We review the recent theoretical and observational developments concerning the interaction of the Large Magellanic Cloud (LMC) with the Milky Way and its neighbourhood. An emerging picture is that the LMC is a fairly massive companion (10-20% of the Milky Way mass) and just passed the pericentre of its orbit, likely for the first time. The gravitational perturbation caused by the LMC is manifested at different levels. The most immediate effect is the deflection of orbits of stars, stellar streams or satellite galaxies passing in the vicinity of the LMC. Less well known but equally important is the displacement (reflex motion) of central regions of the Milky Way about the centre of mass of both galaxies. Since the Milky Way is not a rigid body, this displacement varies with the distance from the LMC, and as a result, the Galaxy is deformed and its outer regions (beyond a few tens kpc) acquire a net velocity with respect to its centre. These phenomena need to be taken into account at the level of precision warranted by current and future observational data, and improvements on the modelling side are also necessary for an adequate interpretation of these data.
Recent measurements suggest that the Large Magellanic Cloud (LMC) may weigh as much as 25\% of the Milky Way. In this work we explore how such a large satellite affects mass estimates of the Milky Way based on equilibrium modelling of the stellar halo or other tracers. In particular, we show that if the LMC is ignored, the Milky Way mass is overestimated by as much as 50\%. This bias is due to the bulk motion in the outskirts of the Galaxy's halo and can be, at least in part, accounted for with a simple modification to the equilibrium modelling. Finally, we show that the LMC has a substantial …
It has recently been shown that the Large Magellanic Cloud (LMC) has a substantial effect on the Milky Way's stellar halo and stellar streams. Here, we explore how deformations of the Milky Way and LMC's dark matter haloes affect stellar streams, and whether these effects are observable. In particular, we focus on the Orphan-Chenab (OC) stream which passes particularly close to the LMC, and spans a large portion of the Milky Way's halo. We represent the Milky Way--LMC system using basis function expansions that capture their evolution in an $N$-body simulation. We present the properties of thi…
The ongoing interaction between the Milky Way (MW) and its largest satellite - the Large Magellanic Cloud (LMC) - creates a significant perturbation in the distribution and kinematics of distant halo stars, globular clusters and satellite galaxies, and leads to biases in MW mass estimates from these tracer populations. We present a method for compensating these perturbations for any choice of MW potential by computing the past trajectory of LMC and MW and then integrating the orbits of tracer objects back in time until the influence of the LMC is negligible, at which point the equilibrium appr…
Motivated by the recent discovery of several dwarfs near the Large Magellanic Cloud (LMC), we study the accretion of massive satellites onto Milky Way (MW)/M31-like halos using the ELVIS suite of N-body simulations. We identify 25 surviving LMC-mass subhalos, and investigate the lower-mass satellites that were associated with these subhalos before they fell into the MW/M31 halos. Typically, 7% of the overall z=0 satellite population of MW/M31 halos were in a surviving LMC-group before falling into the MW/M31 halo. This fraction can vary between 1% and 25%, being higher for groups with higher m…
We assemble a catalogue of candidate Sagittarius stream members with 5d and 6d phase-space information, using astrometric data from Gaia DR2, distances estimated from RR Lyrae stars, and line-of-sight velocities from various spectroscopic surveys. We find a clear misalignment between the stream track and the direction of the reflex-corrected proper motions in the leading arm of the stream, which we interpret as a signature of a time-dependent perturbation of the gravitational potential. A likely cause of this perturbation is the recent passage of the most massive Milky Way satellite - the Larg…
Motivated by recent studies suggesting that the Large Magellanic Cloud (LMC) could be significantly more massive than previously thought, we explore whether the approximation of an inertial Galactocentric reference frame is still valid in the presence of such a massive LMC. We find that previous estimates of the LMC's orbital period and apocentric distance derived assuming a fixed Milky Way are significantly shortened for models where the Milky Way is allowed to move freely in response to the gravitational pull of the LMC. Holding other parameters fixed, the fraction of models favoring first i…
