| Title: |
Counting Little Red Dots at z < 4 with Ground-based Surveys and Spectroscopic Follow-up |
| Authors: |
Yilun Ma; Jenny E. Greene; David J. Setton; Andy D. Goulding; Marianna Annunziatella; Xiaohui Fan; Vasily Kokorev; Ivo Labbe; Jiaxuan Li; Xiaojing Lin; Danilo Marchesini; Jorryt Matthee; Luke Robbins; Anna Sajina; Marcin Sawicki; O. Grace Telford |
| Source: |
The Astrophysical Journal, Vol 1000, Iss 1, p 59 (2026) |
| Publisher Information: |
IOP Publishing |
| Publication Year: |
2026 |
| Collection: |
Directory of Open Access Journals: DOAJ Articles |
| Subject Terms: |
Active galactic nuclei; Black holes; Galaxy formation; High-redshift galaxies; Astrophysics; QB460-466 |
| Description: |
Little red dots (LRDs) are a population of red, compact objects discovered by JWST at z > 4. At 4 < z < 8, they are roughly 100 times more abundant than UV-selected quasars. However, their number density is uncertain at z < 4 due to the small sky coverage and limited blue wavelength coverage of JWST. We present our ground-based search for LRDs at 2 ≲ z ≲ 4, combining ultradeep Hyper Suprime-Cam photometry and various (near-)infrared surveys within a total area of ∼3.1 deg ^2 . We find that for LRDs with M _5500 < −22.5, their number density declines from ∼10 ^−4.5 cMpc ^−3 at z > 4 to ∼10 ^−5.3 cMpc ^−3 at 2.7 < z < 3.7 and ∼10 ^−5.7 cMpc ^−3 at 1.7 < z < 2.7. We also present the Magellan/FIRE spectrum of our first followed-up candidate, DEEP23-z2LRD1 at z _spec = 2.26, as a proof of concept for our sample selection. Similar to high-redshift LRDs, the spectrum of DEEP23-z2LRD1 exhibits broad H α emission with FWHM ≈ 2400 km s ^−1 and with nearly symmetric narrow H α absorption. Additionally, DEEP23-z2LRD1 has extremely narrow [O iii ] lines with FWHM ≈ 140 km s ^−1 , suggesting the presence of an accreting black hole in a low-mass host galaxy. Limited by the angular resolution of ground-based surveys, we emphasize that spectroscopic follow-ups are required to characterize the contamination fraction of this sample and pin down LRD number density at z < 4. |
| Document Type: |
article in journal/newspaper |
| Language: |
English |
| Relation: |
https://doi.org/10.3847/1538-4357/ae4596; https://doaj.org/toc/1538-4357; https://doaj.org/article/58594e06ee324b30a6c8b3f7f9902fac |
| DOI: |
10.3847/1538-4357/ae4596 |
| Availability: |
https://doi.org/10.3847/1538-4357/ae4596; https://doaj.org/article/58594e06ee324b30a6c8b3f7f9902fac |
| Accession Number: |
edsbas.5C1500A0 |
| Database: |
BASE |