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 A spectroscopic survey of late-type giants in the Milky Way disk and local halo substructure

2007 ◽  
Vol 3 (S248) ◽  
pp. 506-507
Author(s):  
A. A. Sheffield ◽  
S. R. Majewski ◽  
A. M. Cheung ◽  
C. M. Hampton ◽  
J. D. Crane ◽  
...  
Keyword(s):  
High Velocity ◽  
Milky Way ◽  
Stellar Populations ◽  
Radial Velocities ◽  
Solar Neighborhood ◽  
Proper Motions ◽  
Late Type ◽  
Halo Stars ◽  
Medium Resolution ◽  
Galactic Stellar Populations

AbstractWe report the results of a survey of late-type giants aimed at understanding the nature of the disk and nearby halo Galactic stellar populations. We have obtained medium resolution (2–4 Å) spectra for 749 late K and early M giants at mid-latitudes selected from the 2MASS catalog with the FOBOS system at Fan Mountain Observatory. These spectra provide radial velocities (RVs) at the 5 km s−1 level, spectroscopic [Fe/H] good to σ[Fe/H] = 0.25 dex, and information on the relative abundances of Mg/Fe and Na/Fe in these stars. Proper motions from UCAC2 are used to search for local substructures, in particular the leading arm of the Sagittarius tidal streamer passing through the solar neighborhood. The combined proper motions and RVs yield full 6D stellar space motions. We have, by way of kinematics, relatively cleanly isolated the thick disk from the typically high velocity substructures that compose the nearby halo.We find evidence for substructure in the kinematics and metallicities of local halo stars.

scholarly journals The RAVE harvest: from the relation between abundances and kinematic of the Milky Way stars to tools for the abundance analysis of the spectra

2013 ◽  
Vol 9 (S298) ◽  
pp. 292-297
Author(s):  
Corrado Boeche ◽  
Keyword(s):  
Milky Way ◽  
Radial Velocities ◽  
Proper Motions ◽  
Chemical Abundances ◽  
Stellar Spectra ◽  
Chemical Gradients ◽  
Single Process ◽  
The Galaxy ◽  
Nearby Stars ◽  
Kinematic Information

AbstractRAVE is a spectroscopic survey of the Milky Way which collected more than 500,000 stellar spectra of nearby stars in the Galaxy. The RAVE consortium analysed these spectra to obtain radial velocities, stellar parameters and chemical abundances. These data, together with spatial and kinematic information like positions, proper motions, and distance estimations, make the RAVE database a rich source for galactic archaeology. I present recent investigations on the chemo-kinematic relations and chemical gradients in the Milky Way disk using RAVE data and compare our results with the Besançon models. I also present the code SPACE, an evolution of the RAVE chemical pipeline, which integrates the measurements of stellar parameters and chemical abundances in one single process.

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 Using ground based data as a precursor for Gaia in getting proper motions of satellites

2017 ◽  
Vol 12 (S330) ◽  
pp. 210-213
Author(s):  
Tobias K. Fritz ◽  
Sean T. Linden ◽  
Paul Zivick ◽  
Nitya Kallivayalil ◽  
Jo Bovy
Keyword(s):  
Adaptive Optics ◽  
Globular Cluster ◽  
Proper Motion ◽  
Milky Way ◽  
Dwarf Galaxy ◽  
Optical Data ◽  
Line Of Sight ◽  
Wide Field ◽  
Proper Motions ◽  
Tidal Stream

AbstractWe present our effort to measure the proper motions of satellites in the halo of the Milky Way with mainly ground based telescopes as a precursor on what is possible with Gaia. For our first study, we used wide field optical data from the LBT combined with a first epoch of SDSS observations, on the globular cluster Palomar 5 (Pal 5). Since Pal 5 is associated with a tidal stream it is very useful to constrain the shape of the potential of the Milky Way. The motion and other properties of the Pal 5 system constrain the inner halo of the Milky Way to be rather spherical. Further, we combined adaptive optics and HST to get an absolute proper motion of the globular cluster Pyxis. Using the proper motion and the line-of-sight velocity we find that the orbit of Pyxis is rather eccentric with its apocenter at more than 100 kpc and its pericenter at about 30 kpc. The dynamics excludes an association with the ATLAS stream, the Magellanic clouds, and all satellites of the Milky Way at least down to the mass of Leo II. However, the properties of Pyxis, like metallicity and age, point to an origin from a dwarf of at least the mass of Leo II. We therefore propose that Pyxis originated from an unknown relatively massive dwarf galaxy, which is likely today fully disrupted. Assuming that Pyxis is bound to the Milky Way we derive a 68% lower limit on the mass of the Milky Way of 9.5 × 1011 M⊙.

