Thus, the SMoC is proven wrong if the following second falsification theorem is true:. This would be the case because if the MW were to have no dark matter dominated satellite galaxies then the model is falsified. In the real world there are only two logically possible outcomes of testing these theorems: Either they are both falsified such that the SMoC is consistent with reality , or they are both true such that the SMoC is falsified as a representation of reality. It is not permitted to have one Falsification Theorem being true and the other one false.
Internal logical in consistency in the present argument would emerge if such data would indicate excellent agreement with the SMoC predictions. The larger part of this contribution is devoted to studying how the observed universe, where excellent data do exist, matches to the SMoC. The argument presented here must be logically sound. Why is this? It would be a circular argument: By adopting Hypothesis 0i GR is valid we are forced to introduce auxiliary Hypothesis 2 DM exists due to the mass-discrepancy observed in galaxies. When a mass-discrepancy is observed as it is in the BTF data of normal galaxies and in dSph satellite galaxies of the MW then taking this to be evidence for DM constitutes a circular argument.
Here the foundations of gravitational theory in the ultra weak field limit are being tested. It has been shown that the SMoC predicts there to be two fundamentally different types of dwarf galaxy. Which types are there in reality? Satellite galaxies are, to a large extend, of the gas-poor type, which is naturally understood as a result of gas being stripped from initial gaseous dIrr-type satellite galaxies Mayer et al.
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To differentiate DM-dominated type A dwarf galaxies from type B dwarfs that contain little or no DM can be achieved by comparing their internal kinematical state. Type B dwarfs of similar baryonic mass, M baryons , as type A dwarfs must have significantly slower motions of their stellar and gas components. A measure of the DM content is the asymptotically flat circular velocity, V c. Figure 2 shows M baryons versus V c data McGaugh for primordial i. There is thus no evidence for the existence of multiple types of rotationally supported dwarf galaxies. The next question to be addressed is if there are two types of pressure supported dwarf galaxies, namely those derived from DM sub-haloes and those derived from TDGs Section 3.
Figure 1 shows an overview of the distribution of pressure-supported stellar systems in the radius—stellar mass plot. Taking R 0. That this relation extends into the ultra-compact dwarf UCD mass regime, which constitutes an extrapolation by at least three orders of magnitude in mass, is noteworthy. It may mean that the genesis of E galaxies and of UCDs may have followed the same physical principles, i.
Note that the rare UCDs are deemed to be related to star clusters Mieske et al. This being a false identification will become apparent in Section 9. This is particularly emphasised by Forbes et al. Thus, two fundamentally different types of satellite galaxies, as ought to exist if the Dual Dwarf Galaxy Theorem were true Section 4 , do not appear to be present. This constitutes a falsification of the Dual Dwarf Galaxy Theorem.
But perhaps the observational data only contain dwarfs of the one type A? The question to be answered now is which type of dwarf galaxies do we have? From past work see Section 3.
Since they are observed to form and because galaxies are known to interact in the real universe they must be around. On the other hand, the existence of type A dwarfs depends solely on the truth of Hypothesis 2 which has until now not been verified. Type A dwarfs are therefore speculative objects, while type B dwarfs are known to form and to survive. If normal dwarf galaxies are DM dominated then the young TDGs of the same baryonic mass and dimension should have smaller rotational velocities.
That is, in the BTF diagramme Figure 2 the latter should lie significantly to the left of the former. That is, only one dynamical type of rotating dwarf galaxy appears to exist. Because the physics of the formation of type A DM-dominated galaxies differs significantly from the formation of type B dwarfs, they should show different radii at a given baryonic mass. This is tested in Figure 4. That is, only one dynamical type of pressure-supported dwarf galaxy appears to exist. This deduction is logically consistent with the observed dynamical evidence that dE galaxies do not contain much if any DM.
If this is true, then other observational data concerning the properties and distribution of dwarf galaxies must be consistent with this deduction. In the following Sections Before continuing with these tests, it is useful to first establish the observational facts on the phase-space distribution of satellite galaxies around the MW, because the MW is our primary auxilliary test case: if the SMoC is falsified Sections 8 and 9 then the excellent MW data should be conform to this.
