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The change in orbital pole direction of particles in the simulation depends on the specific angular momentum they had initially. Panel (a) shows that particles with smaller initial specific angular momentum h ini show larger changes in the direction of their orbital poles as measured by the angle Δθ pole between their orbital pole in the initial and final simulation snapshot. Also shown are the observed MW dwarfs. Panel (b) shows the distribution of Δθ pole for three specific angular momentum bins. Low-angular-momentum particles (red dotted line) are affected most, while high-angular-momentum particles (blue solid line) show the least change in their orbital pole directions.
Source publication
The reflex motion and distortion of the Milky Way (MW) halo caused by the infall of a massive Large Magellanic Cloud (LMC) has been demonstrated to result in an excess of orbital poles of dark matter halo particles toward the LMC orbital pole. This was suggested to help explain the observed preference of MW satellite galaxies to coorbit along the V...
Contexts in source publication
Context 1
... now investigate how the orbital poles change between the initial and the final simulation snapshot to assess how much the LMC-like infall has affected the orbital direction of each individual particle. Panel (a) of Figure 6 plots the angle between the initial and the final direction of orbital poles, Δθ pole . The vast majority of simulation particles (note the logarithmic color scale) overlap with the region covered by the observed MW dwarfs. ...
Context 2
... is a clear tendency for particles with higher initial specific angular momentum to have smaller changes in their orbital pole direction. Panel (b) of Figure 6 confirms this. Low-angular-momentum particles display an extended tail to high Δθ pole , some reaching as high as Δθ pole = 170° and thus almost flip their orbital direction. ...
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Citations
... M94 (Hartke et al. 2018). Recent mergers could also affect the orbits of the GCs as seen in NGC 1316 (e.g., Richtler et al. 2014), affect the modeling of the Milky Way's dark matter halo using stellar streams (e.g., Lilleengen et al. 2023;Erkal et al. 2019;Shipp et al. 2021) and impact the orbits of satellite galaxies (Pawlowski et al. 2022) Overall, the single tracer fits show that the GCs and dwarfs give mutually consistent results that also agree with the fiducial model, while the PNe strongly differ. As a cross-check of the effect of the PNe on the fits, we also performed a fit that used the GCs, dwarfs, and the inner (<1r eff ) PNe, excluding the outer PNe that show unusual rotation around the major axis (Peng et al. 2004a). ...
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... Indeed, the LMC has probably brought in several dwarf satellites in its fall into the MW potential (we consider here the most likely associated systems listed in Battaglia et al. 2022, but see also Correa Magnus & Vasiliev 2022). As they might follow similar orbits, they would not be an independent sample and could increase the presence of dwarf galaxies on the VPOS (Pawlowski et al. 2022). Therefore, in the following section we also take into account the contribution of the LMC satellite system. ...
... We note that the radial velocity pattern is robust and remains unchanged even when we consider the effect of the MW reflex motion caused by the infall of a massive LMC (see e.g. 1 Radial and tangential velocities obtained by transforming the Galactocentric Cartesian coordinate system (x, y, z; V x , V y , V z ) into a spherical one (r, θ, φ; V rad , V θ , V φ ), where the tangential velocity is Pawlowski et al. 2022). This pattern implies that almost all coorbiting VPOS members are currently approaching the MW and thus their respective orbits' pericenters, while the two counterorbiting VPOS members are receding and thus had experienced their last pericentre recently. ...
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Results. Comparing the luminosity distributions of the on-plane and off-plane samples, we find an excess of bright satellites observed on the VPOS. Despite this luminosity gap, we do not observe a significant preference for on-plane or off-plane systems to follow different scaling relations. The on-plane systems also show a striking pattern in their radial velocities and orbital phases: almost all co-orbiting satellites are approaching their pericentre, while both counter-orbiting ones are leaving their last pericentre. This is in contrast to the more random distribution of the off-plane sample. The on-plane systems also tend to have the lowest orbital energies for a given value of angular momentum. These results are robust to the assumed MW potential, even in the case of a potential perturbed by the arrival of a massive Large Magellanic Cloud. Considering them a significant property of the VPOS, we explore several scenarios, all related to the late accretion of satellite systems, which interpret the VPOS as a young structure.
