We study the orbital phase-space of dark matter (DM) halos in the AURIGA suite of cosmological hydrodynamics simulations of Milky Way analogues. We characterise halos by their spherical action distribution, a function of the specific angular momentum, and the radial action, of the DM particles. By comparing DM-only and hydrodynamical simulations of the same halos, we investigate the contraction of DM halos caused by the accumulation of baryons at the centre. We find a small systematic suppression of the radial action in the DM halos of the hydrodynamical simulations, suggesting that the commonly used adiabatic contraction approximation can result in an underestimate of the density by ~ 8%. We apply an iterative algorithm to contract the AURIGA DM halos given a baryon density profile and halo mass, recovering the true contracted DM profiles with an accuracy of ~15%, that reflects halo-to-halo variation. Using this algorithm, we infer the total mass profile of the Milky Way's contracted DM halo. We derive updated values for the key astrophysical inputs to DM direct detection experiments: the DM density and velocity distribution in the Solar neighbourhood.
We determine the Milky Way (MW) mass profile inferred from fitting physically motivated models to the Gaia DR2 Galactic rotation curve and other data. Using various hydrodynamical simulations of MW-mass haloes, we show that the presence of baryons induces a contraction of the dark matter (DM) distribution in the inner regions, r<20 kpc. We provide an analytic expression that relates the baryonic distribution to the change in the DM halo profile. For our galaxy, the contraction increases the enclosed DM halo mass by factors of roughly 1.3, 2 and 4 at radial distances of 20, 8 and 1 kpc, respect…
We describe a simple model which explains the qualitative and (approximate) quantitative features of the distribution of orbital velocities of merging pairs of dark matter halos. Our model considers a primary dark matter halo as a perturber in a background of secondary halos with velocities described by linear theory. By evaluating the ensemble of secondary halos on orbits within the perturbing halo's "loss cone" we derive the distribution of orbital parameters of these captured halos. This model is able provide qualitative explanations for the features of this distribution as measured from N-…
Bar-halo interaction: the role of orbital anisotropy
Institute for Computational Cosmology, Department of Physics, University of Durham（达勒姆大学物理学院计算宇宙学研究所）；School of Sciences, European University Cyprus（塞浦路斯欧洲大学理学院）；Centre for Extragalactic Astronomy, Department of Physics, University of Durham（达勒姆大学物理学院河外天文学中心）
We examine metallicities, ages and orbital properties of halo stars in a Milky-Way like disk galaxy formed in the cosmological hydrodynamical MaGICC simulations. Halo stars were either accreted from satellites or they formed in situ in the disk or bulge of the galaxy and were then kicked up into the halo ("in situ/ kicked-up" stars). Regardless of where they formed both types show surprisingly similar orbital properties: the majority of stars of both types are on short-axis tubes with the same sense of rotation as the disk -- implying that a large fraction of satellites are accreted onto the h…
We explore the kinematics and orbital properties of a sample of red giants in the halo system of the Milky Way that are thought to have formed in globular clusters, based on their anomalously strong UV/blue CN bands. The orbital parameters of the CN-strong halo stars are compared to those of the inner- and outer-halo populations as described by Carollo et al., and to the orbital parameters of globular clusters with well-studied Galactic orbits. The CN-strong field stars and the globular clusters both exhibit kinematics and orbital properties similar to the inner-halo population, indicating tha…
It has recently been proposed that if the Galactic dark matter halo were triaxial it would induce lumpiness in the velocity distribution of halo stars in the Solar Neighbourhood through orbital resonances. These substructures could therefore provide a way of measuring its shape. We explore the robustness of this proposal by integrating numerically orbits starting from a realistic set of initial conditions in dark halo potentials of different shape. We have analysed the resulting velocity distributions in Solar neighbourhood-like volumes, and have performed statistical tests for the presence of…
The Galactic stellar halo is predicted to have formed at least partially from the tidal disruption of accreted dwarf galaxies. This assembly history should be detectable in the orbital and chemical properties of stars. The H3 Survey is obtaining spectra for 200,000 stars, and, when combined with Gaia data, is providing detailed orbital and chemical properties of Galactic halo stars. Unlike previous surveys of the halo, the H3 target selection is based solely on magnitude and Gaia parallax; the survey therefore provides a nearly unbiased view of the entire stellar halo at high latitudes. In thi…
