scholarly journals Cosmological insights into the assembly of the radial and compact stellar halo of the Milky Way

2020 ◽  
Vol 495 (1) ◽  
pp. 29-39 ◽  
Author(s):  
Lydia M Elias ◽  
Laura V Sales ◽  
Amina Helmi ◽  
Lars Hernquist
Keyword(s):  
Cold Dark Matter ◽  
Milky Way ◽  
Early History ◽  
Substantial Contribution ◽  
Hydrodynamic Simulation ◽  
Stellar Halo ◽  
History Of ◽  
Radial Orbital ◽  
Galaxy Assembly ◽  
Gaia Dr2

ABSTRACT Recent studies using Gaia DR2 have identified a massive merger in the early history of the Milky Way (MW) whose debris is dominated by radial and counterrotating orbits. This event, dubbed the Gaia-Enceladus/Gaia-Sausage (GE/GS), is also hypothesized to have built the majority of the inner stellar halo. We use the cosmological hydrodynamic simulation Illustris to place this merger in the context of galaxy assembly within lambda cold dark matter. From ∼150 MW analogues, $\sim \!80 {{ \rm {per\ cent}}}$ have experienced at least one merger of similar mass and infall time as the GE/GS. Within this sample, 37 have debris as radial as the GE/GS, which we dub the ancient radial mergers (ARMs). Counterrotation is not rare among ARMs, with $43 {{ \rm {per\ cent}}}$ having $\gt 40 {{ \rm {per\ cent}}}$ of their debris in counterrotating orbits. However, the compactness inferred for the GE/GS debris given its large radial orbital anisotropy, β, and its substantial contribution to the stellar halo are difficult to reproduce. The median radius of ARM debris is r*,deb ≃ 45 kpc, while GE/GS is thought to be mostly contained within r ∼ 30 kpc. For most MW analogues, few mergers are required to build the inner stellar halo, and ARM debris only accounts for (median) $\sim \!12 {{ \rm {per\ cent}}}$ of inner accreted stars. Encouragingly, we find one ARM that is both compact and dominates the inner halo of its central, making it our best GE/GS analogue. Interestingly, this merger deposits a significant number of stars (M* ≃ 1.5 × 109 M⊙) in the outer halo, suggesting that an undiscovered section of GE/GS may await detection.

scholarly journals Resonant trans-Neptunian objects as a source of Jupiter-family comets

2006 ◽  
Vol 2 (S236) ◽  
pp. 31-34
Author(s):  
E. L. Kiseleva ◽  
V. V. Emel'yanenko
Keyword(s):  
Solar System ◽  
Dynamical Evolution ◽  
Early History ◽  
Substantial Contribution ◽  
Outer Solar System ◽  
Symplectic Integrator ◽  
Relative Fraction ◽  
Outward Transport ◽  
Short Period ◽  
History Of

AbstractThe dynamical interrelation between resonant trans-Neptunian objects and short-period comets is studied. Initial orbits of resonant objects are based on computations in the model of the outward transport of objects during Neptune's migration in the early history of the outer Solar system. The dynamical evolution of this population is investigated for 4.5 Gyr, using a symplectic integrator. Our calculations show that resonant trans-Neptunian objects give a substantial contribution to the planetary region. We have estimated that the relative fraction of objects captured per year from the 2/3 resonance to Jupiter-family orbits with perihelion distances q<2.5 AU is 0.4×10−10 near the present epoch.

scholarly journals A Gaia DR2 view of the open cluster population in the Milky Way

2018 ◽  
Vol 618 ◽  
pp. A93 ◽  
Author(s):  
T. Cantat-Gaudin ◽  
C. Jordi ◽  
A. Vallenari ◽  
A. Bragaglia ◽  
L. Balaguer-Núñez ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
Milky Way ◽  
Galactic Plane ◽  
Galactic Disk ◽  
Open Cluster ◽  
Open Clusters ◽  
Number Of Clusters ◽  
History Of ◽  
Gaia Dr2

