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No [CII] or dust detection in two Little Red Dots at z$_{\rm spec}$ > 7

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arxiv 2503.01945 v2 pith:2TYB562V submitted 2025-03-03 astro-ph.GA

classification astro-ph.GA
keywords lrdssigmacontinuumemissionid2756id9094linesanalyses
verification ladder T0 review T1 audit T2 compute T3 formal
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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.

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Cited by 5 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score. Full citation record

  1. What you see is what you get: empirically measured bolometric luminosities of Little Red Dots

    astro-ph.GA 2025-09 conditional novelty 7.0 of 10

    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.

  2. Reduced Incidence of Little Red Dots at z < 3 from Number Density and Halo Mass Evolution

    astro-ph.GA 2026-06 unverdicted novelty 6.0 of 10

    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.

  3. Investigating Little Red Dots with UV Excess: Are They the High-Redshift Siblings of Blue Hot DOGs?

    astro-ph.GA 2025-08 conditional novelty 6.0 of 10

    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.

  4. Beneath the Surface: >85% of z>5.9 QSOs in Massive Host Galaxies are UV-Faint

    astro-ph.GA 2025-06 conditional novelty 6.0 of 10

    More than 85% of z>5.9 quasars in massive host galaxies are UV-faint, indicating that UV-bright quasars are extreme outliers in black hole mass.

  5. Little Red reionization factories

    astro-ph.GA 2025-08 unverdicted novelty 4.0 of 10

    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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