scholarly journals Modeling mass independent of anisotropy: A comparison between Andromeda and Milky Way satellites

2009 ◽  
Vol 5 (H15) ◽  
pp. 79-79 ◽  
Author(s):  
J. Wolf
Keyword(s):  
Milky Way ◽  
Mass Scale ◽  
Line Of Sight ◽  
Kinematic Data ◽  
Dwarf Spheroidal Galaxies ◽  
Stellar Radius ◽  
Velocity Anisotropy ◽  
Characteristic Radius ◽  
Stellar Velocity ◽  
Mass Profile

Mass profile determinations for dispersion supported galaxies from line-of-sight velocities are subject to large uncertainties associated with the unknown stellar velocity anisotropy. We demonstrate both analytically and with available kinematic data (for systems spanning eight decades in luminosity) that the mass-anisotropy degeneracy is effectively eliminated at a characteristic radius that is close to the 3D deprojected half-light radius of the stars. This allows a simple, yet accurate formula to describe the half-light dark matter masses of all hot systems, including dwarf spheroidal galaxies (dSphs), based on directly observable parameters: M1/2 = 4σ2LOSRhalf/G, where Rhalf is the 2D projected half-light radius and σLOS is the luminosity-weighted square of the line-of-sight velocity dispersion. The fact that masses are well-constrained within a characteristic stellar radius has allowed our group to perform systematic, accurate mass determinations for Milky Way dSphs and to conclude that they all have a common mass scale of approximately 107 M⊙ within 300 pc of their centers. We extend this work to the satellite population of Andromeda using Keck/DEIMOS spectroscopy of individual stars. We find that the Andromeda dSphs are also consistent with sharing a common mass, but that it is offset from the scale of the Milky Way dSphs by a factor of ~2.

scholarly journals Modeling mass independent of anisotropy

2010 ◽  
Vol 6 (S271) ◽  
pp. 110-118
Author(s):  
Joe Wolf
Keyword(s):  
Spatial Variation ◽  
Milky Way ◽  
Velocity Dispersion ◽  
Galaxy Cluster ◽  
Elliptical Galaxies ◽  
Line Of Sight ◽  
Dwarf Spheroidal Galaxies ◽  
Dispersion Profile ◽  
Stellar Velocity ◽  
Dwarf Elliptical Galaxies

AbstractBy manipulating the spherical Jeans equation, Wolf et al. (2010) show that the mass enclosed within the 3D deprojected half-light radius r1/2 can be determined with only mild assumptions about the spatial variation of the stellar velocity dispersion anisotropy as long as the projected velocity dispersion profile is fairly flat near the half-light radius, as is typically observed. They find M1/2 = 3 G−1 〈σ2los〉 r1/2 ≃ 4 G−1 〈σ2los〉 Re, where 〈σ2los〉 is the luminosity-weighted square of the line-of-sight velocity dispersion and Re is the 2D projected half-light radius. This finding can be used to show that all of the Milky Way dwarf spheroidal galaxies (MW dSphs) are consistent with having formed within a halo of mass approximately 3 × 109 M⊙, assuming a ΛCDM cosmology. In addition, the dynamical I-band mass-to-light ratio ϒI1/2 vs. M1/2 relation for dispersion-supported galaxies follows a U-shape, with a broad minimum near ϒI1/2 ≃ 3 that spans dwarf elliptical galaxies to normal ellipticals, a steep rise to ϒI1/2 ≃ 3,200 for ultra-faint dSphs, and a more shallow rise to ϒI1/2 ≃ 800 for galaxy cluster spheroids.

scholarly journals Mass Modelling of dwarf Spheroidal Galaxies

2007 ◽  
Vol 3 (S244) ◽  
pp. 321-325
Author(s):  
Jarosław Klimentowski ◽  
Ewa L. Łokas ◽  
Stelios Kazantzidis ◽  
Francisco Prada ◽  
Lucio Mayer ◽  
...  
Keyword(s):  
Milky Way ◽  
Velocity Dispersion ◽  
Dwarf Galaxy ◽  
Data Sets ◽  
Kinematic Data ◽  
Dwarf Spheroidal Galaxies ◽  
Two Component ◽  
Tidal Tails ◽  
Better Than ◽  
Spheroidal Galaxies

AbstractWe study the origin and properties of unbound stars in the kinematic samples of dwarf spheroidal galaxies. For this purpose we have run a high resolution N-body simulation of a two-component dwarf galaxy orbiting in a Milky Way potential. We create mock kinematic data sets by observing the dwarf in different directions. When the dwarf is observed along the tidal tails the kinematic samples are strongly contaminated by unbound stars from the tails. However, most of the unbound stars can be removed by the method of interloper rejection proposed by den Hartog & Katgert. We model the velocity dispersion profiles of the cleaned-up kinematic samples using solutions of the Jeans equation. We show that even for such a strongly stripped dwarf the Jeans analysis, when applied to cleaned samples, allows us to reproduce the mass and mass-to-light ratio of the dwarf with accuracy typically better than 25%.

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.

