The Cusp–Core Problem in Gas-Poor Dwarf Spheroidal Galaxies

This review deals with the inconsistency of inner dark matter density profiles in dwarf galaxies, known as the cusp–core problem. In particular, we aim to focus on gas-poor dwarf galaxies. One of the most promising solutions to this cold dark matter small-scale issue is the stellar feedback, but it seems to be only designed for gas-rich dwarfs. However, in the regime of classical dwarfs, this core mechanism becomes negligible. Therefore, it is required to find solutions without invoking these baryonic processes as dark matter cores tend to persist even for these dwarfs, which are rather dark-matter-dominated. Here, we have presented two categories of solutions. One consists of creating dark matter cores from cusps within cold dark matter by altering the dark matter potential via perturbers. The second category gathers solutions that depict the natural emergence of dark matter cores in alternative theories. Given the wide variety of solutions, it becomes necessary to identify which mechanism dominates in the central region of galaxies by finding observational signatures left by them in order to highlight the true nature of dark matter.

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Formation of dwarf galaxies and small-scale problems of CDM

Proceedings of the International Astronomical Union ◽

10.1017/s1743921306010234 ◽

2006 ◽

Vol 2 (S235) ◽

pp. 385-388

Author(s):

Oleg Y. Gnedin

Keyword(s):

Dark Matter ◽

Cold Dark Matter ◽

Galactic Halo ◽

Dwarf Galaxies ◽

Small Scale ◽

Dark Matter Halos ◽

Density Profiles ◽

Gas Cooling ◽

Low Efficiency ◽

The Universe

AbstractThe concordance cosmological model based on cold dark matter makes definitive predictions for the growth of galaxies in the Universe, which are being actively studied using numerical simulations. These predictions appear to contradict the observations of dwarf galaxies. Dwarf dark matter halos are more numerous and have steeper central density profiles than the observed galaxies. The first of these small-scale problems, the “missing satellites problem”, can be resolved by accounting for the low efficiency of gas cooling and star formation in dwarf halos. A newly-discovered class of HyperVelocity Stars will soon allow us to test another generic prediction of CDM models, the triaxial shapes of dark matter halos. Measuring the proper motions of HVS will probe the gravitational potential out to 100 kpc and will constrain the axis ratios and the orientation of the Galactic halo.

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New mass bound on fermionic dark matter from a combined analysis of classical dSphs

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz1573 ◽

2019 ◽

Vol 487 (4) ◽

pp. 5711-5720 ◽

Cited By ~ 7

Author(s):

D Savchenko ◽

A Rudakovskyi

Keyword(s):

Dark Matter ◽

Lower Bound ◽

Cold Dark Matter ◽

Pauli Exclusion Principle ◽

Dark Matter Halo ◽

Exclusion Principle ◽

Fermion Mass ◽

Density Profiles ◽

Combined Analysis ◽

Dwarf Spheroidal Galaxies

ABSTRACTDwarf spheroidal galaxies (dSphs) are the most compact dark-matter-dominated objects observed so far. The Pauli exclusion principle limits the number of fermionic dark matter particles that can compose a dSph halo. This results in a well-known lower bound on their particle mass. So far, such bounds were obtained from the analysis of individual dSphs. In this paper, we model dark matter halo density profiles via the semi-analytical approach and analyse the data from eight ‘classical’ dSphs assuming the same mass of dark matter fermion in each object. First, we find out that modelling of Carina dSph results in a much worse fitting quality compared to the other seven objects. From the combined analysis of the kinematic data of the remaining seven ‘classical’ dSphs, we obtain a new 2σ lower bound of m ≳ 190 eV on the dark matter fermion mass. In addition, by combining a sub-sample of four dSphs – Draco, Fornax, Leo I, and Sculptor – we conclude that 220 eV fermionic dark matter appears to be preferred over the standard cold dark matter at about the 2σ level. However, this result becomes insignificant if all seven objects are included in the analysis. Future improvement of the obtained bound requires more detailed data, both from ‘classical’ and ultra-faint dSphs.

