Active galactic nuclei-heated dust revealed in "little red dots"

Abstract

Little red dots (LRDs) are a puzzling population of extragalactic sources whose origin is highly debated. In this {work}, we performed a comprehensive stacking analysis of NIRCam, MIRI, and ALMA images of a large and homogeneously selected sample of LRDs from multiple JWST Legacy fields. We report clear evidence of hot-dust emission in the median stacked spectral energy distribution (SED) that features a rising near-infrared continuum up to rest-frame ${\lambda }_{\mathrm{rest}}$$\sim$ 3$\mu$m, which is best explained by a standard dusty active galactic nucleus (AGN) structure. Although LRDs are likely to be a heterogeneous population, our findings suggest that most ($\gtrsim$50 %) LRDs show AGN-heated dust emission, regardless of whether the optical and ultraviolet (UV) continua are stellar or AGN-dominated. In either case, the best-fit dusty-AGN SED, combined with the lack of X-ray detection in the deep Chandra stacks, suggests that Compton-thick ($N_{\mathrm{H}}$$>$3$\times$10${}^{24}$ cm${}^{-2}$) gas obscuration is common, and likely confined within the dust sublimation radius ($R$${}_{\mathrm{sub}}$$\sim$0.1 pc). Therefore, we argue that AGN-heated dust does not directly obscure either the optical-UV continuum or the broad-line region emission, in order to explain the observed blue UV slopes and prominent Balmer features. While a gas-dust displacement is in line with several models, the formation scenario (in-situ or ex-situ) of this pre-enriched hot dust remains unclear.

Published in A&A. 8 pages + Appendix. 4 tables, 6 figures

References in corpus (36)

• Stellar population synthesis at the resolution of 2003
• Galactic Stellar and Substellar Initial Mass Function
• A Simple Model for the Absorption of Starlight by Dust in Galaxies
• CIGALE: a python Code Investigating GALaxy Emission
• Relations Between Central Black Hole Mass and Total Galaxy Stellar Mass in the Local Universe
• The Assembly of the First Massive Black Holes
• A population of red candidate massive galaxies ~600 Myr after the Big Bang
• The Chandra Deep Field-South Survey: 7 Ms Source Catalogs
• CEERS Key Paper I: An Early Look into the First 500 Myr of Galaxy Formation with JWST
• The dust covering factor in active galactic nuclei
• Bolometric luminosities and Eddington ratios of X-ray selected Active Galactic Nuclei in the XMM-COSMOS survey
• Three-dimensional radiative transfer modeling of AGN dusty tori as a clumpy two-phase medium
• A Two-Parameter Model for the Infrared/Submillimeter/Radio Spectral Energy Distributions of Galaxies and AGN
• JADES. The diverse population of infant Black Holes at 4<z<11: merging, tiny, poor, but mighty
• The origins of massive black holes
• JWST CEERS & JADES Active Galaxies at z = 4-7 Violate the Local $M_{\bullet }-M_{\star }$ Relation at $>3\sigma$: Implications for Low-Mass Black Holes and Seeding Models
• An Atlas of Color-selected Quiescent Galaxies at $z>3$ in Public $JWST$ Fields
• The X-Ray to Mid-Infrared Relation of AGN at High Luminosity
• Automated Mining of the ALMA Archive in the COSMOS Field (A3COSMOS): II. Cold Molecular Gas Evolution out to Redshift 6
• 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
• Mildly Super-Eddington Accretion Onto Slowly-Spinning Black Holes Explains the X-Ray Weakness of the Little Red Dots
• RUBIES: JWST/NIRSpec Confirmation of an Infrared-luminous, Broad-line Little Red Dot with an Ionized Outflow
• JADES -- The Rosetta Stone of JWST-discovered AGN: deciphering the intriguing nature of early AGN
• 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${}^3$COSMOS: A census on the molecular gas mass and extent of main-sequence galaxies across cosmic time
• RUBIES: A Spectroscopic Census of Little Red Dots; All V-Shaped Point Sources Have Broad Lines
• No [CII] or dust detection in two Little Red Dots at z${}_{\mathrm{spec}}$ > 7
• Gas outflows in two recently quenched galaxies at z = 4 and 7
• A${}^3$COSMOS and A${}^3$GOODSS: Continuum Source Catalogues and Multi-band Number Counts
• Narrow line AGN selection in CEERS: spectroscopic selection, physical properties, X-ray and radio analysis
• Another piece to the puzzle: radio detection of a JWST detected AGN candidate
• Lonely Little Red Dots: Challenges to the AGN-nature of little red dots through their clustering and spectral energy distributions
• Little Red Dots as Direct-collapse Black Hole Nurseries
• A${}^3$COSMOS: Measuring the cosmic dust-attenuated star formation rate density at $4<z<5$
• A big red dot at cosmic noon

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• Spectral Uniformity of Little Red Dots: A Natural Outcome of Coevolving Seed Black Holes and Nascent Starbursts
• Investigating the Growth of Little Red Dot Descendants at z<4 with the JWST
• Little Red Dots as Hidden Neutrino Sources
• Born in the Dark: The Catastrophic Collapse of Fuzzy Dark Matter Solitons as the Origin of Little Red Dots
• A Comprehensive JWST/NIRSpec Census of Broad-line Active Galactic Nuclei: Faint, Low-mass Accretors and a Population of Little Red Dots
• Massive black holes in the first billion years with JWST