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Arxiv: Exploring the AGN Fraction of a Sample of JWST's Little Red Dots at 5 < z < 8: Overmassive Black Holes Are Strongly Favored Published: 6/14/2024 9:00:00 PM Updated: 1/16/2025 7:10:39 PM

Paper abstract: JWST is revolutionizing our view of the early Universe by pushing theboundaries of detectable galaxies and black holes in redshift (upward) and mass(downward). The Little Red Dots (LRDs), detected by several surveys at z > 4,present a significant interpretational challenge, as their Spectral EnergyDistributions (SED) can mimic both AGN and stellar population templates. Thisstudy analyzes 19 LRDs from the JADES survey, utilizing NIRCam and MIRIphotometry. By performing SED fitting across a vast parameter space, we explorea broad range of AGN fractions, defined as the ratio of the monochromaticluminosities (AGN, galaxy, and dust) over a specified wavelength range, 0.4 -0.7 \mu m rest-frame. We find that 17 of the 19 LRDs investigated areconsistent with having significant AGN contributions, with best-fitting AGNfractions ranging between 20% and 70%, while one galaxy shows a low AGNcontribution (2%) and another appears to be purely star-forming. Moreover,assuming these LRDs do indeed host AGN, we can place limits on their black holemasses using the inferred AGN bolometric luminosities and adopting theEddington limit. We find that, independent of the specific AGN fractionadopted, the LRDs' black holes are significantly overmassive relative to theirhost galaxies -- by ~ 1 dex, and up to ~ 4 dex in the most extremecases -- compared to the local M_{\bullet} - M_{*} relation. The presenceof overmassive black holes in the high-z Universe may provide the strongestevidence yet of heavy black hole seeding occurring during the cosmic dark ages.