Context. Open clusters are convenient probes of the structure and history of the Galactic disk. They are also fundamental to stellar evolution studies. The second Gaia data release contains precise astrometry at the submilliarcsecond level and homogeneous photometry at the mmag level, that can be used to characterise a large number of clusters over the entire sky. Aims. In this study we aim to establish a list of members and derive mean parameters, in particular distances, for as many clusters as possible, making use of Gaia data alone. Methods. We compiled a list of thousands of known or putative clusters from the literature. We then applied an unsupervised membership assignment code, UPMASK, to the Gaia DR2 data contained within the fields of those clusters. Results. We obtained a list of members and cluster parameters for 1229 clusters. As expected, the youngest clusters are seen to be tightly distributed near the Galactic plane and to trace the spiral arms of the Milky Way, while older objects are more uniformly distributed, deviate further from the plane, and tend to be located at larger Galactocentric distances. Thanks to the quality of Gaia DR2 astrometry, the fully homogeneous parameters derived in this study are the most precise to date. Furthermore, we report on the serendipitous discovery of 60 new open clusters in the fields analysed during this study.

scholarly journals Kinematical & Chemical Characteristics of the Thin and Thick Disks

2008 ◽  
Vol 4 (S254) ◽  
pp. 179-190 ◽  
Author(s):  
Rosemary F. G. Wyse
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Milky Way ◽  
Observational Evidence ◽  
Chemical Characteristics ◽  
Chemical Abundance ◽  
The Galaxy ◽  
History Of ◽  
Thin And Thick Disks ◽  
Thick Disks

AbstractI discuss how the chemical abundance distributions, kinematics and age distributions of stars in the thin and thick disks of the Galaxy can be used to decipher the merger history of the Milky Way, a typical large galaxy. The observational evidence points to a rather quiescent past merging history, unusual in the context of the ‘consensus’ cold-dark-matter cosmology favoured from observations of structure on scales larger than individual galaxies.

scholarly journals Weighing the stellar constituents of the galactic halo with APOGEE red giant stars

2020 ◽  
Vol 492 (3) ◽  
pp. 3631-3646 ◽  
Author(s):  
J Ted Mackereth ◽  
Jo Bovy
Keyword(s):  
Milky Way ◽  
Galactic Halo ◽  
Power Laws ◽  
Stellar Mass ◽  
Giant Star ◽  
Giant Stars ◽  
Stellar Halo ◽  
Tentative Evidence ◽  
History Of ◽  
Red Giant

ABSTRACT The stellar mass in the halo of the Milky Way is notoriously difficult to determine, owing to the paucity of its stars in the solar neighbourhood. With tentative evidence from Gaia that the nearby stellar halo is dominated by a massive accretion event – referred to as Gaia-Enceladus or Sausage – these constraints are now increasingly urgent. We measure the mass in kinematically selected mono-abundance populations (MAPs) of the stellar halo between −3 &lt; [Fe/H] &lt; −1 and 0.0 &lt; [Mg/Fe] &lt; 0.4 using red giant star counts from APOGEE DR14. We find that MAPs are well fit by single power laws on triaxial ellipsoidal surfaces, and we show that that the power-law slope α changes such that high [Mg/Fe] populations have α ∼ 4, whereas low [Mg/Fe] MAPs are more extended with shallow slopes, α ∼ 2. We estimate the total stellar mass to be $M_{*,\mathrm{tot}} = 1.3^{+0.3}_{-0.2}\times 10^{9}\ \mathrm{M_{\odot}}$, of which we estimate ${\sim}0.9^{+0.2}_{-0.1} \times 10^{9}\ \mathrm{M_{\odot}}$ to be accreted. We estimate that the mass of accreted stars with e &gt; 0.7 is M*,accreted, e &gt; 0.7 = 3 ± 1 (stat.) ± 1 (syst.) × 108 M⊙, or ${\sim}30{-}50{{\ \rm per\ cent}}$ of the accreted halo mass. If the majority of these stars are the progeny of a massive accreted dwarf, this places an upper limit on its stellar mass, and implies a halo mass for the progenitor of ∼1010.2 ± 0.2 M⊙. This constraint not only shows that the Gaia-Enceladus/Sausage progenitor may not be as massive as originally suggested, but that the majority of the Milky Way stellar halo was accreted. These measurements are an important step towards fully reconstructing the assembly history of the Milky Way.

