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The positions of Local Group galaxies in an all-sky plot as seen from the midpoint between the MW and M31 (same symbols as in Fig. 1). Compared to Fig. 6 in Pawlowski et al. (2013a) this plot also includes the newly discovered dwarf galaxy Perseus I and the members of the linear NGC 3109 association (grey diamonds), which align with the LGP1 mod members Leo T, Leo A and UGC 4879, indicating that they lie in a common plane which passes through the centre of the LG.
Source publication
The recently discovered dwarf galaxy Perseus I appears to be associated with
the dominant plane of non-satellite galaxies in the Local Group (LG). We
predict its velocity dispersion and those of the other isolated dSphs Cetus and
Tucana to be 6.5, 8.2, and 5.5 km/s, respectively. The NGC 3109 association,
including the recently discovered dwarf gal...
Context in source publication
Context 1
... the NGC 3109 association (receding) and the other three galaxies (slowly approaching) might then be simply due to the stronger gravitational attraction acting on the more nearby galaxies. Indeed, as seen from the center of the LG the members of the NGC 3109 association align along a sim- ilar band as defined by UGC 4879, Leo A and Leo T (see Fig. 2). This indicates that they are in a common plane running through the center of the LG. Fitting a plane to the eight galaxy positions con- firms that the galaxies are confined to a thin planar structure, which we will refer to as the Great Northern Plane. The parameters of the best-fit plane are compiled in Tab. 1. The plane has a ...
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Citations
... The existence of the non-baryonic DM is questioned by a detailed study of properties of faint satellite galaxies of the Milky Way (MW), see Kroupa et al. (2010), which are distributed on a planar structure. Similar alignments were observed also in isolated dwarf galaxies in the local group (Pawlowski and Kroupa, 2013;Pawlowski and McGaugh, 2014) as well as in more distant galaxies (Galianni et al., 2010;Duc et al., 2014). This is a challenge for cosmological simulations, because the DM sub-haloes are assumed to be isotropically distributed. ...
Modified Newtonian equations for gravitational orbits in the expanding Universe indicate that local gravitationally bounded systems like galaxies and planetary systems are unaffected by the expansion of the Universe. This result is derived for the space expansion described by the standard FLRW metric. In this paper, the modified Newtonian equations are derived for the space expansion described by the conformal cosmology (CC) metric. In this metric, the comoving and proper times are different similarly as the comoving and proper distances. As shown by Vavryčuk (Front. Phys. 2022), this metric is advantageous, because it properly predicts the cosmic time dilation, and fits the Type Ia supernova luminosity observations with no need to introduce dark energy. Surprisingly, the solution of the equations for gravitational orbits based on the CC metric behaves quite differently than that based on the FLRW metric. In contrast to the common opinion that local systems resist the space expansion, they expand according to the Hubble flow in the CC metric. The evolution of the local systems with cosmic time is exemplified on numerical modelling of spiral galaxies. The size of the spiral galaxies grows consistently with observations and a typical spiral pattern is well reproduced. The theory predicts flat rotation curves without an assumption of dark matter surrounding the galaxy. The theory resolves challenges to the ΛCDM model such as the problem of faint satellite galaxies, baryonic Tully-Fisher relation or the radial acceleration relation. Furthermore, puzzles in the solar system are successfully explained such as the Faint young Sun paradox or the Moon’s and Titan’s orbit anomalies.
... In addition to the satellite galaxies of the MW and M31, the LG also contains non-satellite dwarf galaxies that can be used to test MOND. Pawlowski & McGaugh (2014a) predicted σ LOS for the isolated LG dwarfs Perseus I, Cetus, and Tucana to be 6.5 km/s, 8.2 km/s, and 5.5 km/s, respectively, with an uncertainty close to 1 km/s in all cases due to the uncertain M /L (see their section 3). Observationally, σ LOS of Perseus I is constrained to 4.2 +3.6 −4.2 km/s, with a 90% confidence level upper limit of 10 km/s (Martin et al. 2014). ...
... The latest measurements for Tucana indicate that its σ LOS = 6.2 +1.6 −1.3 km/s (Taibi et al. 2020), with the more careful analysis and larger sample size allowing the authors to rule out earlier claims that σ LOS > 10 km/s (Fraternali et al. 2009;Gregory et al. 2019). In all three cases, there is good agreement with the a priori MOND prediction, which is just Equation 49 as these dwarfs are quite isolated (Pawlowski & McGaugh 2014a). ...
