No [C
Little Red Dots (LRDs) are compact, point-like sources characterized by their red color and broad Balmer lines; it is a matter of debate whether they are dominated by active galactic nuclei (AGNs) or dusty star-forming galaxies (DSFGs). Here we report two LRDs (ID9094 and ID2756) at zspec > 7 recently discovered in the JWST FRESCO GOODS-North field. Both satisfy the “v-shaped” color and compactness criteria for LRDs and are identified as Type-I AGN candidates based on their broad Hβ emission lines (full width at half maximum: 2280 ± 490 km s−1 for ID9094 and 1070 ± 240 km s−1 for ID2756) and narrow [O <ns0:sc>III</ns0:sc>] lines (≃300 − 400 km s−1). To investigate their nature, we conducted deep NOEMA follow-up observations targeting the [C <ns0:sc>II</ns0:sc>] 158 μm emission line and the 1.3 mm dust continuum. We do not detect [C <ns0:sc>II</ns0:sc>] or 1.3 mm continuum emission for either source. If the two LRDs were DSFGs, we would expect significant detections: > 16σ for [C <ns0:sc>II</ns0:sc>] and > 3σ for the 1.3 mm continuum of ID9094, and > 5σ for the [C <ns0:sc>II</ns0:sc>] of ID2756. Using the 3σ upper limits of [C <ns0:sc>II</ns0:sc>] and 1.3 mm, we performed two analyses: (1) UV-to-far-infrared spectral energy distribution fitting with and without AGN components, and (2) comparison of their properties with the L[C <ns0:sc>II</ns0:sc>]–SFRtot empirical relation. Both analyses are consistent with a scenario in which AGN activity contributes 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.
Publication Details
- Journal
- Springer Link (Chiba Institute of Technology)
- Published
- 2025-08-25
- DOI
- https://doi.org/10.1051/0004-6361/202554361/pdf
- Primary Topic
- Galaxies: Formation, Evolution, Phenomena
- Type
- article
- Field-Weighted Citation Impact
- 0.00