scholarly journals The mass of our Galaxy from satellite proper motions in the Gaia era

2020 ◽  
Vol 494 (4) ◽  
pp. 5178-5193 ◽  
Author(s):  
T K Fritz ◽  
A Di Cintio ◽  
G Battaglia ◽  
C Brook ◽  
S Taibi
Keyword(s):  
Milky Way ◽  
Anisotropy Parameter ◽  
Large Magellanic Cloud ◽  
Mass Determination ◽  
Proper Motions ◽  
Radial Density ◽  
Full Sample ◽  
Scale Free ◽  
Virial Mass ◽  
Gaia Dr2

ABSTRACT We use Gaia DR2 systemic proper motions of 45 satellite galaxies to constrain the mass of the Milky Way using the scale-free mass estimator of Watkins et al. (2010). We first determine the anisotropy parameter β, and the tracer satellites’ radial density index γ to be β = $-0.67^{+0.45}_{-0.62}$ and γ = 2.11 ± 0.23. When we exclude possible former satellites of the Large Magellanic Cloud, the anisotropy changes to β = $-0.21^{+0.37}_{-0.51}$. We find that the index of the Milky Way’s gravitational potential α, which is dependent on the mass itself, is the parameter with the largest impact on the mass determination. Via comparison with cosmological simulations of Milky Way-like galaxies, we carried out a detailed analysis of the estimation of the observational uncertainties and their impact on the mass estimator. We found that the mass estimator is biased when applied naively to the satellites of simulated Milky Way haloes. Correcting for this bias, we obtain for our Galaxy a mass of $0.58^{+0.15}_{-0.14}\times 10^{12}$ M⊙ within 64 kpc, as computed from the inner half of our observational sample, and $1.43^{+0.35}_{-0.32}\times 10^{12}$ M⊙ within 273 kpc, from the full sample; this latter value extrapolates to a virial mass of $M_\mathrm{vir\, \Delta =97}=1.51^{+0.45}_{-0.40} \times 10^{12}\,{\rm M}_{\odot }$ corresponding to a virial radius of Rvir = 308 ± 29 kpc. This value of the Milky Way mass lies in-between other mass estimates reported in the literature, from various different methods.

scholarly journals Reliability of the Measured Velocity Anisotropy of the Milky Way Stellar Halo

2017 ◽  
Vol 841 (2) ◽  
pp. 91 ◽  
Author(s):  
Kohei Hattori ◽  
Monica Valluri ◽  
Sarah R. Loebman ◽  
Eric F. Bell
Keyword(s):  
Milky Way ◽  
Measured Velocity ◽  
Velocity Anisotropy ◽  
Stellar Halo

scholarly journals A large catalog of young active RAVE stars in the Solar neighborhood

2016 ◽  
Vol 12 (S328) ◽  
pp. 143-145
Author(s):  
Maruša Žerjal ◽  
Tomaž Zwitter ◽  
Gal Matijevič ◽  
Keyword(s):  
Main Sequence ◽  
Classification Algorithm ◽  
Radial Velocities ◽  
Solar Neighborhood ◽  
Solar Neighbourhood ◽  
Proper Motions ◽  
Active Stars ◽  
Single Field ◽  
Infrared Triplet

AbstractThe catalog of 38,000 chromospherically active RAVE dwarfs represents one of the largest samples of young active solar-like and later-type single field stars in the Solar neighbourhood. It was established from the unbiased magnitude limited RAVE Survey using an unsupervised stellar classification algorithm based merely on stellar fluxes (Ca II infrared triplet). Using a newly-calibrated age-activity relation, ~15,000 active stars are estimated to be younger than 1 Gyr. Almost 2000 stars are presumably younger than ~100 Myr and possibly still in the pre-main sequence phase, the latter being supported by their significant offset from the main sequence in the NUV − V versus J − K space. 16,000 stars from the sample have positional and velocity vectors available (using TGAS parallaxes and proper motions and radial velocities from RAVE).

