute ∼40% of the rest-frame optical luminosity. However, when MIRI data are included, the long-wavelength emission is well reproduced by stellar populations with strong nebular emission in four sources, independent of the inclusion of an AGN component. Morphological analysis reveals that these systems are compact in the rest-frame optical, while exhibiting more extended structures in the rest-frame UV. These results suggest that AGN activity is not required to explain the observed properties of most narrow-line LRDs in our sample. Instead, they are consistent with being compact, star-forming galaxies, although contributions from low-luminosity or obscured AGN cannot be entirely ruled out. Thus, rest-frame near-infrared observations are essential to interpret LRDs, and infrared excesses alone do not reliably indicate AGN activity.