scholarly journals Scaling Laws for Dark Matter Halos in Late-Type and Dwarf Spheroidal Galaxies

2004 ◽  
Vol 220 ◽  
pp. 377-397 ◽  
Author(s):  
John Kormendy ◽  
K. C. Freeman
Keyword(s):  
Dark Matter ◽  
Galaxy Formation ◽  
Rotation Curve ◽  
Scaling Laws ◽  
Large Population ◽  
Absolute Magnitude ◽  
Density Fluctuations ◽  
Late Type ◽  
Dwarf Spheroidal Galaxies ◽  
Core Rotation

Published mass models fitted to galaxy rotation curves are used to study the systematic properties of dark matter (DM) halos in late-type and dwarf spheroidal (dSph) galaxies. Halo parameters are derived by fitting non-singular isothermals to (V2 – V2vis)1/2, where V(r) is the observed rotation curve and Vvis is the rotation curve of the visible matter. the latter is calculated from the surface brightness assuming that the mass-to-light ratio M/L is constant with radius. “Maximum disk” values of M/L are adjusted to fit as much of the inner rotation curve as possible without making the halo have a hollow core. Rotation curve decomposition becomes impossible fainter than absolute magnitude Mb ≃ −14, where V becomes comparable to the velocity dispersion of the gas. To increase the luminosity range further, we include dSph galaxies, which are physically related to spiral and irregular galaxies. Combining the data, we find that DM halos satisfy well defined scaling laws analogous to the “fundamental plane” relations for elliptical galaxies. Halos in less luminous galaxies have smaller core radii rc, higher central densities ρ0, and smaller central velocity dispersions σ. Scaling laws provide new and detailed constraints on the nature of DM and on galaxy formation and evolution. Some simple implications include:1 – A single, continuous physical sequence of increasing mass extends from dSph galaxies with Mb ≃ −7.6 to Sc I galaxies with Mb ≃ −22.4.2 – the high DM densities in dSph galaxies are normal for such tiny galaxies. Since virialised density depends on collapse redshift zcoll, ρ0 ∝ (1 + zcoll)3, the smallest dwarfs formed at least Δzcoll ≃ 7 earlier than the biggest spirals.3 – the high DM densities of dSphs implies that they are real galaxies formed from primordial density fluctuations. They are not tidal fragments. Tidal dwarfs cannot retain even the low DM densities of their giant-galaxy progenitors. in contrast, dSphs have higher DM densities than do giant-galaxy progenitors.4 – the fact that, as luminosity decreases, dwarf galaxies become much more numerous and also more nearly dominated by DM raises the possibility that there exists a large population of objects that are completely dark. Such objects are a canonical prediction of cold DM theory. If they exist, “empty halos” are likely to be small and dense -that is, darker versions of Draco and UMi.5 – the slopes of the DM parameter correlations provide a measure on galactic mass scales of the slope n of the power spectrum |δk|2 ∝ kn of primordial density fluctuations. Our preliminary results, not yet corrected for baryonic compression of DM, give n ≃ –1.9 ± 0.2. This is consistent with cold DM theory.

scholarly journals Scaling Laws for Dark Matter Halos in Late-Type and Dwarf Spheroidal Galaxies

2014 ◽  
Vol 10 (S311) ◽  
pp. 72-77
Author(s):  
John Kormendy ◽  
K. C. Freeman
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Scaling Laws ◽  
Large Population ◽  
Elliptical Galaxies ◽  
Dark Matter Halos ◽  
Fundamental Plane ◽  
Dwarf Spheroidal Galaxies ◽  
Visible Matter ◽  
Luminous Galaxies

AbstractDark matter (DM) halos of Sc–Im galaxies satisfy structural scaling laws analogous to the fundamental plane relations for elliptical galaxies. Halos in less luminous galaxies have smaller core radii rc, higher central densities ρ^, and smaller central velocity dispersions σ. If dwarf spheroidal (dSph) and dwarf Magellanic irregular (dIm) galaxies lie on the extrapolations of these correlations, then we can estimate their baryon loss relative to that of Sc–Im galaxies. We find that, if there had been no enhanced baryon loss relative to Sc–Im galaxies, typical dSph and dIm galaxies would be brighter by ΔMB ≃ -4.0 mag and ΔMB ≃ -3.5 mag, respectively. Instead, the galaxies lost or retained as gas (in dIm galaxies) baryons that could have formed stars. Also, dSph and dIm galaxies have DM halos that are more massive than we thought, with σ ~ 30 km s−1 or circular-orbit rotation velocities Vcirc ~ 42 km s−1. Comparison of DM and visible matter parameter correlations confirms that, at MV ≳ -18, dSph and dIm galaxies form a sequence of decreasing baryon-to-DM mass ratios in smaller dwarfs. We show explicitly that galaxy baryon content goes to (almost) zero at Vcirc ≲ 42 ± 4 km s−1, in agreement with Vcirc as found from our estimate of baryon depletion. Our results suggest that there may be a large population of DM halos that are dark and undiscovered. This helps to solve the problem that the initial fluctuation spectrum of cold dark matter predicts more dwarf galaxies than we observe.

