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Dark influences: imprints of dark satellites on dwarf galaxies  [PDF]
Tjitske K. Starkenburg,Amina Helmi
Physics , 2014, DOI: 10.1051/0004-6361/201425082
Abstract: In the context of the current $\Lambda$CDM cosmological model small dark matter haloes are abundant and satellites of dwarf galaxies are expected to be predominantly dark. Since low mass galaxies have smaller baryon fractions interactions with these satellites may leave particularly dramatic imprints. We uncover the influence of the most massive of these dark satellites on disky dwarf galaxies and the possible dynamical and morphological transformations that result from these interactions. We use a suite of carefully set-up, controlled simulations of isolated dwarf galaxies. The primary dwarf galaxies have solely a stellar disk in the dark matter halo and the secundaries are completely devoid of baryons. We vary the disk mass, halo concentration, initial disk thickness and inclination of the satellite orbit. The disky dwarf galaxies are heated and disrupted due to the minor merger event, more extremely for higher satellite over disk mass ratios, and the morphology and kinematics are significantly altered. Moreover, for less concentrated haloes the minor merger can completely destroy the disk leaving a low-luminosity spheroidal-like galaxy instead. We conclude that dwarf galaxies are very much susceptible to being disturbed by dark galaxies and that even a minor merger event can significantly disrupt and alter the structure and kinematics of a dwarf galaxy. This process may be seen as a new channel for the formation of dwarf spheroidal galaxies.
Dark Matter in the Milky Way's Dwarf Spheroidal Satellites  [PDF]
Matthew G. Walker
Physics , 2012, DOI: 10.1007/978-94-007-5612-0_20
Abstract: The Milky Way's dwarf spheroidal satellites include the nearest, smallest and least luminous galaxies known. They also exhibit the largest discrepancies between dynamical and luminous masses. This article reviews the development of empirical constraints on the structure and kinematics of dSph stellar populations and discusses how this phenomenology translates into constraints on the amount and distribution of dark matter within dSphs. Some implications for cosmology and the particle nature of dark matter are discussed, and some topics/questions for future study are identified.
M31 Satellite Masses Compared to LCDM Subhaloes  [PDF]
Erik J. Tollerud,Michael Boylan-Kolchin,James S. Bullock
Physics , 2014, DOI: 10.1093/mnras/stu474
Abstract: We compare the kinematics of M31's satellite galaxies to the mass profiles of the subhaloes they are expected to inhabit in LCDM. We consider the most massive subhaloes of an approximately M31-sized halo, following the assumption of a monotonic galaxy luminosity-to-subhalo mass mapping. While this abundance matching relation is consistent with the kinematic data for galaxies down to the luminosity of the bright satellites of the Milky Way and M31, it is not consistent with kinematic data for fainter dwarf galaxies (those with L <~ 10^8 Lsun). Comparing the kinematics of M31's dwarf Spheroidal (dSph) satellites to the subhaloes reveals that M31's dSph satellites are too low density to be consistent with the subhaloes' mass profiles. A similar discrepancy has been reported between Milky Way dSphs and their predicted subhaloes, the "too big to fail" problem. By contrast, total mass profiles of the dwarf Elliptical (and similarly bright) satellites are consistent with the subhaloes. However, they suffer from large systematic uncertainties in their dark matter content because of substantial (and potentially dominant) contributions from baryons within their half-light radii.
Internal Kinematics of Dward Spheroidal Galaxies  [PDF]
Edward W. Olszewski
Physics , 1997,
Abstract: We discuss the quality of kinematic data in dwarf spheroidal galaxies, the current interpretations of those data, and prospects for actually deriving the mass profile in these galaxies. We then discuss stellar populations constraints on some of the models that attempt to explain the kinematics and formation of the dSph's.
