Subhalo abundance matching using progenitor mass at varying redshift: Two modes of stellar mass growth imprinted into the Subaru HSC galaxy clustering

We propose a novel subhalo abundance matching (SHAM) model that uses the virial mass of the main progenitor of each (sub)halo $M_{\mathrm{p}\mathrm{r}\mathrm{o}\mathrm{g}}$ as a proxy of the galaxy stellar mass $M_{\ast }$ at the time of observation. This $M_{\mathrm{p}\mathrm{r}\mathrm{o}\mathrm{g}}$ model predicts the two-point correlation functions depending on the choice of the epoch $z_{\mathrm{p}\mathrm{r}\mathrm{o}\mathrm{g}}$ at which $M_{\mathrm{p}\mathrm{r}\mathrm{o}\mathrm{g}}$ is quoted. With $z_{\mathrm{p}\mathrm{r}\mathrm{o}\mathrm{g}}$ as a fitting parameter, we apply the $M_{\mathrm{p}\mathrm{r}\mathrm{o}\mathrm{g}}$ model to the angular correlation functions measured with varying stellar mass thresholds from $M_{\ast ,\mathrm{l}\mathrm{i}\mathrm{m}}\mathrm{/}(h^{-2}{M}_{\odot })={10}^{11}$ to ${10}^{8.6}$ using a sample of galaxies at $z\simeq 0.4$ from the Subaru Hyper Suprime-Cam survey. The $M_{\mathrm{p}\mathrm{r}\mathrm{o}\mathrm{g}}$ model can reproduce the observations very well over $10h^{-1}\mathrm{k}\mathrm{p}\mathrm{c}\text{–}10h^{-1}\mathrm{M}\mathrm{p}\mathrm{c}$. We find that, for the samples of ${10}^{9.2}\le M_{\ast ,\mathrm{l}\mathrm{i}\mathrm{m}}\mathrm{/}(h^{-2}{M}_{\odot })\le {10}^{10.2}$, the correlation functions predicted by the widely-used $V_{\mathrm{p}\mathrm{e}\mathrm{a}\mathrm{k}}$ model lack amplitudes at $\lesssim 1h^{-1}\mathrm{M}\mathrm{p}\mathrm{c}$, suggesting that $M_{\mathrm{p}\mathrm{r}\mathrm{o}\mathrm{g}}$ is a better proxy of the galaxy stellar mass than conventional $V_{\mathrm{p}\mathrm{e}\mathrm{a}\mathrm{k}}$. The $z_{\mathrm{p}\mathrm{r}\mathrm{o}\mathrm{g}}$ parameter is highest ($z_{\mathrm{p}\mathrm{r}\mathrm{o}\mathrm{g}}\simeq 3$) for intermediate mass galaxies at $M_{\ast }\simeq {10}^{9.9}{h}^{-2}{M}_{\odot }$, and becomes smaller down to $z_{\mathrm{p}\mathrm{r}\mathrm{o}\mathrm{g}}\simeq 1$ for both lower- and higher-mass galaxies. We interpret these trends as reflecting the downsizing in the in-situ star formation in lower-mass galaxies and the larger contribution of the ex-situ stellar mass growth in higher-mass galaxies.