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.

scholarly journals On the Co-orbitation of Satellite Galaxies along the Great Plane of Andromeda: NGC 147, NGC 185, and Expectations from Cosmological Simulations

2021 ◽  
Vol 923 (1) ◽  
pp. 42
Author(s):  
Marcel S. Pawlowski ◽  
Sangmo Tony Sohn
Keyword(s):  
Milky Way ◽  
Detailed Comparison ◽  
Satellite System ◽  
Line Of Sight ◽  
Proper Motions ◽  
Velocity Correlation ◽  
Cosmological Simulations ◽  
Rotating Structure ◽  
Motion Measurements ◽  
Satellite Galaxies

Abstract Half of the satellite galaxies of Andromeda form a narrow plane termed the Great Plane of Andromeda (GPoA), and their line-of-sight velocities display a correlation reminiscent of a rotating structure. Recently reported first proper-motion measurements for the on-plane satellites NGC 147 and NGC 185 indicate that they indeed co-orbit along the GPoA. This provides a novel opportunity to compare the M31 satellite system to ΛCDM expectations. We perform the first detailed comparison of the orbital alignment of two satellite galaxies beyond the Milky Way with several hydrodynamical and dark-matter-only cosmological simulations (Illustris TNG50, TNG100, ELVIS, and PhatELVIS) in the context of the Planes of Satellite Galaxies Problem. In line with previous works, we find that the spatial flattening and line-of-sight velocity correlation are already in substantial tension with ΛCDM, with none of the simulated analogs simultaneously reproducing both parameters. Almost none (3%–4%) of the simulated systems contain two satellites with orbital poles as well aligned with their satellite plane as indicated by the most likely proper motions of NGC 147 and NGC 185. However, within current measurement uncertainties, it is common (≈70%) that the two best-aligned satellites of simulated systems are consistent with the orbital alignment. Yet, the chance that any two simulated on-plane satellites have as well-aligned orbital poles as observed is low (≈4%). We conclude that confirmation of the tight orbital alignment for these two objects via improved measurements, or the discovery of similar alignments for additional GPoA members, holds the potential to further raise the tension with ΛCDM expectations.

scholarly journals Kinematics of highly r-process-enhanced halo stars: Evidence for origins in now-destroyed ultra-faint dwarf galaxies

2019 ◽  
Vol 14 (S353) ◽  
pp. 71-74
Author(s):  
Kaley Brauer ◽  
Alexander P. Ji ◽  
Kohei Hattori ◽  
Sergio Escobar ◽  
Anna Frebel
Keyword(s):  
Milky Way ◽  
Dwarf Galaxies ◽  
Building Blocks ◽  
Specific Chemical ◽  
Halo Stars ◽  
Novel Approach ◽  
Chemical Signatures ◽  
Formation History ◽  
Stellar Halo ◽  
R Process

AbstractThe Milky Way’s stellar halo preserves a fossil record of smaller dwarf galaxies that merged with the Milky Way throughout its formation history. Currently, though, we lack reliable ways to identify which halo stars originated in which dwarf galaxies or even which stars were definitively accreted. Selecting stars with specific chemical signatures may provide a way forward. We investigate this theoretically and observationally for stars with r-process nucleosynthesis signatures. Theoretically, we combine high-resolution cosmological simulations with an empirically-motivated treatment of r-process enhancement. We find that around half of highly r-process-enhanced metal-poor halo stars may have originated in early ultra-faint dwarf galaxies that merged into the Milky Way during its formation. Observationally, we use Gaia DR2 to compare the kinematics of highly r-process-enhanced halo stars with those of normal halo stars. R-process-enhanced stars have higher galactocentric velocities than normal halo stars, suggesting an accretion origin. If r-process-enhanced stars largely originated in accreted ultra-faint dwarf galaxies, halo stars we observe today could play a key role in understanding the smallest building blocks of the Milky Way via this novel approach of chemical tagging

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