Discovery of a luminous Little Red Dot at z~10 in COSMOS-Web based on NIRCam-MIRI selection

Deep IR observations by JWST have discovered a new population of high-redshift compact objects known as "little red dots" (LRDs) with a characteristic V-shape SED with the trough around the Balmer limit. Based on the detection of broad Balmer emission lines, previous studies have suggested that LRDs are low-luminosity AGNs, possibly linked to super-Eddington accretion shortly after seed BH formation. Previous photometric LRD selections have used NIRCam photometry, making them susceptible to contamination by low-redshift interlopers or z~10 galaxies with a stellar-origin Balmer break other than z~10 LRDs. In this study, we propose a new color selection technique for identifying LRDs at z~10, utilizing both NIRCam and MIRI photometry to extend the redshift frontier of LRD studies. Applying this method to COSMOS-Web, the largest NIRCam-MIRI joint survey, we find one solid candidate with a compact morphology, a clear F115W dropout, and a V-shape SED. This candidate with the photometric redshift of ~10.5 represents one of the most distant SMBHs so far, potentially representing the era just after seed BH formation. In the talk, we will present the first constraints on the luminosity function of LRDs at z~10 and discuss the implications of this discovery for our understanding of SMBH evolution in the early Universe.