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Here There Be (Dusty) Monsters: High Redshift AGN are Dustier Than Their Hosts

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arxiv 2410.07340 v1 pith:D55DM5QI submitted 2024-10-09 astro-ph.GA

classification astro-ph.GA
keywords broadnarrowalphabetaconsistentattenuationbalmerblue
verification ladder T0 review T1 audit T2 compute T3 formal
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abstract

JWST spectroscopy has discovered a population of $z \gtrsim 3.5$ galaxies with broad Balmer emission lines, and narrow forbidden lines, that are consistent with hosting active galactic nuclei (AGN). Many of these systems, now known as ``little red dots" (LRDs), are compact and have unique colors that are very red in the optical/near-infrared and blue in the ultraviolet. The relative contribution of galaxy starlight and AGN to these systems remains uncertain, especially for the galaxies with unusual blue+red spectral energy distributions. In this work, we use Balmer decrements to measure the independent dust attenuation of the broad and narrow emission-line components of a sample of 29 broad-line AGN identified from three public JWST spectroscopy surveys: CEERS, JADES, and RUBIES. Stacking the narrow components from the spectra of 25 sources with broad H$\rm{\alpha}$ and no broad H$\rm{\beta}$ results in a median narrow H$\rm{\alpha}$/H$\rm{\beta}$ = $2.47^{+0.05}_{-0.05}$ (consistent with $A_{v} = 0$) and broad H$\rm{\alpha}$/H$\rm{\beta}$ $> 8.85$ ($A_{v} > 3.63$). The narrow and broad Balmer decrements imply little-to-no attenuation of the narrow emission lines, which are consistent with being powered by star formation and located on larger physical scales. Meanwhile, the lower limit in broad H$\rm{\alpha}$/H$\rm{\beta}$ decrement, with broad H$\rm{\beta}$ undetected in the stacked spectrum of 25 broad-H$\rm{\alpha}$ AGN, implies significant dust attenuation of the broad-line emitting region that is presumably associated with the central AGN. Our results indicate that these systems, on average, are consistent with heavily dust-attenuated AGN powering the red parts of their SED while their blue UV emission is powered by unattenuated star formation in the host galaxy.

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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. Two Peas in a Pod: The First Confirmed Dual Active Galactic Nucleus within a Green Pea Galaxy System

    astro-ph.GA 2026-07 conditional novelty 7.0 of 10

    A compact Green Pea galaxy system hosts two resolved, simultaneously accreting supermassive black holes — the first confirmed dual AGN in such a galaxy.

  2. Measurements of the z=4-10 X-ray Luminosity Function: the high space density of moderate-luminosity, obscured AGN

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

    A 32-source X-ray sample yields a z=4-10 AGN luminosity function that is up to two orders of magnitude above model extrapolations at z=7-10.

  3. NEXUS: Spectral Variability of Little Red Dots and Blue Active Galactic Nuclei at $2 \lesssim z \lesssim 6$

    astro-ph.GA 2026-08 conditional novelty 6.0 of 10

    Little Red Dots at z=2-6 show less than 4% intrinsic H-alpha variability on 1-3 month rest-frame timescales, a flat white-noise pattern unlike normal AGNs, implying different broad-line production.

  4. An (in)complete NIRSpec census of Balmer absorption in Type 1 AGN -- radiation-driven outflows in little red dots, quasars and variable stars

    astro-ph.GA 2026-07 conditional novelty 6.0 of 10

    About 44% of little red dots have hydrogen-alpha absorption from outflowing gas, implying radiatively driven outflows rather than static atmospheres.

  5. Little Red Dots are Tidal Disruption Events in Runaway-Collapsing Clusters

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

    Little Red Dots may be tidal disruption events in runaway-collapsing clusters that form intermediate-mass black hole seeds.

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