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Previous studies suggest that compact young early-type galaxies (ETGs) wereformed by recent mergers. However, it has not yet been revealed whether tidalfeatures that are direct evidence of recent mergers are detected frequentlyaround compact young ETGs. Here, we investigate how the fraction of ETGs havingtidal features ($f_{T}$) depends on age and internal structure (compactness,color gradient, and dust lanes) of ETGs, using 650 ETGs with $M_r\le-19.5$ in$0.015\le z\le0.055$ that are in deep coadded images of the Stripe 82 region ofthe Sloan Digital Sky Survey. We find that tidal features are more frequent inyounger ETGs and more compact ETGs, so that compact young ETGs with ages$\lesssim6$ Gyr have high $f_{T}$ of $\sim0.7$ compared to their less compactor old counterparts with ages $\gtrsim9$ Gyr that have $f_{T}\lesssim0.1$.Among compact young ETGs, those with blue cores have $\sim3$ times higher$f_{T}$ than those with red cores. In addition, ETGs with dust lanes have$\sim4$ times higher $f_{T}$ than those without dust lanes. Our results providedirect evidence that compact young ETGs especially with blue cores and ETGswith dust lanes are involved in recent mergers. Based on our results andseveral additional assumptions, we roughly estimate the typical visible time oftidal features after a merger, which is $\sim3$ Gyr in the depth of the Stripe82 coadded images.

Frequency of Tidal Features Correlates with Age and Internal Structure of Early-type Galaxies