We study the distribution of nearby thick disc and halo stars in subspaces defined by their characteristic orbital parameters. Our aim is to establish the origin of the structure reported in particular, in the $R_{\rm max}-z_{\rm max}$ space. To this end, we compute the orbital parameters and frequencies of stars for a generic and for a Stäckel Milky Way potential. We find that for both the thick disc and halo populations very similar prominent substructures are apparent for the generic Galactic potential, while no substructure is seen for the Stäckel model. This indicates that the origin of t…
We select a sample of Milky Way (MW) mass haloes from a high-resolution version of the EAGLE simulation to study their inner dark matter (DM) content and how baryons alter it. As in previous studies, we find that all haloes are more massive at the centre compared to their DM-only (DMO) counterparts at the present day as a result of the dissipational collapse of baryons during the assembly of the galaxy. However, we identify two processes that can reduce the central halo mass during the evolution of the galaxy. Firstly, gas blowouts induced by AGN feedback can lead to a substantial decrease of …
We present theoretical calculations for the differential distribution of stellar orbital eccentricity in a galaxy halo, assuming that the stars constitute a spherical, collisionless system in dynamical equilibrium with a dark matter halo. In order to define the eccentricity e of a halo star for given energy E and angular momentum L, we adopt two types of gravitational potential, such as an isochrone potential and a Navarro-Frenk-White potential, that could form two ends covering in-between any realistic potential of dark matter halo. Based on a distribution function of the form f(E,L) that all…
In Papers I and II of this series, the existence of two distinct halo populations of stars have been found in the solar neighborhood. Precise relative ages and orbital parameters are determined for 67 halo and 16 thick-disk stars having metallicities in the range -1.4 < [Fe/H] < -0.4 to better understand the context of the two halo populations in the formation and evolution of the Galaxy. Ages are derived by comparing the positions of stars in the logT_{eff}-log(g) diagram with isochrones from the Y^2 models interpolated to the exact [Fe/H] and [alpha/Fe] values of each star. Possible systemat…
We present theoretical calculations for the differential distribution of stellar orbital eccentricity for a sample of solar-neighbour halo stars. Two types of static, spherical gravitational potentials are adopted to define the eccentricity e for given energy E and angular momentum L, such as an isochrone potential and a Navarro-Frenk-White potential that can serve as two extreme ends covering in-between any realistic potential of the Milky Way halo. The solar-neighbour eccentricity distribution ΔN(e) is then formulated, based on a static distribution function of the form f(E,L) in which the v…
We investigate the response of self-interacting dark matter (SIDM) halos to the growth of galaxy potentials using idealized simulations, each run in tandem with standard collisionless Cold Dark Matter (CDM). We find a greater diversity in the SIDM halo profiles compared to the CDM halo profiles. If the stellar gravitational potential strongly dominates in the central parts of a galaxy, then SIDM halos can be as dense as CDM halos on observable scales. For extreme cases with highly compact disks core collapse can occur, leading to SIDM halos that are denser and cuspier than their CDM counterpar…
With the use of a detailed Milky Way nonaxisymmetric potential, observationally and dynamically constrained, the effects of the bar and the spiral arms in the Galaxy are studied in the disc and in the stellar halo. Especially the trapping of stars in the disc and Galactic halo by resonances on the Galactic plane, induced by the Galactic bar, has been analysed in detail. To this purpose, a new method is presented to delineate the trapping regions using empirical diagrams of some orbital properties obtained in the Galactic potential. In these diagrams we plot in the inertial Galactic frame a cha…
The orbits of satellite galaxies encode rich information about their histories. We investigate the orbital dynamics and histories of satellite galaxies around Milky Way (MW)-mass host galaxies using the FIRE-2 cosmological simulations, which, as previous works have shown, produce satellite mass functions and spatial distributions that broadly agree with observations. We first examine trends in orbital dynamics at z = 0, including total velocity, specific angular momentum, and specific total energy: the time of infall into the MW-mass halo primarily determines these orbital properties. We then …
The orbital properties of infalling satellite halos set the initial conditions which control the subsequent evolution of subhalos and the galaxies that they host, with implications for mass stripping, star formation quenching, and merging. Using a high-resolution, cosmological N-body simulation, I examine the orbital parameters of satellite halos as they merge with larger host halos, focusing primarily on orbital circularity and pericenter. I explore in detail how these orbital parameters depend on mass and redshift. Satellite orbits become more radial and plunge deeper into their host halo at…