scholarly journals The early merger that made the galaxy’s stellar halo

2019 ◽  
Vol 14 (S353) ◽  
pp. 113-120
Author(s):  
N. Wyn Evans
Keyword(s):  
Milky Way ◽  
Current Understanding ◽  
Proper Motions ◽  
Widespread Acceptance ◽  
Stellar Halo ◽  
History Of ◽  
Milky Way Halo

AbstractThe last two years have seen widespread acceptance of the idea that the Milky Way halo was largely created in an early (8-10 Gyr ago) and massive (>1010Mȯ) merger. The roots of this idea pre-date the Gaia mission, but the exquisite proper motions available from Gaia have made the hypothesis irresistible. We trace the history of this idea, reviewing the series of papers that led to our current understanding.

scholarly journals The tale of the Milky Way globular cluster NGC 6362 – I. The orbit and its possible extended star debris features as revealed by Gaia DR2

2019 ◽  
Vol 489 (4) ◽  
pp. 4565-4573
Author(s):  
Richa Kundu ◽  
José G Fernández-Trincado ◽  
Dante Minniti ◽  
Harinder P Singh ◽  
Edmundo Moreno ◽  
...  
Keyword(s):  
Milky Way ◽  
Galactic Plane ◽  
Vertical Component ◽  
Galactic Disc ◽  
Corotation Radius ◽  
Magnitude Diagram ◽  
The Galaxy ◽  
History Of ◽  
Event Based ◽  
Gaia Dr2

ABSTRACTWe report the identification of possible extended star debris candidates beyond the cluster tidal radius of NGC 6362 based on the second Gaia data release (Gaia DR2). We found 259 objects possibly associated with the cluster lying in the vicinity of the giant branch and 1–2 magnitudes fainter/brighter than the main-sequence turn-off in the cluster colour–magnitude diagram and which cover an area on the sky of ∼4.1 deg2 centred on the cluster. We traced back the orbit of NGC 6362 in a realistic Milky Way potential, using the gravpot16 package, for 3 Gyr. The orbit shows that the cluster shares similar orbital properties as the inner disc, having peri-/apogalactic distances, and maximum vertical excursion from the Galactic plane inside the corotation radius (CR), moving inwards from CR radius to visit the inner regions of the Milky Way. The dynamical history of the cluster reveals that it has crossed the Galactic disc several times in its lifetime and has recently undergone a gravitational shock, ∼15.9 Myr ago, suggesting that less than 0.1 per cent of its mass has been lost during the current disc-shocking event. Based on the cluster’s orbit and position in the Galaxy, we conclude that the possible extended star debris candidates are a combined effect of the shocks from the Galactic disc and evaporation from the cluster. Lastly, the evolution of the vertical component of the angular momentum shows that the cluster is strongly affected dynamically by the Galactic bar potential.

scholarly journals Thousands of Milky Ways: galaxy satellites and building blocks

2009 ◽  
Vol 5 (S262) ◽  
pp. 240-243
Author(s):  
Nelson Padilla ◽  
Claudia Lagos ◽  
Sofía Cora
Keyword(s):  
Active Galactic Nuclei ◽  
Galaxy Formation ◽  
Cold Dark Matter ◽  
Milky Way ◽  
Galactic Nuclei ◽  
Building Blocks ◽  
Chemical Enrichment ◽  
Stellar Formation ◽  
History Of ◽  
The Universe

AbstractA semi-analytic model of galaxy formation with and without active galactic nuclei feedback is used to study the nature of possible building blocks (BBs) of z = 0 galaxies, including those of Milky-Way types. We find that BBs can show an important range of properties arising from environmental variables such as host halo mass, and whether a galaxy is a satellite within its host halo; the stellar formation histories are comparatively faster and the chemical enrichment is more efficient in BBs than in surviving satellites, in accordance with recent metallicity measurements for the Milky Way. These results can be used in combination with observational constraints to continue probing the ability of the cold dark-matter scenario to reproduce the history of galaxy demography in the Universe.

scholarly journals Building Blocks of the Milky Way's Stellar Halo

2015 ◽  
Vol 11 (S317) ◽  
pp. 373-374
Author(s):  
Pim van Oirschot ◽  
Else Starkenburg ◽  
Amina Helmi ◽  
Gijs Nelemans
Keyword(s):  
Galaxy Formation ◽  
Stellar Population ◽  
Milky Way ◽  
Building Blocks ◽  
Formation Model ◽  
Halo Stars ◽  
Stellar Halo ◽  
History Of ◽  
Dynamical Properties ◽  
Star Formation Histories

