The Phantom Dark Matter Halos of the Local Volume in the Context of Modified Newtonian Dynamics

Abstract We explore the predictions of Milgromian gravity (MOND) in the local universe by considering the distribution of the “phantom” dark matter (PDM) that would source the MOND gravitational field in Newtonian gravity, allowing an easy comparison with the dark matter framework. For this, we specifically deal with the quasi-linear version of MOND (QUMOND). We compute the “stellar-to-(phantom)halo mass relation” (SHMR), a monotonically increasing power law resembling the SHMR observationally deduced from spiral galaxy rotation curves in the Newtonian context. We show that the gas-to-(phantom)halo mass relation is flat. We generate a map of the Local Volume in QUMOND, highlighting the important influence of distant galaxy clusters, in particular Virgo. This allows us to explore the scatter of the SHMR and the average density of PDM around galaxies in the Local Volume, ΩPDM ≈ 0.1, below the average cold dark matter density in a ΛCDM universe. We provide a model of the Milky Way in its external field in the MOND context, which we compare to an observational estimate of the escape velocity curve. Finally, we highlight the peculiar features related to the external field effect in the form of negative PDM density zones in the outskirts of each galaxy, and test a new analytic formula for computing galaxy rotation curves in the presence of an external field in QUMOND. While we show that the negative PDM density zones would be difficult to detect dynamically, we quantify the weak-lensing signal they could produce for lenses at z ∼ 0.3.

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Modelling the Rising Tails of Galaxy Rotation Curves

10.20944/preprints201812.0147.v2 ◽

2019 ◽

Author(s):

Fan Zhang

Keyword(s):

Dark Matter ◽

Cold Dark Matter ◽

Weak Field ◽

Rotation Curves ◽

Gravitational Fields ◽

Modified Newtonian Dynamics ◽

Rotation Periods ◽

Weak Field Limit ◽

Modified Gravity Theories ◽

Galaxy Rotation Curves

It is well known but under-appreciated in astrophysical applications, that it is possible for gravity to take on a life of its own in the form of Weyl-curvature-only metrics (note we are referring to the Weyl-only solutions of ordinary General Relativity, we are not considering Weyl conformal gravity or any other modified gravity theories), as numerous examples demonstrate the existence of gravitational fields not being sourced by any matter. In the weak field limit, such autonomous gravitational contents of our universe manifest as solutions to the homogeneous Poisson's equation. In this note, we tentatively explore the possibility that they may perhaps account for some phenomenologies commonly attributed to dark matter. Specifically, we show that a very simple solution of this kind exists that can be utilized to describe the rising tails seen in many galaxy rotation curves, which had been difficult to reconcile within the cold dark matter or modified Newtonian dynamics frameworks. This solution may also help explain the universal $\sim 1$Gyr rotation periods of galaxies in the local universe.

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Modelling the Rising Tails of Galaxy Rotation Curves

10.20944/preprints201812.0147.v1 ◽

2018 ◽

Author(s):

Fan Zhang

Keyword(s):

Dark Matter ◽

Cold Dark Matter ◽

Weak Field ◽

Rotation Curves ◽

Gravitational Fields ◽

Modified Newtonian Dynamics ◽

Rotation Periods ◽

Weak Field Limit ◽

Modified Gravity Theories ◽

Galaxy Rotation Curves

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Baryonic clues to the puzzling diversity of dwarf galaxy rotation curves

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1072 ◽

2020 ◽

Vol 495 (1) ◽

pp. 58-77 ◽

Cited By ~ 8

Author(s):

Isabel M E Santos-Santos ◽

Julio F Navarro ◽

Andrew Robertson ◽

Alejandro Benítez-Llambay ◽

Kyle A Oman ◽

...

Keyword(s):

