No evolution in the number density of little red dots from cosmic dawn to cosmic noon

Federica Loiacono, Roberto Gilli, Marco Mignoli, Marcella Brusa, Francesco Calura, Marco Chiaberge, Andrea Comastri, Quirino D'Amato, Roberto Decarli, Ivan Delvecchio, Kazushi Iwasawa, Ignas Juodžbalis, Giorgio Lanzuisi, Roberto Maiolino, Stefano Marchesi, Giovanni Mazzolari, Colin Norman, Alessandro Peca, Isabella Prandoni, Matteo Sapori, Matilde Signorini, Paolo Tozzi, Eros Vanzella, Cristian Vignali, Fabio Vito, Gianni Zamorani, Anita Zanella

First listed 2026-06-30 | Last updated 2026-06-29

Abstract

We present our search for little red dots (LRDs) in the "J1030 field", a region of the sky around the $z\sim 6.3$ quasar SDSS J1030+0524, observed by the JWST EIGER program. Over 154 point-like sources selected in a JWST-based photometric catalog, we find five broad line emitters (with $FWHM \gtrsim 1000\ \rm km s^{-1}$) that are red ($F200W - F356W > 0$) and are undetected in the X-rays. We use these sources to derive the bolometric luminosity function (LF) of LRDs at $z = 2.4$ and $z = 4.5$. At $z = 2.4$, the space density of LRDs is only a factor of $\sim 2$ lower than that of all pre-JWST active galactic nuclei (AGNs) with bolometric luminosity $L_{\rm bol} \gtrsim 3 \times 10^{44}\ \rm erg\ s^{-1}$. At $z = 4.5$, our estimate is consistent with those derived for LRDs based on larger areas of the sky. A similar behaviour is observed in the black hole mass function. More importantly, we study the number density of LRDs from cosmic dawn to cosmic noon. We find that there is no significant evolution in the abundance of LRDs with $L_{\rm bol} \gtrsim 3 \times 10^{44}\ \rm erg\ s^{-1}$ at $z > 2$. We speculate that the drop at $z < 4$ seen by other studies is due to their sampling of only the bright-end of the LRDs LF. At cosmic noon, the abundance of LRDs is $n = 3.4^{+5.6}_{-2.4} \times 10^{-5}\ \rm Mpc^{-3}$, which is a factor of $\sim 350$ larger than recent model predictions and is comparable with that of X-ray selected AGNs with similar bolometric luminosity. Our result may imply that, if LRDs are the early, rapid stages of supermassive black hole growth, as suggested by some models, then the formation of black hole seeds can be efficient down to epochs as recent as cosmic noon. Alternatively, LRDs may simply be a high-accretion phase in already mature black holes.

Short digest

Using JWST EIGER data in the J1030 field around SDSS J1030+0524, the authors sift 154 compact sources and identify five X-ray-undetected broad-line emitters with red NIRCam colors, then use them to build the little red dot bolometric luminosity function at z = 2.4 and z = 4.5. The key result is demographic: for LRDs with Lbol >= 3 x 10^44 erg s^-1, the number density shows no significant evolution from cosmic dawn to cosmic noon, with a cosmic-noon abundance of 3.4^{+5.6}_{-2.4} x 10^-5 Mpc^-3. At z = 2.4 this puts LRDs only about a factor of two below the full pre-JWST AGN population at similar luminosities, while the inferred black hole mass function shows the same qualitative behavior. That makes LRDs a major accreting black-hole population well past the earliest epochs, either implying efficient seed formation as late as cosmic noon or that LRDs trace a brief high-accretion phase in already mature black holes.

Key figures to inspect

• Figure 3. Use this as the selection figure. It shows how the J1030 point-like sources separate in color-color and color-magnitude space, where the red compact sources lie relative to stars and X-ray AGNs, and which named broad-line X-ray-silent objects enter the final sample. This is the clearest visual definition of how the paper operationally identifies LRD candidates before the luminosity-function analysis.
• Figure 4. Use this as the spectroscopic evidence figure. The line fits demonstrate the broad emission components that qualify the selected objects as broad-line AGN-like sources, including the z ~ 2.4 and z ~ 4.5 members that feed the demographic measurements. It is important because the paper's abundance claims rest on these compact red sources being genuine broad-line emitters rather than photometric interlopers.
• Figure 5. Use this for the X-ray-silence diagnostic. By placing the sources as lower limits in X-ray bolometric correction versus bolometric luminosity, the figure shows how strongly they depart from the classical AGN expectation and quantifies the extreme X-ray weakness that is part of the LRD phenomenology. This matters because the sample is explicitly defined as X-ray-undetected broad-line sources and the comparison anchors them within the broader JWST-discovered X-ray-silent AGN population.
• Figure 7. Use this as the main luminosity-function result. It compares the J1030-based LRD bolometric luminosity function at z = 2.4 and z = 4.5 with previous LRD estimates and with pre-JWST AGN and UV-selected AGN luminosity functions. This figure carries the paper's core quantitative claim that cosmic-noon LRDs remain abundant and that the z = 4.5 estimate is consistent with larger-area studies.
• Figure 9. Use this as the bottom-line synthesis figure. It tracks the abundance of LRDs above the common bolometric-luminosity threshold as a function of redshift and directly shows the paper's headline conclusion of no significant decline from cosmic dawn to cosmic noon. The comparison to classical AGNs, X-ray-selected AGNs, and model predictions makes this the most important single figure for the paper's evolutionary claim.