To explore the origin of high-velocity gas in the direction of the Large Magellanic Cloud (LMC) we analyze absorption lines in the ultraviolet spectrum of a Galactic halo star that is located in front of the LMC at d=9.2 kpc distance. We study the velocity-component structure of low and intermediate metal ions in the spectrum of RXJ0439.8-6809, as obtained with the Cosmic Origins Spectrograph (COS) onboard HST, and measure equivalent widths and column densities for these ions. We supplement our COS data with a Far-Ultraviolet Spectroscopic Explorer spectrum of the nearby LMC star Sk-69 59 and …
We use a distribution function analysis to estimate the mass of the Milky Way out to 100 kpc using a large sample of halo stars. These stars are compiled from the literature, and the vast majority (~98%) have 6D phase-space information. We pay particular attention to systematic effects, such as the dynamical influence of the Large Magellanic Cloud (LMC), and the effect of unrelaxed substructure. The LMC biases the (pre-LMC infall) halo mass estimates towards higher values, while realistic stellar halos from cosmological simulations tend to underestimate the true halo mass. After applying our m…
We study the orbits of ultra-faint dwarf galaxies in the combined presence of the Milky Way and LMC and we find 6 dwarfs which were likely accreted with the LMC (Car 2, Car 3, Hor 1, Hyi 1, Phe 2, Ret 2), in addition to the SMC, representing strong evidence of dwarf galaxy group infall. This procedure depends on the gravitational pull of the LMC, thus allowing us to place a lower bound on the Cloud's mass of $M_{\rm LMC} > 1.24\times10^{11} M_\odot$. This mass estimate is validated by applying the technique to a cosmological zoom-in simulation of a Milky Way-like galaxy with an LMC analogue wh…
We have used \textit{Far Ultraviolet Spectroscopic Explorer (FUSE)} observations of the Large Magellanic Cloud (LMC) to determine the O {\small VI} column densities in the Milky Way (MW) towards 6 LMC lines of sight. The mean column density of O {\small VI} in the MW is found to be log N(O {\small VI})=14.257$_{-0.084}^{+0.096}$. The results confirm the patchiness of O {\small VI} absorption in the MW and the column densities are higher or comparable to the LMC.
Dwarf galaxies provide a unique opportunity for studying the evolution of the Milky Way (MW) and the Local Group as a whole. Analysing the running solar apex based on the kinematics of the MW satellites, we discovered an unexpected behaviour of the dipole term of the radial velocity distribution as a function of the galactocentric distance. The nearby satellites (<100 kpc) have a bulk motion with an amplitude of 140-230 km/s while the more distant ones show an isotropic distribution of the radial velocities. Such strong solar apex variations can not be explained by the net rotation of the sate…
Kinematic Signatures in the Stellar Halo from Cosmological Encounters between the Milky Way and its Clouds
University of Pennsylvania（宾夕法尼亚大学）；Institute for Astronomy, University of Hawai‘i（夏威夷大学天体物理研究所）；University of Washington（华盛顿大学）；Boston University（波士顿大学）；Carnegie Observatories（卡内基观测站）；California Institute of Technology（加州理工学院）
Quantifying the Milky Way, LMC and their interaction using all-sky kinematics of outer halo stars
University College London（伦敦大学学院）；University of Maryland, College Park（马里兰大学帕克分校）；Center for Astrophysics | Harvard & Smithsonian（哈佛-史密森尼天体物理中心）；Flatiron Institute（平坦研究所）
Indications of disequilibrium throughout the Milky Way (MW) highlight the need for compact,flexible, non-parametric descriptions of phase--space distributions of galaxies. We present a new representation of the current Dark Matter (DM) distribution and potential derived from N-body simulations of the Milky Way and Large Magellanic Cloud (LMC) system using Basis Function Expansions (BFEs). We incorporate methods to maximize the physical signal in the representation. As a result, the simulations of $10^8$ DM particles representing the MW--LMC system can be described by 354 coefficients. We find …
In a companion paper by Koposov et al., RR Lyrae from \textit{Gaia} Data Release 2 are used to demonstrate that stars in the Orphan stream have velocity vectors significantly misaligned with the stream track, suggesting that it has received a large gravitational perturbation from a satellite of the Milky Way. We argue that such a mismatch cannot arise due to any realistic static Milky Way potential and then explore the perturbative effects of the Large Magellanic Cloud (LMC). We find that the LMC can produce precisely the observed motion-track mismatch and we therefore use the Orphan stream to…
