Searcharxiv⌕ Search

arXiv subjects

Marcel S. Pawlowski

Publications and source records attributed to Marcel S. Pawlowski.

At least 37 records · Page 2Linked to original sources
arXiv2024

Lopsided distribution of MATLAS and ELVES dwarf satellite systems around isolated host galaxies

The properties of satellite dwarf galaxies pose important empirical constraints to verify cosmological models on galaxy scales. Their phase-space correlations, in particular, offer interesting insights into various models. Next to the planes-of-satellites phenomenon, the lopsided distribution of satellites relative to their host galaxy has been studied observationally and in cosmological simulations. It is still unclear how observed lopsidedness aligns with expectations from simulations. We measure lopsidedness in observed isolated satellite systems using six different metrics. We study 47 systems from the MATLAS survey beyond the Local Volume (LV) as well as 21 LV satellite systems from the ELVES survey. We find that the so-called wedge metric, counting the number of dwarfs in wedges with varying opening angles, is best suited to capture a system's overall lopsidedness. Under this metric, our analysis reveals that ~16 percent of the tested satellite systems exhibit a statistically significant degree of lopsidedness when compared to systems with randomly generated satellite position angles. This presents a notable excess over the expected 5% (2 sigma level) of significantly lopsided systems in a sample with no overall inherent lopsidedness. However, using multiple metrics provides a more complete picture. Combining all tested metrics, the number of significantly lopsided systems increases to ~21 percent. Contrary to recent results from the literature, we find more lopsided systems among the red early-type galaxies in the MATLAS survey compared to the mostly blue late-type hosts in ELVES. We further find that satellite galaxies at larger distances from the host, potentially recently accreted, are likely the primary contributors to the reported excess of lopsidedness. Our results enable comparisons with similar systems in simulations to assess consistency with the standard model.

astro-ph.GA↗
arXiv2024

The satellite galaxy plane of NGC 4490 in light of ΛCDM - Sparsity of similarly extreme analogs and a possible role of satellite pairs

The galaxy system around NGC4490 was recently highlighted to display a flattened, kinematically correlated structure reminiscent of satellite galaxy planes around other hosts. Since known satellite planes are in tension with $Λ$CDM expectations from cosmological simulations, we quantitatively assess for the first time the tension posed by the NGC4490 system. We measure the on-sky flattening as the major-to-minor axis ratio b/a of the satellite distribution and their line-of-sight kinematic correlation. Analogs are selected in the IllustrisTNG-50 simulation and their flattening and correlation are similarly measured. We confirm the strong kinematic coherence of all 12 observed objects with available line-of-sight velocities (of 14 in total): the northern ones approach and the southern ones recede relative to the host. The spatial distribution of all 14 objects is substantially flattened with b/a=0.38 (0.26 considering only the 12 objects with velocities). Such extreme arrangements are rare in the simulation at 0.21-0.35%. This would drop further if at least one of the two satellite objects without velocities is confirmed to follow the kinematic trend, and would become zero if both are rejected as non-members. We also identify a likely galaxy pair in the observed system, and find a similar pair in the best-matching simulated analog. Our findings establish NGC4490 as another strong example of a satellite plane in the Local Volume. This emphasizes that planes of satellites are a more general issue faced by $Λ$CDM also beyond the Local Group. The tension with typical systems in simulations suggests that the observed one requires a specific formation scenario, potentially connected to the larger-scale galaxy alignment in its vicinity. The presence of galaxy pairs in the observed and a simulated system hints at the importance such groupings may have to understand satellite planes.

astro-ph.GA↗
arXiv2024

A too-many dwarf satellite galaxies problem in the MATLAS low-to-moderate density fields

Dwarf galaxy abundances can serve as discernment tests for models of structure formation. Previous small-scale tensions between observations and dark matter-only cosmological simulations may have been resolved with the inclusion of baryonic processes; however, these successes have been largely concentrated on the Local Group dwarfs the feedback models were initially calibrated on. We investigate whether the $Λ$CDM model can reliably reproduce dwarf abundances in the MATLAS low-to-moderate density fields that are centred upon early-type host galaxies beyond the Local Volume. We carried out mock observations of MATLAS-like fields with the high-resolution hydrodynamic simulation IllustrisTNG-50. We used matching selection criteria and compared the properties of dwarfs contained within them with their MATLAS analogues. Although simulated MATLAS-like dwarfs demonstrate photometric properties that are consistent with the observed galaxy population and follow the same scaling relations, TNG50 underestimates the number of dwarf galaxies in isolated MATLAS fields at the 6 sigma level. This significance is maintained within crowded fields containing more than a single bright host. Our 55-62% estimate of the fraction of background galaxies is in agreement with estimates by MATLAS, but is wholly insufficient to alleviate this discrepancy in dwarf abundances. Any incompleteness in the observed fields further exacerbates this tension. We identified a "too-many-satellites" problem in $Λ$CDM, emphasising the need for the continued testing and refining of current models of galaxy formation in environments beyond the Local Group.