... This almost linear association (Bellazzini et al. 2013) consists of several dwarf galaxies moving away from the LG with rather high RVs. The NGC 3109 association was studied in more detail by Pawlowski & McGaugh (2014a) in light of other LG structures like the satellite planes (Section 5.6). Their work reached a similar conclusion regarding the high RVs. ...
Astronomical observations reveal a major deficiency in our understanding of physics—the detectable mass is insufficient to explain the observed motions in a huge variety of systems given our current understanding of gravity, Einstein’s General theory of Relativity (GR). This missing gravity problem may indicate a breakdown of GR at low accelerations, as postulated by Milgromian dynamics (MOND). We review the MOND theory and its consequences, including in a cosmological context where we advocate a hybrid approach involving light sterile neutrinos to address MOND’s cluster-scale issues. We then test the novel predictions of MOND using evidence from galaxies, galaxy groups, galaxy clusters, and the large-scale structure of the universe. We also consider whether the standard cosmological paradigm (LCDM) can explain the observations and review several previously published highly significant falsifications of it. Our overall assessment considers both the extent to which the data agree with each theory and how much flexibility each has when accommodating the data, with the gold standard being a clear a priori prediction not informed by the data in question. Our conclusion is that MOND is favoured by a wealth of data across a huge range of astrophysical scales, ranging from the kpc scales of galactic bars to the Gpc scale of the local supervoid and the Hubble tension, which is alleviated in MOND through enhanced cosmic variance. We also consider several future tests, mostly at scales much smaller than galaxies.
... Such structures are difficult to explain using dissipationless haloes of CDM, as first pointed out by Kroupa et al. (2005) and more recently by Pawlowski et al. (2014), who considered and excluded a wide range of different proposed 1 Hints of the M31 SP were already evident in Metz et al. (2007) and Metz, Kroupa & Jerjen (2009a). Hints of the Cen A SP were evident in Tully et al. (2015), but the two planes they identified were later revealed to be part of one thicker plane (Müller et al. 2016). ...
... Due to the high MW-M31 relative velocity around the time of their flyby, they would likely have gravitationally slingshot several LG dwarfs out at high speed. As discussed further in Section 4.2.2, this could lead to the existence of LG dwarfs with an unusually high RV in a ΛCDM context, such as the dwarfs in the NGC 3109 association (Pawlowski & McGaugh 2014;Peebles 2017). These could be backsplash from the MW-M31 flyby, a scenario that was considered in detail by Banik & Zhao (2018c). ...
... Beyond the MW, another important line of evidence for a past encounter with M31 is provided by the kinematics of the NGC 3109 association ≈ 1.5 Mpc away (Pawlowski & McGaugh 2014). Those authors discussed how the high RV of NGC 3109 implies that it should have been close to the MW ≈ 9 Gyr ago based on looking at the problem backwards in time. ...
The existence of mutually correlated thin and rotating planes of satellite galaxies around both the Milky Way (MW) and Andromeda (M31) calls for an explanation. Previous work in Milgromian dynamics (MOND) indicated that a past MW-M31 encounter might have led to the formation of these satellite planes. We perform the first-ever hydrodynamical MOND simulation of the Local Group using Phantom of RAMSES. We show that an MW-M31 encounter at $z \approx 1$, with a perigalactic distance of about 80 kpc, can yield two disc galaxies at $z=0$ oriented similarly to the observed galactic discs and separated similarly to the observed M31 distance. Importantly, the tidal debris are distributed in phase space similarly to the observed MW and M31 satellite planes, with the correct preferred orbital pole for both. The MW-M31 orbital geometry is consistent with the presently observed M31 proper motion despite this not being considered as a constraint when exploring the parameter space. The mass of the tidal debris around the MW and M31 at $z=0$ compare well with the mass observed in their satellite systems. The remnant discs of the two galaxies have realistic radial scale lengths and velocity dispersions, and the simulation naturally produces a much hotter stellar disc in M31 than in the MW. However, reconciling this scenario with the ages of stellar populations in satellite galaxies would require that a higher fraction of stars previously formed in the outskirts of the progenitors ended up within the tidal debris, or that the MW-M31 interaction occurred at $z>1$.
... Such structures are difficult to explain using dissipationless haloes of CDM, as first pointed out by Kroupa et al. (2005) and more recently by Pawlowski et al. (2014), who considered and excluded a wide range of different proposed explanations within the ΛCDM context. For instance, accreting most satellites as a single group (Metz et al. 2009b) or along a single filament would yield some anisotropy, but not enough to explain the very thin MW SP (Shao et al. 2018). ...