An important test of the nature and origin of the MW satellite galaxies is provided by their distribution in phase-space. Detailed predictions have been made on this in the framework of the SMoC Section 3. If they were to be dwarfs of type A then they would have independent formation and evolution histories since each would have formed within its own DM halo independently of the other DM haloes. If, on the other hand, the satellites are of type B and stem from one encounter that involved the young MW then they would be highly correlated in phase-space Section 3.
Here the following question is addresed: How are the satellite galaxies and the globular clusters and streams in the outer halo of the MW distributed in phase space? The highly anisotropic distribution of the known dSph satellites, of the two Magellanic Cloud satellite galaxies and of some globular clusters, as well as the association with the Magellanic Stream about the MW in a vast band on the Galactic sky, had been noted more than thirty years ago Lynden-Bell ; Kunkel A number of subsequent research papers continuously enhanced the discrepancy, and Metz et al.
Is the DoS a physical structure of the MW? If it is an unlikely chance occurrence among the 9 classical dSph satellites, or if the 13 UFD satellite galaxies are not physically related to the classical dwarfs, then the UFDs cannot be distributed in the same DoS. Furthermore, if the DoS is not physical, then the orbital angular momenta of the satellite galaxies would not align with the normal vector of the DoS. And, if the DoS is not physical then no other objects or structures e.
Instead, a vast polar structure VPOS surrounding the MW emerges which contains a highly significant overabundance of all mentioned components Pawlowski et al. The individual components of this VPOS are discussed next, and Figures 5—9 below visualise how these fit together and how a single model can account for this structure. The ultra-faint dwarfs — UFDs — have different discovery histories than the classical satellites.
The latter were discovered mostly on photographic plates prior to about the year and their census is complete over most of the sky apart in the regions obscured by the MW disk. The sky coverage is not complete, but the coverage extends over most part of the northern hemisphere therewith being a cone rather than a slab with small regions having also been surveyed in the southern Galactic hemisphere see figure 1 in Metz et al.
If there had been any observational bias that might have led to the discovery of those classical dSph satellites that, by an as yet unknown reason, lie in a DoS, then the UFDs clearly cannot be subject to the same bias. Fitting a plane to the classical satellites yields the well-known DoS. Thus, the parent phase-space distributions of the classical dwarfs and of the UFDs can be taken to be equal. Therefore they have a common origin , because if this were not to be the case an unnatural coincidence would need to be postulated without a known physical mechanism.
The same disk-fitting algorithm used to quantify the DoS of the classical dSph satellites and of the UFDs can be applied to obtain the best-fitting planar description of the three GC populations Pawlowski et al. This is the exactly expected orientation for a component which is associated with the MW disk and bulge. For the OHGCs, on the other hand, no good plane solution is found. Again, this is exactly as expected because the OHGCs form a spheroidal distribution. This is remarkable and cannot be due to observational bias.
Furthermore, the known stellar and gaseous streams within and around the MW can be analysed in terms of their orientations. Using a method introduced in Pawlowski et al. It turns out that half of the stream normals cluster around the above two DoS and the two DoYHGCs, an alignment which has a likelihood of 0. The actual chance of finding the degree of orientation evident in the MW streams is smaller, because it would be expected that the streams predominantly map the continuous addition of material into the MW disk.
That is, the stream normals ought to be preferentially oriented towards the poles of the MW. The chance that the normals of the disks fitted to the classical dSph satellites, the UFD satellites, the inner and outer YHGCs as well as to the stellar and gaseous streams all cluster around the same region on the Galactic sky is smaller than 2. It is significantly smaller still because this number only considers the YHGCs and streams.
A consistency check on the physical reality of the VPOS is provided by the motions of its constituents. These need to be confined within the VPOS for it to be a physical structure. At present only the motions of the nearest satellite galaxies are known. The Sculptor dSph has an orbital angular momentum direction which places it within the DoS but on a retrograde orbit relative to the average direction of the other orbits.
It follows that of the eight satellite galaxies with proper motion measurements, seven appear to orbit within the DoS with one being within the DoS but on a retrograde orbit compared to the six others. One satellite, namely Sagittarius, orbits approximately perpendicularly both to the DoS and to the MW disk. Sagittarius may have been deflected onto its present highly bound orbit. Such a scenario has been studied for the first time by Zhao and will need to be re-investigated in view of the most recent data on the Sagittarius stream e. Carlin et al. Figures 5 and 6 show the VPOS face-on and edge-on, respectively.
