NEXUS: A Spectroscopic Census of Broad-line AGNs and Little Red Dots at 3\lesssim z\lesssim 6

2025/05/26 by Ming-Yang Zhuang, Junyao Li, Zhuang, Ming-Yang +13 · 4 citations
Computer Science · Physics and Astronomy · #Advanced Data Storage Technologies #Astronomy and Astrophysical Research #Astrophysics of Galaxies (astro-ph.GA) #Computational Physics and Python Applications #FOS: Physical sciences

paper · pdf · doi:10.48550/arxiv.2505.20393

openalex publication_date 2025/05/26 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28

Abstract

We present a spectroscopic sample of 23 broad-line AGNs (BLAGNs) at 3\lesssim z\lesssim 6 selected using F322W2+F444W NIRCam/WFSS grism spectroscopy of the central 100 \rm arcmin² area of the NEXUS survey. Among these BLAGNs, 15 are classified as Little Red Dots (LRDs) based on their rest-frame UV-optical spectral slopes and compact morphology. The number density of LRDs is ∼ 10^-5 \rm cMpc^-3, with a hint of declining towards the lower end of the probed redshift range. These BLAGNs and LRDs span broad Hα luminosities of ∼ 10^42.2-10^43.7 \rm erg s^-1, black hole masses of ∼ 10^6.3-10^8.4 M_\odot, and Eddington ratios of ∼ 0.1-1 (median value 0.4), though the black hole mass and Eddington ratio estimates carry large systematic uncertainties. Half of the LRDs show strong Balmer absorption, suggesting high-density gas surrounding the line-emitting region. We detect extended (hundreds of parsec) rest-frame UV-optical emission from the host galaxy in the majority of these LRDs, which contributes significantly or even dominantly to their total UV emission. This host emission largely accounts for the peculiar UV upturn of the LRD spectral energy distribution. We also measure the small-scale (\lesssim 1 \rm cMpc) clustering of these BLAGNs and LRDs by cross-correlating with a photometric galaxy sample. Extrapolating the power-law two-point correlation function model to large linear scales, we infer a linear bias of 3.30_-2.04^+2.88 and typical halo masses of a few × 10¹¹ h^-1M_\odot for BLAGNs at the sample median redshift of z∼ 4.5. However, the inferred linear bias and halo masses of LRDs, while formally consistent with those for BLAGNs at ∼ 1.5σ, appear too large to be compatible with their space density, suggesting LRDs may have strong excess clustering on small scales.

Cited by

• Too Quiet for Comfort: Local Little Red Dots Lack Variability over Decades
• Little Red Dots as Globular Clusters in Formation
• NEXUS: A Search for Nuclear Variability with the First Two JWST NIRCam Epochs
• Spectral Uniformity of Little Red Dots: A Natural Outcome of Coevolving Seed Black Holes and Nascent Starbursts

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