Little red dots as young supermassive black holes in dense ionized cocoons

Abstract

The James Webb Space Telescope (JWST) has uncovered many compact galaxies at high redshift with broad hydrogen and helium lines, including the enigmatic population of little red dots (LRDs). The nature of these galaxies is debated and is attributed to supermassive black holes (SMBHs) or intense star formation. They exhibit unusual properties for SMBHs, such as black holes that are overmassive for their host galaxies and extremely weak X-ray and radio emission. Here we show that in most objects studied with the highest-quality JWST spectra, the lines are broadened by electron scattering with a narrow intrinsic core. The data require very high electron column densities and compact sizes (light days), which, when coupled with their high luminosities, can be explained only by SMBH accretion. The narrow intrinsic line cores imply black hole masses of $10^{5-7}$ $M_{\odot }$, two orders of magnitude lower than previous estimates. These are the lowest mass black holes known at high redshift, to our knowledge, and suggest a population of young SMBHs. They are enshrouded in a dense cocoon of ionized gas producing broad lines from which they are accreting close to the Eddington limit, with very mild neutral outflows. Reprocessed nebular emission from this cocoon dominates the optical spectrum, explaining most LRD spectral characteristics, including the weak radio and X-ray emission.

arXiv comment47 pages, 24 figures, 3 tables. Manuscript accepted in Nature

References in corpus (43)

• SciPy 1.0--Fundamental Algorithms for Scientific Computing in Python
• Array Programming with NumPy
• Astropy: A Community Python Package for Astronomy
• emcee: The MCMC Hammer
• The Astropy Project: Building an inclusive, open-science project and status of the v2.0 core package
• The Dust Content and Opacity of Actively Star-Forming Galaxies
• Revisiting the Unified Model of Active Galactic Nuclei
• Relations Between Central Black Hole Mass and Total Galaxy Stellar Mass in the Local Universe
• Estimating Black Hole Masses in Active Galaxies Using the Halpha Emission Line
• Inferring the star-formation histories of massive quiescent galaxies with BAGPIPES: Evidence for multiple quenching mechanisms
• The Near-Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope I. Overview of the instrument and its capabilities
• Intrinsic disc emission and the Soft X-ray Excess in AGN
• Dwarf Galaxies with Optical Signatures of Active Massive Black Holes
• CEERS Key Paper I: An Early Look into the First 500 Myr of Galaxy Formation with JWST
• JADES. The diverse population of infant Black Holes at 4<z<11: merging, tiny, poor, but mighty
• Double-Peaked Low-Ionization Emission Lines in Active Galactic Nuclei
• Stellar Velocity Dispersion Measurements in High-Luminosity Quasar Hosts and Implications for the AGN Black Hole Mass Scale
• JADES NIRSpec Initial Data Release for the Hubble Ultra Deep Field: Redshifts and Line Fluxes of Distant Galaxies from the Deepest JWST Cycle 1 NIRSpec Multi-Object Spectroscopy
• RUBIES: Evolved Stellar Populations with Extended Formation Histories at $z\sim 7-8$ in Candidate Massive Galaxies Identified with JWST/NIRSpec
• The broad emission-line region: the confluence of the outer accretion disc with the inner edge of the dusty torus
• Double-peaked profiles: ubiquitous signatures of disks in the Broad Emission Lines of Active Galactic Nuclei
• RUBIES: a complete census of the bright and red distant Universe with JWST/NIRSpec
• The JWST-PRIMAL Legacy Survey. A JWST/NIRSpec reference sample for the physical properties and Lyman-$\alpha$ absorption and emission of $\sim 500$ galaxies at $z=5.5-13.4$
• A dormant, overmassive black hole in the early Universe
• A dusty compact object bridging galaxies and quasars at cosmic dawn
• Deciphering the JWST spectrum of a 'little red dot' at $z\sim 4.53$: An obscured AGN and its star-forming host
• JADES -- The Rosetta Stone of JWST-discovered AGN: deciphering the intriguing nature of early AGN
• The shape of broad-line profiles in AGN
• First high energy observations of Narrow Line Seyfert 1s with INTEGRAL/IBIS
• A remarkable Ruby: Absorption in dense gas, rather than evolved stars, drives the extreme Balmer break of a Little Red Dot at $z=3.5$
• A local baseline of the black hole mass scaling relations for active galaxies. IV. Correlations between $M_{\mathrm{BH}}$ and host galaxy $\sigma$, stellar mass, and luminosity
• Spherical symmetry in the kilonova AT2017gfo/GW170817
• Helium in natal HII regions: the origin of the X-ray absorption in gamma-ray burst afterglows
• Evidence for an intermediate line region in AGN's inner torus region and its evolution from narrow to broad line Seyfert I galaxies
• Electron scattering wings on lines in interacting supernovae
• Evidence for Line Broadening by Electron Scattering in the Broad Line Region of NGC 4395
• RUBIES: A Spectroscopic Census of Little Red Dots; All V-Shaped Point Sources Have Broad Lines
• The flux ratio of the [N II]$\lambda \lambda$ 6548, 6583 Å lines in sample of Active Galactic Nuclei Type 2
• 21 Balmer Jump Street: The Nebular Continuum at High Redshift and Implications for the Bright Galaxy Problem, UV Continuum Slopes, and Early Stellar Populations
• Measuring the Hubble constant with kilonovae using the Expanding Photosphere Method
• Another piece to the puzzle: radio detection of a JWST detected AGN candidate
• The radio properties of the JWST-discovered AGN
• Spectroscopic AGN survey at $z$ $\sim$ 2 with NTT/SOFI for GRAVITY+ observations

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• A direct black hole mass measurement in a Little Red Dot at the Epoch of Reionization
• Spectral Uniformity of Little Red Dots: A Natural Outcome of Coevolving Seed Black Holes and Nascent Starbursts
• Connecting the Dots: UV-Bright Companions of Little Red Dots as Lyman-Werner Sources Enabling Direct Collapse Black Hole Formation
• Primordial Black-Hole-Based Pathways to Little Red Dots
• JADES Dark Horse: demonstrating high-multiplex observations with JWST/NIRSpec dense-shutter spectroscopy in the JADES Origins Field
• The Cliff: A Metal-Poor Little Red Dot Hosting an Overmassive Black Hole at $z=3.55$
• The X-ray weakness of Little Red Dots and JWST-selected AGN: comparison with local AGN in different accretion regimes
• Toward Black Hole Stars: supermassive black hole growth in nuclear clusters via stellar-object and gas accretion
• Discovery of low-redshift analogues to "Little Red Dots" in DESI: A later evolutionary stage of compact LRDs?
• Massive black holes in the first billion years with JWST
• Mass and Spin Growth of Very Massive Stars in Star Clusters Potentially Associated with Little Red Dots
• Smoluchowski Coagulation Equation and the Evolution of Primordial Black Hole Clusters
• The Structure and Evolution of LRDs: Insights from JWST NIRSpec Medium and High Resolution Spectroscopy at $z\sim 4$
• Born in the Dark: The Catastrophic Collapse of Fuzzy Dark Matter Solitons as the Origin of Little Red Dots
• Rapid sinking and efficient mergers of supermassive black holes in compact high-redshift galaxies
• A Comprehensive JWST/NIRSpec Census of Broad-line Active Galactic Nuclei: Faint, Low-mass Accretors and a Population of Little Red Dots
• (Re)solving the Complex Multiscale Morphology and V-shaped Spectral Energy Distribution of a Newly Discovered Strongly Lensed Little Red Dot in A383