It is useful to study how the various components are arranged in the VPOS. As is suggested by Figure 7 , the UFD satellites which are fainter and thus have a smaller baryonic mass have a somewhat larger dispersion in D DoS values than the classical dSph satellites, which have larger baryonic masses. Is this mass segregation towards the mid-plane of the VPOS? The existence of this VPOS, or disk-like polar arrangement of baryonic matter on a vast scale about the MW, stands beyond any reasonable amount of doubt.
It is incompatible with being derived from accreted dark-matter sub-structures, taking the likelihoods from Section From Section The observed phase-space distribution of the MW satellites can be compared to the allowed phase-space region assuming they are of type A. To obtain significant anisotropies in the luminous sub-halo distribution the following problem needs to be overcome: a physical process needs to be found which allows star formation only in sub-haloes that are highly correlated in phase-space, while all the others remain dark. However, no such physical mechanism is available within the SMoC despite many attempts Metz et al.
These calculations provide the following data which have been published by the seminal work of Libeskind et al. The remaining types of galaxies which are in similar DM host haloes are not specified by the authors. This appears to be in disagreement with the real population of galaxies, since Disney et al. The observed uniformity is a significant failure of the cosmological model, because of the large variation expected within the SMoC: Each DM host halo has a different merger history this is the invariant baryonic galaxy problem , Kroupa et al.
Of the original sample of host haloes, about 0. According to these numbers, and if the SMoC were valid, then the MW and its phase-space correlated bright satellites would be a highly significant exception of likelihood 0. This likelihood is lower still because neither the thinness of the model DoS nor the orientation of the DoS, being polar relative to the disk of the host galaxy, are taken into account. Andromeda is a galaxy similar to the MW but somewhat more complex, Hammer et al.
The SMoC can thus be discarded with better than But are we not merely making ever more precise demands to the point that yes, the MW is a unique case just as each and every galaxy is e. Hammer et al. The above argument rests on generic properties of the Local Group in how likely it is for a group of two major galaxies to contain, in the SMoC, two similar MW-type galaxies which have similar satellite systems whereby at least one of them has an anisotropic satellite distribution.
Nevertheless, this one test alone would not suffice to discard the SMoC, because it can always be argued that the Local Group happens to be an exception given the unique properties we are interested in. Ignoring the falsification of the SMoC through the Dual Dwarf Galaxy Theorem Sections 8 and 9 , a relevant question that may be answered by considering the catalogues of numerical SMoC simulations is how often groups of galaxies occur in the model which have properties similar to those of the Local Group by consisting of two major and similar disk galaxies.
Such Local-Group-type systems are common in the real universe with the majority of galaxies being disk galaxies in such groups Karachentsev ; Marino et al. The invariant baryonic galaxy problem discussed above would indicate that in the SMoC such groups would be rare. Indeed, Forero-Romero et al. In the present context, the following statement by Libeskind et al. All haloes possess a population of sub-haloes that rotates in the same direction as the main halo and three of them possess, in addition, a population that rotates in the opposite direction.
These configurations arise from the filamentary accretion of sub-haloes. Quasi-planar distributions of coherently rotating satellites, such as those inferred in the Milky Way and other galaxies, arise naturally in simulations of a CDM universe. Indeed, Pawlowski et al. Considering this sub-set the authors conclude that the disk-like distribution of MW satellites arises naturally in the SMoC. They do not state however, why the vast number of sub-haloes on other orbits should not play a role in establishing the satellite population.
That is, which physics would be active to select no other than those sub-haloes to make stars which happen to be in the disk-like sub-sample is not specified. Given that the host halo spin tends to roughly align with the spin of the host disk galaxy, the Lovell et al.
Can the sub-grid parametrisation of baryonic physics be responsible for the disagreement between model and observation? This cannot be the case because the phase-space occupied by dark matter sub-haloes and the star-formation processes within them are uncorrelated. Indeed, the large volume of published galaxy formation models up until not counting the contribution by Lovell et al. The vast number of galaxy-formation simulations are thus quite consistent with each other, which is an important consistency check on the physics used in the simulations: the reported research see Footnote 14 shows an internal consistency within the framework of the SMoC.
This conclusion is based on one auxiliary test, as discussed here. If one type of test falsifies Hypothesis A, and if it is a robust test, then other independent tests ought to yield the same conclusion. In the following five additional and independent tests of Hypotheses A are performed for MW satellites. Assume that Hypothesis A Section 4 is true. Then by energy conservation the dSph satellite galaxies must show a correlation between their luminosity, L , and hypothesised dark-matter halo mass, M DM , which is deduced from observations of the density and velocity dispersion profiles of the dSph satellites by solving the Newtonian Jeans equation e.
