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1. The All-sky Impact of the LMC on the Milky Way Circumgalactic Medium

   https://doi.org/10.3847/1538-4357/adbf1d  

   Carr, Christopher; Bryan, Greg L; Garavito-Camargo, Nicolás; Besla, Gurtina; Setton, David J; Johnston, Kathryn V; Su, Kung-Yi (April 2025, The Astrophysical Journal)

   Abstract The first infall of the LMC into the Milky Way (MW) represents a large and recent disruption to the MW circumgalactic medium (CGM). In this work, we use idealized, hydrodynamical simulations of an MW-like CGM embedded in a dark matter halo with an infalling LMC-like satellite initialized with its own CGM to understand how the encounter is shaping the global physical and kinematic properties of the MW CGM. First, we find that the LMC drives order-unity enhancements in MW CGM density, temperature, and pressure due to a $\mathcal{M}\approx 2$shock from the supersonic CGM–CGM collision. The resulting shock front extends from the LMC to beyond ∼R_200,MW, amplifying column densities, X-ray brightness, thermal Sunyaev–Zeldovich distortion, and potentially synchrotron emission from cosmic rays over large angular scales across the southern hemisphere. Second, the MW’s reflex motion relative to its outer halo induces a dipole in CGM radial velocities, withv_R ± 30–50 km s⁻¹atR > 50 kpc in the northern and southern hemispheres, respectively, consistent with measurements in the stellar halo. Finally, ram pressure strips most of the LMC’s CGM, leaving ∼10⁸⁻⁹M_⊙warm ionized gas along the past orbit of the LMC, moving at high radial and/or tangential velocities ∼50–100 kpc from the MW. Massive satellites like the LMC leave their mark on the CGM structure of their host galaxies, and signatures of such interactions may be observable in key all-sky tracers of the MW CGM and those of other massive galaxies. 

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2. Observations of a Magellanic Corona

   https://doi.org/10.1038/s41586-022-05090-5  

   Krishnarao, Dhanesh; Fox, Andrew J.; D’Onghia, Elena; Wakker, Bart P.; Cashman, Frances H.; Howk, J. Christopher; Lucchini, Scott; French, David M.; Lehner, Nicolas (September 2022, Nature)

   Abstract The Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC) are the closest massive satellite galaxies of the Milky Way. They are probably on their first passage on an infalling orbit towards our Galaxy 1 and trace the continuing dynamics of the Local Group 2 . Recent measurements of a high mass for the LMC ( M halo  ≈ 10 11.1–11.4   M ⊙ ) 3–6 imply that the LMC should host a Magellanic Corona: a collisionally ionized, warm-hot gaseous halo at the virial temperature (10 5.3–5.5  K) initially extending out to the virial radius (100–130 kiloparsecs (kpc)). Such a corona would have shaped the formation of the Magellanic Stream 7 , a tidal gas structure extending over 200° across the sky 2,8,9 that is bringing in metal-poor gas to the Milky Way 10 . Here we show evidence for this Magellanic Corona with a potential direct detection in highly ionized oxygen (O +5 ) and indirectly by means of triply ionized carbon and silicon, seen in ultraviolet (UV) absorption towards background quasars. We find that the Magellanic Corona is part of a pervasive multiphase Magellanic circumgalactic medium (CGM) seen in many ionization states with a declining projected radial profile out to at least 35 kpc from the LMC and a total ionized CGM mass of log 10 ( M H II,CGM / M ⊙ ) ≈ 9.1 ± 0.2. The evidence for the Magellanic Corona is a crucial step forward in characterizing the Magellanic group and its nested evolution with the Local Group. 

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3. Braving the Storm: Quantifying Disk-wide Ionized Outflows in the Large Magellanic Cloud with ULLYSES

   https://doi.org/10.3847/1538-4357/ad64d2  

   Zheng_郑, Yong_永; Tchernyshyov, Kirill; Olsen, Knut; Choi, Yumi; Bustard, Chad; Roman-Duval, Julia; Zhu, Robert; Di_Teodoro, Enrico_M; Werk, Jessica; Putman, Mary; et al (October 2024, The Astrophysical Journal)