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Ejection of supermassive black holes and implications for merger rates in fuzzy dark matter haloes

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2972 ◽

2020 ◽

Vol 499 (2) ◽

pp. 2575-2586

Author(s):

Amr A El-Zant ◽

Zacharias Roupas ◽

Joseph Silk

Keyword(s):

Dark Matter ◽

Active Galactic Nuclei ◽

Detection Rate ◽

Cold Dark Matter ◽

Dwarf Galaxies ◽

Event Rate ◽

Galactic Nuclei ◽

Merging Galaxies ◽

Dwarf Spheroidal Galaxies ◽

Order Of Magnitude

ABSTRACT Fuzzy dark matter (FDM) consisting of ultralight axions has been invoked to alleviate galactic-scale problems in the cold dark matter scenario. FDM fluctuations, created via the superposition of waves, can impact the motion of a central supermassive black hole (SMBH) immersed in an FDM halo. The SMBH will undergo a random walk, induced by FDM fluctuations, that can result in its ejection from the central region. This effect is strongest in dwarf galaxies, accounting for wandering SMBHs and the low detection rate of active galactic nuclei in dwarf spheroidal galaxies. In addition, a lower bound on the allowed axion masses is inferred both for Sagitarius A* and heavier SMBH; to avoid ejection from the galactic centres, axion masses of the order of 10−22 eV or lighter are excluded. Stronger limits are inferred for merging galaxies. We find that the event rate of SMBH mergers in FDM haloes and the associated SMBH growth rates can be reduced by at least an order of magnitude.

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The coherent motion of Cen A dwarf satellite galaxies remains a challenge for ΛCDM cosmology

Astronomy and Astrophysics ◽

10.1051/0004-6361/202039973 ◽

2021 ◽

Vol 645 ◽

pp. L5

Author(s):

Oliver Müller ◽

Marcel S. Pawlowski ◽

Federico Lelli ◽

Katja Fahrion ◽

Marina Rejkuba ◽

...

Keyword(s):

Dark Matter ◽

Cold Dark Matter ◽

Similar Case ◽

Dwarf Galaxies ◽

Elliptical Galaxy ◽

Satellite System ◽

Coherent Motion ◽

Small Scale ◽

Planar Structures ◽

Scale Challenges

The plane-of-satellites problem is one of the most severe small-scale challenges for the standard Λ cold dark matter (ΛCDM) cosmological model: Several dwarf galaxies around the Milky Way and Andromeda co-orbit in thin, planar structures. A similar case has been identified around the nearby elliptical galaxy Centaurus A (Cen A). In this Letter, we study the satellite system of Cen A, adding twelve new galaxies with line-of-sight velocities from VLT/MUSE observations. We find that 21 out of 28 dwarf galaxies with measured velocities share a coherent motion. Similarly, flattened and coherently moving structures are found only in 0.2% of Cen A analogs in the Illustris-TNG100 cosmological simulation, independently of whether we use its dark-matter-only or hydrodynamical run. These analogs are not co-orbiting, and they arise only by chance projection, thus they are short-lived structures in such simulations. Our findings indicate that the observed co-rotating planes of satellites are a persistent challenge for ΛCDM, which is largely independent from baryon physics.

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To β or not to β: can higher order Jeans analysis break the mass–anisotropy degeneracy in simulated dwarfs?

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2352 ◽

2020 ◽

Vol 498 (1) ◽

pp. 144-163

Author(s):

A Genina ◽

J I Read ◽

C S Frenk ◽

S Cole ◽

A Benítez-Llambay ◽

...

