Satellite galaxies are predicted to generate gravitational density wakes as they orbit within the dark matter (DM) halos of their hosts, causing their orbits to decay over time. The recent infall of ...the Milky Way's (MW) most massive satellite galaxy, the Large Magellanic Cloud (LMC), affords us the unique opportunity to study this process in action. In this work, we present high-resolution (mdm = 4 × 104M ) N-body simulations of the MW-LMC interaction over the past 2 Gyr. We quantify the impact of the LMC's passage on the density and kinematics of the MW's DM halo and the observability of these structures in the MW's stellar halo. The LMC is found to generate a pronounced wake, which we decompose in Transient and Collective responses, in both the DM and stellar halos. The wake leads to overdensities and distinct kinematic patterns that should be observable with ongoing and future surveys. Specifically, the Collective response will result in redshifted radial velocities of stars in the north and blueshifts in the south, at distances >45 kpc. The Transient response traces the orbital path of the LMC through the halo (50-200 kpc), resulting in a stellar overdensity with a distinct, tangential kinematic pattern that persists to the present day. The detection of the MW's halo response will constrain the infall mass of the LMC, its orbital trajectory, and the mass of the MW, and it may inform us about the nature of the DM particle itself.
ABSTRACT
We analyse an N-body simulation of the interaction of the Milky Way (MW) with a Sagittarius-like dSph (Sgr), looking for signatures which may be attributed to its orbital history in the ...phase space volume around the Sun in light of Gaia DR2 discoveries. The repeated impacts of Sgr excite coupled vertical and radial oscillations in the disc which qualitatively, and to a large degree quantitatively are able to reproduce many features in the 6D Gaia DR2 samples, from the median VR, Vϕ, V$z$ velocity maps to the local δρ($v$$z$, $z$) phase-space spiral which is a manifestation of the global disc response to coupled oscillations within a given volume. The patterns in the large-scale velocity field are well described by tightly wound spirals and vertical corrugations excited from Sgr’s impacts. We show that the last pericentric passage of Sgr resets the formation of the local present-day δρ($v$$z$, $z$) spiral and situate its formation around 500-800 Myr. As expected δρ(vz, $z$) grows in size and decreases in woundedness as a function of radius in both the Gaia DR2 data and simulations. This is the first N-body model able to explain so many of the features in the data on different scales. We demonstrate how to use the full extent of the Galactic disc to date perturbations dating from Myr to Gyr, probe the underlying potential and constrain the mass-loss history of Sgr. δρ(vz, $z$) looks the same in all stellar populations age bins down to the youngest ages which rules out a bar buckling origin.
The Triangulum–Andromeda stellar clouds (TriAnd1 and TriAnd2) are a pair of concentric ring- or shell-like overdensities at large R (≈30 kpc) and Z (≈−10 kpc) in the Galactic halo that are thought to ...have been formed from the accretion and disruption of a satellite galaxy. This paper critically reexamines this formation scenario by comparing the number ratio of RR Lyrae to M giant stars associated with the TriAnd clouds with other structures in the Galaxy. The current data suggest a stellar population for these overdensities (f
RR: MG < 0.38 at 95 per cent confidence) quite unlike any of the known satellites of the Milky Way (f
RR: MG ≈ 0.5 for the very largest and f
RR: MG ≫ 1 for the smaller satellites) and more like the population of stars born in the much deeper potential well inhabited by the Galactic disc (f
RR: MG < 0.01). N-body simulations of a Milky Way-like galaxy perturbed by the impact of a dwarf galaxy demonstrate that, in the right circumstances, concentric rings propagating outwards from that Galactic disc can plausibly produce similar overdensities. These results provide dramatic support for the recent proposal by Xu et al. that, rather than stars accreted from other galaxies, the TriAnd clouds could represent stars kicked out from our own disc. If so, these would be the first populations of disc stars to be found in the Galactic halo and a clear signature of the importance of this second formation mechanism for stellar haloes more generally. Moreover, their existence at the very extremities of the disc places strong constraints on the nature of the interaction that formed them.
