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.
With the release of Gaia DR2, it is now possible to measure the proper motions (PMs) of the lowest-mass, ultrafaint satellite galaxies in the Milky Way's (MW) halo for the first time. Many of these ...faint satellites are posited to have been accreted as satellites of the Magellanic Clouds (MCs). Using their six-dimensional phase-space information, we calculate the orbital histories of 13 ultrafaint satellites and five classical dwarf spheroidals in a combined MW+LMC+SMC potential to determine which galaxies are dynamically associated with the MCs. These 18 galaxies are separated into four classes: (i) long-term Magellanic satellites that have been bound to the MCs for at least the last two consecutive orbits around the MCs (Carina 2, Carina 3, Horologium 1, Hydrus 1); (ii) Magellanic satellites that were recently captured by the MCs < 1 Gyr ago (Reticulum 2, Phoenix 2); (iii) MW satellites that have interacted with the MCs (Sculptor 1, Tucana 3, Segue 1); and (iv) MW satellites (Aquarius 2, Canes Venatici 2, Crater 2, Draco 1, Draco 2, Hydra 2, Carina, Fornax, Ursa Minor). Results are reported for a range of MW and LMC masses. Contrary to previous work, we find no dynamical association between Carina, Fornax, and the MCs. Finally, we determine that the addition of the SMC's gravitational potential affects the longevity of satellites as members of the Magellanic system (long-term versus recently captured), but it does not change the total number of Magellanic satellites.
Abstract
We present predictions for the quenching of star formation in satellite galaxies of the Local Group from a suite of 30 cosmological zoom simulations of Milky Way-like host galaxies. The ...Auriga simulations resolve satellites down to the luminosity of the classical dwarf spheroidal galaxies of the Milky Way. We find strong mass-dependent and distance-dependent quenching signals, where dwarf systems beyond 600 kpc are only strongly quenched below a stellar mass of 107 M⊙. Ram pressure stripping appears to be the dominant quenching mechanism and 50 per cent of quenched systems cease star formation within 1 Gyr of first infall. We demonstrate that systems within a host galaxy’s R200 radius are comprised of two populations: (i) a first infall population that has entered the host halo within the past few Gyrs and (ii) a population of returning ‘backsplash’ systems that have had a much more extended interaction with the host. Backsplash galaxies that do not return to the host galaxy by redshift zero exhibit quenching properties similar to galaxies within R200 and are distinct from other external systems. The simulated quenching trend with stellar mass has some tension with observations, but our simulations are able reproduce the range of quenching times measured from resolved stellar populations of Local Group dwarf galaxies.
The mass of the Milky Way from satellite dynamics Callingham, Thomas M; Cautun, Marius; Deason, Alis J ...
Monthly notices of the Royal Astronomical Society,
04/2019, Letnik:
484, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Abstract
We present and apply a method to infer the mass of the Milky Way (MW) by comparing the dynamics of MW satellites to those of model satellites in the eagle cosmological hydrodynamics ...simulations. A distribution function (DF) for galactic satellites is constructed from eagle using specific angular momentum and specific energy, which are scaled so as to be independent of host halo mass. In this two-dimensional space, the orbital properties of satellite galaxies vary according to the host halo mass. The halo mass can be inferred by calculating the likelihood that the observed satellite population is drawn from this DF. Our method is robustly calibrated on mock eagle systems. We validate it by applying it to the completely independent suite of 30 auriga high-resolution simulations of MW-like galaxies: the method accurately recovers their true mass and associated uncertainties. We then apply it to 10 classical satellites of the MW with six-dimensional phase-space measurements, including updated proper motions from the Gaia satellite. The mass of the MW is estimated to be $M_{200}^{\rm {MW}}=1.17_{-0.15}^{+0.21}\times 10^{12}\, \mathrm{M}_{\odot }$ (68 per cent confidence limits). We combine our total mass estimate with recent mass estimates in the inner regions of the Galaxy to infer an inner dark matter (DM) mass fraction $M^\rm {DM}(\lt 20~\rm {kpc})/M^\rm {DM}_{200}=0.12$, which is typical of ${\sim }10^{12}\, \mathrm{M}_{\odot }$ lambda cold dark matter haloes in hydrodynamical galaxy formation simulations. Assuming a Navarro, Frenk and White (NFW) profile, this is equivalent to a halo concentration of $c_{200}^{\rm {MW}}=10.9^{+2.6}_{-2.0}$.
