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 Starburst Feedback in Local, Massive Galaxies

2006 ◽  
Vol 2 (S235) ◽  
pp. 280-283
Author(s):  
Crystal L. Martin
Keyword(s):  
Surface Brightness ◽  
Milky Way ◽  
Velocity Dispersion ◽  
Rotation Speed ◽  
Far Infrared ◽  
Elliptical Galaxies ◽  
Evolutionary Path ◽  
Sky Surveys ◽  
Massive Galaxies ◽  
Stellar Velocity

Major mergers of gas-rich galaxies, each comparable in mass to the Milky Way, are rare at the present epoch. These events were readily identifed, however, two decades ago in far-infrared sky surveys (Soifer et al. 1986, 1987). Removal of the dust enshrouding these starbursts was almost immediately proposed as an evolutionary path to quasar formation (Sanders 1988). Recent measurements of the stellar velocity dispersion, rotation speed, and stellar surface brightness profile of these mergers suggest ULIRGs are indeed progenitors of field elliptical galaxies (Genzel et al. 2001; Tacconi et al. 2002).

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 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 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

scholarly journals The Search for Dark Matter in Draco and Ursa Minor: A Three Year Progress Report

1987 ◽  
Vol 117 ◽  
pp. 153-160 ◽  
Author(s):  
M. Aaronson ◽  
E. Olszewski
Keyword(s):  
Dark Matter ◽  
Velocity Dispersion ◽  
Progress Report ◽  
Radial Velocities ◽  
Circumstantial Evidence ◽  
Dwarf Spheroidal Galaxies ◽  
Ursa Minor ◽  
Stellar Velocity ◽  
Atmospheric Motions ◽  
Matter Component

We report the cumulative results of an on-going effort to measure the stellar velocity dispersion in two nearby dwarf spheroidal galaxies. Radial velocities having an accuracy ≲ 2 km s−1 have now been secured for ten stars in Ursa Minor and eleven stars in Draco (including 16 K giants and 5 C types). Most objects have been observed at two or more epochs. Stars having non-variable velocities yield in both dwarfs a large (∼ 10 km s−1) dispersion. These results cannot be explained by atmospheric motions, and circumstantial evidence suggests that the effects of undetected binaries are also not likely to be important. Instead, it seems that both spheroidals contain a substantial dark matter component, which therefore must be “cold” in form.

scholarly journals GMOS Spectroscopy of Globular Clusters in Dwarf Elliptical Galaxies

2007 ◽  
Vol 3 (S246) ◽  
pp. 429-430
Author(s):  
Bryan W. Miller ◽  
Jennifer Lotz ◽  
Michael Hilker ◽  
Markus Kissler-Patig ◽  
Thomas Puzia
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Elliptical Galaxies ◽  
Preliminary Results ◽  
Dwarf Elliptical Galaxies ◽  
Milky Way Halo

AbstractWe present a Gemini/GMOS program to measure spectroscopic metallicities and ages of globular clusters (GCs) and nuclei in dwarf elliptical galaxies in the Virgo and Fornax Clusters. Preliminary results indicate that the globular clusters are old and metal-poor, very similar to the GCs in the Milky Way halo. The nuclei tend to be more metal-rich than the globular clusters but more metal-poor and older, on average, than the stars in the bodies of the galaxies. The [α/Fe] ratio appears to be solar for the GCs, nuclei, and dEs, but the uncertainties do not exclude some globular clusters from being enhanced in alpha elements.

scholarly journals The radial velocity dispersion profile of the Galactic halo: constraining the density profile of the dark halo of the Milky Way

2005 ◽  
Vol 364 (2) ◽  
pp. 433-442 ◽  
Author(s):  
Giuseppina Battaglia ◽  
Amina Helmi ◽  
Heather Morrison ◽  
Paul Harding ◽  
Edward W. Olszewski ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Density Profile ◽  
Milky Way ◽  
Velocity Dispersion ◽  
Galactic Halo ◽  
Dark Halo ◽  
Dispersion Profile

scholarly journals STRIDES: Spectroscopic and photometric characterization of the environment and effects of mass along the line of sight to the gravitational lenses DES J0408–5354 and WGD 2038–4008