Klimentowski et al. Note that the statistical correlation between L and M DM does not rely on the details of baryonic physical processes, since the binding energy of the structure dictates what can form within it by whatever process, as long as the processes are generically the same in all satellites i. That such a correlation exists among galaxies interpreting their matter content within the SMoC is very well established e.
Leauthaud et al. However, it has already been shown that the dSph satellite galaxies of the MW violate the expected correlation Mateo et al. Kroupa et al. In other words, as Wolf et al. The faintest MW dSph seem to have formed in dark matter haloes that are at least as massive as those of the brightest MW dSph, despite the almost five orders of magnitude spread in luminosity between them.
Tollerud et al. In summary: The hypothesis that the SMoC models of dSph satellite galaxies represent the real dSph satellite galaxies can thus be discarded with a confidence of It is popularly there exists a vast number of research papers on this problem claimed to be solved within the SMoC Kroupa et al. Font et al. If the SMoC were true then even within the solar neighbourhood there ought to be hundreds of concentrated dark matter clumps Diemand et al.
According to these state-of-the-art SMoC computations there ought to be about additional faint satellite galaxies within the MW DM halo which must be discovered e. According to Boylan-Kolchin et al. Secondly, assuming the SMoC to be true and each dSph satellite galaxy to be embedded in a DM halo, the form of the mass function MF of these observed luminous DM haloes is not in agreement with the theoretically expected MF of luminous sub-haloes. In particular, the observed sample of satellites has a significant overabundance of M 0.
Thirdly, as documented in figure 2 in Kroupa et al. Boylan-Kolchin et al. To solve this problem, Boylan-Kolchin et al. However, this is not conform to known physical laws. Fourthly, in modelling galaxy formation within the SMoC it has to be assumed that the galaxy formation efficiency decreases sharply with decreasing DM halo mass because the DM halo mass function rises steeply with decreasing mass. They emphasise that this is not easily accommodated within the SMoC. In summary, the number and DM halo mass distribution of MW satellite galaxies is in highly significant disagreement with the expectations from the SMoC and there is no physically known process that may be able to solve the disagreements.
Any internal sub-structure is thus phase-mixed away on a time scale of a few Myr, which is why GCs appear as perfectly smooth, symmetric and spheroidal stellar systems despite being immersed in the tidal field of the MW. In this context, Hayashi et al. Our modeling suggests that the true tidal radii of dSph lie well beyond the putative tidal cutoff observed in the surface brightness profile, suggesting that the latter are not really tidal in origin but rather features in the light profile of limited dynamical relevance.
From the sample of 24 dSph satellite galaxies, too many show non-spherical and in many cases also asymmetric morphologies. Among the faintest satellites, Hercules is highly elliptical and somewhat amorphous Coleman et al. Sand et al. That even the classical bright dSph satellites of the MW have substantial ellipticities is evident from table 1 in Lokas In summary, while a homogeneous statistical study of the morphological appearance of each dSph satellite is wanted, the above examples and reasults already demonstrate that the notion that the satellites are immersed in DM haloes appears to be unphysical because there are too many satellites with distorted morphologies.
This is in full consistency with the conclusions of Sections The conventional Newtonian interpretation of the MW dSph satellite galaxies is that they are hosted within DM-sub-haloes. This appears to be the case for the Andromeda satellites as well Tollerud et al. To account for the existence of the DoS, and if the satellites were of type A i. They would thus have fallen in from large distances, and dynamical friction would have decayed and circularised their initial orbits to the present-day orbits about the MW.
This is in contradiction to the Jeans modelling. In summary, there is therefore no consistent combined solution of the existence of the DoS, the orbital angular momenta and masses of the dSph satellites within the framework of the SMoC. All independent tests concerning dSph satellite galaxies Sections While Hypothesis A can by now be taken to have been disproven, it is nevertheless of use to point out the following mutually excluding results based on excellent high resolution simulations of the formation of MW-type galaxies and their satellites within the SMoC framework:.