ABSTRACT
Using a set of 15 high-resolution magnetohydrodynamic cosmological simulations of Milky Way formation, we investigate the origin of the baryonic material found in stars at redshift zero. We ...find that roughly half of this material originates from subhalo/satellite systems and half is smoothly accreted from the intergalactic medium. About $90 {{\ \rm per\ cent}}$ of all material has been ejected and re-accreted in galactic winds at least once. The vast majority of smoothly accreted gas enters into a galactic fountain that extends to a median galactocentric distance of ∼20 kpc with a median recycling time-scale of ∼500 Myr. We demonstrate that, in most cases, galactic fountains acquire angular momentum via mixing of low angular momentum, wind-recycled gas with high angular momentum gas in the circumgalactic medium (CGM). Prograde mergers boost this activity by helping to align the disc and CGM rotation axes, whereas retrograde mergers cause the fountain to lose angular momentum. Fountain flows that promote angular momentum growth are conducive to smooth evolution on tracks quasi-parallel to the disc sequence of the stellar mass-specific angular momentum plane, whereas retrograde minor mergers, major mergers, and bar-driven secular evolution move galaxies towards the bulge sequence. Finally, we demonstrate that fountain flows act to flatten and narrow the radial metallicity gradient and metallicity dispersion of disc stars, respectively. Thus, the evolution of galactic fountains depends strongly on the cosmological merger history and is crucial for the chemodynamical evolution of Milky-Way-sized disc galaxies.
ABSTRACT
We use a distribution function analysis to estimate the mass of the Milky Way (MW) out to 100 kpc using a large sample of halo stars. These stars are compiled from the literature, and the ...vast majority (${\sim } 98{{\ \rm per\ cent}}$) 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 haloes from cosmological simulations tend to underestimate the true halo mass. After applying our method to the MW data, we find a mass within 100 kpc of M (<100 kpc) = 6.07 ± 0.29 (stat.) ± 1.21 (sys.) × 1011 M⊙. For this estimate, we have approximately corrected for the reflex motion induced by the LMC using the Erkal et al. model, which assumes a rigid potential for the LMC and MW. Furthermore, stars that likely belong to the Sagittarius stream are removed, and we include a 5 per cent systematic bias, and a 20 per cent systematic uncertainty based on our tests with cosmological simulations. Assuming the mass–concentration relation for Navarro–Frenk–White haloes, our mass estimate favours a total (pre-LMC infall) MW mass of M200c = 1.01 ± 0.24 × 1012 M⊙, or (post-LMC infall) mass of M200c = 1.16 ± 0.24 × 1012 M⊙ when a 1.5 × 1011 M⊙ mass of a rigid LMC is included.
ABSTRACT
We use cosmological, magnetohydrodynamical simulations of Milky Way-mass galaxies from the Auriga project to study their enrichment with rapid neutron capture (r-process) elements. We ...implement a variety of enrichment models from both binary neutron star mergers and rare core-collapse supernovae. We focus on the abundances of (extremely) metal-poor stars, most of which were formed during the first ∼Gyr of the Universe in external galaxies and later accreted on to the main galaxy. We find that the majority of metal-poor stars are r-process enriched in all our enrichment models. Neutron star merger models result in a median r-process abundance ratio, which increases with metallicity, whereas the median trend in rare core-collapse supernova models is approximately flat. The scatter in r-process abundance increases for models with longer delay times or lower rates of r-process-producing events. Our results are nearly perfectly converged, in part due to the mixing of gas between mesh cells in the simulations. Additionally, different Milky Way-mass galaxies show only small variation in their respective r-process abundance ratios. Current (sparse and potentially biased) observations of metal-poor stars in the Milky Way seem to prefer rare core-collapse supernovae over neutron star mergers as the dominant source of r-process elements at low metallicity, but we discuss possible caveats to our models. Dwarf galaxies that experience a single r-process event early in their history show highly enhanced r-process abundances at low metallicity, which is seen both in observations and in our simulations. We also find that the elements produced in a single event are mixed with ≈108 M⊙ of gas relatively quickly, distributing the r-process elements over a large region.
Vertically extended, high velocity dispersion stellar distributions appear to be a ubiquitous feature of disc galaxies, and both internal and external mechanisms have been proposed to be the major ...driver of their formation. However, it is unclear to what extent each mechanism can generate such a distribution, which is likely to depend on the assembly history of the galaxy. To this end, we perform 16 high-resolution cosmological-zoom simulations of Milky Way-sized galaxies using the state-of-the-art cosmological magnetohydrodynamical code arepo, and analyse the evolution of the vertical kinematics of the stellar disc in connection with various heating mechanisms. We find that the bar is the dominant heating mechanism in most cases, whereas spiral arms, radial migration and adiabatic heating from mid-plane density growth are all subdominant. The strongest source, though less prevalent than bars, originates from external perturbations from satellites/subhaloes of masses log10(M/M⊙) ≳ 10. However, in many simulations the orbits of newborn star particles become cooler with time, such that they dominate the shape of the age–velocity dispersion relation and overall vertical disc structure unless a strong external perturbation takes place.
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.
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