Dark Matter ◽

Surface Density ◽

Rotation Curve ◽

Cold Dark Matter ◽

Dwarf Galaxy ◽

High Surface ◽

Curve Shape ◽

Disc Galaxy ◽

Rotation Curves ◽

Galaxy Rotation Curves

ABSTRACT We use a compilation of disc galaxy rotation curves to assess the role of the luminous component (‘baryons’) in the rotation curve diversity problem. As in earlier work, we find that rotation curve shape correlates with baryonic surface density: high surface density galaxies have rapidly rising rotation curves consistent with cuspy cold dark matter haloes; slowly rising rotation curves (characteristic of galaxies with inner mass deficits or ‘cores’) occur only in low surface density galaxies. The correlation, however, seems too weak to be the main driver of the diversity. In addition, dwarf galaxies exhibit a clear trend, from ‘cuspy’ systems where baryons are unimportant in the inner mass budget to ‘cored’ galaxies where baryons actually dominate. This trend constrains the various scenarios proposed to explain the diversity, such as (i) baryonic inflows and outflows during galaxy formation; (ii) dark matter self-interactions; (iii) variations in the baryonic mass structure coupled to rotation velocities through the ‘mass discrepancy–acceleration relation’ (MDAR); or (iv) non-circular motions in gaseous discs. Together with analytical modelling and cosmological hydrodynamical simulations, our analysis shows that each of these scenarios has promising features, but none seems to fully account for the observed diversity. The MDAR, in particular, is inconsistent with the observed trend between rotation curve shape and baryonic importance; either the trend is caused by systematic errors in the data or the MDAR does not apply. The origin of the dwarf galaxy rotation curve diversity and its relation to the structure of cold dark matter haloes remains an open issue.

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Modeling the Rising Tails of Galaxy Rotation Curves

Galaxies ◽

10.3390/galaxies7010027 ◽

2019 ◽

Vol 7 (1) ◽

pp. 27 ◽

Cited By ~ 1

Author(s):

Fan Zhang

Keyword(s):

Dark Matter ◽

Cold Dark Matter ◽

Weak Field ◽

Rotation Curves ◽

Gravitational Fields ◽

Modified Newtonian Dynamics ◽

Rotation Periods ◽

Weak Field Limit ◽

Modified Gravity Theories ◽

Galaxy Rotation Curves

It is well known, but under-appreciated in astrophysical applications, that it is possible for gravity to take on a life of its own in the form of Weyl-curvature-only metrics (note that we are referring to the Weyl-only solutions of ordinary General Relativity; we are not considering Weyl conformal gravity or any other modified gravity theories), as numerous examples demonstrate the existence of gravitational fields not being sourced by any matter. In the weak field limit, such autonomous gravitational contents of our universe manifest as solutions to the homogeneous Poisson’s equation. In this note, we tentatively explore the possibility that they may perhaps account for some phenomenologies commonly attributed to dark matter. Specifically, we show that a very simple solution of this kind exists that can be utilized to describe the rising tails seen in many galaxy rotation curves, which had been difficult to reconcile within the cold dark matter or modified Newtonian dynamics frameworks. This solution may also help explain the universal ∼1 Gyr rotation periods of galaxies in the local universe.

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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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MODIFIED GRAVITY AS A COMMON CAUSE FOR COSMIC ACCELERATION AND FLAT GALAXY ROTATION CURVES

International Journal of Modern Physics D ◽

10.1142/s0218271812420023 ◽

2012 ◽

Vol 21 (11) ◽

pp. 1242002 ◽

Cited By ~ 4

Author(s):

PRITI MISHRA ◽

TEJINDER P. SINGH

Keyword(s):

Dark Matter ◽

Dark Energy ◽

Cosmic Acceleration ◽

Accelerating Universe ◽

Rotation Curves ◽

Common Cause ◽

Order Of Magnitude ◽

Flat Rotation Curves ◽

Acceleration Of The Universe ◽

Galaxy Rotation Curves

Flat galaxy rotation curves and the accelerating Universe both imply the existence of a critical acceleration, which is of the same order of magnitude in both the cases, in spite of the galactic and cosmic length scales being vastly different. Yet, it is customary to explain galactic acceleration by invoking gravitationally bound dark matter, and cosmic acceleration by invoking a "repulsive" dark energy. Instead, might it not be the case that the flatness of rotation curves and the acceleration of the Universe have a common cause? In this essay we propose a modified theory of gravity. By applying the theory on galactic scales we demonstrate flat rotation curves without dark matter, and by applying it on cosmological scales we demonstrate cosmic acceleration without dark energy.

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The weak lensing radial acceleration relation: Constraining modified gravity and cold dark matter theories with KiDS-1000

Astronomy and Astrophysics ◽

10.1051/0004-6361/202040108 ◽

2021 ◽

Vol 650 ◽

pp. A113

Author(s):

Margot M. Brouwer ◽

Kyle A. Oman ◽

Edwin A. Valentijn ◽

Maciej Bilicki ◽

Catherine Heymans ◽

...

