Origin of the Local Group satellite planes

Banik, Indranil; O’Ryan, David; Zhao, Hongsheng

doi:10.1093/mnras/sty919

Cited by 42 publications

(54 citation statements)

References 154 publications

(253 reference statements)

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“…The outer particles of each disk generally ended up preferentially rotating within a certain plane. If the flyby occurred in a particular orientation, then both simulated 'satellite planes' matched the orientations and spatial extents of the corresponding observed structures (Banik et al 2018). Their best-fitting simulation also matched several other constraints like the timing argument, the statement that the MW and M31 must have been on the Hubble flow at very early times but still end up with their presently observed separation and relative velocity (Kahn & Woltjer 1959).…”

Section: Introductionsupporting

confidence: 57%

Testing gravity with wide binary stars like α Centauri

Banik

Zhao

2018

Monthly Notices of the Royal Astronomical Society

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111

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We consider the feasibility of testing Newtonian gravity at low accelerations using wide binary (WB) stars separated by 3 kAU. These systems probe the accelerations at which galaxy rotation curves unexpectedly flatline, possibly due to Modified Newtonian Dynamics (MOND). We conduct Newtonian and MOND simulations of WBs covering a grid of model parameters in the system mass, semi-major axis, eccentricity and orbital plane. We self-consistently include the external field (EF) from the rest of the Galaxy on the Solar neighbourhood using an axisymmetric algorithm. For a given projected separation, WB relative velocities reach larger values in MOND. The excess is ≈ 20% adopting its simple interpolating function, as works best with a range of Galactic and extragalactic observations. This causes noticeable MOND effects in accurate observations of ≈ 500 WBs, even without radial velocity measurements.We show that the proposed Theia mission may be able to directly measure the orbital acceleration of Proxima Centauri towards the 13 kAU-distant α Centauri. This requires an astrometric accuracy of ≈ 1 µas over 5 years. We also consider the long-term orbital stability of WBs with different orbital planes. As each system rotates around the Galaxy, it experiences a time-varying EF because this is directed towards the Galactic Centre. We demonstrate approximate conservation of the angular momentum component along this direction, a consequence of the WB orbit adiabatically adjusting to the much slower Galactic orbit. WBs with very little angular momentum in this direction are less stable over Gyr periods. This novel direction-dependent effect might allow for further tests of MOND.

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Section: Introductionsupporting

confidence: 57%

Testing gravity with wide binary stars like α Centauri

Banik

Zhao

2018

Monthly Notices of the Royal Astronomical Society

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111

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“…For example, Ref. [43] estimates for the local groups g ex ≈ 2.2 × 10 −2 a 0 . If all else was exact, with no measurement errors, and no departure from any of our assumptions, except that of isolation, then departures of σ M /σ from unity would only be due to the EFE, and be given, for g ex g, by 6 MOND predicts an acceleration discrepancy ≈ a0/ḡ, withḡ the larger of the internal and external accelerations.…”