AbstractWe study the assembly history of the stellar halo of Milky Way-like galaxies using the six high-resolution Aquarius dark matter simulations combined with the Munich-Groningen semi-analytic galaxy formation model. Our goal is to understand the stellar population contents of the building blocks of the Milky Way halo, including their star formation histories and chemical evolution, as well as their internal dynamical properties. We are also interested in how they relate or are different from the surviving satellite population. Finally, we will use our models to compare to observations of halo stars in an attempt to reconstruct the assembly history of the Milky Way's stellar halo itself.

scholarly journals A ‘Universal’ Density Profile for the Outer Stellar Halos of Galaxies

2016 ◽  
Vol 11 (S321) ◽  
pp. 84-86
Author(s):  
Rhea-Silvia Remus ◽  
Andreas Burkert ◽  
Klaus Dolag
Keyword(s):  
Star Formation ◽  
High Resolution ◽  
Total Mass ◽  
Milky Way ◽  
Mass Range ◽  
Density Profiles ◽  
Formation History ◽  
Stellar Halo ◽  
History Of ◽  
Free Parameters

AbstractThe outer stellar halos of galaxies contain vital information about the formation history of galaxies, since the relaxation timescales in the outskirts are long enough to keep the memory, while the information about individual formation events in the central parts has long been lost due to mixing, star formation and relaxation. To unveil some of the information encoded in these faint outer halo regions, we study the stellar outskirts of galaxies selected from a fully hydrodynamical high-resolution cosmological simulation, called Magneticum. We find that the density profiles of the outer stellar halos of galaxies over a broad mass range can be well described by an Einasto profile. For a fixed total mass range, the free parameters of the Einasto fits are closely correlated. Galaxies which had more (dry) merger events tend to have lesser curved outer stellar halos, however, we find no indication that the amount of curvature is correlated with galaxy morphology. The Einasto-like shape of the outer stellar halo densities can also explain the observed differences between the Milky Way and Andromeda outer stellar halos.

scholarly journals Where did the globular clusters of the Milky Way form? Insights from the E-MOSAICS simulations

2020 ◽  
Vol 495 (4) ◽  
pp. 4248-4267 ◽  
Author(s):  
Benjamin W Keller ◽  
J M Diederik Kruijssen ◽  
Joel Pfeffer ◽  
Marta Reina-Campos ◽  
Nate Bastian ◽  
...  
Keyword(s):  
Star Formation ◽  
Globular Clusters ◽  
Milky Way ◽  
Ex Situ ◽  
History Of ◽  
Natural Outcome ◽  
Minor Mergers ◽  
Galaxy Assembly ◽  
Simple Picture

ABSTRACT Globular clusters (GCs) are typically old, with most having formed at z ≳ 2. This makes understanding their birth environments difficult, as they are typically too distant to observe with sufficient angular resolution to resolve GC birth sites. Using 25 cosmological zoom-in simulations of Milky Way-like galaxies from the E-MOSAICS project, with physically motivated models for star formation, feedback, and the formation, evolution, and disruption of GCs, we identify the birth environments of present-day GCs. We find roughly half of GCs in these galaxies formed in situ (52.0 ± 1.0 per cent) between z ≈ 2–4, in turbulent, high-pressure discs fed by gas that was accreted without ever being strongly heated through a virial shock or feedback. A minority of GCs form during mergers (12.6 ± 0.6 per cent in major mergers, and 7.2 ± 0.5 per cent in minor mergers), but we find that mergers are important for preserving the GCs seen today by ejecting them from their natal, high density interstellar medium (ISM), where proto-GCs are rapidly destroyed due to tidal shocks from ISM substructure. This chaotic history of hierarchical galaxy assembly acts to mix the spatial and kinematic distribution of GCs formed through different channels, making it difficult to use observable GC properties to distinguish GCs formed in mergers from ones formed by smooth accretion, and similarly GCs formed in situ from those formed ex situ. These results suggest a simple picture of GC formation, in which GCs are a natural outcome of normal star formation in the typical, gas-rich galaxies that are the progenitors of present-day galaxies.

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