... Due to the high MW-M31 relative velocity around the time of their flyby, they would likely have gravitationally slingshot several LG dwarfs out at high speed. As discussed further in Section 4.2.2, this could lead to the existence of LG dwarfs with an unusually high RV in a ΛCDM context, such as the dwarfs in the NGC 3109 association (Pawlowski & McGaugh 2014;Peebles 2017). These could be backsplash from the MW-M31 flyby, a scenario that was considered in detail by Banik & Zhao (2018c). ...
... Beyond the MW, another important line of evidence for a past encounter with M31 is provided by the kinematics of the NGC 3109 association ≈ 1.5 Mpc away (Pawlowski & McGaugh 2014). Those authors discussed how the high RV of NGC 3109 implies that it should have been close to the MW ≈ 9 Gyr ago based on looking at the problem backwards in time. ...
The existence of mutually correlated thin and rotating planes of satellite galaxies around both the Milky Way (MW) and Andromeda (M31) calls for an explanation. Previous work in Milgromian dynamics (MOND) indicated that a past MW-M31 encounter might have led to the formation of these satellite planes. We perform the first-ever hydrodynamical MOND simulation of the Local Group using phantom of ramses. We show that an MW-M31 encounter at z ≈ 1, with a perigalactic distance of about 80 kpc, can yield two disc galaxies at z = 0 oriented similarly to the observed galactic discs and separated similarly to the observed M31 distance. Importantly, the tidal debris are distributed in phase space similarly to the observed MW and M31 satellite planes, with the correct preferred orbital pole for both. The MW-M31 orbital geometry is consistent with the presently observed M31 proper motion despite this not being considered as a constraint when exploring the parameter space. The mass of the tidal debris around the MW and M31 at z = 0 compare well with the mass observed in their satellite systems. The remnant discs of the two galaxies have realistic radial scale lengths and velocity dispersions, and the simulation naturally produces a much hotter stellar disc in M31 than in the MW. However, reconciling this scenario with the ages of stellar populations in satellite galaxies would require that a higher fraction of stars previously formed in the outskirts of the progenitors ended up within the tidal debris, or that the MW-M31 interaction occurred at z > 1.
... Because of this EFE, a rotationally supported (pressure supported) system in isolation is expected to have a higher rotational velocity (velocity dispersion) than the same system around a massive host (e.g. Wu et al. 2007;Gentile et al. 2007b;McGaugh & Milgrom 2013a,b;Pawlowski & McGaugh 2014;Pawlowski et al. 2015;McGaugh 2016;Hees et al. 2016;Haghi et al. 2016;Müller et al. 2019;Chae et al. 2020Chae et al. , 2021. In particular, the latter should not follow the RAR, which is contrary to the case of the more isolated systems that should lie on the RAR. ...
The tight radial acceleration relation (RAR) obeyed by rotationally supported disk galaxies is one of the most successful a priori predictions of the modified Newtonian dynamics (MOND) paradigm on galaxy scales. Another important consequence of MOND as a classical modification of gravity is that the strong equivalence principle (SEP) – which requires the dynamics of a small, free-falling, self-gravitating system not to depend on the external gravitational field in which it is embedded – should be broken. Multiple tentative detections of this so-called external field effect (EFE) of MOND have been made in the past, but the systems that should be most sensitive to it are galaxies with low internal gravitational accelerations residing in galaxy clusters within a strong external field. Here, we show that ultra-diffuse galaxies (UDGs) in the Coma cluster do lie on the RAR, and that their velocity dispersion profiles are in full agreement with isolated MOND predictions, especially when including some degree of radial anisotropy. However, including a breaking of the SEP via the EFE seriously deteriorates this agreement. We discuss various possibilities to explain this within the context of MOND, including a combination of tidal heating and higher baryonic masses. We also speculate that our results could mean that the EFE is screened in cluster UDGs. The fact that this would happen precisely within galaxy clusters, where classical MOND fails, could be especially relevant to the nature of the residual MOND missing mass in clusters of galaxies.
... These are galaxies with the necessary data (e.g., atomic gas mass, some measure of the outer circular speed). We restrict ourselves to traditional members of the Local Group (Mateo 1998), and do not include other nearby galaxies like those of the outlying NGC 3109 association at D ; 1.3 Mpc (see Pawlowski & McGaugh 2014) or more distant (∼2 Mpc) objects like NGC 55, GR 8, IC 5152, and UGCA 438. In particular, NGC 3109 and NGC 55 are in the SPARC sample (Lelli et al. 2016b) and have been used to set our baseline BTFR calibration ). ...
