scholarly journals The Effect of Tidal Stripping on Composite Stellar Populations in Dwarf Spheroidal Galaxies

2010 ◽  
Vol 2010 ◽  
pp. 1-14 ◽  
Author(s):  
Laura V. Sales ◽  
Amina Helmi ◽  
Giuseppina Battaglia
Keyword(s):  
Dark Matter ◽  
Mass Loss ◽  
Milky Way ◽  
Velocity Dispersion ◽  
Local Group ◽  
Stellar Populations ◽  
Dwarf Spheroidal Galaxies ◽  
Stellar Component ◽  
Dwarf Spheroidals ◽  
Matter Component

We use N-body simulations to study the effects of tides on the kinematical structure of satellite galaxies orbiting a Milky Way-like potential. Here we focus on the evolution of a spherical, dark matter dominated satellite, which is modelled with two stellar components set ab initio to be spatially and kinematically segregated, in a way that resembles the configuration of the metal poor and metal rich stellar populations in several dwarf spheroidals of the Local Group. We find that an important attenuation of the initial differences in the distribution of the two stellar components occurs for orbits with small pericentric radii. This is mainly due to (i) the loss of the gravitational support provided by the dark matter component after tidal stripping takes place and (ii) tides preferentially affect the more extended stellar component, leading to a net decrease in its velocity dispersion as a response for the mass loss, which thus shrinks the kinematical gap. We apply these ideas to the Sculptor and Carina dwarf spheroidals. Differences in their orbits might help to explain why in the former a clear kinematical separation between metal poor and metal rich stars is apparent, while in Carina this segregation is significantly more subtle.

scholarly journals Evidence for Light-weight Local Group Dwarf Spheroidal Galaxies

2004 ◽  
Vol 220 ◽  
pp. 365-366
Author(s):  
J. R. Kuhn ◽  
D. Kocevski
Keyword(s):  
Dark Matter ◽  
Milky Way ◽  
Local Group ◽  
Light Weight ◽  
Natural Explanation ◽  
Dwarf Spheroidal Galaxies ◽  
Ursa Minor ◽  
Matter Component ◽  
Morphological State ◽  
Spheroidal Galaxies

A simple and natural explanation for the dynamics and morphology of the Local Group Dwarf Spheroidal galaxies, Draco (Dra) and Ursa Minor (UMi), is that they are weakly unbound stellar systems with no significant dark matter component. A gentle, but persistent, Milky Way (MW) tide has left them in their current kinematic and morphological state (the “parametric tidal excitation”). A new test of a dark matter dominated dS potential follows from a careful observation of the “clumpiness” of the dS stellar surface density.

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 Stellar Populations and Dark Matter in the Milky Way Disk and in Local Group Galaxies

2008 ◽  
Vol 4 (S254) ◽  
pp. 49-60
Author(s):  
Eva K. Grebel
Keyword(s):  
Dark Matter ◽  
Chemical Evolution ◽  
Age Structure ◽  
Milky Way ◽  
Local Group ◽  
Galactic Disk ◽  
Stellar Populations ◽  
Short Overview

AbstractOur knowledge on the age structure, the chemical evolution, and the kinematics of the Galactic disk has grown substantially during the last years. Recent results on the properties of the stellar populations in the Galactic disk are summarized, and ongoing and future surveys and facilities are discussed. A short overview of recent mass estimates for the Milky Way is presented, and a brief summary of some of the key properties of the Galactic companions is given. The coming decade promises major breakthroughs in understanding our Milky Way, its disk, and the role of its satellites.

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 Heating of Milky Way disc stars by dark matter fluctuations in cold dark matter and fuzzy dark matter paradigms

2019 ◽  
Vol 485 (2) ◽  
pp. 2861-2876 ◽  
Author(s):  
Benjamin V Church ◽  
Philip Mocz ◽  
Jeremiah P Ostriker
Keyword(s):  
Dark Matter ◽  
Galaxy Formation ◽  
Quantum Interference ◽  
Cold Dark Matter ◽  
Milky Way ◽  
Velocity Dispersion ◽  
Formation Rate ◽  
Density Fluctuations ◽  
Particle Mass ◽  
Small Scale