Keyword(s):

Dark Matter ◽

Cold Dark Matter ◽

Dwarf Galaxies ◽

Local Environment ◽

Higher Order ◽

Analysis Method ◽

Density Profiles ◽

Velocity Anisotropy ◽

Density Distributions ◽

Mass Profiles

ABSTRACT We test a non-parametric higher order Jeans analysis method, GravSphere, on 32 simulated dwarf galaxies comparable to classical Local Group dwarfs like Fornax. The galaxies are selected from A Project Of Simulating The Local Environment (APOSTLE) suite of cosmological hydrodynamics simulations with cold dark matter (CDM) and self-interacting dark matter (SIDM) models, allowing us to investigate cusps and cores in density distributions. We find that, for CDM dwarfs, the recovered enclosed mass profiles have a bias of no more than 10 per cent, with a 50 per cent scatter in the inner regions and a 20 per cent scatter near the half-light radius, consistent with standard mass estimators. The density profiles are also recovered with a bias of no more than 10 per cent and a scatter of 30 per cent in the inner regions. For SIDM dwarfs, the mass and density profiles are recovered within our 95 per cent confidence intervals but are biased towards cuspy dark matter distributions. This is mainly due to a lack of sufficient constraints from the data. We explore the sources of scatter in the accuracy of the recovered profiles and suggest a χ2 statistic to separate successful models from biased ones. Finally, we show that the uncertainties on the mass profiles obtained with GravSphere are smaller than those for comparable Jeans methods and that they can be further improved if stronger priors, motivated by cosmological simulations, are placed on the velocity anisotropy. We conclude that GravSphere is a promising Jeans-based approach for modelling dark matter distributions in dwarf galaxies.

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Probing the nature of dark matter with accreted globular cluster streams

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3597 ◽

2020 ◽

Vol 501 (1) ◽

pp. 179-200 ◽

Cited By ~ 1

Author(s):

Khyati Malhan ◽

Monica Valluri ◽

Katherine Freese

Keyword(s):

Dark Matter ◽

Globular Cluster ◽

Particle Physics ◽

Cold Dark Matter ◽

Dwarf Galaxies ◽

Density Profiles ◽

Parallel Structures ◽

Stellar Streams ◽

Future Data ◽

Low Mass

ABSTRACT The steepness of the central density profiles of dark matter (DM) in low-mass galaxy haloes (e.g. dwarf galaxies) is a powerful probe of the nature of DM. We propose a novel scheme to probe the inner profiles of galaxy subhaloes using stellar streams. We show that the present-day morphological and dynamical properties of accreted globular cluster (GC) streams – those produced from tidal stripping of GCs that initially evolved within satellite galaxies and later merged with the Milky Way (MW) – are sensitive to the central DM density profile and mass of their parent satellites. GCs that accrete within cuspy cold dark matter (CDM) subhaloes produce streams that are physically wider and dynamically hotter than streams that accrete inside cored subhaloes. A first comparison of MW streams ‘GD-1’ and ‘Jhelum’ (likely of accreted GC origin) with our simulations indicates a preference for cored subhaloes. If these results hold up in future data, the implication is that either the DM cusps were erased by baryonic feedback, or their subhaloes naturally possessed cored density profiles implying particle physics models beyond CDM. Moreover, accreted GC streams are highly structured and exhibit complex morphological features (e.g. parallel structures and ‘spurs’). This implies that the accretion scenario can naturally explain the recently observed peculiarities in some of the MW streams. We also propose a novel mechanism for forming ‘gaps’ in stellar streams when the remnant of the parent subhalo (which hosted the GC) later passes through the GC stream. This encounter can last a longer time (and have more of an impact) than the random encounters with DM subhaloes previously considered, because the GC stream and its parent subhalo are on similar orbits with small relative velocities. Current and future surveys of the MW halo will uncover numerous faint stellar streams and provide the data needed to substantiate our preliminary tests with this new probe of DM.

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NIHAO – XXV. Convergence in the cusp-core transformation of cold dark matter haloes at high star formation thresholds

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3028 ◽

2020 ◽

Vol 499 (2) ◽

pp. 2648-2661

Author(s):

Aaron A Dutton ◽

Tobias Buck ◽

Andrea V Macciò ◽

Keri L Dixon ◽

Marvin Blank ◽

...