... Pawlowski & McGaugh 2014;McGaugh 2016b;Famaey et al. 2018). ...
We explore the baryonic Tully–Fisher relation in the Local Group. Rotationally-supported Local Group galaxies adhere precisely to the relation defined by more distant galaxies. For pressure-supported dwarf galaxies, we determine the scaling factor β c that relates their observed velocity dispersion to the equivalent circular velocity of rotationally-supported galaxies of the same mass such that V o = β c σ * . For a typical mass-to-light ratio ϒ * = 2 M ☉ / L ☉ in the V band, we find that β c = 2. More generally, log β c = 0.25 log ϒ * + 0.226 . This provides a common kinematic scale relating pressure and rotationally-supported dwarf galaxies.
... In addition to the satellite galaxies of the MW and M31, the LG also contains non-satellite dwarf galaxies that can be used to test MOND. Pawlowski & McGaugh (2014a) predicted σ LOS for the isolated LG dwarfs Perseus I, Cetus, and Tucana to be 6.5 km/s, 8.2 km/s, and 5.5 km/s, respectively, with an uncertainty close to 1 km/s in all cases due to the uncertain M * /L (see their section 3). Observationally, σ LOS of Perseus I is constrained to 4.2 +3.6 −4.2 km/s, with a 90% confidence level upper limit of 10 km/s (Martin et al. 2014). ...
... The latest measurements for Tucana indicate that its σ LOS = 6.2 +1.6 −1.3 km/s (Taibi et al. 2020), with the more careful analysis and larger sample size allowing the authors to rule out earlier claims that σ LOS > 10 km/s (Fraternali et al. 2009;Gregory et al. 2019). In all three cases, there is good agreement with the a priori MOND prediction, which is just Equation 41 as these dwarfs are quite isolated (Pawlowski & McGaugh 2014a). ...
... This almost linear association (Bellazzini et al. 2013) consists of several dwarf galaxies moving away from the LG at rather high RVs. The NGC 3109 association was studied in more detail by Pawlowski & McGaugh (2014a) in light of other LG structures like the satellite planes (Section 5.6). Their work reached a similar conclusion regarding the high RV. ...
Astronomical observations reveal a major deficiency in our understanding of physics $-$ the detectable mass is insufficient to explain the observed motions in a huge variety of systems given our current understanding of gravity, Einstein's General theory of Relativity (GR). This missing gravity problem may indicate a breakdown of GR at low accelerations, as posited by Milgromian dynamics (MOND). We review the MOND theory and its consequences, including in a cosmological context where we advocate a hybrid approach involving light sterile neutrinos to address MOND's cluster-scale issues. We then test the novel predictions of MOND using evidence from galaxies, galaxy groups, galaxy clusters, and the large scale structure of the Universe. We also consider whether the standard cosmological paradigm ($\Lambda$CDM) can explain the observations, and review several previously published highly significant falsifications of it. Our overall assessment considers both the extent to which the data agree with each theory and how much flexibility each has when accommodating the data, with the gold standard being a clear a priori prediction not informed by the data in question. We also consider some future tests. Our conclusion is that MOND is favoured by a wealth of data across a huge range of astrophysical scales, ranging from the kpc scales of galactic bars to the Gpc scale of the local supervoid and the Hubble tension, which is alleviated in MOND through enhanced cosmic variance.
... The criterion imposed by equation 2 will often but not always succeed in distinguishing dwarfs that should and should not fall on the BTFR (see discussion in McGaugh & Wolf 2010). This is an important distinction in MOND, which is the only theory that has demonstrated the ability to predict velocity dispersions in advance of their observation (McGaugh & Milgrom 2013a,b;Pawlowski & McGaugh 2014;McGaugh 2016b;Famaey et al. 2018). ...
We explore the Baryonic Tully-Fisher Relation in the Local Group. Rotationally supported Local Group galaxies adhere precisely to the relation defined by more distant galaxies. For pressure supported dwarf galaxies, we determine the scaling factor $\beta_c$ that relates their observed velocity dispersion to the equivalent circular velocity of rotationally supported galaxies of the same mass such that $V_o = \beta_c \sigma_*$. For a typical mass-to-light ratio $\Upsilon_* = 2\;\mathrm{M}_{\odot}/\mathrm{L}_{\odot}$ in the $V$-band, we find that $\beta_c = 2$. More generally, $\log \beta_c = 0.25 \log \Upsilon_* +0.226$. This provides a common kinematic scale relating pressure and rotationally supported dwarf galaxies.