Reconciling mass estimates of ultradiffuse galaxies Laporte, Chervin F P; Agnello, Adriano; Navarro, Julio F
Monthly notices of the Royal Astronomical Society,
03/2019, Letnik:
484, Številka:
1
Journal Article
We study the formation and evolution of brightest cluster galaxies starting from a z = 2 population of quiescent ellipticals and following them to z = 0. To this end, we use a suite of nine ...high-resolution dark matter only simulations of galaxy clusters in a Λ cold dark matter (ΛCDM) universe. We develop a scheme in which simulation particles are weighted to generate realistic and dynamically stable stellar density profiles at z = 2. Our initial conditions assign a stellar mass to every identified dark halo as expected from abundance matching; assuming that there exists a one-to-one relation between the visible properties of galaxies and their host haloes. We set the sizes of the luminous components according to the observed relations for z ∼ 2 massive quiescent galaxies. We study the evolution of the mass-size relation, the fate of satellite galaxies and the mass aggregation of the cluster central. From z = 2, these galaxies grow on average in size by a factor of 5 to 10 and in galaxy mass by 2 to 3. The stellar mass of our simulated BCGs grow by a factor of ∼2.1 in the range 0.3 < z < 1.0, consistent with observations, and by a factor of ∼1.4 in the range 0.0 < z < 0.3. Furthermore, the non-central galaxies evolve on to the present-day mass-size relation by z = 0. Assuming passively evolving stellar populations, we present surface brightness profiles for our cluster centrals which resemble those observed for the cDs in similar mass clusters both at z = 0 and at z = 1. This demonstrates that the ΛCDM cosmology does indeed predict minor and major mergers to occur in galaxy clusters with the frequency and mass ratio distribution required to explain the observed growth in size of passive galaxies since z = 2. Our experiment shows that brightest cluster galaxies could, in principle, form through dissipationless mergers of quiescent massive z = 2 galaxies, without substantial additional star formation.
We present cosmological N-body resimulations of the assembly of the Brightest Cluster Galaxies (BCGs) in rich clusters. At z = 2, we populate dark matter subhaloes with self-gravitating stellar ...systems whose abundance and structure match observed high-redshift galaxies. By z = 0, mergers have built much larger galaxies at cluster centre. Their dark matter density profiles are shallower than in corresponding dark-matter-only simulations, but their total mass density profiles (stars + dark matter) are quite similar. Differences are found only at radii where the effects of central black holes may be significant. Dark matter density slopes shallower than γ = 1.0 occur for r/r
200 < 0.015, close to the half-light radii of the BCGs. Our experiments support earlier suggestions that NFW-like profiles are an attractor for the hierarchical growth of structure in collisionless systems – total mass density profiles asymptote to the solution found in dark-matter-only simulations over the radial range where mergers produce significant mixing between stars and dark matter. Simulated dark matter fractions are substantially higher in BCGs than in field ellipticals, reaching 80 per cent within the half-light radius. We also estimate that supermassive black hole mergers should create BCG cores as large as r
c ∼ 3 kpc. The good agreement of all these properties with recent observational studies of BCG structure suggests that dissipational processes have not played a dominant role in the assembly of the observed systems.
ABSTRACT Using Gaia second data release (DR2), we trace the Anticentre Stream (ACS) in various stellar populations across the sky and find that it is kinematically and spatially decoupled from the ...Monoceros Ring. Using stars from lamost and segue, we show that the ACS is systematically more metal-poor than Monoceros by 0.1 dex with indications of a narrower metallicity spread. Furthermore, the ACS is predominantly populated of old stars ($\sim 10\, \rm {Gyr}$), whereas Monoceros has a pronounced tail of younger stars ($6-10\, \rm {Gyr}$) as revealed by their cumulative age distributions. Put together, all of this evidence support predictions from simulations of the interaction of the Sagittarius dwarf with the Milky Way, which argue that the ACS is the remains of a tidal tail of the Galaxy excited during Sgr’s first pericentric passage after it crossed the virial radius, whereas Monoceros consists of the composite stellar populations excited during the more extended phases of the interaction. Importantly, the ACS can be viewed as a stand-alone fossil of the chemical enrichment history of the Galactic disc.
Our Galaxy is thought to have an active evolutionary history, dominated over the past ten billion years or so by star formation, the accretion of cold gas and, in particular, the merging of clumps of ...baryonic and dark matter. The stellar halo-the faint, roughly spherical component of the Galaxy-reveals rich 'fossil' evidence of these interactions, in the form of stellar streams, substructures and chemically distinct stellar components. The effects of interactions with dwarf galaxies on the content and morphology of the Galactic disk are still being explored. Recent studies have identified kinematically distinct stellar substructures and moving groups of stars in our Galaxy, which may have extragalactic origins. There is also mounting evidence that stellar overdensities (regions with greater-than-average stellar density) at the interface between the outer disk and the halo could have been caused by the interaction of a dwarf galaxy with the disk. Here we report a spectroscopic analysis of 14 stars from two stellar overdensities, each lying about five kiloparsecs above or below the Galactic plane-locations suggestive of an association with the stellar halo. We find that the chemical compositions of these two groups of stars are almost identical, both within and between these overdensities, and closely match the abundance patterns of stars in the Galactic disk. We conclude that these stars came from the disk, and that the overdensities that they are part of were created by tidal interactions of the disk with passing or merging dwarf galaxies.
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