Keyword(s):

Dark Matter ◽

Star Formation ◽

Galaxy Formation ◽

Cold Dark Matter ◽

Dwarf Galaxies ◽

Dwarf Galaxy ◽

Good Description ◽

Good Match ◽

Virial Mass ◽

Density Threshold

ABSTRACT We use cosmological hydrodynamical galaxy formation simulations from the NIHAO project to investigate the response of cold dark matter (CDM) haloes to baryonic processes. Previous work has shown that the halo response is primarily a function of the ratio between galaxy stellar mass and total virial mass, and the density threshold above which gas is eligible to form stars, n[cm−3]. At low n all simulations in the literature agree that dwarf galaxy haloes are cuspy, but at high n ≳ 100 there is no consensus. We trace halo contraction in dwarf galaxies with n ≳ 100 reported in some previous simulations to insufficient spatial resolution. Provided the adopted star formation threshold is appropriate for the resolution of the simulation, we show that the halo response is remarkably stable for n ≳ 5, up to the highest star formation threshold that we test, n = 500. This free parameter can be calibrated using the observed clustering of young stars. Simulations with low thresholds n ≤ 1 predict clustering that is too weak, while simulations with high star formation thresholds n ≳ 5, are consistent with the observed clustering. Finally, we test the CDM predictions against the circular velocities of nearby dwarf galaxies. Low thresholds predict velocities that are too high, while simulations with n ∼ 10 provide a good match to the observations. We thus conclude that the CDM model provides a good description of the structure of galaxies on kpc scales provided the effects of baryons are properly captured.

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Dark matter-deficient dwarf galaxies form via tidal stripping of dark matter in interactions with massive companions

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab093 ◽

2021 ◽

Vol 502 (2) ◽

pp. 1785-1796

Author(s):

R A Jackson ◽

S Kaviraj ◽

G Martin ◽

J E G Devriendt ◽

A Slyz ◽

...

Keyword(s):

Dark Matter ◽

Galaxy Evolution ◽

Cold Dark Matter ◽

Dwarf Galaxies ◽

Stellar Mass ◽

Matter Content ◽

Mass Relation ◽

Potential Wells ◽

Tidal Interactions ◽

New Interactions

ABSTRACT In the standard ΛCDM (Lambda cold dark matter) paradigm, dwarf galaxies are expected to be dark matter-rich, as baryonic feedback is thought to quickly drive gas out of their shallow potential wells and quench star formation at early epochs. Recent observations of local dwarfs with extremely low dark matter content appear to contradict this picture, potentially bringing the validity of the standard model into question. We use NewHorizon, a high-resolution cosmological simulation, to demonstrate that sustained stripping of dark matter, in tidal interactions between a massive galaxy and a dwarf satellite, naturally produces dwarfs that are dark matter-deficient, even though their initial dark matter fractions are normal. The process of dark matter stripping is responsible for the large scatter in the halo-to-stellar mass relation in the dwarf regime. The degree of stripping is driven by the closeness of the orbit of the dwarf around its massive companion and, in extreme cases, produces dwarfs with halo-to-stellar mass ratios as low as unity, consistent with the findings of recent observational studies. ∼30 per cent of dwarfs show some deviation from normal dark matter fractions due to dark matter stripping, with 10 per cent showing high levels of dark matter deficiency (Mhalo/M⋆ < 10). Given their close orbits, a significant fraction of dark matter-deficient dwarfs merge with their massive companions (e.g. ∼70 per cent merge over time-scales of ∼3.5 Gyr), with the dark matter-deficient population being constantly replenished by new interactions between dwarfs and massive companions. The creation of these galaxies is therefore a natural by-product of galaxy evolution and their existence is not in tension with the standard paradigm.

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