Kinematical & Chemical Characteristics of the Thin and 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.

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The chemical fingerprints of the thin and the thick disk

Proceedings of the International Astronomical Union ◽

10.1017/s1743921308027592 ◽

2008 ◽

Vol 4 (S254) ◽

pp. 197-202

Author(s):

Sofia Feltzing ◽

Sally Oey ◽

Thomas Bensby

Keyword(s):

Past History ◽

Thick Disk ◽

Chemical Abundance ◽

Dwarf Stars ◽

Abundance Patterns ◽

The Galaxy ◽

Thin And Thick Disks ◽

Thick Disks ◽

Definition Of ◽

Galactic Stellar Populations

AbstractThe past history and origin of the different Galactic stellar populations are manifested in their different chemical abundance patterns. We obtained new elemental abundances for 553 F and G dwarf stars, to more accurately quantify these patterns for the thin and thick disks. However, the exact definition of disk membership is not straightforward. Stars that have a high likelihood of belonging to the thin disk show different abundance patterns from those for the thick disk. In contrast, we show that stars for the Hercules Stream do not show unique abundance patterns, but rather follow those of the thin and thick disks. This strongly suggests that the Hercules Stream is a feature induced by internal dynamics within the Galaxy rather than the remnant of an accreted satellite.

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Origin of the galaxy morphology

Symposium - International Astronomical Union ◽

10.1017/s0074180900207614 ◽

2003 ◽

Vol 208 ◽

pp. 431-432

Author(s):

N. Nakasato

Keyword(s):

Dark Matter ◽

Star Formation ◽

High Resolution ◽

Cold Dark Matter ◽

Star Formation History ◽

The Galaxy ◽

Particle Hydrodynamics ◽

History Of ◽

Analytic Models ◽

Galaxy Morphology

In the current most plausible Cold Dark Matter (CDM) cosmology, larger halos increase their mass by the progressive mergers of smaller clumps. Due to these progressive merger events, galaxies have formed and evolved. Such merger events could trigger star bursts depending on mass of a merging object. In other words, star formation history reflects the strength of the interaction between a galaxy and merging objects. Also, a several merger events strongly affect the development of the morphology of galaxies as assumed in semi-analytic models. In the most advanced semi-analytic models, N-body simulations of dark matter particles are used to obtain the merging history of halos. By combining the description of radiative cooling, hydrodynamics and star formation with the obtained merging history, such models successfully have explained the various qualitative predictions. Here, we show the results of similar approach but using a fullly numerical model. In contrast to the semi-analytic models, we use our high resolution Smoothed Particle Hydrodynamics (SPH) models. With our SPH code, we try to tackle the problem of the galaxy morphology. We have done a several handful high-resolution SPH simulations and analyzed the merging history of such models. Accordingly, we can see the relation between the obtained morphology and the merging history or other physical properties of the model.

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A dark matter profile to model diverse feedback-induced core sizes of ΛCDM haloes

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2101 ◽

2020 ◽

Vol 497 (2) ◽

pp. 2393-2417 ◽

Cited By ~ 5

Author(s):

Alexandres Lazar ◽

James S Bullock ◽

Michael Boylan-Kolchin ◽

T K Chan ◽

Philip F Hopkins ◽

...

Keyword(s):

Dark Matter ◽

Galaxy Formation ◽

Cold Dark Matter ◽

Milky Way ◽

Dark Matter Halo ◽

Constant Density ◽

Core Formation ◽

Density Profiles ◽

The Galaxy ◽

Two Parameter

ABSTRACT We analyse the cold dark matter density profiles of 54 galaxy haloes simulated with Feedback In Realistic Environments (FIRE)-2 galaxy formation physics, each resolved within $0.5{{\ \rm per\ cent}}$ of the halo virial radius. These haloes contain galaxies with masses that range from ultrafaint dwarfs ($M_\star \simeq 10^{4.5}\, \mathrm{M}_{\odot }$) to the largest spirals ($M_\star \simeq 10^{11}\, \mathrm{M}_{\odot }$) and have density profiles that are both cored and cuspy. We characterize our results using a new, analytic density profile that extends the standard two-parameter Einasto form to allow for a pronounced constant density core in the resolved innermost radius. With one additional core-radius parameter, rc, this three-parameter core-Einasto profile is able to characterize our feedback-impacted dark matter haloes more accurately than other three-parameter profiles proposed in the literature. To enable comparisons with observations, we provide fitting functions for rc and other profile parameters as a function of both M⋆ and M⋆/Mhalo. In agreement with past studies, we find that dark matter core formation is most efficient at the characteristic stellar-to-halo mass ratio M⋆/Mhalo ≃ 5 × 10−3, or $M_{\star } \sim 10^9 \, \mathrm{M}_{\odot }$, with cores that are roughly the size of the galaxy half-light radius, rc ≃ 1−5 kpc. Furthermore, we find no evidence for core formation at radii $\gtrsim 100\ \rm pc$ in galaxies with M⋆/Mhalo < 5 × 10−4 or $M_\star \lesssim 10^6 \, \mathrm{M}_{\odot }$. For Milky Way-size galaxies, baryonic contraction often makes haloes significantly more concentrated and dense at the stellar half-light radius than DMO runs. However, even at the Milky Way scale, FIRE-2 galaxy formation still produces small dark matter cores of ≃ 0.5−2 kpc in size. Recent evidence for a ∼2 kpc core in the Milky Way’s dark matter halo is consistent with this expectation.

