LRD host galaxies show average metallicity 0.08 Z_sun with narrow stable range, challenging pristine-gas formation models while ruling out typical local AGN.
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Defines a sample of ~1300 SDSS quasars as Local Red Dots matching LRD photometric colors at z~0.4-0.8, with a V-shaped subset showing Balmer absorption and [NeV] emission, and SEDs modeled as reddened AGN plus host galaxy that match LRD stacks.
Lyα observations of Little Red Dots show luminosities and equivalent widths like normal star-forming galaxies but lower Lyα/Hα ratios and extended asymmetric emission, supporting a two-component model with host-scale gas.
The survey identifies 27 low-redshift LRDs with compact morphology, V-shaped continua, broad Balmer lines with extreme decrements, and ubiquitous outflows, matching high-z counterparts and yielding a number density lower limit of 7.5e-10 cMpc^-3.
Spectroscopic study of 11 LRDs at z~4 finds AGN origin for optical emission via broad Hα correlations and introduces a clumpy envelope model with growth timescales of 10^5-10^7 years.
Little Red Dots show soft ionizing spectra consistent with massive stars, based on high H-alpha EWs and low HeII/H-beta ratios that rule out hard AGN spectra via Cloudy modeling.
LRDs at z~3-7 exhibit an L_Hα,broad-L_bol scaling relation enhanced by a factor of ~40 compared to low-z Type 1 AGN, explained via Cloudy modeling with near-unity covering factor and high column density.
Analysis of ~100 JWST LRDs finds redder, compact UV emission with Fe II/Mg II ~8-10 and correlations suggesting central red continuum (β_UV~0) beyond host galaxy contribution.
UV-bright companions to Little Red Dots provide Lyman-Werner fluxes of J21 ~ 10^2.5-10^5 that can suppress H2 cooling and enable direct collapse to massive black holes.
FIRE-2 simulations with gravitational torque-driven and free-fall accretion models predict enough high-redshift AGN to explain little red dots, with a super-Eddington Eddington-limited scenario for M_BH >= 2e5 Msun in M_star >= 2e7 Msun galaxies reproducing key observations.
Narrow-line diagnostics on ~20 LRDs indicate that stellar photoionization alone cannot explain the observed ratios in many objects, implying anisotropic ionizing radiation from complex gas geometry.
JWST data on LRDs and LBDs show AGN-like excitation, strong Lyα with broad components, and X-ray weakness, implying clumpy or equatorial geometries around growing black holes rather than complete gas envelopes.
Bayesian continuum fitting of 66 LRDs shows the BH* model fits ~6% best, rising to ~40% under AGN-disfavoring priors, with most objects stellar/AGN-dominated and possible evolutionary trends.
JWST IFU spectroscopy of six z~6 galaxies finds broad Balmer lines in two objects, a strong correlation of broad-line presence with Lyα luminosity yielding AGN fractions >77% above and <15% below 10^44 erg/s, plus extended star-forming gas in non-AGN hosts.
Simulations show heavy-seed formation with BH-BH mergers or Bondi accretion under weak feedback can assemble 10^6-10^7 solar mass black holes at z greater than or equal to 9.
A sample of 36 spectroscopically confirmed LRDs shows broad-line detections in >90%, spectral variety including Balmer breaks and blackbody fits, H-alpha to 5100A continuum correlation, no redshift evolution, declining space density toward z~2 opposite normal AGNs, and clustering in ~10^11 solar mas
LRDs require Compton-thick gas at moderate metallicity plus high accretion rates producing weak X-rays to explain their non-detection, implying they are not chemically pristine.
Local compact AGN-hosting dwarf galaxies with V-shaped SEDs are more evolved than high-redshift Little Red Dots, indicating distinct formation pathways.
A z=1.715 radio-loud quasar exhibits a ~10,000 K blackbody UV continuum and three-component blackbody photometry, marking it as a candidate transitional Little Red Dot.
Higher Eddington ratio AGN exhibit increased [O III] outflow incidence and reduced obscuration, supporting radiative feedback as the regulator.
A bias-controlled quasar sample of ~2000 objects demonstrates that the X-ray-to-UV luminosity relation remains constant from redshift 0.7 to 5.
Simulations show VMS in star clusters reach 10^3-10^4 solar masses with dimensionless spins >10 under bloated accretion conditions, potentially forming spinning IMBHs that produce GW bursts like GW190521.
Simulations and analytic modeling predict that the supermassive black hole to stellar mass ratio peaks at several percent around redshift 7-10 before declining toward the present day.
SKAO continuum surveys will detect radio emission from JWST AGN and LRDs and distinguish between Compton-thick absorption, intrinsically weak accretion, and dense gas cocoon scenarios.
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The X-ray-to-UV relation does not evolve in homogeneous quasar samples
A bias-controlled quasar sample of ~2000 objects demonstrates that the X-ray-to-UV luminosity relation remains constant from redshift 0.7 to 5.