The velocity, position, and action variable evolution of a tidal stream drawn out of a star cluster in a triaxial isochrone potential containing a sub-halo population reproduces many of the orbital effects of more general cosmological halos but allows easy calculation of orbital actions. We employ a spherical shell code which we show accurately reproduces the results of a tree gravity code for a collisionless star cluster. Streams from clusters on high eccentricity orbits, $e\gtrsim 0.6$, can spread out so much that the amount of material at high enough surface density to stand out on the sky …
We investigate the orbital motions of dwarf spheroidal galaxies (dSphs) in the halo of the Milky Way (MW) to understand their possible effects on the diversity of the star formation histories seen in these MW satellites. In this work, we explicitly consider a time-varying gravitational potential due to the growth of the MW's dark halo mass to calculate the long-term orbital evolutions of the dSphs, guided with {\it Gaia} DR2 proper motions, over the past 13.5 billion years. We find that the infall time of a satellite, defined at which the galaxy first crosses within the growing virial radius o…
We have used the galaxy modeling algorithm \texttt{GravPot16}, to explore the more probable orbital elements of a sample of 64 selected N-rich stars across the Milky Way. Using the newly measured proper motions from \texttt{Gaia} DR2 with existing line-of-sight velocities from APOGEE-2 survey and spectrophotometric distance estimations from the \texttt{StarHorse}. We adopted a set of high-resolution particle simulations evolved in the same steady-state Galactic potential model with a bar, in order to identify the groups of N-rich stars that have a high probability of belonging to the bulge/bar…
Using spectral methods, we analyse the orbital structure of prolate/triaxial dark matter (DM) halos in N-body simulations to understand the processes that drive the evolution of shapes of DM halos and elliptical galaxies in which central masses are grown. A longstanding issue is whether the change in the shapes of DM halos is the result of chaotic scattering of box orbits, or whether they change shape adiabatically in response to the evolving galactic potential. We use orbital frequencies to classify orbits, to quantify orbital shapes, and to identify resonant orbits and chaotic orbits. The fr…
Dynamical friction vs. subhalo heating in Cold Dark Matter haloes
Institute of Corpuscular Physics (IFIC), CSIC–Universitat de València（核物理研究所（IFIC），西班牙科学研究中心-瓦伦西亚大学）；VALER；Institute for Astronomy, University of Edinburgh（爱丁堡大学天文研究所）；Istituto dei Sistemi Complessi, Consiglio Nazionale delle Ricerche（复杂系统研究所，意大利国家研究委员会）；Osservatorio Astrofisico di Arcetri, Istituto Nazionale di Astrofisica（阿切特里天体物理观测台，意大利国家天体物理研究所）；Istituto nazionale di Fisica Nucleare（意大利国家核物理研究所）；McWilliams centre for Cosmology and Astrophysics, Department of Physics, Carnegie Mellon University（卡内基梅隆大学物理学院麦克威廉斯宇宙学与天体物理学中心）
We use a sample of 220 face-on bulge-less galaxies situated in the low density environment to estimate their total mass via orbital motions of supposed rare satellites. Our inspection reveals 43 dwarf companions having the mean projected separation of 130 kpc and the mean-square velocity difference of 96 km/s. For them, we obtain the mean orbital-mass-to-K-band luminosity ratio of $20\pm3$. Seven bulge-less spirals in the Local Volume are also characterized by the low mean ratio, $M_{orb}/L_K = 22\pm5$. We conclude that bulge-less Sc-Scd-Sd galaxies have poor dark halos, about two times lower …
The phase space coordinates of individual halo stars obtained by Galactic surveys enable the computation of their full 3-dimensional orbits. Spectral analysis of halo orbits can be used to construct "frequency maps" which provide a compact representation of the 6-dimensional phase space distribution function. Frequency maps identify important major orbit families, and the orbital abundances reflect the shape and orientation of the dark matter halo relative to the disk. We apply spectral analysis to halo orbits in a series of controlled simulations of disk galaxies. Although the shape of the si…
Central galaxies (CGs) in galaxy groups and clusters are believed to form and assemble a good portion of their stellar mass at early times, but they also accrete significant mass at late times via galactic cannibalism, that is merging with companion group or cluster galaxies that experience dynamical friction against the common host dark-matter halo. The effect of these mergers on the structure and kinematics of the CG depends not only on the properties of the accreted satellites, but also on the orbital parameters of the encounters. Here we present the results of numerical simulations aimed a…