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Tidal Tails and the Shape of the Dark Matter Halo

Publications of the Astronomical Society of Australia ◽

10.1071/as04080 ◽

2005 ◽

Vol 22 (3) ◽

pp. 190-194 ◽

Cited By ~ 2

Author(s):

Geraint F. Lewis ◽

Rodrigo A. Ibata

Keyword(s):

Dark Matter ◽

Cold Dark Matter ◽

Milky Way ◽

Dwarf Galaxy ◽

Observational Evidence ◽

Dark Matter Halo ◽

Dark Matter Halos ◽

Fundamental Understanding ◽

Tidal Tails ◽

Precise Interpretation

AbstractCold dark matter cosmologies successfully accounts for the distribution of matter on large scales. On smaller scales, these cosmological models predict that galaxies like our own Milky Way should be enveloped in massive dark matter halos. Furthermore, these halos should be significantly flattened or even triaxial. Recent observational evidence, drawn from the demise of the Sagittarius dwarf galaxy as it is cannibalized by our own, indicates that the potential of the Milky Way must be close to spherical. While the precise interpretation of the observational evidence is under debate, an apparently spherical halo may signify a pronounced failing of dark matter models, and may even indicate a failure in our fundamental understanding of gravity.

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The mass of the Milky Way from satellite dynamics

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz365 ◽

2019 ◽

Vol 484 (4) ◽

pp. 5453-5467 ◽

Cited By ~ 37

Author(s):

Thomas M Callingham ◽

Marius Cautun ◽

Alis J Deason ◽

Carlos S Frenk ◽

Wenting Wang ◽

...

Keyword(s):

Dark Matter ◽

Galaxy Formation ◽

Cold Dark Matter ◽

Milky Way ◽

Dimensional Space ◽

Dimensional Phase Space ◽

The Galaxy ◽

Galactic Satellites ◽

Mass Estimate ◽

True Mass

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 $c_{200}^{\rm {MW}}=10.9^{+2.6}_{-2.0}$.

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The impact of inelastic self-interacting dark matter on the dark matter structure of a Milky Way halo

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3315 ◽

2020 ◽

Author(s):

Kun Ting Eddie Chua ◽

Karia Dibert ◽

Mark Vogelsberger ◽

Jesús Zavala

Keyword(s):

Dark Matter ◽

High Speed ◽

Cold Dark Matter ◽

Milky Way ◽

Direct Detection ◽

Major Axis ◽

Inelastic Collisions ◽

Axis Ratio ◽

Lower Velocity ◽

The Impact

Abstract We study the effects of inelastic dark matter self-interactions on the internal structure of a simulated Milky Way (MW)-size halo. Self-interacting dark matter (SIDM) is an alternative to collisionless cold dark matter (CDM) which offers a unique solution to the problems encountered with CDM on sub-galactic scales. Although previous SIDM simulations have mainly considered elastic collisions, theoretical considerations motivate the existence of multi-state dark matter where transitions from the excited to the ground state are exothermic. In this work, we consider a self-interacting, two-state dark matter model with inelastic collisions, implemented in the Arepo code. We find that energy injection from inelastic self-interactions reduces the central density of the MW halo in a shorter timescale relative to the elastic scale, resulting in a larger core size. Inelastic collisions also isotropize the orbits, resulting in an overall lower velocity anisotropy for the inelastic MW halo. In the inner halo, the inelastic SIDM case (minor-to-major axis ratio s ≡ c/a ≈ 0.65) is more spherical than the CDM (s ≈ 0.4), but less spherical than the elastic SIDM case (s ≈ 0.75). The speed distribution f(v) of dark matter particles at the location of the Sun in the inelastic SIDM model shows a significant departure from the CDM model, with f(v) falling more steeply at high speeds. In addition, the velocity kicks imparted during inelastic collisions produce unbound high-speed particles with velocities up to 500 km s−1 throughout the halo. This implies that inelastic SIDM can potentially leave distinct signatures in direct detection experiments, relative to elastic SIDM and CDM.

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Probing non-spherical dark halos in the Galactic dwarf satellites

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313006789 ◽

2013 ◽

Vol 9 (S298) ◽

pp. 411-411

Author(s):

Kohei Hayashi ◽

Masashi Chiba

Keyword(s):

Dark Matter ◽

Cold Dark Matter ◽

Milky Way ◽

Velocity Dispersion ◽

Line Of Sight ◽

Spherical Structure ◽

Spherical Models ◽

Galactic Satellites ◽

Best Fitting

AbstractWe construct axisymmetric mass models for dwarf spheroidal (dSph) galaxies in the Milky Way to obtain realistic limits on the non-spherical structure of their dark halos. This is motivated by the fact that the observed luminous parts of the dSphs are actually non-spherical and cold dark matter models predict non-spherical virialized dark halos on sub-galactic scales. Applying these models to line-of-sight velocity dispersion profiles along three position angles in six Galactic satellites, we find that the best fitting cases for most of the dSphs yield not spherical but oblate and flattened dark halos. We also find that the mass of the dSphs enclosed within inner 300 pc varies depending on their total luminosities, contrary to the conclusion of previous spherical models. This suggests the importance of considering non-spherical shapes of dark halos in dSph mass models.

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