In a detailed discussion of the problem at hand, Deason et al. The observed MW satellite system is arranged in a large polar disk-like structure and the satellites are void of gas. Both, recent and long-past accretion into the MW halo of the same satellites is not physically possible. Apart from this inconsistency arrived at in the SMoC, infall of a group of dwarf galaxies as the origin of the phase-space correlation is ruled out by the following reasons Metz et al.
But all known groups of dwarf galaxies have diameters of a few hundred kpc. It would thus be necessary to postulate that the MW accreted a group of a type which does not exist any longer.
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Secondly, there would then be no endemic luminous DM sub-haloes of the MW. The missing satellite problem would then become a catastrophic failure, since all simulations of major galaxy formation require them to have hundreds of luminous satellites that have individual in-fall histories. While there is a strong notion and peer-pressure 12 that Hypothesis 0i must be valid on galactic and cosmological scales, it is quite remarkable that all tests Sections 8, 9, 10 and It could well have been different: We could have had the situation that one of the tests fails, but that others show consistency of the models with the data.
In this case the challenge would have to have been to understand the remaining failure given the otherwise agreement. However, the consistent failure, always in the same sense that the observational data are in conflict with Hypothesis A, i. This cannot be the case if DM defines the rotation velocities of the dIrr galaxies.
This cannot be the case if dE and dSph galaxies formed in a mass-dominating DM halo. The dSph satellites of the MW and to a certain degree also of Andromeda have a highly significant phase-space correlation which, for the MW, is a vast polar structure. The dSph satellites of the MW and Andromeda have constant DM sub-halo masses over many orders of magnitude of luminosity in violation of the necessary correlation between the two quantities if the satellites were in their own DM sub-haloes.
The DM-mass function of the observed MW satellite galaxies does not agree with the theoretical one of luminous sub-haloes derived from the SMoC. Too many dSph satellites show morphological distortions which ought not to be the case if they were embedded in their own mass-dominating DM sub-haloes. Finally, the emergence in the SMoC of a group of galaxies with the generic properties of the Local Group two similar spirals, each with at least 11 luminous satellites is negligibly small. Therefore, Hypothesis A needs to be discarded. That is, dwarf galaxies cannot be of type A and therefore they cannot be embedded in DM sub-haloes.
By Section 4, the allowed alternative is then for dwarf satellite galaxies to be TDGs, as is indeed already suggested by points 1. In the above Section The existence of this structure is perfectly consistent with the falsification of the Dual Dwarf Galaxy Theorem in Sections 8— How does the theoretical and observational evidence on dE galaxies in general, and dSph satellites in particular stand up to this interpretation? Are there other extragalactic satellite galaxy systems which also show phase-space correlations? It is well known that star clusters and TDGs form in one and the same galaxy—galaxy encounter.
Such objects may evolve through the merging of the clusters to spheroidal dwarf galaxies Kroupa such that the progenitors of the faint MW satellites may have looked similar to these Tadpole objects. The highest-ever-resolution particle-mesh computation by Bournaud et al. These have resolution-given radii of tens of pc and form due to the pressured colliding inter stellar media of the two galaxies.
The phase-space density of matter in the tidal arm is comparable to that of the pre-collision galactic disk from where it stems because the flow in phase-space is incompressible for two-body relaxation-free, i. Therefore, regions which become self-gravitating within the tidal arm due to density variations along it should have, approximately, the matter density of galactic disks. The average density of young TDGs must therefore be comparable to roughly 0.
This is similar to the typical density of baryonic matter within a disk galaxy. For a radial exponential disk scale-length of 3. Sale et al. A lower density cutoff for TDGs is given by the necessity for self-gravitation to be sufficiently strong to overcome tidal shear. That is,. Such objects are not likely to form since regions of the extend implied are not likely to be filled with matter, the tidal tails usually being more confined. But if they would form, then they would not readily be found by observation because they have low projected densities. Such an object would not likely survive its first perigalactic passage, but sub-regions of sufficient self-binding energy may.
The VPOS is composed of satellite galaxies, globular clusters and stellar and gaseous streams Section The pioneering work of Bournaud et al. Streams then arise from these DM-free TDGs and star clusters as they dissolve over time through energy-equipartition driven evaporation of stars in the collisional systems i.