The spin, $λ$, of dark matter (DM) halos in cosmological simulations follows a log normal distribution and has little correlation with galaxy observables. As such, there is currently no way to infer the $λ$ parameter of individual halos hosting observed galaxies. We present here a first attempt to measure $λ$ starting from the dynamically distinct stellar components identified in high-resolution cosmological simulations with Galactic Structure Finder. In a subsample of NIHAO galaxies, we find tight correlations between the total angular momentum (AM) of the DM halos, $J_h$, and the azimuthal A…
The kinematics and stellar populations of the low-mass nearby S0 galaxy NGC 5102 are studied from integral field spectra taken with the Multi-Unit Spectroscopic Explorer (MUSE). The kinematic maps reveal for the first time that NGC 5102 has the characteristic 2 sigma peaks indicative of galaxies with counter-rotating discs. This interpretation is quantitatively confirmed by fitting two kinematic components to the observed spectra. Through stellar population analysis we confirm the known young stellar population in the centre and find steep age and metallicity gradients. We construct axisymmetr…
We study the orbital properties of dark matter haloes by combining a spectral method and cosmological simulations of Milky Way-sized galaxies. We compare the dynamics and orbits of individual dark matter particles from both hydrodynamic and $N$-body simulations, and find that the fraction of box, tube and resonant orbits of the dark matter halo decreases significantly due to the effects of baryons. In particular, the central region of the dark matter halo in the hydrodynamic simulation is dominated by regular, short-axis tube orbits, in contrast to the chaotic, box and thin orbits dominant in …
The condensation of gas and stars in the inner regions of dark matter halos leads to a more concentrated dark matter distribution. While this effect is based on simple gravitational physics, the question of its validity in hierarchical galaxy formation has led to an active debate in the literature. We use a collection of several state-of-the-art cosmological hydrodynamic simulations to study the halo contraction effect in systems ranging from dwarf galaxies to clusters of galaxies, at high and low redshift. The simulations are run by different groups with different codes and include hierarchic…
Stellar pulsation is nowadays a widely understood subject. However, there has been no research about the effects of pulsations on the star's orbital dynamics throughout the galaxy. We investigate whether these oscillations can cause chaotic behaviour in the stellar orbit if it is immersed in background dark matter halos. We show that for a certain range of parameters of the pulsating object these effects are present in a general background matter field. However, for the typical range of parameters of realistic astrophysical scenarios, these effects are too small to be detectable.
Observations of strong gravitational lensing, stellar kinematics, and larger-scale tracers enable accurate measures of the distribution of dark matter (DM) and baryons in massive early-type galaxies (ETGs). While such techniques have been applied to galaxy-scale and cluster-scale lenses, the paucity of intermediate-mass systems with high-quality data has precluded a uniform analysis of mass-dependent trends. With the aim of bridging this gap, we present new observations and analyses of 10 group-scale lenses at <z>=0.36 characterized by Einstein radii theta_Ein=2.5"-5.1" and a mean halo mass of…
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$\times 10^{11}$M$\odot$) 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 (DM) particles from the present-day random distribution. Instead, the orbital poles of particles beyond $R\approx 50$kpc cluster near the present-day orbital pole of th…
We use cosmological hydrodynamical zoom-in simulations with the SPH code gasoline of four haloes of mass M_{200} \sim 10^{13}\Msun to study the response of the dark matter to elliptical galaxy formation. Our simulations include metallicity dependent gas cooling, star formation, and feedback from massive stars and supernovae, but not active galactic nuclei (AGN). At z=2 the progenitor galaxies have stellar to halo mass ratios consistent with halo abundance matching, assuming a Salpeter initial mass function. However by z=0 the standard runs suffer from the well known overcooling problem, overpr…
Disk galaxies can exchange angular momentum and baryons with their host dark matter (DM) halos. These halos possess internal spin, `lambda', which is insignificant rotationally but does affect interactions between the baryonic and DM components. While statistics of prograde and retrograde spinning halos in galaxies is not available at present, the existence of such halos is important for galaxy evolution. In the previous works, we analyzed dynamical and secular evolution of stellar bars in prograde spinning halos and the DM response to the bar perturbation, and found that it is modified by the…
The Galactic orbits of 27 440 stars of all classes with accurate coordinates and parallaxes of more than 3 mas from the Hipparcos catalogue, proper motions from the Tycho-2 catalogue, and radial velocities from the Pulkovo Compilation of Radial Velocities (PCRV) are analyzed. The sample obtained is much more representative than the Geneva-Copenhagen survey and other studies of Galactic orbits in the solar neighborhood. An estimation of the influence of systematic errors in the velocities on orbital parameters shows that the errors of the proper motions due to the duplicity of stars are tangibl…
