Investigating the Growth of Little Red Dot Descendants at z<4 with the JWST

Abstract

One of JWST's most remarkable discoveries is a population of compact red galaxies known as Little Red Dots (LRDs). Their existence raises many questions about their nature, origin, and evolution. These galaxies show a steep decline in number density-nearly two orders of magnitude-from $z=6$ to $z=3$. In this study, we explore their potential evolution by identifying candidate descendants in CEERS, assuming a single evolutionary path: the development of a blue star-forming outskirt around the red compact core. Our color-magnitude selection identifies galaxies as red as LRDs at $z<4$, surrounded by young, blue stellar outskirts. Morphological parameters were derived from single Sérsic profile fits; physical properties were obtained from SED fitting using a stellar-only model. These "post-LRD" candidates show LRD-like features with $M_{\ast }\sim 10^{10}{M}_{\odot }$, central densities ($\hat{I}{\pounds }_{\ast }\sim 10^{11}{M}_{\odot }{\text{kpc}}^{-2}$ ), compact sizes, and red rest-frame colors, but with an added extended component. Their number density at $z=3\pm 0.5$ ( $\sim 10^{-4.15}{\text{Mpc}}^{-3}$) matches that of LRDs at $5<z<7$ , supporting a possible evolutionary link. We observe a redshift-dependent increase in outskirts mass fraction and galaxy size-from $\sim 250$ pc at $z=5$ to $\sim 600$ pc at $z=3$-suggesting global stellar growth. Meanwhile, the core remains red and compact, but the V-shaped SED fades as the outskirts grow. These findings support an evolutionary scenario in which LRDs gradually acquire an extended stellar component over cosmic time by cold accretion. This may explain the apparent decline in their observed number density at lower redshift.

Accepted for Publication in A&A