scholarly journals What is the Milky Way outer halo made of?

2017 ◽  
Vol 608 ◽  
pp. A145 ◽  
Author(s):  
G. Battaglia ◽  
P. North ◽  
P. Jablonka ◽  
M. Shetrone ◽  
D. Minniti ◽  
...  
Keyword(s):  
Milky Way ◽  
Formation Rate ◽  
Large Magellanic Cloud ◽  
Solar Neighborhood ◽  
Asymptotic Giant Branch ◽  
Chemical Abundance ◽  
Data Set ◽  
Halo Stars ◽  
Stellar Halo ◽  
Giant Branch Stars

In a framework where galaxies form hierarchically, extended stellar haloes are predicted to be an ubiquitous feature around Milky Way-like galaxies and to consist mainly of the shredded stellar component of smaller galactic systems. The type of accreted stellar systems are expected to vary according to the specific accretion and merging history of a given galaxy, and so is the fraction of stars formed in situ versus accreted. Analysis of the chemical properties of Milky Way halo stars out to large Galactocentric radii can provide important insights into the properties of the environment in which the stars that contributed to the build-up of different regions of the Milky Way stellar halo formed. In this work we focus on the outer regions of the Milky Way stellar halo, by determining chemical abundances of halo stars with large present-day Galactocentric distances, >15 kpc. The data-set we acquired consists of high resolution HET/HRS, Magellan/MIKE and VLT/UVES spectra for 28 red giant branch stars covering a wide metallicity range, −3.1 ≲ [Fe/H] ≲−0.6. We show that the ratio of α-elements over Fe as a function of [Fe/H] for our sample of outer halo stars is not dissimilar from the pattern shown by MW halo stars from solar neighborhood samples. On the other hand, significant differences appear at [Fe/H] ≳−1.5 when considering chemical abundance ratios such as [Ba/Fe], [Na/Fe], [Ni/Fe], [Eu/Fe], [Ba/Y]. Qualitatively, this type of chemical abundance trends are observed in massive dwarf galaxies, such as Sagittarius and the Large Magellanic Cloud. This appears to suggest a larger contribution in the outer halo of stars formed in an environment with high initial star formation rate and already polluted by asymptotic giant branch stars with respect to inner halo samples.

scholarly journals Chemical abundances of field halo stars - Implications for the building blocks of the Milky Way

2019 ◽  
Vol 14 (S351) ◽  
pp. 24-33
Author(s):  
Miho N. Ishigaki
Keyword(s):  
Milky Way ◽  
Building Blocks ◽  
Chemical Information ◽  
Wide Field ◽  
Chemical Abundance ◽  
Chemical Abundances ◽  
Halo Stars ◽  
Dimensional Phase Space ◽  
Stellar Halo ◽  
Detailed Chemical

AbstractI would like to review recent efforts of detailed chemical abundance measurements for field Milky Way halo stars. Thanks to the advent of wide-field spectroscopic surveys up to a several kpc from the Sun, large samples of field halo stars with detailed chemical measurements are continuously expanding. Combination of the chemical information and full six dimensional phase-space information is now recognized as a powerful tool to identify cosmological accretion events that have built a sizable fraction of the present-day stellar halo. Future observational prospects with wide-field spectroscopic surveys and theoretical prospects with supernova nucleosynthetic yields are also discussed.

scholarly journals Measuring the Stellar Halo Velocity Anisotropy With 3D Kinematics

2015 ◽  
Vol 11 (S317) ◽  
pp. 288-289
Author(s):  
Emily C. Cunningham ◽  
Alis J. Deason ◽  
Puragra Guhathakurta ◽  
Constance M. Rockosi ◽  
Roeland P. van der Marel ◽  
...  
Keyword(s):  
Milky Way ◽  
Anisotropy Parameter ◽  
Radial Velocities ◽  
Solar Neighborhood ◽  
Line Of Sight ◽  
Proper Motions ◽  
Velocity Anisotropy ◽  
Halo Stars ◽  
Stellar Halo ◽  
Kinematic Information

AbstractWe present the first measurement of the anisotropy parameter β using 3D kinematic information outside of the solar neighborhood. Our sample consists of 13 Milky Way halo stars with measured proper motions and radial velocities in the line of sight of M31. Proper motions were measured using deep, multi-epoch HST imaging, and radial velocities were measured from Keck II/DEIMOS spectra. We measure β = −0.3−0.9+0.4, which is consistent with isotropy, and inconsistent with measurements in the solar neighborhood. We suggest that this may be the kinematic signature of a relatively early, massive accretion event, or perhaps several such events.