In the $Λ$CDM model of structure formation galactic haloes build up by accretion of mass and mergers of smaller subunits. The most recent massive merger event experienced by the Milky Way (MW) halo was the accretion of the Large Magellanic Cloud (LMC; which has a stellar mass of $\sim \; 10^9M_\odot$). Recent analyses of galactic stellar data from the \textit{Gaia} satellite have uncovered an earlier massive accretion event, the Gaia-Enceladus-Sausage (GES), which merged with the MW around 10 Gyr ago. Here, we use the EAGLE cosmological hydrodynamics simulation to study properties of simulated…
Stars slingshotted by the supermassive black hole at the Galactic centre will escape the Milky Way so quickly that their trajectories will be almost straight lines. Previous works have shown how these `hypervelocity stars' are subsequently deflected by the gravitational field of the Milky Way and the Large Magellanic Cloud (LMC), but have neglected to account for the reflex motion of the Milky Way in response to the fly by of the LMC. A consequence of this motion is that the hypervelocity stars we see on the outskirts of the Milky Way today were ejected from where the Milky Way centre was hund…
Gravitational interactions between the Large Magellanic Cloud (LMC) and the stellar and dark matter halo of the Milky Way are expected to give rise to disequilibrium phenomena in the outer Milky Way. A local wake is predicted to trail the orbit of the LMC, while a large-scale over-density is predicted to exist across a large area of the northern Galactic hemisphere. Here we present the detection of both the local wake and Northern over-density (hereafter the "collective response") in an all-sky star map of the Galaxy based on 1301 stars at 60<R_gal<100 kpc. The location of the wake is in good …
We present a proper motion investigation of a sample of Be star candidates towards the Magellanic Clouds, which has resulted in the identification of separate populations, in the Galactic foreground and in the Magellanic background. Be stars are broadly speaking B-type stars that have shown emission lines in their spectra. In this work, we studied a sample of 2446 and 1019 Be star candidates towards the LMC and SMC respectively, taken from the literature and proposed as possible Be stars due to their variability behaviour in the OGLE-II I band. JHKs magnitudes from the IRSF catalog and proper …
Modeling the recent interactions between the Magellanic Clouds and Milky Way
Montana State University（蒙大拿州立大学）；Center for Computational Astrophysics, Flatiron Institute（计算天体物理中心，富尔顿研究所）；University of Lancashire（兰开夏大学）；Queen’s University（女王大学）
This paper explores the effect of the LMC on the mass estimates obtained from the timing argument. We show that accounting for the presence of the LMC systematically lowers the Local Group mass ($M_{\rm LG}$) derived from the relative motion of the Milky Way--Andromeda pair. Motivated by this result we apply a Bayesian technique devised by Peñarrubia et al. (2014) to simultaneously fit (i) distances and velocities of galaxies within 3~Mpc and (ii) the relative motion between the Milky Way and Andromeda derived from HST observations, with the LMC mass ($M_{\rm LMC}$) as a free parameter. Our an…
Recent observations have constrained the orbit and structure of the Large Magellanic Cloud (LMC), implying a well-constrained pericentric passage about the Milky Way (MW) ~ 50 Myr ago. In this scenario, the LMC's gaseous disk has recently experienced maximal ram pressure stripping, suggesting the current extent of its HI disk directly probes the medium in which it is moving. From the observed stellar and HI distributions of the system we find evidence of a truncated gas profile along the windward ``leading edge' of the LMC disk, despite a far more extended stellar component. We explore the imp…
Using action-based distribution function for the dynamical model of the Milky Way we have estimated its total mass and its density profile. Constraints are coming from the globular cluster proper motions from Gaia EDR3, from the rotation curve based on Gaia DR2 data, and from the vertical force data. We use Bayesian Markov chain Monte Carlo method to explore the parameters, for which the globular cluster distribution function and the Galactic potential are fully constrained. Numerical simulations are used to study the uncertainties on the potential constraint if considering a possible massive …
Observational work have shown that the two brightest satellite galaxies of the Milky Way (MW), the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC), are rare amongst MW analogues. It is then interesting to know whether the presence of massive satellite has any effect on the whole satellite population in MW analogues. In this article, we investigate this problem using a semi-analytical model combined with the Millennium-II Simulation. MW-analogous galaxies are defined to have similar stellar mass or dark matter halo mass to the MW. We find that, in the first case, the halo mass…