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... Furthermore, it is challenging for simulations to properly reproduce the metallicity-luminosity relation (Simon & Geha 2007 ;Kirby et al. 2013 ;Sanati et al. 2023 ) showing that the predicted star-formation histories and/or stellar yields for the UFDs are not correct, or that the observations are still incomplete and that specific efforts should be put on that front. A final, well-known example is the plane of satellites observed in several galaxy groups (Lynden-Bell 1976 ;Kunkel & Demers 1976 ;P a wlowski et al. 2022 ) stating that the existence of a rotationally supported, thin polar structure around galaxies such as the MW is extremely improbable, therefore questioning the validity of the current standard cosmological model. These issues will only be solved through a careful analysis of the properties of the faintest satellite galaxies of the MW. ...
We present a new spectroscopic study of 175 stars in the vicinity of the dwarf galaxy Hercules (d ∼132 kpc) with data from the Anglo-Australian Telescope and its AAOmega spectrograph together with the Two Degree Field multi-object system to solve the conundrum that whether Hercules is tidally disrupting. We combine broadband photometry, proper motions from Gaia, and our Pristine narrow-band and metallicity-sensitive photometry to efficiently weed out the Milky Way contamination. Such cleaning is particularly critical in this kinematic regime, as both the transverse and heliocentric velocities of Milky Way populations overlap with Hercules. Thanks to this method, three new member stars are identified, including one at almost 10rh of the satellite. All three have velocities and metallicities consistent with that of the main body. Combining this new dataset with the entire literature cleaned out from contamination shows that Hercules does not exhibit a velocity gradient (d〈v〉/dχ $= 0.1^{+0.4}_{-0.2}$ km s−1 arcmin−1, 1.6 km s−1 arcmin−1 as a 3σ upper limit) and, as such, does not show evidence to undergo tidal disruption.
... Garavito-Camargo et al. [133] suggested that the LMC-induced perturbation of satellite orbits may bring them closer to the alignment due to several factors: the direct action of the massive LMC, the kinematic offset of the outer halo with respect to the observer in the inner Milky Way, and the associated deformations in the Galactic gravitational potential (both the local wake and the global dipole perturbation). Other studies [37,134] found the effect to be rather weak and insufficient to explain the observed degree of clustering of orbital planes, not least because many of these galaxies are fairly distant to be significantly affected. However, a comprehensive analysis of this phenomenon using suitably chosen Milky Way-LMC analogues from cosmological simulations has not yet been performed. ...
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.
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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.
... It is worth noticing that once we average the kinematic response, our results depend on the intrinsic properties of the tracer and its ability to 'feel' the perturbation of the underlying gravitational potential Garavito-Camargo et al. 2021;Correa Magnus & Vasiliev 2022;Pawlowski et al. 2022). Therefore, the DM particles in our simulations may not have the same kinematics properties distribution as we see for the MW satellites. ...
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 satellites, as it would require an enormously high rotation rate (~970 km/s). If we exclude the LMC and its most closely related members from our sample, this does not suppress the bulk motion of the nearby satellites strongly enough. Nevertheless, we have demonstrated that the observed peculiar kinematics of the MW satellites can be explained by a perturbation caused by the first infall of the LMC. First, we `undone' the effect of the perturbation by integrating the orbits of the MW satellites backwards (forwards) with (without) massive LMC. It appears that the present-day peculiar enhancement of the solar apex in the inner halo is diminished the most in the case of 2x10^{11} Msun LMC. Next, in self-consistent high-resolution N-body simulations of the MW-LMC interaction, we found that the solar apex shows the observed behaviour only for the halo particles with substantial angular momentum, comparable to that of the MW satellites.
... Previous work has found that the MW dSphs share a common orientation and that it may be related to the Vast Polar Orbital structure (Sanders & Evans 2017). The Vast Polar Orbital structure and orbital poles alignment may be caused by the LMC (Garavito-Camargo et al. 2021), but Pawlowski et al. (2022) show the magnitude of the LMC perturbation is too small to fully explain the Vast Polar Orbital structure. ...
