The VMC Survey. XXV. The 3D structure of the Small Magellanic Cloud from Classical Cepheids

TL;DR

This study uses near-infrared photometry of Classical Cepheids in the Small Magellanic Cloud to map its 3D structure, revealing a heavily elongated shape and supporting models of recent interactions between the Magellanic Clouds.

Contribution

It provides the first detailed 3D distribution of CCs in the SMC using multi-band light curves, offering new insights into the galaxy's structure and interaction history.

Findings

The SMC's CCs are distributed in a heavily elongated 3D shape over 25-30 kpc.

The age distribution of CCs is bimodal with peaks at 120 and 220 Myr.

The spatial distribution of young and old CCs differs significantly.

Abstract

The "VISTA near-infrared YJKs survey of the Magellanic System" (VMC) is collecting deep Ks-band time-series photometry of pulsating stars hosted by the two Magellanic Clouds and their connecting Bridge. Here we present YJKs light curves for a sample of 717 Small Magellanic Cloud (SMC) Classical Cepheids (CCs). These data, complemented with our previous results and V magnitude from literature, allowed us to construct a variety of period-luminosity and period-Wesenheit relationships, valid for Fundamental, First and Second Overtone pulsators. These relations provide accurate individual distances to CCs in the SMC over an area of more than 40 sq. deg. Adopting literature relations, we estimated ages and metallicities for the majority of the investigated pulsators, finding that: i) the age distribution is bimodal, with two peaks at 120+-10 and 220+-10 Myr; ii) the more metal-rich CCs appear to be located closer to the centre of the galaxy. Our results show that the three-dimensional distribution of the CCs in the SMC, is not planar but heavily elongated for more than 25-30 kpc approximately in the east/north-east towards south-west direction. The young and old CCs in the SMC show a different geometric distribution. Our data support the current theoretical scenario predicting a close encounter or a direct collision between the Clouds some 200 Myr ago and confirm the presence of a Counter-Bridge predicted by some models. The high precision three-dimensional distribution of young stars presented in this paper provides a new testbed for future models exploring the formation and evolution of the Magellanic System.