Large-scale assembly bias of dark matter halos

A recent study by Farnes (2018, A&A, 620, A92) proposed an alternative cosmological model in which both dark matter and dark energy are replaced with a single fluid of negative mass. This paper presents a critical review of that model. A number of problems and discrepancies with observations are identified. For instance, the predicted shape and density of galactic dark matter halos are incorrect. Also, halos would need to be less massive than the baryonic component, otherwise they would become gravitationally unstable. Perhaps the most challenging problem in this theory is the presence of a large-scale version of the “runaway effect”, which would result in all galaxies moving in random directions at nearly the speed of light. Other more general issues regarding negative mass in general relativity are discussed, such as the possibility of time-travel paradoxes.

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Surveying for Dwarf Galaxies Within Voids FN2 and FN8

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316010681 ◽

2014 ◽

Vol 11 (S308) ◽

pp. 614-615

Author(s):

Stephen McNeil ◽

Chris Draper ◽

J. Ward Moody

Keyword(s):

Dark Matter ◽

Galaxy Formation ◽

Large Scale ◽

Dwarf Galaxies ◽

Low Density ◽

Dark Matter Halos ◽

Void Volumes ◽

Four Square ◽

Large Scale Structure Formation

AbstractThe presence or absence of dwarf galaxies with Mr' > -14 in low-density volumes correlates with dark matter halos and how they affect galaxy formation. We are conducting a redshifted Hα imaging survey for dwarf galaxies with Mr' > -13 in the heart of the well-defined voids FN2 and FN8 using the KPNO 4m Mayall telescope and Mosaic Imager. These data have furnished over 600 strong candidates in a four square degree area. Follow-up spectra finding none of these candidates to be within the void volumes will constrain the dwarf population there to be 2 to 8% of the cosmic mean. Conversely, finding even one Hα dwarf in the void heart will challenge several otherwise successful theories of large-scale structure formation.

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Globular Clusters and Streaming Velocities: Testing the New Formation Channel in High-resolution Cosmological Simulations

The Astrophysical Journal ◽

10.3847/1538-4357/ac27aa ◽

2021 ◽

Vol 922 (2) ◽

pp. 193

Author(s):

Anna T. P. Schauer ◽

Volker Bromm ◽

Michael Boylan-Kolchin ◽

Simon C. O. Glover ◽

Ralf S. Klessen

Keyword(s):

Dark Matter ◽

Early Universe ◽

Globular Clusters ◽

Large Scale ◽

Compact Star ◽

Star Clusters ◽

Dark Matter Halos ◽

Metal Enrichment ◽

Hydrodynamical Simulations ◽

Population Iii

Abstract The formation of globular clusters and their relation to the distribution of dark matter have long puzzled astronomers. One of the most recently proposed globular cluster formation channels ties ancient star clusters to the large-scale streaming velocity of baryons relative to dark matter in the early universe. These streaming velocities affect the global infall of baryons into dark matter halos, the high-redshift halo mass function, and the earliest generations of stars. In some cases, streaming velocities may result in dense regions of dark matter-free gas that becomes Jeans unstable, potentially leading to the formation of compact star clusters. We investigate this hypothesis using cosmological hydrodynamical simulations that include a full chemical network and the formation and destruction of H2, a process crucial for the formation of the first stars. We find that high-density gas in regions with significant streaming velocities is indeed somewhat offset from the centers of dark matter halos, but this offset is typically significantly smaller than the virial radius. Gas outside of dark matter halos never reaches Jeans-unstable densities in our simulations. We postulate that low-level (Z ≈ 10−3 Z ⊙) metal enrichment by Population III supernovae may enable cooling in the extra-virial regions, allowing gas outside of dark matter halos to cool to the cosmic microwave background temperature and become Jeans unstable. Follow-up simulations that include both streaming velocities and metal enrichment by Population III supernovae are needed to understand if streaming velocities provide one path for the formation of globular clusters in the early universe.

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