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 A Model for the Sequence of Elliptical Galaxies

1987 ◽  
Vol 117 ◽  
pp. 367-367
Author(s):  
Rosemary F. G. Wyse ◽  
Bernard J. T. Jones
Keyword(s):  
Dark Matter ◽  
Power Spectrum ◽  
Galaxy Formation ◽  
Cold Dark Matter ◽  
Initial Conditions ◽  
Elliptical Galaxy ◽  
Elliptical Galaxies ◽  
Density Fluctuations ◽  
Analytic Approximation ◽  
Non Linear

We present a simple model for the formation of elliptical galaxies, based on a binary clustering hierarchy of dark matter, the chemical enrichment of the gas at each level being controlled by supernovae. The initial conditions for the non-linear phases of galaxy formation are set by the post-recombination power spectrum of density fluctuations. We investigate two models for this power spectrum - the first is a straightforward power law, |δk|2 ∝ kn, and the second is Peeble's analytic approximation to the emergent spectrum in a universe dominated by cold dark matter. The normalisation is chosen such that on some scale, say M ∼ 1012M⊙, the objects that condense out have properties - radius and velocity dispersion - resembling ‘typical’ galaxies. There is some ambiguity in this due to the poorly determined mass-to-light ratio of a typical elliptical galaxy — we look at two normalisations, σ1D ∼ 350kms−1 and σ1D ∼ 140kms−1. The choice determines which of Compton cooling or hydrogen cooling is more important during the galaxy formation period. The non-linear behaviour of the perturbations is treated by the homogeneous sphere approximation.

scholarly journals Vertical Motion and the Thickness of Hi Disks: Implications for Galactic Mass Models

1983 ◽  
Vol 100 ◽  
pp. 69-76
Author(s):  
P. C. van der Kruit ◽  
G. S. Shostak
Keyword(s):  
Dark Matter ◽  
Mass Distribution ◽  
Rotation Curve ◽  
Spiral Galaxies ◽  
Galactic Plane ◽  
Vertical Motion ◽  
Late Type ◽  
Rotation Curves ◽  
Central Bulge ◽  
Local Value

Most studies of the mass distribution in spiral galaxies have been based on the observed rotation curves. A serious ambiguity in this approach has always been that the rotation curve contains in itself no information on the mass distribution in the direction perpendicular to the galactic plane. The usual assumption has been that the mass in late type galaxies is distributed as the light, namely outside the central bulge in a highly flattened disk. In recent years it has been found that the rotation curves decline little or not at all, indicating large increases in the local value of M/L with increasing galactocentric radius (e.g. Bosma and van der Kruit, 1979). On the basis of dynamical arguments involving stability it has been suspected that the material giving rise to the large values of M/L - the “dark matter” - is distributed in the halos of these galaxies, so that the assumption of a flat mass distribution would have to be wrong.

scholarly journals Galaxy formation from dry and hydro simulations

2009 ◽  
Vol 5 (H15) ◽  
pp. 85-85
Author(s):  
Luca Ciotti
Keyword(s):  
Dark Matter ◽  
Galaxy Formation ◽  
Scaling Laws ◽  
High Redshift ◽  
Elliptical Galaxies ◽  
Dark Matter Halos ◽  
Galaxy Mergers ◽  
Lower Redshift

AbstractThe effects of dry and wet merging on the Scaling Laws (SLs) of elliptical galaxies (Es) are discussed. It is found that the SLs, possibly established at high redshift by the fast collapse of gas-rich and clumpy stellar distributions in preexisting dark matter halos following the cosmological SLs, are compatible with a (small) number of galaxy mergers at lower redshift.

