Depth estimation of the Large and Small Magellanic Clouds

TL;DR

This study estimates the three-dimensional structure of the Large and Small Magellanic Clouds using red clump stars, revealing their depth profiles, variations, and possible bulge and halo features.

Contribution

It provides detailed depth measurements of the Magellanic Clouds' structures using photometric data and accounts for various effects, offering new insights into their three-dimensional geometry.

Findings

LMC bar is flared with an average depth of 4.0 kpc.

Northern LMC disk is deeper than the southern disk.

SMC shows increased depth near the optical center, suggesting a bulge.

Abstract

We used the red clump stars from the photometric data of the Optical Gravitational Lensing Experiment(OGLE II) survey and the Magellanic Cloud Photometric Survey (MCPS) for both the Clouds to estimate the depth.The observed dispersion in the magnitude and colour distribution of red clump stars is used to estimate the depth, after correcting for population effects, internal reddening within the Clouds and photometric errors.The observed dispersion due to the line of sight depth ranges from 0.023 mag to 0.45 mag (a depth of 500 pc to 10.4 kpc) for LMC and from 0.025 to 0.34 magnitude(a depth of 670 pc to 9.53 kpc).The depth profile of the LMC bar indicates that it is flared.The average depth in the bar region is 4.0$\pm$1.4 kpc. The northern disk is found to have depth(4.17$\pm$0.97 kpc)larger than the southern part of the disk (2.63$\pm$0.8kpc).There is no indication of depth variation between the eastern and the western disk.The average depth for the disk is 3.44$\pm$ 1.16 kpc.In the case of SMC, the bar depth(4.90$\pm$1.23 kpc)and the disk depth (4.23$\pm$1.48kpc)are found to be within the standard deviations.A prominent feature in the SMC is the increase in depth near the optical center.The large dispersions estimated for the LMC bar and the northern disk suggest that the LMC either has large depth and/or different stellar populations in these regions.The halo of the LMC(using RR Lyrae stars)is found to have larger depth compared to the disk/bar,which supports the existence of an inner halo for the LMC.On the other hand, the estimated depths for the halo(RR Lyrae stars)and disk are found to be similar,for the SMC bar region. Thus,increased depth and enhanced stellar as well as HI density near the optical center suggests that the SMC may have a bulge.