We present results of the first dynamical stream fits to the recently discovered Tucana III stream. These fits assume a fixed Milky Way potential and give proper motion predictions, which can be tested with the upcoming Gaia Data Release 2. These fits reveal that Tucana III is on an eccentric orbit around the Milky Way and, more interestingly, that Tucana III passed within 15 kpc of the Large Magellanic Cloud (LMC) approximately 75 Myr ago. Given this close passage, we fit the Tucana III stream in the combined presence of the Milky Way and the LMC. We find that the predicted proper motions dep…
We present N-body and hydrodynamical simulations of the response of the Milky Way's baryonic disc to the presence of the Large Magellanic Cloud during a first infall scenario. For a fiducial galactic model reproducing the gross properties of the Galaxy, we explore a set of six initial conditions for the LMC of varying mass which all evolve to fit the measured constraints on its current position and velocity with respect to the Galactic Center. We find that the LMC can produce strong disturbances - warping of the stellar and gaseous discs - in the Galaxy, without violating constraints from the …
The Milky Way - Large Magellanic Cloud Interaction with Simulation Based Inference
University College London（伦敦大学学院）；Center for Computational Astrophysics, Flatiron Institute（计算天体物理学中心，平顿研究所）；Center for Astrophysics | Harvard & Smithsonian（哈佛-史密森尼天体物理中心）；University of Maryland, College Park（马里兰大学帕克分校）；The Ohio State University（俄亥俄州立大学）
LMC-induced Perturbations in the Milky Way Halo:I. HaloDance Simulation Suite and Observational Forecasts
Department of Astronomy, The Ohio State University（俄亥俄州立大学天文学系）；Center for Cosmology and AstroParticle Physics (CCAPP), The Ohio State University（俄亥俄州立大学宇宙学与高能粒子物理中心）；National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University（北京师范大学天文与前沿科学研究院）
We predict and compare the distributions and properties of hyper-velocity stars (HVSs) ejected from the centres of the Milky Way (MW) and the Large Magellanic Cloud (LMC). In our model, HVSs are ejected at a constant rate -- equal in both galaxies -- via the Hills mechanism and are propagated in a combined potential, where the LMC orbits the MW on its first infall. By selecting $m>2\, \mathrm{M_\odot}$ HVSs well-separated from the Magellanic Clouds and Galactic midplane, we identify mock HVSs which would stand out from ordinary stars in the stellar halo in future data releases from the Gaia sa…
Given recent developments in our understanding of the Large Magellanic Cloud's (LMC) impact on the Milky Way's (MW) dark matter subhalo population, we compare the signatures of dark matter and baryonic physics on subhalos in MW systems with realistic LMC analogs. In particular, we study the effects of self-interacting dark matter (SIDM), warm dark matter (WDM), and the Galactic disk on the peak maximum circular velocity ($V_{\mathrm{peak}}$) function, radial distribution, and spatial distribution of MW and LMC-associated subhalos using cosmological dark matter-only zoom-in simulations of MW+LM…
Using proper motion measurements from Gaia DR2, we probe the origin of 26 previously known hypervelocity stars (HVSs) around the Milky Way. We find that a significant fraction of these stars have a high probability of originating close to the Milky Way centre, but there is one obvious outlier. HVS3 is highly likely to be coming almost from the centre of the Large Magellanic Cloud (LMC). During its closest approach, $21.1^{+6.1}_{-4.6}$ Myr ago, it had a relative velocity of $870^{+69}_{-66}$ kms$^{-1}$ with respect to the LMC. This large kick velocity is only consistent with the Hills mechanis…
The Magellanic Clouds are often considered as outliers in the satellite system of the Milky Way because they are irregular and gas-rich galaxies. From their large relative motion, they are likely from their first pass near the Milky Way, possibly originating from another region of the Local Group or its outskirts. M31 could have been in a merger stage in its past and we investigate whether or not the Large Magellanic Cloud could have been a tidal dwarf expelled during this event. Such an hypothesis is tested in the frame of present-day measurements and uncertainties of the relative motions of …
We combine Gaia EDR3 astrometry with accurate photometry and utilize a probabilistic mixture model to measure the systemic proper motion of 52 dwarf spheroidal (dSph) satellite galaxies of the Milky Way (MW). For the 46 dSphs with literature line-of-sight velocities we compute orbits in both a MW and a combined MW + Large Magellanic Cloud (LMC) potential and identify Car II, Car III, Hor I, Hyi I, Phx II, and Ret II as likely LMC satellites. 40% of our dSph sample has a >25% change in pericenter and/or apocenter with the MW + LMC potential. For these orbits, we Monte Carlo sample over the obse…
