JADES: Rest-frame UV-to-NIR Size Evolution of Massive Quiescent Galaxies from Redshift z = 5 to z = 0.5

We present the UV-to-NIR size evolution of a sample of $161$ quiescent galaxies (QGs) with $M_{\ast} > 10^{10}\ M_{\odot}$ over $0.5 < z < 5$ . With deep multi-band NIRCam images in GOODS-South from JADES, we measure the effective radii ($R_{e}$ ) of the galaxies at rest-frame $0.3$ , $0.5$ and $1\ \mu\mathrm{m}$ . On average, QGs are $45\%$ ($15\%$ ) more compact at rest-frame $1\ \mu\mathrm{m}$ than they are at $0.3\ \mu\mathrm{m}$ ($0.5\ \mu\mathrm{m}$ ). Regardless of wavelengths, the $R_{e}$ of QGs strongly evolves with redshift, and this evolution depends on stellar mass. For lower-mass QGs with $M_{\ast} = 10^{10.0}-10^{10.6}\ M_{\odot}$ , the evolution follows $R_{e} \sim (1 + z)^{-1.1}$ , whereas it becomes steeper, following $R_{e} \sim (1 + z)^{-1.7}$ , for higher-mass QGs with $M_{\ast} > 10^{10.6}\ M_{\odot}$ . To constrain the physical mechanisms driving the apparent size evolution, we study the relationship between $R_{e}$ and the formation redshift ($z_{\mathrm{form}}$ ) of QGs. For lower-mass QGs, this relationship is broadly consistent with $R_{e} \sim (1 + z_{\mathrm{form}})^{-1}$ , in line with the expectation of the progenitor effect. For higher-mass QGs, the relationship between $R_{e}$ and $z_{\mathrm{form}}$ depends on stellar age. Older QGs have a steeper relationship between $R_{e}$ and $z_{\mathrm{form}}$ than that expected from the progenitor effect alone, suggesting that mergers and/or post-quenching continuous gas accretion drive additional size growth in very massive systems. We find that the $z > 3$ and $z_{\mathrm{form}}$ QGs in our sample are very compact, with mass surface densities $\Sigma_{e} \geq 10^{10}\ M_{\odot}/\mathrm{kpc}^{2}$ and $z_{\mathrm{form}}$ , and their $R_{e}$ are possibly even smaller than anticipated from the size evolution measured for lower-redshift QGs. Finally, we take a close look at the structure of GS-9209, one of the earliest confirmed massive QGs at $z_{\mathrm{spec}} \sim 4.7$ . From UV to NIR, GS-9209 becomes increasingly compact, and its light profile becomes more spheroidal, showing that the color gradient is already present in this earliest massive QG.

eprint arXiv:2401.00934