We construct new estimates on the Galactic escape speed at various Galactocentric radii using the latest data release of the Radial Velocity Experiment (RAVE DR4). Compared to previous studies we have a database larger by a factor of 10 as well as reliable distance estimates for almost all stars. Our analysis is based on the statistical analysis of a rigorously selected sample of 90 high-velocity halo stars from RAVE and a previously published data set. We calibrate and extensively test our method using a suite of cosmological simulations of the formation of Milky Way-sized galaxies. Our best …
A cosmological zoom-in simulation which develops into a Milky Way-like halo is started at redshift 7. The initial dark matter distribution is seeded with dense star clusters, median mass $5\times 10^5 M_\sun$, placed in the largest sub-halos present, which have a median peak circular velocity of 25 \kms. Three simulations are initialized using the same dark matter distribution, with the star clusters started on approximately circular orbits having initial median radii 6.8 kpc, 0.14 kpc, and, at the exact center of the sub-halos. The simulations are evolved to the current epoch at which time th…
The ultra-light dark matter (ULDM) model has become a popular dark matter scenario nowadays. The mass of the ULDM particles is extremely small so that they can exhibit wave properties in the central dark matter halo region. Numerical simulations show that a soliton core with an almost constant mass density would be formed inside the ULDM halo. If our Galactic Centre has a dark matter soliton core, some of the stars orbiting about the supermassive black hole (Sgr A*) would be crossing the soliton core boundary. In this article, we report the first theoretical study on how the dark matter solito…
Context: The Einasto model has become one of the most popular models for describing the density profile of dark matter haloes. There have been relatively few comprehensive studies on the dynamical structure of the Einasto model, mainly because only a limited number of properties can be calculated analytically. Aims: We want to systematically investigate the photometric and dynamical structure of the family of Einasto models over the entire model parameter space. Methods: We used the SpheCow code to explore the properties of the Einasto model. We systematically investigated how the most importa…
Spin$-$orbit alignment (SOA; i.e., the vector alignment between the halo spin and the orbital angular momentum of neighboring halos) provides an important clue to how galactic angular momenta develop. For this study, we extract virial-radius-wise contact halo pairs with mass ratios between 1/10 and 10 from a set of cosmological $N$-body simulations. In the spin--orbit angle distribution, we find a significant SOA in that 52.7%$\pm$0.2% of neighbors are on the prograde orbit. The SOA of our sample is mainly driven by low-mass target halos ($<10^{11.5}h^{-1}M_{\odot}$) with close merging neighbo…
The initial orbits of infalling subhalos largely determine the subsequent evolution of the subhalos and satellite galaxies therein and shed light on the assembly of their hosts. Using a large set of cosmological simulations of various resolutions, we quantify the orbital distribution of subhalos at infall time and its mass and redshift dependence in a large dynamic range. We further provide a unified and accurate model validated across cosmic time, which can serve as the initial condition for semi-analytic models. We find that the infall velocity $v$ follows a nearly universal distribution pea…
We present the abundance analysis of 97 nearby metal-poor (-3.3<[Fe/H]<-0.5) stars having kinematics characteristics of the Milky Way (MW) thick disk, inner, and outer stellar halos. The high-resolution, high-signal-to-noise optical spectra for the sample stars have been obtained with the High Dispersion Spectrograph mounted on the Subaru Telescope. Abundances of Fe, Mg, Si, Ca and Ti have been derived using a one-dimensional LTE abundance analysis code with Kurucz NEWODF model atmospheres. By assigning membership of the sample stars to the thick disk, inner or outer halo components based on t…
Using realistic cosmological simulations of Milky Way sized haloes, we study their dynamical state and the accuracy of inferring their mass profiles with steady-state models of dynamical tracers. We use a new method that describes the phase-space distribution of a steady-state tracer population in a spherical potential without any assumption regarding the distribution of their orbits. Applying the method to five haloes from the Aquarius $Λ$CDM N-body simulation, we find that dark matter particles are an accurate tracer that enables the halo mass and concentration parameters to be recovered wit…