We present an analysis of physical and morphological properties of an interacting pair of dwarf galaxies UGC 4703 located at the vicinity of an isolated Milky-Way (MW) type spiral galaxy NGC 2718. Based on the comparison of physical and morphological properties with that of the Large and Small Magellanic Clouds (LMC and SMC), we report that the UGC 4703 pair-NGC 2718 system is probably an LMC-SMC-MW analogue. Located at a sky projected distance of 81 kpc from NGC 2718, we find that UGC 4703 is clearly interacting with its nearby smaller mass companion UGC 4703B forming a bridge of stellar stre…
We present a 6-D map of the Orphan-Chenab (OC) stream by combining the data from Southern Stellar Stream Spectroscopic Survey ($S^5$) and {\it Gaia}. We reconstruct the proper motion, radial velocity, distance, on-sky track and stellar density along the stream with spline models. The stream has a total luminosity of $M_V=-8.2$ and metallicity of $\mathrm{[Fe/H]}=-1.9$, similar to classical Milky Way (MW) satellites like Draco. The stream shows drastic changes in its physical width varying from 200 pc to 1 kpc, but a constant line of sight velocity dispersion of 5 km/ss. Despite the large appar…
The Large Magellanic Cloud (LMC) is the most luminous satellite galaxy of the Milky Way and owing to its companion, the Small Magellanic Cloud (SMC), represents an excellent laboratory to study the interaction of dwarf galaxies. The aim of this study is to investigate the kinematics of the outer regions of the LMC by using stellar proper motions to understand the impact of interactions, e.g. with the SMC about 250 Myr ago. {We calculate proper motions using multi-epoch $K_\mathrm{s}$-band images from the VISTA survey of the Magellanic Clouds system (VMC). Observations span a time baseline of 2…
The Milky Way Tomography with Subaru Hyper Suprime-Cam: Implications for the past orbit of the Large Magellanic Cloud
Astronomical Institute, Tohoku University（东北大学天文学研究所）；The William H. Miller III, Dept. of Physics & Astronomy, Johns Hopkins University（约翰斯·霍普金斯大学物理与天文系威廉·H·米勒三世中心）
Observations show that the ISM contains sub-structure on scales less than 1 pc, detected in the form of spatial and temporal variations in column densities or optical depth. Despite the number of detections, the nature and ubiquity of the small-scale structure in the ISM is not yet fully understood. We use UV absorption data mainly from FUSE and partly from STIS of six LMC stars (Sk-67°111, LH54-425, Sk-67°107, Sk-67°106, Sk-67°104, and Sk-67°101), all located within 5 arcmin of each other, and analyse the physical properties of the Galactic disc gas in front of the LMC on sub-pc scales. We an…
Reconstructing the orbits of Milky Way dwarf galaxies: A Large Magellanic Cloud perspective
Instituto de Astrofísica de Andalucía, CSIC（安达卢西亚天体物理研究所，西班牙高等科学理事会）；Space Telescope Science Institute（太空望远镜科学研究所）；Center for Astrophysical Sciences, The William H. Miller III Department of Physics & Astronomy, Johns Hopkins University（约翰斯·霍普金斯大学天体物理学中心威廉·H·米勒三世物理与天文系）；Instituto de Astrofísica de Canarias（加那利天体物理研究所）；Departamento de Astrofísica, Universidad de La Laguna（拉帕鲁纳大学天体物理系）；Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences（波兰科学院尼古拉·哥白尼天文学中心）；Institute for Astronomy, University of Edinburgh（爱丁堡大学天体物理研究所）；David A. Dunlap Department of Astronomy & Astrophysics, University of Toronto（多伦多大学大卫·A·邓普克天文与天体物理系）；AURA for the European Space Agency (ESA), Space Telescope Science Institute（欧洲空间局（ESA）AURA机构太空望远镜科学研究所）；Department of Astronomy, Univer（天文学系）
Discovery of the First Five Carbon-Enhanced Metal-Poor Stars in the LMC
University of Pennsylvania（宾夕法尼亚大学）；University of Chicago（芝加哥大学）；Kavli Institute for Cosmological Physics, University of Chicago（芝加哥大学卡弗里宇宙物理学研究所）；NSF-Simons AI Institute for the Sky (SkAI)（NSF-Simons 天空人工智能研究所（SkAI））；Monash University（莫纳什大学）；Flatiron Institute（平坦研究所）；Montana State University（蒙大拿州立大学）；University of Illinois at Urbana-Champaign（伊利诺伊大学厄巴纳-香槟分校）；Universidad Católica del Norte（北方天主教大学）
Bound orbits have traditionally been assigned to the Large and Small Magellanic Clouds (LMC and SMC, respectively) in order to provide a formation scenario for the Magellanic Stream (MS) and its Leading Arm (LA), two prominent neutral hydrogen (HI) features connected to the LMC and SMC. However, Hubble Space Telescope (HST) measurements of the proper motions of the LMC and SMC have challenged the plausibility of bound orbits, causing the origin of the MS to re-emerge as a contested issue. We present a new tidal model in which structures resembling the bifurcated MS and elongated LA are able to…