Dwarf spheroidal galaxies and Bose-Einstein condensate dark matter  [PDF]
Alberto Diez-Tejedor,Alma X. Gonzalez-Morales,Stefano Profumo
Physics , 2014, DOI: 10.1103/PhysRevD.90.043517
Abstract: We constrain the parameters of a self-interacting massive dark matter scalar particle in a condensate using the kinematics of the eight brightest dwarf spheroidal satellites of the Milky Way. For the case of a repulsive self-interaction the condensate develops a mass density profile with a characteristic scale radius that is closely related to the fundamental parameters of the theory. We find that the velocity dispersion of dwarf spheroidal galaxies suggests a scale radius of the order of 1 kpc, in tension with previous results found using the rotational curve of low-surface-brightness and dwarf galaxies. The new value is however favored marginally by the constraints coming from the number of relativistic species at Big-Bang nucleosynthesis. We discuss the implications of our findings for the particle dark matter model and argue that while a single classical coherent state can correctly describe the dark matter in dwarf spheroidal galaxies, it cannot play, in general, a relevant role for the description of dark matter in bigger objects.
Dwarf spheroidal galaxy kinematics and spiral galaxy scaling laws  [PDF]
Paolo Salucci,Mark I. Wilkinson,Matthew G. Walker,Gerard F. Gilmore,Eva K. Grebel,Andreas Koch,Christiane Frigerio Martins,Rosemary F. G. Wyse
Physics , 2011, DOI: 10.1111/j.1365-2966.2011.20144.x
Abstract: Kinematic surveys of the dwarf spheroidal (dSph) satellites of the Milky Way are revealing tantalising hints about the structure of dark matter (DM) haloes at the low-mass end of the galaxy luminosity function. At the bright end, modelling of spiral galaxies has shown that their rotation curves are consistent with the hypothesis of a Universal Rotation Curve whose shape is supported by a cored dark matter halo. In this paper, we investigate whether the internal kinematics of the Milky Way dSphs are consistent with the particular cored DM distributions which reproduce the properties of spiral galaxies. Although the DM densities in dSphs are typically almost two orders of magnitude higher than those found in (larger) disk systems, we find consistency between dSph kinematics and Burkert DM haloes whose core radii r0 and central densities {\rho}0 lie on the extrapolation of the scaling law seen in spiral galaxies: log {\rho}0 \simeq {\alpha} log r0 + const with 0.9 < {\alpha} < 1.1. We similarly find that the dSph data are consistent with the relation between {\rho}0 and baryon scale length seen in spiral galaxies. While the origin of these scaling relations is unclear, the finding that a single DM halo profile is consistent with kinematic data in galaxies of widely varying size, luminosity and Hubble Type is important for our understanding of observed galaxies and must be accounted for in models of galaxy formation.
Tidal Dwarf Galaxies and Missing Baryons  [PDF]
Frederic Bournaud
Advances in Astronomy , 2010, DOI: 10.1155/2010/735284
Abstract: Tidal dwarf galaxies form during the interaction, collision, or merger of massive spiral galaxies. They can resemble “normal” dwarf galaxies in terms of mass, size, and become dwarf satellites orbiting around their massive progenitor. They nevertheless keep some signatures from their origin, making them interesting targets for cosmological studies. In particular, they should be free from dark matter from a spheroidal halo. Flat rotation curves and high dynamical masses may then indicate the presence of an unseen component, and constrain the properties of the “missing baryons,” known to exist but not directly observed. The number of dwarf galaxies in the Universe is another cosmological problem for which it is important to ascertain if tidal dwarf galaxies formed frequently at high redshift, when the merger rate was high, and many of them survived until today. In this paper, “dark matter” is used to refer to the nonbaryonic matter, mostly located in large dark halos, that is, CDM in the standard paradigm, and “missing baryons” or “dark baryons” is used to refer to the baryons known to exist but hardly observed at redshift zero, and are a baryonic dark component that is additional to “dark matter”. 1. Introduction: The Formation of Tidal Dwarf Galaxies Tidal dwarf galaxy (TDG) is, per definition, a massive, gravitationally bound object of gas and stars, formed during a merger or distant tidal interaction between massive spiral galaxies, and is as massive as a dwarf galaxy [1] (Figure 1). It should also be relatively long-lived, so that it survives after the interaction, either orbiting around its massive progenitor or expelled to large distances. This requires a lifetime of at least 1 gigayear, and a transient structure during a galaxy interaction would not deserve to be considered as a real TDG. The formation of TDGs in mergers has been postulated for decades [2], including potential candidates in the Antennae galaxies (NGC4038/39) [3], and became an increasingly active research topic after the study of these tidal dwarf candidates by Mirabel et al. [4]. Figure 1: NGC7252 (a) is a recent merger of two spiral galaxies into a partially-relaxed central spheroidal galaxy. Two massive TDGs are found near the tip of the two long tidal tails (blue = HI, pink = H – image courtesy of Pierre-Alain Duc). AM 1353-272 (b) does not have prominent, massive TDGs at the tip of tidal tails, but has instead may lower-mass objects all along its tail [ 5]. The bright spot on the northern tail is a foreground star. Tidal tails are a common feature in galaxy interactions.