Making counter-orbiting tidal debris
The gaseous streams in the VPOS may be either ancient remnants from the original tidal material from the encounter or gas that has been ram-pressure stripped or otherwise from the satellite galaxies. Theoretical results on this suggestion do not exist yet. Can a structure such as the VPOS be obtained naturally in galaxy—galaxy encounters? A large number of galaxy—galaxy encounters have been calculated by Pawlowski et al. An encounter with a smaller young galaxy is also possible. A bulge forms in such a major encounter and a disk can regrow e. In some of the galaxy—galaxy encounters by Pawlowski et al.
Documented for the first time by Pawlowski et al. These models show how the ratio of pro- and counter-rotating tidal debris about the MW significantly constrains the allowed encounter. The phase-space constraints provided by the VPOS allow a re-construction of the events that played a role in forming the young MW. The encounter had to have been near-polar relative to the young MW and the incoming galaxy must have been close to edge-on.
Figure 8 shows a sequence of images of such interacting pairs in the present universe. In Figure 8 is also shown a time-sequence of a model fly-by encounter involving the young MW and a young galaxy of similar mass as the young MW. The distribution of orbital poles of tidal debris on the Galactic sky that this model produces is shown in Figure 9. Striking is that the directions of orbital angular momenta of the tidal debris in the model populate the same diagonal region from the upper left to below centre in Figure 9 on the Galactic sky as the actual real VPOS does.
The existence of counter-rotating tidal debris is also evident, coinciding well with the orbital-angular-momentum direction of Sculptor. The model shown has not been created to match the data particularly well, and other models computed by Pawlowski et al. Would it leave visible morphological evidence? This is an important question, and it turns out that the MW bulge may hold clues.
Within the Local Group there exists a near-to-perfectly linear correlation between bulge mass and the number of satellite galaxies Figure 10 : M33 has no bulge and no known satellite galaxies, while Andromeda has a more massive bulge and more satellites than the MW and is in general more complex with a probably more recent merger event than the MW Hammer et al.
Evidently, the validity of such a correlation needs to be tested with galaxies beyond the Local Group. Karachentsev et al. In effect, Figure 10 shows a correlation between the colour or bulge-to-disk ratio of the host galaxy and the number of its satellites. A correlation as evident in Figure 10 ought to arise naturally if the majority of satellite galaxies are ancient TDGs, because bulges form in major galaxy—galaxy encounters Hammer et al. When the encounter or merger is over, the bulges may regrow disks from accreting gas Hammer et al.
The combination of chemical and age constraints available on the growth of the MW bulge e. It is known that present-day disk galaxies are sustaining their SFRs through on-going gas accretion. That disk galaxies regrow their disks after significant encounters which may produce thickened older disk components has been demonstrated in models e. The existence of the VPOS with counter-rotating constituents, and the MW having a bulge and a thickened disk are thus understandable as structures created in an early encounter between the young MW and another galaxy.
It will be interesting to investigate if this entire MW structure of VPOS, bulge and thick disk can be created using one self-consistent simulation. Indeed, currently there are two galaxies that may have been involved: the LMC is on about the right orbit already Pawlowski et al.
And alternatively, Andromeda is also close to the DoS in projection figure 1 in Metz et al. Galaxy interactions, bulge formation and the associated emergence of TDGs would have been most common in the early universe when the young galaxies were spaced closer to each other and when they were presumably more gas rich than today. This is consistent with the bulges and satellite galaxies being typically old. It is thus proven that VPOSs emerge naturally from galaxy—galaxy encounters, and that they allow a reconstruction of the encounter.
It needs to be studied how unique such a reconstruction is. That is, which range of initial conditions galaxy mass ratios, relative inclinations and orbital angular momenta are allowed given the properties and constituents of the real VPOS. According to the evidence uncovered in the course of this work Pawlowski et al.
The correlation between bulges and the number of satellites evident in the Local Group is consistent with bulges being produced during galaxy encounters.
The fly-by event would have pulled a tidal arm out of the passing galaxy which fell onto the young MW thereby forming the polar ring. At the same time, star-formation throughout the tidal arm would have produced the young halo globular clusters YHGCs , and the TDG precursors of the present-day ancient dSph and UDF galaxies out to distances of s of kpc. The tidal perturbation would have lead to bar formation in the young MW which would have formed a bulge-component as well as a thickened disk. Other observational evidence for the MW possibly being a polar ring galaxy was presented by Haud If the MW were unique, confidence in this scenario would be eroded.