astro-ph.GA↗
arXiv2024

Satellite group infall into the Milky Way: exploring the Crater-Leo case with new HST proper motions

Context. Within $Λ$ Cold Dark Matter ($Λ$CDM) simulations, Milky Way-like galaxies accrete some of their satellite galaxies in groups of 3-5 members rather than individually. It was also suggested that this might be the reason behind the origin of satellite planes. Objects accreted in groups are expected to share similar specific total energy and angular momentum, and also identical orbital planes and directions. Aims. Looking at observations of Milky Way satellites, the dwarf galaxies Leo II, IV, V, Crater II, and the star cluster Crater 1 were proposed to be a vestige of group infall. The suggested "Crater-Leo group" shows a coherent distance gradient and all these objects align along a great circle on the sky. We use proper motion data to investigate whether the phase-space distribution of the members of the proposed group are indeed consistent with group infall. Methods. To further investigate this possibility, we use Gaia Data Release 3 (DR3) and new Hubble Space Telescope (HST) proper motions, $(μ_{α*}, μ_δ) = (-0.1921 \pm 0.0514, -0.0686 \pm 0.0523)$ mas yr$^{-1}$ for Leo IV and $(μ_{α*}, μ_δ) = (0.1186 \pm 0.1943, -0.1183 \pm 0.1704)$ mas yr$^{-1}$ for Leo V, to derive accurate orbital properties for the proposed group objects. In addition, we explore other possible members of this putative association. Results. Leo II, Leo IV, and Crater 1 show orbital properties consistent with those we predict from assuming group infall. However, our results suggest that Crater II was not accreted with the rest of the objects. If confirmed with increasingly accurate proper motions in the future, the Crater-Leo objects appear to constitute the first identified case of a cosmologically expected, typical group infall event, as opposed to the highly hierarchical Magellanic Cloud system.

astro-ph.GA↗
arXiv2024

A too-many dwarf galaxy satellites problem in the M83 group

Dwarf galaxies in groups of galaxies provide excellent test cases for models of structure formation. This led to a so-called small-scale crisis, including the famous missing satellite and too-big-to-fail problems. It was suggested that these two problems are solved by the introduction of baryonic physics in cosmological simulations. We test for the nearby grand spiral M83 - a Milky Way sibling - whether its number of dwarf galaxy companions is compatible with today's $Λ$ + Cold Dark Matter model using two methods: with cosmological simulations that include baryons, as well as with theoretical predictions from the sub-halo mass function. By employing distance measurements we recover a list of confirmed dwarf galaxies within 330 kpc around M83 down to a magnitude of $M_V =-10$. We found that both the state-of-the-art hydrodynamical cosmological simulation Illustris-TNG50 and theoretical predictions agree with the number of confirmed satellites around M83 at the bright end of the luminosity function (>10$^8$ solar masses) but underestimate it at the faint end (down to 10$^6$ solar masses) at more than 3$σ$ and 5$σ$ levels, respectively. This indicates a too-many satellites problem in $Λ$CDM for M83. The actual degree of tension to cosmological models is underestimated, because the number of observed satellites is incomplete due to the high contamination of spurious stars and galactic cirrus.