Neutrinos and the dark matter problem

1994 ◽  
Vol 346 (1678) ◽  
pp. 121-135 ◽  
Keyword(s):  
Dark Matter ◽  
Galaxy Formation ◽  
Cold Dark Matter ◽  
Mass Density ◽  
Rest Mass ◽  
Density Fluctuations ◽  
Fine Tuning ◽  
Cosmological Argument ◽  
The Mean ◽  
The Universe

Theoretical and experimental arguments suggest that the mean mass density of our universe is close to the closure value and that most of the mass in the universe consists of weakly interacting non-baryonic particles. Among the plethora of candidates that have been proposed as the dark matter, the neutrino remains the only particle known to exist, even though the issue of a neutrino mass remains unresolved. It was shown several years ago that neutrinos alone cannot provide the dark matter because physical processes in the early universe would have wiped out primordial density fluctuations on the scale of galaxies and below. The idea that cosmic strings or textures may seed galaxy formation in a neutrino-dominated universe has not yet been demonstrated to be viable. On the other hand, a model in which the bulk of the dark matter is cold and neutrinos with a mass of ca . 10 eV provide a ca . 30% contribution can, in principle, overcome many of the objections against the standard cold dark matter cosmogony. Although subject to the usual ‘fine-tuning’ criticism, these mixed dark matter models represent the best cosmological argument in favour of a non-zero rest mass for the neutrino.

scholarly journals Exploring extensions to the standard cosmological model and the impact of baryons on small scales

2020 ◽  
Vol 497 (3) ◽  
pp. 3809-3829 ◽  
Author(s):  
Sam G Stafford ◽  
Shaun T Brown ◽  
Ian G McCarthy ◽  
Andreea S Font ◽  
Andrew Robertson ◽  
...  
Keyword(s):  
Dark Matter ◽  
Standard Model ◽  
Galaxy Formation ◽  
Mass Function ◽  
Density Fluctuations ◽  
Density Profiles ◽  
The Standard Model ◽  
Small Scales ◽  
Standard Cosmological Model ◽  
The Impact

ABSTRACT It has been claimed that the standard model of cosmology (ΛCDM) cannot easily account for a number of observations on relatively small scales, motivating extensions to the standard model. Here, we introduce a new suite of cosmological simulations that systematically explores three plausible extensions: warm dark matter, self-interacting dark matter, and a running of the scalar spectral index of density fluctuations. Current observational constraints are used to specify the additional parameters that come with these extensions. We examine a large range of observable metrics on small scales, including the halo mass function, density, and circular velocity profiles, the abundance of satellite subhaloes, and halo concentrations. For any given metric, significant degeneracies can be present between the extensions. In detail, however, the different extensions have quantitatively distinct mass and radial dependencies, suggesting that a multiprobe approach over a range of scales can be used to break the degeneracies. We also demonstrate that the relative effects on the radial density profiles in the different extensions (compared to the standard model) are converged down to significantly smaller radii than are the absolute profiles. We compare the derived cosmological trends with the impact of baryonic physics using the EAGLE and ARTEMIS simulations. Significant degeneracies are also present between baryonic physics and cosmological variations (with both having similar magnitude effects on some observables). Given the inherent uncertainties both in the modelling of galaxy formation physics and extensions to ΛCDM, a systematic and simultaneous exploration of both is strongly warranted.

scholarly journals Galaxy Formation: Confrontation with Observations

1987 ◽  
Vol 124 ◽  
pp. 391-413
Author(s):  
Joseph Silk
Keyword(s):  
Dark Matter ◽  
Star Formation ◽  
Galaxy Formation ◽  
Cold Dark Matter ◽  
Dwarf Galaxies ◽  
Density Fluctuations ◽  
Inflationary Cosmology ◽  
Lyman Alpha ◽  
Gaussian Density

The implications for galaxy formation of inflationary cosmology are reviewed. In particular, I explore some implications of the hypothesis that galaxies form from adiabatic, gaussian density fluctuations in a cold dark matter–dominated universe. Topics discussed include protogalaxies and the epoch of galaxy formation, Lyman alpha clouds, dark halos and dwarf galaxies. Finally I describe how environmental biasing may arise as a consequence of tidally induced star formation in protoclusters.

scholarly journals Mass models of three southern late-type dwarf spirals

1985 ◽  
Vol 106 ◽  
pp. 95-96
Author(s):  
C. Carignan
Keyword(s):  
Dark Matter ◽  
Spatial Distribution ◽  
Rotation Curve ◽  
Spiral Galaxies ◽  
Theoretical Studies ◽  
Late Type ◽  
Fundamental Parameters ◽  
Luminous Matter ◽  
Scale Length

Although rotation-curve studies of spiral galaxies have unambiguously established the presence of dark matter, and theoretical studies have shown that its location is likely to be in a separate spheroidal halo component (Binney, 1978; Tubbs and Sanders, 1979; Monet, Richstone and Schechter, 1981), very little is known about its spatial distribution and its nature. Recently, Faber and Lin (Faber and Lin, 1983; Lin and Faber, 1983) have shown that, if one can get a rough idea of fundamental parameters like the halo scale length and the halo-to-disk ratio, it is also possible to put strong constraints on the nature of non-luminous matter.

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