We combine Gaia early data release 3 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 use a Monte Carlo sample for the observational uncertainties for each dSph and the uncertainties in the MW and LMC potentials. We predict that Ant II, Boo III, Cra II, Gru II, and Tuc III should be tidally disrupting by comparing each dSph's average density relative to the MW density at its pericenter. dSphs with large ellipticity (CVn I, Her, Tuc V, UMa I, UMa II, UMi, Wil 1) show a preference for their orbital direction to align with their major axis even for dSphs with large pericenters. We compare the dSph radial orbital phase to subhalos in MW-like N -body simulations and infer that there is not an excess of satellites near their pericenter. With projections of future Gaia data releases, we find that dSph's orbital precision will be limited by uncertainties in the distance and/or MW potential rather than in proper motion precision. Finally, we provide our membership catalogs to enable community follow-up.
... Indeed, a more recent study showed that the LMC should have brought in "about 2 satellites with M > 10 5 M " (Santos-Santos et al. 2021). Given also that the direct gravitational effect of the LMC is insufficient to induce a sufficiently strong clustering of orbital poles (Garavito-Camargo et al. 2021;Correa Magnus & Vasiliev 2022;Pawlowski et al. 2022), some other explanation is required for the 8/11 classical MW satellites that orbit within a common plane (Pawlowski & Kroupa 2020). ...
Astronomical observations reveal a major deficiency in our understanding of physics—the detectable mass is insufficient to explain the observed motions in a huge variety of systems given our current understanding of gravity, Einstein’s General theory of Relativity (GR). This missing gravity problem may indicate a breakdown of GR at low accelerations, as postulated by Milgromian dynamics (MOND). We review the MOND theory and its consequences, including in a cosmological context where we advocate a hybrid approach involving light sterile neutrinos to address MOND’s cluster-scale issues. We then test the novel predictions of MOND using evidence from galaxies, galaxy groups, galaxy clusters, and the large-scale structure of the universe. We also consider whether the standard cosmological paradigm (LCDM) can explain the observations and review several previously published highly significant falsifications of it. Our overall assessment considers both the extent to which the data agree with each theory and how much flexibility each has when accommodating the data, with the gold standard being a clear a priori prediction not informed by the data in question. Our conclusion is that MOND is favoured by a wealth of data across a huge range of astrophysical scales, ranging from the kpc scales of galactic bars to the Gpc scale of the local supervoid and the Hubble tension, which is alleviated in MOND through enhanced cosmic variance. We also consider several future tests, mostly at scales much smaller than galaxies.
Zusammenfassung
Die Milchstraße, wie auch die Andromeda‐ und Centaurus‐A‐Galaxien, ist von Satellitengalaxien umgeben. Die Verteilung und Bewegung dieser kleineren Galaxien ist überraschend abgeflacht und kohärent und erinnert an rotierende Satellitenebenen. Im kosmologischen Standardmodell, das auf der Existenz Dunkler Materie basiert, sollten Satellitengalaxiensysteme deutlich zufälliger arrangiert sein. Strukturen ähnlich den beobachteten Satellitenebenen sind in kosmologischen Simulationen sehr selten, weshalb sich aus diesen Beobachtungen das Satellitengalaxien‐Ebenen‐Problem des kosmologischen Modells ergibt.
We propose a scenario in which the Large Magellanic Cloud (LMC) is on its second passage around the Milky Way. Using a series of tailored N-body simulations, we demonstrate that such orbits are consistent with current observational constraints on the mass distribution and relative velocity of both galaxies. The previous pericentre passage of the LMC could have occurred 5–10 Gyr ago at a distance ≳ 100 kpc, large enough to retain its current population of satellites. The perturbations of the Milky Way halo induced by the LMC look nearly identical to the first-passage scenario, however, the distribution of LMC debris is considerably broader in the second-passage model. We examine the likelihood of current and past association with the Magellanic system for dwarf galaxies in the Local Group, and find that in addition to 10–11 current LMC satellites, it could have brought a further 4–6 galaxies that have been lost after the first pericentre passage. In particular, four of the classical dwarfs – Carina, Draco, Fornax and Ursa Minor – each have a ∼50 per cent probability of once belonging to the Magellanic system, thus providing a possible explanation for the ‘plane of satellites’ conundrum.