2020 ◽  
Vol 498 (3) ◽  
pp. 3241-3274 ◽  
Author(s):  
E J Buckley-Geer ◽  
H Lin ◽  
C E Rusu ◽  
J Poh ◽  
A Palmese ◽  
...  
Keyword(s):  
Time Delay ◽  
Velocity Dispersion ◽  
Line Of Sight ◽  
Wide Field ◽  
Gravitational Lenses ◽  
Mass Model ◽  
Stellar Velocity ◽  
Unit Density ◽  
Shift Criterion

ABSTRACT In time-delay cosmography, three of the key ingredients are (1) determining the velocity dispersion of the lensing galaxy, (2) identifying galaxies and groups along the line of sight with sufficient proximity and mass to be included in the mass model, and (3) estimating the external convergence κext from less massive structures that are not included in the mass model. We present results on all three of these ingredients for two time-delay lensed quad quasar systems, DES J0408–5354 and WGD 2038–4008 . We use the Gemini, Magellan, and VLT telescopes to obtain spectra to both measure the stellar velocity dispersions of the main lensing galaxies and to identify the line-of-sight galaxies in these systems. Next, we identify 10 groups in DES J0408–5354 and two groups in WGD 2038–4008 using a group-finding algorithm. We then identify the most significant galaxy and galaxy-group perturbers using the ‘flexion shift’ criterion. We determine the probability distribution function of the external convergence κext for both of these systems based on our spectroscopy and on the DES-only multiband wide-field observations. Using weighted galaxy counts, calibrated based on the Millennium Simulation, we find that DES J0408–5354 is located in a significantly underdense environment, leading to a tight (width $\sim 3{{\ \rm per\ cent}}$), negative-value κext distribution. On the other hand, WGD 2038–4008 is located in an environment of close to unit density, and its low source redshift results in a much tighter κext of $\sim 1{{\ \rm per\ cent}}$, as long as no external shear constraints are imposed.

scholarly journals The Dynamical Mass of the Young Cluster W3 in NGC 7252: Heavy-Weight Globular Cluster or Ultra-Compact Dwarf Galaxy?

2005 ◽  
Vol 13 ◽  
pp. 169-170
Author(s):  
Claudia Maraston ◽  
N. Bastian ◽  
R. P. Saglia ◽  
Markus Kissler-Patig ◽  
François Schweizer ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Stellar Population ◽  
Milky Way ◽  
Dwarf Galaxy ◽  
Elliptical Galaxies ◽  
Star Cluster ◽  
Dynamical Mass ◽  
Fundamental Plane ◽  
Dwarf Elliptical Galaxies ◽  
First Time

AbstractWe have measured the dynamical mass of the highly luminous star cluster W3 in the young merger remnant galaxy NGC 7252. The value is Mdyn = (8 ± 2) × 107M⊙, and represents the highest dynamically-confirmed mass for an extra-galactic star cluster so far. The dynamical mass is in excellent agreement with the luminous mass (Maraston et al. 2001). This results from the use of stellar population models that include correctly the brightest AGB stellar phase, dominant in young stellar populations. To classify W3, we employ the fundamental plane of stellar systems (Bender, Burstein & Faber 1992), for the first time in these kinds of studies. We find that W3 lies far from typical Milky Way globular clusters, but it is also far from the heavyweights ωCen in the Milky Way and G1 in M31, because it is too extended for its mass, and from dwarf elliptical galaxies because it is much more compact for its mass. Instead W3 lies close to the ultra-compact Fornax objects (Drinkwater et al. 2003) and to the compact elliptical M32, possibly shedding light on the still mysterious nature of these objects. A previously deserted region of the fundamental plane starts to be populated.

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