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No [CII] or dust detection in two Little Red Dots at z$_{\rm spec}$ > 7
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abstract
Little Red Dots (LRDs) are compact, point-like sources characterized by their red color and broad Balmer lines, which have been debated to be either dominated by active galactic nuclei (AGN) or dusty star-forming galaxies (DSFGs). Here we report two LRDs (ID9094 and ID2756) at z$_{\rm spec}$>7, recently discovered in the JWST FRESCO GOODS-North field. Both satisfy the "v-shape" colors and compactness criteria for LRDs and are identified as Type-I AGN candidates based on their broad H$\beta$ emission lines (full width at half maximum: 2280$\pm$490 km/s for ID9094 and 1070$\pm$240 km/s for ID2756) and narrow [OI] lines ($\sim$ 300-400 km/s). To investigate their nature, we conduct deep NOEMA follow-up observations targeting the [CII] 158${\rm \mu m}$ emission line and the 1.3 mm dust continuum. We do not detect [CII] or 1.3 mm continuum emission for either source. Notably, in the scenario that the two LRDs were DSFGs, we would expect significant detections: $>16\sigma$ for [CII] and $>3\sigma$ for the 1.3 mm continuum of ID9094, and $>5\sigma$ for [CII] of ID2756. Using the 3$\sigma$ upper limits of [CII] and 1.3 mm, we perform two analyses: (1) UV-to-FIR spectral energy distribution (SED) fitting with and without AGN components, and (2) comparison of their properties with the L$_{[CII]}$-SFR$_{tot}$ empirical relation. Both analyses are consistent with a scenario where AGN activity may contribute to the observed properties, though a dusty star-forming origin cannot be fully ruled out. Our results highlight the importance of far-infrared observations for studying LRDs, a regime that remains largely unexplored.
Forward citations
Cited by 10 Pith papers
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Little Red Dots as Hidden Neutrino Sources
Little Red Dots can contribute ~30% of the diffuse neutrino background at TeV-sub-PeV energies through photomeson production in black hole envelopes, with modified flavor ratios at higher energies.
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What you see is what you get: empirically measured bolometric luminosities of Little Red Dots
Directly integrating the observed spectra of two Little Red Dots shows the bolometric luminosity is dominated by rest-frame optical light, lowering implied black hole masses to about 10^5 to 10^7 solar masses.
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Dust in the Average Galaxy: Attenuation, Emission, and Opacity from 0<z<7
UV/optical attenuation underpredicts IR luminosity by 3-10x across 0<z<7 while κ_UV/κ_FIR falls by over an order of magnitude, pointing to evolving dust grain properties in average galaxies.
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Reduced Incidence of Little Red Dots at z < 3 from Number Density and Halo Mass Evolution
LRDs transition from underdense low-halo-mass environments at z>4 to typical galaxy conditions by z~3.5, with halo growth leading to larger sizes and SED changes that explain their disappearance at lower redshifts.
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Reduced Incidence of Little Red Dots at z < 3 from Number Density and Halo Mass Evolution
Little red dots shift from underdense, low-halo-mass environments at z>4 to ordinary galaxy environments by z~3.5, explaining their declining abundance at z<3.
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Investigating Little Red Dots with UV Excess: Are They the High-Redshift Siblings of Blue Hot DOGs?
Little Red Dots are not the high-redshift relatives of Blue-excess Hot DOGs; they have less dust obscuration, little hot dust, and likely a different power source.
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A "Black Hole Star" Reveals the Remarkable Gas-Enshrouded Hearts of the Little Red Dots
A source 660 million years after the Big Bang is interpreted as a black hole star with a dust-free dense gas atmosphere, implying Little Red Dots have black hole masses overestimated by orders of magnitude.
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Learning the Universe at High Redshifts: Impact of Accretion Modeling on Early Black Hole Growth
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.
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Compact, AGN-hosting Dwarf Galaxies with "Little Red Dots"-like SEDs in the Local Universe
Local compact AGN-hosting dwarf galaxies with V-shaped SEDs are more evolved than high-redshift Little Red Dots, indicating distinct formation pathways.
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Little Red reionization factories
LRDs may drive cosmic reionization: tidal fields are said to funnel intergalactic hydrogen into colliding streams at LRD sites, igniting starbursts that ionize the gas.
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