A new method of estimating the mass-to-light ratio of the Ursa Minor dwarf spheroidal galaxy  [PDF]
M. A. Gomez-Flechoso,D. Martinez-Delgado
Physics , 2003, DOI: 10.1086/374858
Abstract: Dwarf satellite galaxies undergo strong tidal forces produced by the main galaxy potential. These forces disturb the satellite, producing asymmetries in its stellar distribution, tidal tail formation, and modifications of the velocity dispersions profiles. Most of these features are observed in the Ursa Minor (UMi) dwarf spheroidal galaxy, which is one of the closest satellites of the Milky Way. These features show that UMi is been tidally disrupted and probably not in virial equilibrium. The high velocity dispersion of UMi could also be a reflection of this tidal disruption and not the signature of the large dark matter content that would be deduced if virial equilibrium is assumed. In order to avoid the uncertainty produced when virial equilibrium is assumed in systems in strong tidal fields, we present a new method of calculating the mass-to-luminosity ratio of disrupted dwarf galaxies. This method is based on numerical simulations and only takes into account the shape of the dwarf density profile and the tidal tail brightness, but does not depend on the kinematics of the dwarf. Applying this method to UMi, we obtain a mass-to-luminosity relation of 12, which is lower than the value obtained assuming virial equilibrium (M/L=60). In addition, if UMi has a large dark-matter content, it will be impossible to reproduce a tidal tail as luminous as the one observed.
The Kinematics of Dwarf Spheroidal Galaxies  [PDF]
Mario Mateo
Physics , 1997,
Abstract: I review observational data on the kinematic properties of dwarf spheroidal galaxies in the halo of the Milky Way and beyond. The present data confirm previous claims that these galaxies have unusually large central velocity dispersions. `Simple' sources of bias such as binary stars, internal atmospheric motions, measurement errors, and small sample sizes cannot explain the large dispersions measures in all dSph systems. Recent data suggest that in some of these dwarfs the veolocity dispersion profiles are flat out to their classical tidal radii. I discuss how these results can (or cannot) be understood by invoking a variety of distinct models, including classical dark matter halos, tidal disruption and MOND.
The Baryons in the Milky Way Satellites  [PDF]
Owen H. Parry,Vincent R. Eke,Carlos S. Frenk,Takashi Okamoto
Physics , 2011, DOI: 10.1111/j.1365-2966.2011.19971.x
Abstract: We investigate the formation and evolution of satellite galaxies using smoothed particle hydrodynamics (SPH) simulations of a Milky Way(MW)-like system, focussing on the best resolved examples, analogous to the classical MW satellites. Comparing with a pure dark matter simulation, we find that the condensation of baryons has had a relatively minor effect on the structure of the satellites' dark matter halos. The stellar mass that forms in each satellite agrees relatively well over three levels of resolution (a factor of ~64 in particle mass) and scales with (sub)halo mass in a similar way in an independent semi-analytical model. Our model provides a relatively good match to the average luminosity function of the MW and M31. To establish whether the potential wells of our satellites are realistic, we measure their masses within observationally determined half-light radii, finding that the most massive examples have somewhat higher mass-to-light ratios than those derived for the MW dSphs from stellar kinematic data. A statistical test yields a ~9 percent probability that the simulated and observationally derived distributions of masses are consistent. Our results may suggest that either the MW halo is less massive than assumed in our simulations (~1.4e12 M_sun) or that there is substantial scatter in the satellite luminosity function or distribution of mass-to-light ratios at fixed host halo mass. Alternatively, feedback processes not properly captured by our simulations may have reduced the central densities of (sub)halos, or the subhalos may have initially formed with lower concentrations as would be the case, for example, if the dark matter were made of warm, rather than cold particles.
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