(LRDs)$^2$: The Low-ReDshift Little Red Dots Survey. II. DESI DR1 Sample

Xiaojing Lin, Xiaohui Fan, Zheng Cai, Yichen Liu, Fengwu Sun, Fuyan Bian, Mingyu Li, Junjie Mao, Jenny E. Greene, Hanpu Liu, Jiaxuan Li, Weizhe Liu, Yilun Ma, Zechang Sun, Zijian Zhang

First listed 2026-05-20 | Last updated 2026-05-20

Abstract

JWST has revealed a substantial population of "Little Red Dots" (LRDs) at $z>4$, challenging conventional AGN frameworks. However, the low-redshift regime remains largely unexplored. In the second paper of the (LRDs)$^2$ series, we present a systematic selection from DESI DR1 and identify 27 LRDs at $z=0.2-0.9$, yielding a number density lower limit of $7.5 \times 10^{-10}$ cMpc$^{-3}$. We conducted near-IR spectroscopic follow-up observations for 18 of them, revealing their full SED shapes and emission lines. These low-$z$ LRDs share the hallmark properties of their high-$z$ counterparts: compact morphology, V-shaped UV-optical continua, broad Balmer emission with extreme decrements (median H$α$/H$β\sim 16$), frequent Balmer absorption (67%), and blackbody-like optical-to-near-IR continua. All have low metallicity, occupy the same regions in the BPT diagram as high-$z$ LRDs, and have softer ionizing spectra than typical AGNs. The consistency between low-$z$ and high-$z$ LRD properties indicates the same physical processes at work. The correlation between broad-line Balmer luminosity and $L_{5100}$ deviates from that of local type-1 AGNs, limiting the direct application of local BH mass calibrations. Ionized [O III] outflows are ubiquitous (78%). One LRD at $z=0.196$, J1717+3807, shows robust long-term variability in $i$ and WISE bands. The optical-to-NIR continua of LRDs reveal a wide range of temperatures $\sim 2000-4700$ K (peak $0.6-1.5$ $μ$m), with a subset showing cooler and larger envelopes than those at high $z$. Low-$z$ LRDs serve not only as proximate laboratories for probing the nature of LRDs, but also trace the cosmic evolution of this population from the cosmic dawn to the present day.

Short digest

This paper builds the first systematic DESI DR1 sample of low-redshift little red dots, identifying 27 LRDs at z=0.2-0.9 and obtaining near-IR follow-up for 18 to recover their full continua and line properties. The main result is that these objects look strikingly like the JWST high-z population: they are compact, show V-shaped UV-optical SEDs, broad Balmer emission with extreme decrements, frequent Balmer absorption, low metallicity line ratios, and soft ionizing spectra. That makes the low-z sample a nearby laboratory for the same underlying phenomenon, while also revealing ubiquitous ionized [O III] outflows and a broad range of blackbody-like continuum temperatures around 2000-4700 K. A key caution is that the broad-line Balmer luminosity versus L5100 relation differs from local type-1 AGNs, so standard single-epoch black hole mass calibrations may not transfer directly to LRDs.

Key figures to inspect

• Figure 1. Use this as the sample-definition figure. It lays out the full DESI DR1 selection logic step by step, making clear how the authors isolated a clean low-z LRD sample and why the final 27 objects are intended to be directly comparable to JWST-selected LRDs rather than to generic broad-line AGN.
• Figure 5. This is one of the paper's most important result figures because it shows the Hα and Hβ luminosity relations against L5100 for total, broad, and narrow components. The offset from the local type-1 AGN correlations is the observational basis for the paper's warning that standard local single-epoch black hole mass recipes should not be applied naively to LRDs.
• Figure 10. Choose this for the ionizing-spectrum and metallicity argument. The He II/Hβ versus [N II]/Hα comparison places the DESI LRDs in the wider low-z and high-z context and supports the paper's claim that LRDs have low metallicities and softer ionizing continua than typical AGN.
• Figure 14. This figure captures the outflow result that the abstract emphasizes. By comparing the [O III]-based outflow velocities of DESI LRDs with star-forming galaxies and AGN samples, it shows that ionized outflows are common in the population and helps frame whether LRD feedback looks ordinary or unusual.
• Figure 16. Use this as the late-paper synthesis figure for the continuum physics. The H-R-diagram-style presentation of blackbody peak wavelength, luminosity, effective temperature, and implied radius makes the evolutionary point concrete by showing that low-z LRDs span a wide temperature range and include cooler, larger-envelope systems than many high-z examples.