Evolution of 3-dimensional Shape of Passively Evolving and Star-forming Galaxies at $z<1$

Using the HST/ACS $I_{\mathrm{F}814\mathrm{W}}$-band data, we investigated distribution of apparent axial ratios of $\sim 21000$ galaxies with $M_V<-20$ at $0.2<z<1.0$ in the COSMOS field as a function of stellar mass, specific star formation rate (sSFR), and redshift. We statistically estimated intrinsic 3-dimensional shapes of these galaxies by fitting the axial-ratio distribution with triaxial ellipsoid models characterized by face-on (middle-to-long) and edge-on (short-to-long) axial ratios $B\mathrm{/}A$ and $C\mathrm{/}A$. We found that the transition from thin disk to thick spheroid occurs at $\mathrm{\Delta }$MS $\sim -1$ dex, i.e., 10 times lower sSFR than that of the main sequence for galaxies with $M_{\rm star} = 10^{10}$--$10^{11} M_{\odot}$at$0.2<z<1.0$. Furthermore, the intrinsic thickness ($C\mathrm{/}A$) of passively evolving galaxies with $M_{\rm star}=10^{10}$--$10^{11}M_{\odot}$significantlydecreaseswithtimefrom$C/A \sim 0.40$--$0.50$at$z\sim 0.8$to$C/A\sim0.33$--$0.37$at$z\sim0.4$, while those galaxies with $M_{\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{r}}>{10}^{11}{M}_{\odot }$ have $C\mathrm{/}A\sim 0.5$ irrespective of redshift. On the other hand, star-forming galaxies on the main sequence with ${10}^{9.5}$–${10}^{11}{M}_{\odot }$ show no significant evolution in their shape at $0.2<z<1.0$, but their thickness depends on stellar mass;more massive star-forming galaxies tend to have lower $C\mathrm{/}A$ (thinner shape) than low-mass ones. These results suggest that some fraction of star-forming galaxies with a thin disk, which started to appear around $z\sim 1$, quench their star formation without violent morphological change, and these newly added quiescent galaxies with a relatively thin shape cause the significant evolution in the axial-ratio distribution of passively evolving galaxies with $M_{\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{r}}<{10}^{11}{M}_{\odot }$ at $z<1$.