   Abstract The Large Magellanic Cloud (LMC) is home to many Hiiregions, which may lead to significant outflows. We examine the LMC’s multiphase gas (T∼10^4-5K) in Hi, Sii, Siiv, and Civusing 110 stellar sight lines from the Hubble Space Telescope’s Ultraviolet Legacy Library of Young Stars as Essential Standards program. We develop a continuum fitting algorithm based on the concept of Gaussian process regression and identify reliable LMC interstellar absorption overv_helio= 175–375 km s⁻¹. Our analyses show disk-wide ionized outflows in Siivand Civacross the LMC with bulk velocities of ∣v_{out, bulk}∣ ∼ 20–60 km s⁻¹, which indicates that most of the outflowing mass is gravitationally bound. The outflows’ column densities correlate with the LMC’s star formation rate surface densities (Σ_SFR), and the outflows with higher Σ_SFRtend to be more ionized. Considering outflows from both sides of the LMC as traced by Civ, we conservatively estimate a total outflow rate of ${\dot{M}}_{\mathrm{out}}\gtrsim 0.03M_{\odot }{\mathrm{yr}}^{-1}$and a mass-loading factor ofη≳ 0.15. We compare the LMC’s outflows with those detected in starburst galaxies and simulation predictions, and find a universal scaling relation of $\mid v_{\mathrm{out},\mathrm{bulk}}\mid \propto {\mathrm{\Sigma }}_{\mathrm{SFR}}^{0.23}$over a wide range of star-forming conditions (Σ_SFR∼ 10^−4.5–10²M_⊙yr⁻¹kpc⁻²). Lastly, we find that the outflows are corotating with the LMC’s young stellar disk and the velocity field does not seem to be significantly impacted by external forces; we thus speculate on the existence of a bow shock leading the LMC, which may have shielded the outflows from ram pressure as the LMC orbits the Milky Way. 

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4. Response of the LMC’s Bar to a Recent SMC Collision and Implications for the SMC’s Dark Matter Profile

   https://doi.org/10.3847/1538-4357/ade0ae  

   Rathore, Himansh; Besla, Gurtina; Daniel, Kathryne J; Beraldo_e_Silva, Leandro (July 2025, The Astrophysical Journal)

   Abstract The LMC’s stellar bar is offset from the outer disk center, tilted from the disk plane, and does not drive gas inflows. These properties are atypical of bars in gas-rich galaxies, yet the LMC bar’s strength and radius are similar to typical barred galaxies. UsingN-body hydrodynamic simulations, we show that the LMC’s unusual bar is explainable if there was a recent collision (impact parameter ≈2 kpc) between the LMC and SMC. Pre-collision, the simulated bar is centered and coplanar. Post-collision, the simulated bar is offset (≈1.5 kpc) and tilted (≈8 $\stackrel{\text{°}}{.}$6). The simulated bar offset reduces with time, and comparing with the observed offset (≈0.8 kpc) suggests the timing of the true collision to be 150–200 Myr ago. Then, 150 Myr post-collision, the LMC’s bar is centered with its dark matter (DM) halo, whereas the outer disk center is separated from the DM center by ≈1 kpc. The SMC collision produces a tilted-ring structure for the simulated LMC, consistent with observations. Post-collision, the simulated LMC bar’s pattern speed decreases by a factor of 2. We also provide a generalizable framework to quantitatively compare the LMC’s central gas distribution in different LMC–SMC interaction scenarios. We demonstrate that the SMC’s torques on the LMC’s bar during the collision are sufficient to explain the observed bar tilt, provided the SMC’s total mass within 2 kpc was (0.8–2.4) × 10⁹M_⊙. Therefore, the LMC bar’s tilt constrains the SMC’s pre-collision DM profile, and requires the SMC to be a DM-dominated galaxy. 

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5. The Clustering of Orbital Poles Induced by the LMC: Hints for the Origin of Planes of Satellites

   https://doi.org/10.3847/1538-4357/ac2c05  

   Garavito-Camargo, Nicolás; Patel, Ekta; Besla, Gurtina; Price-Whelan, Adrian M.; Gómez, Facundo A.; Laporte, Chervin F.; Johnston, Kathryn V. (December 2021, The Astrophysical Journal)

   Abstract A significant fraction of Milky Way (MW) satellites exhibit phase-space properties consistent with a coherent orbital plane. Using tailored N -body simulations of a spherical MW halo that recently captured a massive (1.8 × 10 11 M ⊙ ) LMC-like satellite, we identify the physical mechanisms that may enhance the clustering of orbital poles of objects orbiting the MW. The LMC deviates the orbital poles of MW dark matter particles from the present-day random distribution. Instead, the orbital poles of particles beyond R ≈ 50 kpc cluster near the present-day orbital pole of the LMC along a sinusoidal pattern across the sky. The density of orbital poles is enhanced near the LMC by a factor δ ρ max = 30% (50%) with respect to underdense regions and δ ρ iso = 15% (30%) relative to the isolated MW simulation (no LMC) between 50 and 150 kpc (150–300 kpc). The clustering appears after the LMC’s pericenter (≈50 Myr ago, 49 kpc) and lasts for at least 1 Gyr. Clustering occurs because of three effects: (1) the LMC shifts the velocity and position of the central density of the MW’s halo and disk; (2) the dark matter dynamical friction wake and collective response induced by the LMC change the kinematics of particles; (3) observations of particles selected within spatial planes suffer from a bias, such that measuring orbital poles in a great circle in the sky enhances the probability of their orbital poles being clustered. This scenario should be ubiquitous in hosts that recently captured a massive satellite (at least ≈1:10 mass ratio), causing the clustering of orbital poles of halo tracers. 

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