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"Little red dots" cannot reside in the same dark matter halos as comparably luminous unobscured quasars

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arxiv 2409.18208 v2 pith:SCPJZAEI submitted 2024-09-26 astro-ph.GA astro-ph.CO

classification astro-ph.GAastro-ph.CO
keywords lrdsquasarsunobscuredbolometricluminositiesmathrmpopulationuv-selected
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abstract

The James Webb Space Telescope (JWST) has uncovered a new population of candidate broad-line AGN emerging in the early Universe, named ''little red dots'' (LRDs) because of their compactness and red colors at optical wavelengths. LRDs appear to be surprisingly abundant ($\approx 10^{-5}\,\mathrm{cMpc}^{-3}$) given that their inferred bolometric luminosities largely overlap with the ones of the UV-luminous quasars identified at high $z$ in wide-field spectroscopic surveys. In this work, we investigate how the population of LRDs and/or other UV-obscured AGN relates to the one of unobscured, UV-selected quasars. By comparing their number densities, we infer an extremely large and rapidly evolving obscured:unobscured ratio, ranging from $\approx20:1$ at $z\approx4$ to $\approx2300:1$ at $z\approx7$, and possibly extending out to very high ($\approx10^{47}\,\mathrm{erg}\,\mathrm{s}^{-1}$) bolometric luminosities. This large obscured:unobscured ratio is incompatible with the UV-luminous duty cycle measured for unobscured quasars at $z\approx4-6$, suggesting that LRDs are too abundant to be hosted by the same halos as unobscured quasars. This implies that either (a) the bolometric luminosities of LRDs are strongly overestimated (possibly because LRDs are dominated by stellar galaxy light) or (b) LRDs follow different scaling relations than the ones of UV-selected quasars, representing a new population of accreting SMBHs emerging in the early Universe. A direct comparison between the clustering of LRDs and the one of faint UV-selected quasars will ultimately confirm these findings, and shed light on key properties of LRDs such as their host mass distribution and duty cycle. We provide a mock analysis for the clustering of LRDs and show that it is feasible with current and upcoming JWST surveys.

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Forward citations

Cited by 5 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score. Full citation record

  1. Not-quite-primordial black holes

    astro-ph.CO 2025-06 conditional novelty 7.0 of 10

    Modest small-scale density fluctuations can make halos at z>200 where CMB radiation suppresses molecular cooling, letting gas collapse directly into black hole seeds that match JWST counts.

  2. Environmental Evidence for Overly Massive Black Holes in Low Mass Galaxies and a Black Hole - Halo Mass Relation at $z \sim 5$

    astro-ph.GA 2024-12 conditional novelty 7.0 of 10

    Faint broad-line AGN at redshift 4 to 5 appear to live in low-mass galaxies of about 50 million solar masses, implying black holes that are an order of magnitude heavier than their host stellar mass.

  3. Lonely Little Red Dots: Challenges to the AGN-nature of little red dots through their clustering and spectral energy distributions

    astro-ph.GA 2025-06 conditional novelty 6.0 of 10

    Little red dots sit in lower-density environments than typical galaxies, and Bayesian model comparison favors non-AGN interpretations for most of them.

  4. Another piece to the puzzle: radio detection of a JWST detected AGN candidate

    astro-ph.GA 2025-01 conditional novelty 6.0 of 10

    A multi-field radio search of JWST AGN candidates yields one radio detection and stacking limits that are not yet deep enough to confirm or rule out radio-weakness.

  5. An unambiguous AGN and a Balmer break in an Ultraluminous Little Red Dot at z=4.47 from Ultradeep UNCOVER and All the Little Things Spectroscopy

    astro-ph.GA 2024-12 conditional novelty 6.0 of 10

    An ultraluminous little red dot at z=4.47 shows unambiguous broad-line AGN signatures and a Balmer break that favors a massive, old, extremely dense stellar core.

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