Section: External-field Effect?mentioning

confidence: 99%

MOND in galaxy groups: A superior sample

Milgrom

2019

Phys. Rev. D

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Intermediate-richness galaxy groups are an important testing ground for MOND. First, they constitute a distinct type of galactic systems, with their own evolution histories and underlying physical processes; second, they probe little-chartered regions of parameter space, as they have baryonic masses similar to massive galaxies, and similar velocity dispersions, but much larger sizes -similar to cluster cores (or even to clusters), but much lower dispersions. Importantly in the context of MOND, they have the lowest internal accelerations reachable inside galactic systems. Following my recent analysis of MOND in galaxy groups, I came across a much superior sample, which I analyze here. This extensive catalog permits strict quality cuts that still leave a large sample of 56 mediumrichness groups, better suited for dynamical analysis -e.g., in having a large number (≥ 15) of members with measured velocities. I find that these groups obey the deep-MOND relation between baryonic mass, MM , and velocity dispersion, σ: MM Ga0 = (81/4)σ 4 , with individual, MOND, mass-to-light ratios, MM /LK of order 1 M /LK, , and a sample median value of (MM /LK) med = 0.7 M /LK, . These compare well with stellar values deduced for single galaxies, and with values deduced from population-synthesis analyses. In contrast, the dynamical, Newtonian M d /LK values are much larger -several tens solar units, and (M d /LK) med = 37 M /LK, . The same MOND relation describes (isolated) dwarf spheroidals -two-three orders smaller in size, and seven-eight orders lower in mass. The groups conformation to the MOND relation is equivalent to their lying on the deep-MOND branch of the "mass-discrepancy-acceleration relation", g ≈ (gN a0) 1/2 , for g as low as a few percents of a0 (gN is the Newtonian, baryonic, gravitational acceleration, and g the actual one). This argues against systematic departure from MOND at extremely low accelerations (as has been suggested). This conformation also argues against the hypothesis that the remaining MOND conundrum in cluster cores bespeaks a breakdown of MOND on large-distance scales; our groups are as large as cluster cores, but do not show obvious disagreement with MOND. I also discuss the possible presence of the idiosyncratic, MOND external-field effect.PACS numbers: 04.50. Kd, 95.35.+d

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“…Fossils left over from this merging history orbit the galaxy as satellite galaxies, but the observed very significant phase-space correlation of satellite galaxies around the MW (Kroupa et al 2005;Pawlowski et al 2012;Pawlowski & Kroupa 2020), Andromeda (Metz et al 2007;Ibata et al 2013) and Cen A (Müller et al 2018) is inconsistent with the observed satellites being such fossils (Pawlowski 2018). The mutual alignment of the MW and Andromeda satellite population have not found an explanation in standard-dark-matter models, but appear to arise naturally in Milgromian dynamics (Bílek et al 2018;Banik et al 2018b). Moreover, given the non-detection of dark-matter-particles despite a significant effort to find them (Bertone & Tait 2018) and astronomical arguments suggesting dark matter not to exist (Kroupa et al 2010;Kroupa 2012, it is necessary to also begin to investigate if non-dark-matterbased models lead to objects which resemble observed galaxies.…”

Section: Introductionmentioning

confidence: 99%

The Formation of Exponential Disk Galaxies in MOND

Wittenburg

Kroupa

Famaey

2020

ApJ

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The formation and evolution of galaxies is highly dependent on the dynamics of stars and gas, which is governed by the underlying law of gravity. To investigate how the formation and evolution of galaxies takes place in Milgromian gravity (MOND), we present full hydrodynamical simulations with the Phantom of Ramses (POR) code. These are the first-ever galaxy formation simulations done in MOND with detailed hydrodynamics, including star formation, stellar feedback, radiative transfer and supernovae. These models start from simplified initial conditions, in the form of isolated, rotating gas spheres in the early Universe. These collapse and form late-type galaxies obeying several scaling relations, which was not a priori expected. The formed galaxies have a compact bulge and a disk with exponentially decreasing surface mass density profiles and scale lengths consistent with observed galaxies, and vertical stellar mass distributions with distinct exponential profiles (thin and thick disk). This work thus shows for the first time that disk galaxies with exponential profiles in both gas and stars are a generic outcome of collapsing gas clouds in MOND. These models have a slight lack of stellar angular momentum because of their somewhat compact stellar bulge, which is connected to the simple initial conditions and the negligible later gas accretion. We also analyse how the addition of more complex baryonic physics changes the main resulting properties of the models and find this to be negligibly so in the Milgromian framework.

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Origin of the Local Group satellite planes

Cited by 42 publications

References 154 publications

Testing gravity with wide binary stars like α Centauri

Testing gravity with wide binary stars like α Centauri

MOND in galaxy groups: A superior sample

The Formation of Exponential Disk Galaxies in MOND

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