Star clusters in the Magellanic Clouds

II. Age-dating, classification, and spatio-temporal distribution of the SMC clusters^⋆,⋆⋆

¹ Indian Institute of Astrophysics, Koramangala II Block, Bangalore 560034, India
e-mail: prasanta@iiap.res.in, purni@iiap.res.in
² Yonsei University Observatory, 120-749 Seoul, Republic of Korea

Received: 2 November 2017
Accepted: 29 March 2018

Abstract

Aims. We aim to estimate the age and reddening parameters of already identified star clusters within the Small Magellanic Cloud (SMC) in a consistent way using available photometric data, classify them based on their mass and strength, and study their spatiotemporal distribution.

Methods. We have used a semi-automated quantitative method, developed in the first paper of this series (Paper I), to estimate the cluster parameters using the V and I band photometric data from the Optical Gravitational Lensing Experiment (OGLE) III survey.

Results. We estimated parameters of 179 star clusters (17 are newly parameterised) and classified them into four groups. We present an online catalogue of parameters as well as cleaned and isochrone-fitted colour magnitude diagrams of 179 clusters.

We compiled age information of 468 clusters by combining previous studies with our catalogue, to study their spatio-temporal distribution. Most of the clusters located in the southern part of the SMC are in the age range 600 Myr–1.25 Gyr, whereas, the clusters younger than 100 Myr are mostly found in the northern SMC, with the central SMC showing continuous cluster formation. The peak of the cluster age distribution is identified at 130 ± 35 Myr, very similar to the Large Magellanic Cloud (LMC) in Paper I.

Conclusions. We suggest that the burst of cluster formation at 130 Myr is due to the most recent LMC-SMC interaction. 90% of the studied sample is found to have mass < 1700 M_⊙, suggesting that the SMC is dominated by low mass clusters. There is tentative evidence for compact clusters in the LMC when compared to those in the Galaxy and the SMC. A progressive shifting of cluster location from the south to north of the SMC is identified in last ~600 Myr. The details of spatio-temporal distribution of clusters presented in two videos as part of this study can be used as a tool to constrain details of the recent LMC-SMC interactions.