astro-ph.GA↗
arXiv2024

The phase-space distribution of the M81 satellite system

The spatial distribution of dwarf galaxies around their host galaxies is a critical test for the standard model of cosmology because it probes the dynamics of dark matter halos and is independent of the internal baryonic processes of galaxies. Co-moving planes-of-satellites have been found around the Milky Way, the Andromeda galaxy, and the nearby CenA galaxy, which seem to be at odds with the standard model of galaxy formation. Another nearby galaxy group, with a putative flattened distribution of dwarfs, is the M81 group. We present a quantitative analysis of the distribution of the M81 satellites using a Hough transform to detect linear structures. We confirm a flattened distribution of dwarf galaxies. Depending on the morphological type, we find a minor-to-major axis ratio of the satellite distribution to be 0.5 (all types) or 0.3 (dSph), which is in line with previous results for the M81 group. Comparing the orientation of this flattened structure in 3D with the surrounding large-scale matter distribution, we find a strong alignment with the local sheet and the planes-of-satellites around the Andromeda galaxy and Cen A. Employing velocities for a sub-sample of the dwarfs, we find no signal of co-rotation. Comparing the flattening and motion of the M81 dwarf galaxy system with IllustrisTNG50 we find good agreement between observations and simulations, but caution that i) velocity information of half of the satellites is missing, ii) velocities are coming mainly from dwarf irregulars clustered around NGC3077, which may hint towards an infall of a dwarf galaxy group and iii) some of the dwarfs may actually be tidal dwarf galaxies. From the missing velocities, we predict that the observed frequency within TNG may range between 2 to 29 per cent. Any conclusions about the agreement/disagreement with cosmological models needs to wait for a more complete picture of the dwarf galaxy system.

astro-ph.GA↗
arXiv2023

New dwarf galaxy candidates in the sphere of influence of the Sombrero galaxy

We report the discovery of 40 new satellite dwarf galaxy candidates in the sphere of influence of the Sombrero galaxy (M104) the most luminous galaxy in the Local Volume. Using the Subaru Hyper Suprime-Cam, we surveyed 14.4 square degrees of its surroundings, extending to the virial radius. Visual inspection of the deep images and GALFIT modelling yielded a galaxy sample highly complete down to $M_{g}\sim-9$ ($L_{g}\sim3\times 10^{5}\,L_\odot$) and spanning magnitudes $-16.4 < M_g < -8$ and half-light radii $50\,pc\ <\ r_e\ <\ 1600\,pc$ assuming the distance of M104. These 40 new, out of which 27 are group members with high confidence, double the number of potential satellites of M104 within the virial radius, placing it among the richest hosts in the Local Volume. Using a Principle Component Analysis (PCA), we find that the entire sample of candidates consistent with an almost circular on-sky distribution, more circular than any comparable environment found in the Illustris TNG100-1 simulation. However the distribution of the high probability sample is more oblate and consistent with the simulation. The cumulative satellite luminosity function is broadly consistent with analogues from the simulation, albeit it contains no bright satellite with $M_{g}<-16.4$ ($L_{g}\sim3 \times 10^{8}\,L_\odot$), a $2.3\,σ$ occurrence. Follow-up spectroscopy to confirm group membership will begin to demonstrate how these systems can act as probes of the structure and formation history of the halo of M104.

astro-ph.GA↗
arXiv2023

What new observations tell us about Planes of Satellite Galaxies

I briefly discuss the current state of the Planes of Satellite Galaxies Problem in light of some new observational data for satellite galaxies of the Milky Way, Andromeda, Centaurus A, and other systems beyond the Local Group. In particular, I present how a new proper motion measurment for Leo I enhances the overall orbital coherence among the MW's classical satellites and thus its tension with cosmological expectations.

astro-ph.GA↗
arXiv2023

The accretion history of the Milky Way. II. Internal kinematics of globular clusters and of dwarf galaxies

We study how structural properties of globular clusters and dwarf galaxies are linked to their orbits in the Milky Way halo. From the inner to the outer halo, orbital energy increases and stellar-systems gradually move out of internal equilibrium: in the inner halo, high-surface brightness globular clusters are at pseudo-equilibrium, while further away, low-surface brightness clusters and dwarfs appear more tidally disturbed. Dwarf galaxies are the latest to arrive into the halo as indicated by their large orbital energies and pericenters, and have no time for more than one orbit. Their (gas-rich) progenitors likely lost their gas during their recent arrival in the Galactic halo. If dwarfs are at equilibrium with their dark matter (DM) content, the DM density should anti-correlate with pericenter. However, the transformation of DM dominated dwarfs from gas-rich rotation-supported into gas-poor dispersion-supported systems is unlikely accomplished during a single orbit. We suggest instead that the above anti-correlation is brought by the combination of ram-pressure stripping and of Galactic tidal shocks. Recent gas removal leads to an expansion of their stellar content caused by the associated gravity loss, making them sufficiently fragile to be transformed near pericenter passage. Out of equilibrium dwarfs would explain the observed anti-correlation of kinematics-based DM density with pericenter without invoking DM density itself, questioning its previous estimates. Ram-pressure stripping and tidal shocks may contribute to the dwarf velocity dispersion excess. It predicts the presence of numerous stars in their outskirts and a few young stars in their cores.