scholarly journals The mass of the Milky Way out to 100 kpc using halo stars

2020 ◽  
Author(s):  
Alis J Deason ◽  
Denis Erkal ◽  
Vasily Belokurov ◽  
Azadeh Fattahi ◽  
Facundo A Gómez ◽  
...  
Keyword(s):  
Distribution Function ◽  
Mass Concentration ◽  
Milky Way ◽  
Function Analysis ◽  
Large Magellanic Cloud ◽  
Systematic Bias ◽  
Cosmological Simulations ◽  
Halo Stars ◽  
Systematic Effects ◽  
Mass Estimate

Abstract We use a distribution function analysis to estimate the mass of the Milky Way out to 100 kpc using a large sample of halo stars. These stars are compiled from the literature, and the vast majority ($\sim \! 98\%$) 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 halos from cosmological simulations tend to underestimate the true halo mass. After applying our method to the Milky Way data we find a mass within 100 kpc of M( < 100kpc) = 6.07 ± 0.29(stat.) ± 1.21(sys.) × 1011M⊙. 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% systematic bias, and a 20% 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) Milky Way mass of M200c = 1.01 ± 0.24 × 1012M⊙, or (post-LMC infall) mass of M200c = 1.16 ± 0.24 × 1012 M⊙ when a 1.5 × 1011M⊙ mass of a rigid LMC is included.

scholarly journals Equilibrium models of the Milky Way mass are biased high by the LMC

2020 ◽  
Vol 498 (4) ◽  
pp. 5574-5580 ◽  
Author(s):  
Denis Erkal ◽  
Vasily A Belokurov ◽  
Daniel L Parkin
Keyword(s):  
Milky Way ◽  
Large Magellanic Cloud ◽  
Substantial Effect ◽  
Magellanic Cloud ◽  
Equilibrium Models ◽  
Simple Modification ◽  
Bulk Motion ◽  
Stellar Halo ◽  
Large Satellite

ABSTRACT Recent measurements suggest that the Large Magellanic Cloud (LMC) may weigh as much as 25 per cent of the Milky Way (MW). In this work, we explore how such a large satellite affects mass estimates of the MW based on equilibrium modelling of the stellar halo or other tracers. In particular, we show that if the LMC is ignored, the MW mass within 200 kpc is overestimated by as much as 50 per cent. This bias is due to the bulk motion in the outskirts of the Galaxy’s halo and can be, at least in part, accounted for with a simple modification to the equilibrium modelling. Finally, we show that the LMC has a substantial effect on the orbit Leo I which acts to increase its present-day speed relative to the MW. We estimate that accounting for a $1.5\times 10^{11} \, \mathrm{M}_\odot$ LMC would lower the inferred MW mass to $\sim 10^{12} \, \mathrm{M}_\odot$.

scholarly journals Frequency maps as a probe of secular evolution in the Milky Way

2012 ◽  
Vol 10 (H16) ◽  
pp. 349-349
Author(s):  
Monica Valluri
Keyword(s):  
Dark Matter ◽  
Distribution Function ◽  
Phase Space ◽  
Milky Way ◽  
Space Distribution ◽  
Compact Representation ◽  
Phase Space Distribution ◽  
Secular Evolution ◽  
Halo Stars ◽  
Stellar Halo

AbstractThe frequency analysis of the orbits of halo stars and dark matter particles from a cosmological hydrodynamical simulation of a disk galaxy from the MUGS collaboration (Stinson et al. 2010) shows that even if the shape of the dark matter halo is nearly oblate, only about 50% of its orbits are on short-axis tubes, confirming a previous result: under baryonic condensation all orbit families can deform their shapes without changing orbital type (Valluri et al. 2010). Orbits of dark matter particles and halo stars are very similar reflecting their common accretion origin and the influence of baryons. Frequency maps provide a compact representation of the 6-D phase space distribution that also reveals the history of the halo (Valluri et al. 2012). The 6-D phase space coordinates for a large population of halo stars in the Milky Way that will be obtained from future surveys can be used to reconstruct the phase-space distribution function of the stellar halo. The similarity between the frequency maps of halo stars and dark matter particles (Fig. 1) implies that reconstruction of the stellar halo distribution function can reveal the phase space distribution of the unseen dark matter particles and provide evidence for secular evolution. MV is supported by NSF grant AST-0908346 and the Elizabeth Crosby grant.

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