ABSTRACT Although highly successful on cosmological scales, cold dark matter (CDM) models predict unobserved overdense ‘cusps’ in dwarf galaxies and overestimate their formation rate. We consider an ultralight axion-like scalar boson which promises to reduce these observational discrepancies at galactic scales. The model, known as fuzzy dark matter (FDM), avoids cusps, suppresses small-scale power, and delays galaxy formation via macroscopic quantum pressure. We compare the substructure and density fluctuations of galactic dark matter haloes comprised of ultralight axions to conventional CDM results. Besides self-gravitating subhaloes, FDM includes non-virialized overdense wavelets formed by quantum interference patterns, which are an efficient source of heating to galactic discs. We find that, in the solar neighbourhood, wavelet heating is sufficient to give the oldest disc stars a velocity dispersion of ${\sim } {30}{\, \mathrm{km\, s}^{-1}}$ within a Hubble time if energy is not lost from the disc, the velocity dispersion increasing with stellar age as σD ∝ t0.4 in agreement with observations. Furthermore, we calculate the radius-dependent velocity dispersion and corresponding scaleheight caused by the heating of this dynamical substructure in both CDM and FDM with the determination that these effects will produce a flaring that terminates the Milky Way disc at $15\!-\!20{\, \mathrm{kpc}}$. Although the source of thickened discs is not known, the heating due to perturbations caused by dark substructure cannot exceed the total disc velocity dispersion. Therefore, this work provides a lower bound on the FDM particle mass of ma > 0.6 × 10−22 eV. Furthermore, FDM wavelets with this particle mass should be considered a viable mechanism for producing the observed disc thickening with time.

scholarly journals An updated detailed characterization of planes of satellites in the MW and M31

2020 ◽  
Vol 499 (3) ◽  
pp. 3755-3774
Author(s):  
Isabel M Santos-Santos ◽  
Rosa Domínguez-Tenreiro ◽  
Marcel S Pawlowski
Keyword(s):  
Milky Way ◽  
Velocity Dispersion ◽  
Local Group ◽  
Normal Density ◽  
Detailed Characterization ◽  
Kinematic Data ◽  
Positional Analysis ◽  
Form Part

ABSTRACT We present a detailed characterization of planes of satellite galaxies in the Milky Way (MW) and M31. For a positional analysis, we introduce an extension to the ‘4-galaxy-normal density plot’ method from Pawlowski, Kroupa & Jerjen. It finds the normal directions to the predominant planar configurations of satellites of a system, yielding for each a collection of planes of increasing member satellites. This allows to quantify the quality of planes in terms of population (Nsat) and spatial flattening (c/a). We apply this method to the latest data for confirmed MW and M31 satellite samples, with 46 and 34 satellites, respectively. New MW satellites form part of planes previously identified from a smaller sample of Nsat= 27: we identify a new plane with Nsat = 39 as thin as the VPOS-3 (c/a ∼ 0.2), and with roughly the same normal direction; so far the most populated plane that thin reported in the Local Group. We introduce a new method to determine, using kinematic data, the axis of maximum co-orbitation of MW satellites. Interestingly, this axis approximately coincides with the normal to the former plane: $\ge 45\pm 5{{\ \rm per\ cent}}$ of satellites co-orbit. In M31 we discover a plane with Nsat = 18 and c/a ∼ 0.15, i.e. quality comparable to the GPoA, and perpendicular to it. This structure is viewed face-on from the Sun making it susceptible to M31 satellite distance uncertainties. An estimation of the perpendicular velocity dispersion suggests that it is dynamically unstable. Finally we find that mass is not a property determining a satellite’s membership to good quality planes.

scholarly journals Too big to fail in light of Gaia

2019 ◽  
Vol 490 (1) ◽  
pp. 231-242 ◽  
Author(s):  
Manoj Kaplinghat ◽  
Mauro Valli ◽  
Hai-Bo Yu
Keyword(s):  
Dark Matter ◽  
Milky Way ◽  
Large Scatter ◽  
Too Big To Fail ◽  
Dwarf Spheroidal Galaxies ◽  
Ursa Minor ◽  
Spheroidal Galaxies

ABSTRACT We point out an anticorrelation between the central dark matter (DM) densities of the bright Milky Way dwarf spheroidal galaxies (dSphs) and their orbital pericenter distances inferred from Gaia data. The dSphs that have not come close to the Milky Way centre (like Fornax, Carina and Sextans) are less dense in DM than those that have come closer (like Draco and Ursa Minor). The same anticorrelation cannot be inferred for the ultrafaint dSphs due to large scatter, while a trend that dSphs with more extended stellar distributions tend to have lower DM densities emerges with ultrafaints. We discuss how these inferences constrain proposed solutions to the Milky Way’s too-big-to-fail problem and provide new clues to decipher the nature of DM.

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.

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