Star clusters as tracers of interactions in Stephan's Quintet (Hickson Compact Group 92)

Stephan's Quintet (SQ; also known as Hickson Compact Group 92) is a compact group of galaxies that exhibits numerous signs of interactions between its members. Using high-resolution (004 per pixel) images of SQ in B ₄₃₈, V ₆₀₆, and I ₈₁₄ bands from the Early Release Science project obtained with the Wide Field Camera 3 on the Hubble Space Telescope, we identify 496star cluster candidates (SCCs), located throughout the galaxies themselves as well as in intergalactic regions. Our photometry goes 2mag deeper and covers an additional three regions, the Old Tail, NGC7317, and the southern debris region (SDR), compared to previous work. Through comparison of the B ₄₃₈ - V ₆₀₆ and V ₆₀₆ - I ₈₁₄ colors of the SCCs with simple stellar population synthesis models, we are able to constrain cluster ages. In particular, the most massive galaxy of SQ, NGC7319, exhibits continuous star formation throughout its history, although at a lower rate over the past few tens ofMyr. NGC7318 A/B and the northern star burst region both show ongoing active star formation; there are a number of star clusters that are younger than 10Myr. NGC7318 A/B also features a peculiar gap in the color distribution of the star clusters that can be used to date the onset of the recent burst. The majority of the SCCs detected in the Young Tail were formed 150-200Myr ago, whereas the tight distribution of star cluster colors in the Old Tail allows us to constrain its age of formation to 400Myr ago. The star clusters in the SDR are seemingly divided into two groups with ages of 50 and 500Myr, and virtually all of the SCCs detected in NGC7317 are over 2Gyr old. Based on these ages, we estimate time intervals for the interactions between SQ members that triggered the massive star cluster formation.