Notwithstanding these examples, the Tadpole galaxy is an ongoing merger with a tidal tail with many star clusters within it. The most prominent one of mass 1. Finally, the Dentist Chair is an example of an interacting galaxy with tidal tails which contain many TDG candidates in a highly phase-space correlated overall structure Weilbacher et al. The above examples are extragalactic systems in the local universe which are surrounded by prominent young to intermediate-age correlated phase-space structures which include gaseous streams, star clusters and TDGs.
Such vast structures evolve over many orbital times but remain evident for longer than a Hubble time in phase space due to the conservation of orbital angular momentum and energy. Thus, phase-space correlated assemblages of stellar and gaseous streams, young TDGs as well as old dSph satellite galaxies exist in the Local Universe. These are probably not rare, given that such systems are hard to find because of their low surface densities and the faintness of the satellite galaxies.
An important task will be to survey as many nearby galaxies as possible for the faintest streams and possibly associated faint satellite galaxies to quantify the frequency of occurrence of such correlated systems. In Section 9 the coincidence of dE galaxies with observed and model TDGs in the radius—baryonic-mass diagramme has already emerged, suggesting that the majority if not all dwarf satellite galaxies may be TDGs, whereby RPDGs may also play a role in the dwarf population of galaxy clusters.
This is consistent with some of the observed extragalactic dSph satellites being in phase-space correlated structures Section They have also demonstrated that the morphology—density relation is reproduced: poor groups of galaxies end up having fewer dwarf galaxy members than rich groups and clusters of galaxies. Also, the stellar mass-to-light ratios of dE galaxies are fully consistent with them not having DM e.
Lisker and references therein , which is expected for this class of object since TDGs cannot capture significant amounts of DM even if it were to exist Section 3. Concerning the putative DM content of dE galaxies, the clash with the SMoC is so significant that some authors speculate baryonic processes to be responsible for pushing out the DM to radii where it is dynamically unimportant Forbes et al. However, none of the realistic galaxy evolution or formation simulations has ever resulted in the DM being pushed out to the degree required.
The majority of TDGs would have been produced in the young universe and are thus metal poor. The presently born TDGs are a minority since galaxy—galaxy encounters are today rarer and the galaxies are not as gas rich as in the cosmological past. Therefore the metallicity criterion for distinguishing TDGs from normal dwarf galaxies cannot be applied as a robust test for TDG status. TDGs, once they decouple, begin their own chemo-dynamical evolution and thus follow the mass—metallicity relation Recchi et al.
That even low-mass TDGs survive for a Hubble time despite being on eccentric orbits about their host galaxy has been shown by Kroupa and Casas et al. From the above it would thus appear that the existing data and theoretical work are consistent with dE galaxies being old TDGs. Given that is seems unlikely for the vast majority of contemporary astronomers to be interpreting the data so wrongly, it may therefore be that we are here missing some essential aspect of the SMoC.
Perhaps the SMoC is valid after all, and there are unknown baryonic processes which would account for, among the other issues, i TDGs lying on the DM-defined BTF relation, ii TDGs coinciding with dE galaxies in the radius—baryonic-mass diagramme, iii dE galaxies not having evidence for DM, iv the existence of the VPOS around the MW, v correlated phase-space structures composed of satellite galaxies about other host galaxies, and vi the existence of a host-galaxy-bulge-mass—number-of-satellite correlation.
Here is a dialogue which is based on true conversations that occurred in November in Bonn and January in Vienna:. Also, what about the more isolated dwarf-galaxy groups Tully et al. We can in actuality constrain the relevant sub-grids physics in order to match the observations. The solution is to move away from DM on galaxy scales and to accept that gravity in non-Newtonian. Then we can understand the satellites as being TDGs. And they appear to be dominated by DM if we interpret the motions of their stars in Newtonian dynamics, but in actuality what we are seeing is non-Newtonian dynamics.
The high dynamical mass-luminosity ratios suggest that TDGs, once formed, connect to thin dark-matter filaments from which they accrete kinematically cold DM. At this age, there is not enough time for them to connect to the postulated thin DM filaments which must originate from outside the virial radius of the host DM halo if it were to exist.
So actually two different dominant types of DM exotic and gas would be involved in these two age groups. Nothing is wrong with that.
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This clearly cannot be the case if they are a fundamentally different type of galaxies than the normal DM-dominated ones. See e. Are you then implying that the large body of research output from the SMoC community over the past 5 to 10 years claiming to solve the missing satellite problem is essentially unbelievable? It seems that this statement would suggest that these many published results 14 cannot be resorted to in order to test the SMoC? If this were the case, then the whole model becomes untestable.
