TY - JOUR
T1 - An Investigation into the Selection and Colors of Little Red Dots and Active Galactic Nuclei
AU - Hainline, Kevin N.
AU - Maiolino, Roberto
AU - Juodžbalis, Ignas
AU - Scholtz, Jan
AU - Übler, Hannah
AU - D’Eugenio, Francesco
AU - Helton, Jakob M.
AU - Sun, Yang
AU - Sun, Fengwu
AU - Robertson, Brant
AU - Tacchella, Sandro
AU - Bunker, Andrew J.
AU - Carniani, Stefano
AU - Charlot, Stephane
AU - Curtis-Lake, Emma
AU - Egami, Eiichi
AU - Johnson, Benjamin D.
AU - Lin, Xiaojing
AU - Lyu, Jianwei
AU - Pérez-González, Pablo G.
AU - Rinaldi, Pierluigi
AU - Silcock, Maddie S.
AU - Venturi, Giacomo
AU - Williams, Christina C.
AU - Willmer, Christopher N. A.
AU - Willott, Chris
AU - Zhang, Junyu
AU - Zhu, Yongda
N1 - © 2025. The Author(s). Published by the American Astronomical Society. This is an open access article distributed under the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/
PY - 2025/2/1
Y1 - 2025/2/1
N2 - Recently, a large number of compact sources at z > 4 with blue UV slopes and extremely red rest-frame optical slopes have been found in James Webb Space Telescope (JWST) extragalactic surveys. As a subsample of these sources, commonly called “little red dots” (LRDs), have been spectroscopically observed to host a broad-line active galactic nucleus (AGN), they have been the focus of multiple recent studies in an attempt to understand the origin of their UV and optical emission. Here, we assemble a sample of 123 LRDs from the literature along with spectroscopic and photometric JWST-identified samples of AGNs to compare their colors and spectral slopes. We find that while obscured AGNs at z < 6 have highly dissimilar colors to LRDs, unobscured AGNs at z < 6 span a wide range of colors, with only a subsample showing colors similar to LRDs. At z > 6, the majority of the unobscured AGNs that have been found in these samples are LRDs, but this may be related to the fact that these sources are at large bolometric luminosities. Because LRDs occupy a unique position in galaxy color space, they are more straightforward to target, and the large number of broad-line AGNs that do not have LRD colors and slopes are therefore underrepresented in many spectroscopic surveys because they are more difficult to preselect. Current LRD selection techniques return a large and disparate population, including many sources having 2–5 μm colors impacted by emission-line flux boosting in individual filters.
AB - Recently, a large number of compact sources at z > 4 with blue UV slopes and extremely red rest-frame optical slopes have been found in James Webb Space Telescope (JWST) extragalactic surveys. As a subsample of these sources, commonly called “little red dots” (LRDs), have been spectroscopically observed to host a broad-line active galactic nucleus (AGN), they have been the focus of multiple recent studies in an attempt to understand the origin of their UV and optical emission. Here, we assemble a sample of 123 LRDs from the literature along with spectroscopic and photometric JWST-identified samples of AGNs to compare their colors and spectral slopes. We find that while obscured AGNs at z < 6 have highly dissimilar colors to LRDs, unobscured AGNs at z < 6 span a wide range of colors, with only a subsample showing colors similar to LRDs. At z > 6, the majority of the unobscured AGNs that have been found in these samples are LRDs, but this may be related to the fact that these sources are at large bolometric luminosities. Because LRDs occupy a unique position in galaxy color space, they are more straightforward to target, and the large number of broad-line AGNs that do not have LRD colors and slopes are therefore underrepresented in many spectroscopic surveys because they are more difficult to preselect. Current LRD selection techniques return a large and disparate population, including many sources having 2–5 μm colors impacted by emission-line flux boosting in individual filters.
KW - Active galactic nuclei
KW - James Webb Space Telescope
U2 - 10.3847/1538-4357/ad9920
DO - 10.3847/1538-4357/ad9920
M3 - Article
SN - 0004-637X
VL - 979
SP - 1
EP - 14
JO - The Astrophysical Journal
JF - The Astrophysical Journal
IS - 2
M1 - 138
ER -