The Carnegie Hubble Program: The Distance and Structure of the SMC as Revealed by Mid-infrared Observations of Cepheids

TL;DR

This study uses mid-infrared observations of Cepheids to precisely measure the distance and three-dimensional structure of the Small Magellanic Cloud, confirming its tilt and elongation.

Contribution

It provides the first precise mid-infrared distance measurement to the SMC and maps its three-dimensional structure using Cepheid variables.

Findings

SMC distance modulus is 18.96 mag, about 62 kpc away.

SMC is tilted and elongated, with a 20 kpc depth difference.

Results agree with previous Cepheid, RR Lyrae, and red giant branch studies.

Abstract

Using Spitzer observations of classical Cepheids we have measured the true average distance modulus of the SMC to be $18.96 \pm 0.01_{stat} \pm 0.03_{sys}$ mag (corresponding to $62 \pm 0.3$ kpc), which is $0.48 \pm 0.01$ mag more distant than the LMC. This is in agreement with previous results from Cepheid observations, as well as with measurements from other indicators such as RR Lyrae stars and the tip of the red giant branch. Utilizing the properties of the mid--infrared Leavitt Law we measured precise distances to individual Cepheids in the SMC, and have confirmed that the galaxy is tilted and elongated such that its eastern side is up to 20 kpc closer than its western side. This is in agreement with the results from red clump stars and dynamical simulations of the Magellanic Clouds and Stream.