One cannot test the whole SMoC just on one single galaxy. We are within the MW and the data are poor. The surveys suffer from serious obscuration and there are whole regions of the sky where we cannot even look at properly, like in the disk of the MW. You need to use other galaxies. The surveys are sufficiently complete to allow robust tests. For example, the SDSS is a cone such that the disk-like distribution of ultra-faint satellites cannot be due to selective surveying. The surveys for the brighter satellites and the young halo globular clusters have a quite complete sky coverage.
The tests do not rely on a single property of the MW but on generic features that together signal a failure. Instead, the SMoC is mostly valid but needs to be slightly modified. We could postulate that this dark force becomes active when the thermal temperature of the baryons has decayed sufficiently, so that structure formation in the early universe is not affected. The dark force may have a number of components that couple differently to the different constituents, and all of these may be time variable e.
So I see absolutely no reason to discard the SMoC in favour of a purely speculative and ad-hock modification of Newtonian dynamics in the ultra-weak field limit, such as what Milgromian dynamics, i. MOND, is. Thus, if, by virtue of their phase-space correlation they are TDGs, then the only logically allowed solution is to discard the SMoC entirely and to consider modified gravity models. Finally, the extensive effort world-wide to detect DM particles in terrestrial experiments has so far not been successful e.
The Dark Matter Crisis: Falsification of the Current Standard Model of Cosmology
Baudis The search for a DM-particle-annihilation or DM-particle-decay signature from regions where high DM densities are measured assuming Newtonian dynamics to be valid has also been unsuccessful e. Increasing loss of confidence is suffered by the experiments having to postulate ever decreasing interaction cross sections for the putative DM particles, significantly below and away from the originally favoured ones.
There exists no falsifiable prediction concerning the DM particles. That the SMoC needs to be discarded as a model of the real universe is true even if cold DM filaments or dark forces Section 14 were to exist because structure formation simulations would have to be repeated with these ingredients. That is, the currently available cosmological models would need to be revised substantially.
But the revisions would be many, since many new degrees of freedom appear with the notion of a multi-component dark force Section Predictability of this model would not be given any longer, since any new discordant observation would be accounted for, at least in principle, by new parameters in the dark sector. A simpler and more elegant option may be obtained by considering non-Newtonian alternatives and therewith the foundations of the SMoC. Since Albert Einstein constrained his ansatz on gravitation by solar system i. Newtonian dynamics, it is useful to reconsider this assumption.
But the speculation that exotic DM particles exist that are to be dynamically relevant in galaxies cannot be understood within the SMoPP, have not been discovered by direct experiment despite a highly significant effort world-wide over the past decades to detect them, and lead to the contradictions with astronomical observations that constitute the falsification of the SMoC above. The discrepancy between Newtonian dynamics and the dynamics observed in galaxies is concisely documented as the mass-discrepancy introduced by McGaugh The observational data are plotted in Figure The observed mass-discrepancy data follow a well defined correlation with acceleration.
The MDA data show that the discrepancy and thus evidence for DM only appears when the observed true acceleration, a , is smaller than a critical acceleration a 0 ,.
localgas – Lifecycle of gas in galaxies: A local perspective
The critical acceleration a 0 constitutes a constant of nature. It is constrained by e. Figure 11 demonstrates the excellent agreement between the prediction 15 of Milgromian dynamics and the data. Concerning the MW, it is useful to graph the Milgromian radial acceleration as a function of r Figure What is Milgromian dynamics i.
The existence of transition functions is well know in physics, notable examples being the transitions from quantum mechanics to classical mechanics and from relativistic to classical speeds. This is a highly attractive option because the SMoPP is the most successful physical theory at hand, and because gravitation remains poorly understood as we still do not know how matter couples to space-time and which of the two is an emergent property.
And, a scalar tensor vector gravity theory leading to modified gravity, or MOG is suggested by Moffat according to which, effectively, far from a source gravity is stronger than the Newtonian prediction, while at shorter distances it is compensated by a vector-field-generated repulsive fifth force. This can also be viewed as a Yukawa-type modification of the gravitational force due to a point source. Recent searches Clear All. Update Location. If you want NextDay, we can save the other items for later.
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