SMASHing the LMC: A Tidally Induced Warp in the Outer LMC and a Large-scale Reddening Map

Abstract

We present a study of the three-dimensional (3D) structure of the Large Magellanic Cloud (LMC) using ∼2.2 million red clump (RC) stars selected from the Survey of the MAgellanic Stellar History. To correct for line-of-sight dust extinction, the intrinsic RC color and magnitude and their radial dependence are carefully measured by using internal nearly dust-free regions. These are then used to construct an accurate 2D reddening map (165 deg 2 area with ∼10 resolution) of the LMC disk and the 3D spatial distribution of RC stars. An inclined disk model is fit to the 2D distance map, yielding a best-fit inclination angle i = 25.86 +0.73 −1.39 degrees with random errors of ±0.19 • and line-ofnodes position angle θ = 149.23 +6.43 −8.35 degrees with random errors of ±0.49 • . These angles vary with galactic radius, indicating that the LMC disk is warped and twisted likely due to the repeated tidal interactions with the Small Magellanic Cloud (SMC). For the first time, our data reveal a significant warp in the southwestern part of the outer disk starting at ρ ∼7 • that departs from the defined LMC plane up to ∼4 kpc toward the SMC, suggesting that it originated from a strong interaction with the SMC. In addition, the inner disk encompassing the off-centered bar appears to be tilted up to 5-15 • relative to the rest of the LMC disk. These findings on the outer warp and the tilted bar are consistent with the predictions from the Besla et al. simulation of a recent direct collision with the SMC.

A SkyMapper view of the Large Magellanic Cloud: the dynamics of stellar populations

“…For example, asHelmi et al (2018) suggests, if the dynamical centre were fixed as the photometric centre fromvan der Marel (2001), then the their proper motion would be (1.890, 0.314)mas yr −1 . For Carbon Stars, the best-fitting configuration parameter θ agrees well with other works listed in the table, and i agrees closely with the purely geometric measurement fromInno et al (2016) andChoi et al (2018) .…”

“…For example, in the SMC, the gas outflow found by McClure-Griffiths et al (2018) and the shell of young stars recently studied by Martinez-Delgado et al (2019) are both indicative of possible interactions with the LMC. For the LMC, Choi et al (2018) recently identified an outer warp in the disk, and a tilted bar, using red clump stars, consistent with a close encounter with the SMC (see also, Besla et al 2012;Noël et al 2013;Guglielmo et al 2014;Carrera et al 2017;Zivick et al 2019, etc). Joshi & Panchal (2019) found a common enhancement of the Cepheid population in both the LMC and SMC, suggesting an interaction ∼ 200 Myr ago between the Clouds.…”

“…Additionally, radio observations of the gaseous components of the LMC, and the more extensive Magellanic System, have revealed the signatures of historical LMC-SMC interactions (e.g. Staveley-Smith et al 2003;Brüns et al 2005;Tepper-García et al 2019), events that are E-mail: zwan3791@uni.sydney.edu.au also now known to be encoded in the structure of the peripheral stellar component (Olsen & Salyk 2002;Belokurov et al 2016;Besla et al 2016;Mackey et al 2017;Choi et al 2018;Nidever et al 2018;Mackey et al 2018;Vasiliev 2018). Most recently, identified low-surface brightness stellar arms around the LMC from the panoramic view of RGB stars, further highlighting the results of the LMC-SMC-MW interactions.…”

Revealing the tidal scars of the Small Magellanic Cloud

“…2002 ;Peñarrubia et al 2016;Choi et al 2018;Erkal et al 2019). Proper motion studies show that the LMC's disc has a clockwise rotation in the plane of the sky, suggesting an inner region that is relatively "unperturbed" (van der Marel & Kallivayalil 2014;Gaia Collaboration et al 2016).…”

Empirical Calibration of the Reddening Maps in the Magellanic Clouds

“…The intrinsic (J − K) 0 color was obtained with the star formation history. Choi et al (2018) measured E(g − i) color excess of the red clump stars covering 165 deg 2 of the LMC disk. To obtain the intrinsic (g − i) 0 color of the red clump, they measured color in the outer regions, assuming negligible internal dust contribution in those fields.…”