Constraining the Milky Way non-axisymmetries with Gaia

2019 ◽  
Vol 14 (S353) ◽  
pp. 61-64
Author(s):  
B. Famaey ◽  
G. Monari ◽  
A. Siebert ◽  
O. Bienaymé ◽  
R. Ibata ◽  
...  
Keyword(s):  
Velocity Field ◽  
Milky Way ◽  
Galactic Disk ◽  
Kinematic Data ◽  
The Status ◽  
Stellar Velocity ◽  
Current Modelling

AbstractThe unprecedented amount and accuracy of kinematic data from the second release of the Gaia mission have started revolutionizing our understanding of the dynamics of the Milky Way disk. The detailed stellar velocity field in the Galactic disk should allow us to constrain with unprecedented precision the parameters of the non-axisymmetric modes of the disk. We present here the status of our current modelling efforts in this area, and their implication on the dynamics of the Galactic bar in particular.

scholarly journals Kinematics of Milky Way Satellites: Mass Estimates, Rotation Limits, and Proper Motions

2010 ◽  
Vol 2010 ◽  
pp. 1-11 ◽  
Author(s):  
Louis E. Strigari
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Milky Way ◽  
Dark Matter Halo ◽  
Data Sets ◽  
Proper Motions ◽  
Kinematic Data ◽  
Velocity Anisotropy ◽  
Mass Distributions ◽  
Wide Range

In the past several years kinematic data sets from Milky Way satellite galaxies have greatly improved, furthering the evidence that these systems are the most dark matter dominated objects known. This paper discusses a maximum likelihood formalism that extracts important quantities from these kinematic data sets, including the amplitude of a rotational signal, proper motions, and the mass distributions. Using a simple model for galaxy rotation it is shown that the expected error on the amplitude of a rotational signal is∼0.5 kms−1with∼103stars from either classical or ultra-faint satellites. As an example Sculptor is analyzed for the presence of a rotational signal; no significant detection of rotation is found, with a 90% c.l. upper limit of∼2 kms−1. A criterion for model selection is presented that determines the parameters required to describe the dark matter halo density profiles and the stellar velocity anisotropy. Applied to four data sets with a wide range of velocities, models with variable velocity anisotropy are preferred relative to those with constant velocity anisotropy, and that central dark matter profiles both less cuspy and more cuspy than Lambda-Cold Dark Matter-based fits are equally acceptable.

Variation of the amount of hydrogen along the galactic ridge

1967 ◽  
Vol 31 ◽  
pp. 171-172
Author(s):  
Th. Schmidt-Kaler
Keyword(s):  
Surface Brightness ◽  
Milky Way ◽  
Neutral Hydrogen ◽  
Line Of Sight ◽  
Optical Surface ◽  
Hydrogen Density ◽  
Continuous Radiation ◽  
Galactic Longitude

The integralNHof neutral-hydrogen density along the line of sight is determined from the Kootwijk and Sydney surveys. The run ofNHwith galactic longitude agrees well with that of thermal continuous radiation and that of the optical surface brightness of the Milky Way.

scholarly journals Probing non-spherical dark halos in the Galactic dwarf satellites

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.

scholarly journals Pushing back the limits: detailed properties of dwarf galaxies in a ΛCDM universe

2018 ◽  
Vol 616 ◽  
pp. A96 ◽  
Author(s):  
Yves Revaz ◽  
Pascale Jablonka
Keyword(s):  
Star Formation ◽  
Local Group ◽  
Dwarf Galaxies ◽  
Mass Scale ◽  
Dwarf Spheroidal Galaxies ◽  
The Galaxy ◽  
Dynamical Simulations ◽  
Ursa Minor ◽  
Stellar Properties ◽  
Star Formation Histories

We present the results of a set of high-resolution chemo-dynamical simulations of dwarf galaxies in a ΛCDM cosmology. Out of an original (3.4 Mpc/h)3 cosmological box, a sample of 27 systems are re-simulated from z = 70 to z = 0 using a zoom-in technique. Gas and stellar properties are confronted to the observations in the greatest details: in addition to the galaxy global properties, we investigated the model galaxy velocity dispersion profiles, half-light radii, star formation histories, stellar metallicity distributions, and [Mg/Fe] abundance ratios. The formation and sustainability of the metallicity gradients and kinematically distinct stellar populations are also tackled. We show how the properties of six Local Group dwarf galaxies, NGC 6622, Andromeda II, Sculptor, Sextans, Ursa Minor and Draco are reproduced, and how they pertain to three main galaxy build-up modes. Our results indicate that the interaction with a massive central galaxy could be needed for a handful of Local Group dwarf spheroidal galaxies only, the vast majority of the systems and their variety of star formation histories arising naturally from a ΛCDM framework. We find that models fitting well the local Group dwarf galaxies are embedded in dark haloes of mass between 5 × 108 to a few 109 M⊙, without any missing satellite problem. We confirm the failure of the abundance matching approach at the mass scale of dwarf galaxies. Some of the observed faint however gas-rich galaxies with residual star formation, such as Leo T and Leo P, remain challenging. They point out the need of a better understanding of the UV-background heating.

scholarly journals STELLAR VELOCITY DISPERSION AND ANISOTROPY OF THE MILKY WAY INNER HALO

2015 ◽  
Vol 813 (2) ◽  
pp. 89 ◽  
Author(s):  
Charles King III ◽  
Warren R. Brown ◽  
Margaret J. Geller ◽  
Scott J. Kenyon
Keyword(s):  
Milky Way ◽  
Velocity Dispersion ◽  
Stellar Velocity
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