The orbital parameters of dark matter (DM) subhaloes play an essential role in determining their mass-loss rates and overall spatial distribution within a host halo. Haloes in cosmological simulations grow by a combination of relatively smooth accretion and more violent mergers, and both processes will modify subhalo orbits. To isolate the impact of the smooth growth of the host halo from other relevant mechanisms, we study subhalo orbital evolution using numerical calculations in which subhaloes are modelled as massless particles orbiting in a time-varying spherical potential. We find that th…
We study the total density distribution in the central regions (~ 1 effective radius, $R_e$) of early-type galaxies (ETGs), using data from SPIDER and $\rm ATLAS^{3D}$. Our analysis extends the range of galaxy stellar mass ($M_{\star}$) probed by gravitational lensing, down to ~ $10^{10}\, \rm M_{\odot}$. We model each galaxy with two components (dark matter halo + stars), exploring different assumptions for the dark matter (DM) halo profile (i.e. NFW, NFW-contracted, and Burkert profiles), and leaving stellar mass-to-light ($M_{\star}/L$) ratios as free fitting parameters to the data. For all…
Using the phat-ELVIS suite of Milky Way-size halo simulations, we show that subhalo orbital pericenters, $r_{\rm peri}$, correlate with their dark matter halo structural properties. Specifically, at fixed maximum circular velocity, $V_{\rm max}$, subhalos with smaller $r_{\rm peri}$ are more concentrated (have smaller $r_{\rm max}$ values) and have lost more mass, with larger peak circular velocities, $V_{\rm peak}$, prior to infall. These trends provide information that can tighten constraints on the inferred $V_{\rm max}$ and $V_{\rm peak}$ values for known Milky Way satellites. We illustrat…
We used the Revised Flat Galaxy Catalog (RFGC) to select 817 ultra-flat (UF) edge-on disk galaxies with blue and red apparent axial ratios of $(a/b)_B > 10.0$ and $(a/b)_R > 8.5$. The sample covering the whole sky, except the Milky Way zone, contains 490 UF galaxies with measured radial velocities. Our inspection of the neighboring galaxies around them revealed only 30 companions with radial velocity difference of $\midΔV\mid<500$ km s$^{-1}$ inside the projected separation of $R_p < 250$ kpc. Wherein, the wider area around the UF galaxy within $R_p < 750$ kpc contains no other neighbors brigh…
The degeneracy among the disk, bulge and halo contributions to galaxy rotation curves prevents an understanding of the distribution of baryons and dark matter in disk galaxies. In an attempt to break this degeneracy, we present an analysis of the spiral galaxy strong gravitational lens SDSS J2141-0001, discovered as part of the SLACS survey. We present new Hubble Space Telescope multicolor imaging, gas and stellar kinematics data derived from long-slit spectroscopy, and K-band LGS adaptive optics imaging, both from the Keck telescopes. We model the galaxy as a sum of concentric axisymmetric bu…
We use simulations of Milky Way-sized dark matter haloes from the Aquarius Project to investigate the orbits of substructure haloes likely, according to a semi-analytic galaxy formation model, to host luminous satellites. These tend to populate the most massive subhaloes and are on more radial orbits than the majority of subhaloes found within the halo virial radius. One reason for this (mild) kinematic bias is that many low-mass subhaloes have apocentres that exceed the virial radius of the main host; they are thus excluded from subhalo samples identified within the virial boundary, reducing …
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 towards the LMC orbital pole. This was suggested to help explain the observed preference of MW satellite galaxies to co-orbit along the Vast Polar Structure (VPOS). We test this idea by correcting the positions and velocities of the MW satellites for the Galactocentric-distance-dependent shifts inferred from a LMC-infall simulation. While this should substantially reduce the observe…
Large spectroscopic surveys of the Milky Way have revealed that a small population of stars in the halo have light element abundances comparable to those found in globular clusters. The favoured explanation for the peculiar abundances of these stars is that they originated inside a globular cluster and were subsequently lost. Using orbit calculations we assess the likelihood that an existing sample of 57 field stars with globular cluster-like CN band strength originated in any of the currently known Milky Way globular clusters. Using Sloan Digital Sky Survey and Gaia data, we determine orbits …
The latest edition of the APOGEE-2/DR14 survey catalogue and the first \texttt{Payne} data release of APOGEE abundance determinations by Ting et al. are examined. We identify 31 previously unremarked metal-poor giant stars with anomalously high levels of nitrogen in the chemical space defined by [Fe/H] and [N/Fe]. The APOGEE chemical abundance patterns of such objects revealed that these are chemically distinct from the Milky Way (MW) in most chemical elements. We have found all these objects have a [N/Fe]$>+0.5$, and are thus identified here as nitrogen-rich stars. An orbital analysis of thes…