... [astro-ph.GA] 23 Aug 2021 A&A proofs: manuscript no. MATLAS-planes have been three discoveries of non-satellite planes (dwarfs located outside the virial volume of any galaxy) in the Local Group (LG): the Local Group Planes 1 and 2 (LG P1 , LG P2 ; ) and the Great Northern Plane (GNP; Pawlowski & McGaugh 2014). ...
It was first observed in the 1970s that the dwarf galaxies surrounding our Milky Way, so-called satellites, appear to be arranged in a thin, vast plane. Similar discoveries have been made around additional galaxies in the local Universe such as Andromeda, Centaurus A, and potentially M83. In the specific cases with available kinematic data, the dwarf satellites also appear to preferentially co-orbit their massive host galaxy. Planes of satellites are rare in the lambda cold dark matter ($\Lambda$CDM) paradigm, although they may be a natural consequence of projection effects. Such a phase-space correlation, however, remains difficult to explain. In this work we analyzed the 2D spatial distribution of 2210 dwarf galaxies around early-type galaxies (ETGs) in the low-to-medium density fields of the "Mass Assembly of early-Type GaLAxies with their fine Structures" (MATLAS) survey. Under the assumption that the dwarfs are satellite members of the central massive ETG, we identified flattened structures using both a variation in the Hough transform and total least square (TLS) fitting. In 119 satellite systems, we find 31 statistically significant flattened dwarf structures using a combination of both methods with subsequent Monte Carlo (MC) simulations with random data. The vast majority of these dwarf structures lie within the estimated virial radii of the massive host. The major axes of these systems are aligned better than 30{\deg} with the estimated orientation of the large-scale structure in nine (50%) cases. Additional distance measurements and future kinematic studies will be required to confirm the planar nature of these structures and to determine if they are corotating systems.
... Nevertheless, the results remained almost unchanged, with the only major difference being that Tucana became consistent with the model. An important clue is that nearly all the high-velocity galaxies (HVGs) are part of the NGC 3109 association, which was previously identified as having properties that are difficult to understand in ΛCDM (Pawlowski & McGaugh 2014a). The heliocentric RV of NGC 3109 is 403 km/s, which translates to 170 km/s in the Galactocentric frame, slightly below the expected value for a pure Hubble flow (without gravity) centred on the LG barycentre. ...
... This was discussed in great detail by , who suggested that the HVGs must have been correlated in some way based purely on how they define a thin plane. A correlation becomes almost inevitable when we consider that most if not all of the HVGs are actually located quite close to a line (Pawlowski & McGaugh 2014a). ...
... Our results in Figure 9 show that a backsplasher of this mass is highly implausible in a model where galaxies have dark matter haloes that would inevitably create significant dynamical friction during interactions (Privon et al. 2013;Kroupa 2015). Since there are no analogues to NGC 3109 for an assumed mass of just 10 10.5 M , it is clear that the galaxy and the rest of its association pose severe problems for ΛCDM if their high RVs indicate that they are backsplash from the MW or M31, as argued here and in previous works (Teyssier et al. 2012;Pawlowski & McGaugh 2014a;. ...
The dwarf galaxy NGC 3109 is receding 105 km/s faster than expected in a $\Lambda$CDM timing argument analysis of the Local Group and external galaxy groups within 8 Mpc (Banik \& Zhao 2018). If this few-body model accurately represents long-range interactions in $\Lambda$CDM, this high velocity suggests that NGC 3109 is a backsplash galaxy that was once within the virial radius of the Milky Way and was slingshot out of it. Here, we use the Illustris TNG300 cosmological hydrodynamical simulation and its merger tree to identify backsplash galaxies. We find that backsplashers as massive ($\geq 4.0 \times 10^{10} M_\odot$) and distant ($\geq 1.2$ Mpc) as NGC 3109 are extremely rare, with none having also gained energy during the interaction with their previous host. This is likely due to dynamical friction. Since we identified 13225 host galaxies similar to the Milky Way or M31, we conclude that postulating NGC 3109 is a backsplash galaxy causes $>3.96\sigma$ tension with the expected distribution of backsplashers in $\Lambda$CDM. We show that the dark matter only version of TNG300 yields much the same result, demonstrating its robustness to how the baryonic physics is modelled. If instead NGC 3109 is not a backsplasher, consistency with $\Lambda$CDM would require the 3D timing argument analysis to be off by 105 km/s for this rather isolated dwarf, which we argue is unlikely. We discuss a possible alternative scenario for NGC 3109 and the Local Group satellite planes in the context of MOND, where the Milky Way and M31 had a past close flyby $7-10$ Gyr ago.