Keyword(s):

Dark Matter ◽

Galaxy Formation ◽

Modified Gravity ◽

Cold Dark Matter ◽

Weak Lensing ◽

Mass Relation ◽

Gravitational Acceleration ◽

Radial Acceleration ◽

The Galaxy ◽

The Difference

We present measurements of the radial gravitational acceleration around isolated galaxies, comparing the expected gravitational acceleration given the baryonic matter (gbar) with the observed gravitational acceleration (gobs), using weak lensing measurements from the fourth data release of the Kilo-Degree Survey (KiDS-1000). These measurements extend the radial acceleration relation (RAR), traditionally measured using galaxy rotation curves, by 2 decades in gobs into the low-acceleration regime beyond the outskirts of the observable galaxy. We compare our RAR measurements to the predictions of two modified gravity (MG) theories: modified Newtonian dynamics and Verlinde’s emergent gravity (EG). We find that the measured relation between gobs and gbar agrees well with the MG predictions. In addition, we find a difference of at least 6σ between the RARs of early- and late-type galaxies (split by Sérsic index and u − r colour) with the same stellar mass. Current MG theories involve a gravity modification that is independent of other galaxy properties, which would be unable to explain this behaviour, although the EG theory is still limited to spherically symmetric static mass models. The difference might be explained if only the early-type galaxies have significant (Mgas ≈ M⋆) circumgalactic gaseous haloes. The observed behaviour is also expected in Λ-cold dark matter (ΛCDM) models where the galaxy-to-halo mass relation depends on the galaxy formation history. We find that MICE, a ΛCDM simulation with hybrid halo occupation distribution modelling and abundance matching, reproduces the observed RAR but significantly differs from BAHAMAS, a hydrodynamical cosmological galaxy formation simulation. Our results are sensitive to the amount of circumgalactic gas; current observational constraints indicate that the resulting corrections are likely moderate. Measurements of the lensing RAR with future cosmological surveys (such as Euclid) will be able to further distinguish between MG and ΛCDM models if systematic uncertainties in the baryonic mass distribution around galaxies are reduced.

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Aging haloes: implications of the magnitude gap on conditional statistics of stellar and gas properties of massive haloes

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa291 ◽

2020 ◽

Vol 493 (1) ◽

pp. 1361-1374 ◽

Cited By ~ 2

Author(s):

Arya Farahi ◽

Matthew Ho ◽

Hy Trac

Keyword(s):

Dark Matter ◽

Galaxy Formation ◽

Large Scale ◽

Cold Dark Matter ◽

Stellar Mass ◽

Formation Time ◽

Gas Content ◽

Mass Relation ◽

Cold Dark Matter Model ◽

Conditional Statistics

ABSTRACT Cold dark matter model predicts that the large-scale structure grows hierarchically. Small dark matter haloes form first. Then, they grow gradually via continuous merger and accretion. These haloes host the majority of baryonic matter in the Universe in the form of hot gas and cold stellar phase. Determining how baryons are partitioned into these phases requires detailed modelling of galaxy formation and their assembly history. It is speculated that formation time of the same mass haloes might be correlated with their baryonic content. To evaluate this hypothesis, we employ haloes of mass above $10^{14}\, \mathrm{M}_{\odot }$ realized by TNG300 solution of the IllustrisTNG project. Formation time is not directly observable. Hence, we rely on the magnitude gap between the brightest and the fourth brightest halo galaxy member, which is shown that traces formation time of the host halo. We compute the conditional statistics of the stellar and gas content of haloes conditioned on their total mass and magnitude gap. We find a strong correlation between magnitude gap and gas mass, BCG stellar mass, and satellite galaxies stellar mass, but not the total stellar mass of halo. Conditioning on the magnitude gap can reduce the scatter about halo property–halo mass relation and has a significant impact on the conditional covariance. Reduction in the scatter can be as significant as 30 per cent, which implies more accurate halo mass prediction. Incorporating the magnitude gap has a potential to improve cosmological constraints using halo abundance and allows us to gain insight into the baryon evolution within these systems.

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On galaxy rotation curves from a continuum mechanics approach to modified gravity

International Journal of Modern Physics D ◽

10.1142/s0218271818500074 ◽

2018 ◽

Vol 27 (02) ◽

pp. 1850007 ◽

Cited By ~ 5

Author(s):

Christian G. Böhmer ◽

Nicola Tamanini ◽

Matthew Wright

Keyword(s):

General Relativity ◽

Dark Matter ◽

Continuum Mechanics ◽

Modified Gravity ◽

Galactic Rotation ◽

Dark Matter Halos ◽

Additional Structure ◽

Rotation Curves ◽

Small Deviations ◽

Galaxy Rotation Curves

We consider a modification of General Relativity motivated by the treatment of anisotropies in Continuum Mechanics. The Newtonian limit of the theory is formulated and applied to galactic rotation curves. By assuming that the additional structure of spacetime behaves like a Newtonian gravitational potential for small deviations from isotropy, we are able to recover the Navarro–Frenk–White profile of dark matter halos by a suitable identification of constants. We consider the Burkert profile in the context of our model and also discuss rotation curves more generally.

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