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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. A Physically Motivated Framework to Compare Pair Fractions of Isolated Low- and High-mass Galaxies across Cosmic Time

   https://doi.org/10.3847/1538-4357/ad19d0  

   Chamberlain, Katie; Besla, Gurtina; Patel, Ekta; Rodriguez-Gomez, Vicente; Torrey, Paul; Martin, Garreth; Johnson, Kelsey; Kallivayalil, Nitya; Patton, David; Pearson, Sarah; et al (February 2024, The Astrophysical Journal)

   Abstract Low-mass galaxy pair fractions are understudied, and it is unclear whether low-mass pair fractions evolve in the same way as more massive systems over cosmic time. In the era of JWST, Roman, and Rubin, selecting galaxy pairs in a self-consistent way will be critical to connect observed pair fractions to cosmological merger rates across all mass scales and redshifts. Utilizing the Illustris TNG100 simulation, we create a sample of physically associated low-mass (10⁸<M_*< 5 × 10⁹M_⊙) and high-mass (5 × 10⁹<M_*< 10¹¹M_⊙) pairs betweenz= 0 and 4.2. The low-mass pair fraction increases fromz= 0 to 2.5, while the high-mass pair fraction peaks atz= 0 and is constant or slightly decreasing atz> 1. Atz= 0 the low-mass major (1:4 mass ratio) pair fraction is 4× lower than high-mass pairs, consistent with findings for cosmological merger rates. We show that separation limits that vary with the mass and redshift of the system, such as scaling by the virial radius of the host halo (r_sep< 1R_vir), are critical for recovering pair fraction differences between low-mass and high-mass systems. Alternatively, static physical separation limits applied equivalently to all galaxy pairs do not recover the differences between low- and high-mass pair fractions, even up to separations of 300 kpc. Finally, we place isolated mass analogs of Local Group galaxy pairs, i.e., Milky Way (MW)–M31, MW–LMC, LMC–SMC, in a cosmological context, showing that isolated analogs of LMC–SMC-mass pairs and low-separation (<50 kpc) MW–LMC-mass pairs are 2–3× more common atz≳ 2–3. 

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3. Identifying Dwarfs of MC Analog GalaxiEs (ID-MAGE): The Search for Satellites around Low-mass Hosts

   https://doi.org/10.3847/1538-4357/ade9a4  

   Hunter, Laura Congreve; Mutlu-Pakdİl, Burçİn; Sand, David J; Bennet, Paul; Khim, Donghyeon J; Crnojević, Denija; Doliva-Dolinsky, Amandine; Durodola, Emmanuel; Fielder, Catherine; Goebel-Bain, Rowan; et al (August 2025, The Astrophysical Journal)

   Abstract We present results from Identifying Dwarfs of MC Analog GalaxiEs (ID-MAGE), a survey aimed at identifying and characterizing unresolved satellite galaxies around 35 nearby LMC- and SMC-mass hosts (D = 4−10 Mpc). We use archival DESI Legacy Survey imaging data and perform an extensive search for dwarf satellites, extending out to a radius of 150 kpc (∼R_vir). We identify 355 candidate satellite galaxies, including 264 new discoveries. Extensive tests with injected galaxies demonstrate that the survey is complete down toM_V ∼ −9.0 (assuming the distance of the host) andμ_0,V ∼ 26 mag arcsec⁻²(assuming ann = 1 Sérsic profile). We perform consistent photometry, via Sérsic profile fitting, on all candidates and have initiated a comprehensive follow-up campaign to confirm and characterize candidates. Through a systematic visual inspection campaign, we classify the top candidates as high-likelihood satellites. On average, we find 4.0 ± 1.4 high-likelihood candidate satellites per LMC-mass host and 2.1 ± 0.6 per SMC-mass host, which is within the range predicted by cosmological models. We use this sample to establish upper and lower estimates on the satellite luminosity function of LMC-/SMC-mass galaxies. ID-MAGE nearly triples the number of low-mass galaxies surveyed for satellites with well-characterized completeness limits, providing a unique data set to explore small-scale structure and dwarf galaxy evolution around low-mass hosts in diverse environments. 

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4. Mapping the Distorted Dark Matter Distribution of the LMC–SMC System Prior to Milky Way Infall with Basis Function Expansions

   https://doi.org/10.3847/1538-4357/ae4a9d  

   Foote, Hayden R; Rathore, Himansh; Besla, Gurtina; Garavito-Camargo, Nicolás; Patel, Ekta; Petersen, Michael S; Weinberg, Martin D; Gómez, Facundo A; Laporte, Chervin_F P (April 2026, The Astrophysical Journal)

   Abstract The SMC orbits within the LMC’s dark matter (DM) halo in a ∼1:10 mass-ratio encounter. The LMC–Milky Way (MW) interaction is also ∼1:10, and is expected to perturb the MW’s DM distribution. However, no framework exists to quantify the severity of these perturbations over multiple pericenters and longer periods of time, such as the LMC–SMC interaction history. We construct basis function expansions of a high-resolutionN-body simulation of the Clouds interacting in isolation and analyze their DM distributions at an epoch approximating the time of their infall to the MW. Our goal is to quantify how the Clouds distort each other’s DM distributionswithoutthe MW. The LMC halo’s response to the SMC includes a ∼20 kpc long dynamical friction wake and the displacement of the LMC’s density center during each SMC pericenter, which produces two overdensities in the LMC halo (at ∼60 and ∼100 kpc) at MW infall. The SMC’s tidal radius at infall is just ∼4 kpc, at which point the SMC has lost two-thirds of its initial DM mass to the LMC. The distortions to the Clouds’ halos produce a highly asymmetric acceleration field. Accurate orbit integration in the LMC–SMC system must account for the time-dependent shapes of both halos. The SMC-induced perturbations in the LMC DM halo resemble the MW–LMC system, and persist over multiple SMC pericenters. We conclude that 1:10 satellite–host encounters induce characteristic deformations in both DM halos across host-mass scales, with implications for merger rates and tests of DM models. 

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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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