astro-ph.GA↗
arXiv2023

The Accretion History of the Milky Way: III. Hydrodynamical Simulations of Galactic Dwarf Galaxies at First Infall

Most Milky Way dwarf galaxies are much less bound to their host than are relics of Gaia-Sausage-Enceladus and Sgr. These dwarfs are expected to have fallen into the Galactic halo less than 3 Gyr ago, and will therefore have undergone no more than one full orbit. Here, we have performed hydrodynamical simulations of this process, assuming that their progenitors are gas-rich, rotation-supported dwarfs. We follow their transformation through interactions with the hot corona and gravitational field of the Galaxy. Our dedicated simulations reproduce the structural properties of three dwarf galaxies: Sculptor, Antlia II and, with somewhat a lower accuracy, Crater II. This includes reproducing their large velocity dispersions, which are caused by ram-pressure stripping and Galactic tidal shocks. Differences between dwarfs can be interpreted as due to different orbital paths, as well as to different initial conditions for their progenitor gas and stellar contents. However, we failed to suppress in a single orbit the rotational support of our Sculptor analog if it is fully dark-matter dominated. In addition, we have found that classical dwarf galaxies like Sculptor may have stellar cores sufficiently dense to survive the pericenter passage through adiabatic contraction. On the contrary, our Antlia II and Crater II analogs are tidally stripped, explaining their large sizes, extremely low surface brightnesses, and velocity dispersion. This modeling explains differences between dwarf galaxies by reproducing them as being at different stages of out-of-equilibrium stellar systems.

astro-ph.GA↗
arXiv2023

The imprint of galaxy mergers on satellite planes in a cosmological context

Flattened and kinematically correlated planes of dwarf satellite galaxies have been observed in the Local Volume. The slinging out of satellites during host galaxy mergers has been suggested as a formation mechanism for these peculiar structures. We statistically examined the impact of major mergers on present-time satellite systems for the first time in a full cosmological context using the IllustrisTNG suite of hydrodynamic simulations. Mergers with mass ratios above 1/3 generally have a negligible or adverse impact on the phase-space correlation of observationally motivated satellites. Even high-angular momentum mergers are inefficient at slinging satellites outward due to the extended nature of simulated satellite distributions. Furthermore, any potential merger imprint is partially washed out by post-merger accretion of satellites, while satellites bound to the merging haloes since the merger's beginning are disrupted and stripped of mass - minimising the merger's influence on the present-time distribution of the most massive satellites after 2-5 Gyr. Constraining our sample to satellites bound to their host throughout the full duration of their system's last merger, we recover no particular improvement in their phase-space correlation. Instead, such participant satellites experience a contraction of their radial distribution during and after the merger, resulting in smaller absolute plane heights (but comparable axis ratios). Overall, major mergers do not appear to form correlated planes in a statistical sample. Mergers that efficiently transfer their angular momentum to satellite distributions can marginally enhance their phase-space correlation, but cannot form highly flattened and orbitally coherent configurations as observed in our local Universe.

astro-ph.GA↗
arXiv2023

Measuring galaxy cluster mass profiles into the low acceleration regime with galaxy kinematics

We probe the dynamical mass profiles of 10 galaxy clusters from the HIghest X-ray FLUx Galaxy Cluster Sample (HIFLUGCS) using galaxy kinematics. We numerically solve the spherical Jeans equation, and parameterize the dynamical mass profile and the galaxy velocity anisotropy profile using two general functions to ensure that our results are not biased towards any specific model. The mass-velocity anisotropy degeneracy is ameliorated by using two "virial shape parameters" that depend on the fourth moment of velocity distribution. The resulting velocity anisotropy estimates consistently show a nearly isotropic distribution in the inner regions, with an increasing radial anisotropy towards large radii. We compare our derived dynamical masses with those calculated from X-ray gas data assuming hydrostatic equilibrium, finding that massive and rich relaxed clusters generally present consistent mass measurements, while unrelaxed or low-richness clusters have systematically larger total mass than hydrostatic mass by an average of 50\%. This might help alleviate current tensions in the measurement of $σ_8$, but it also leads to cluster baryon fractions below the cosmic value. Finally, our approach probes accelerations as low as $10^{-11}$ m s$^{-2}$, comparable to the outskirts of individual late-type galaxies. We confirm that galaxy clusters deviate from the radial acceleration relation defined by galaxies.

astro-ph.CO↗
arXiv2023

Classifying the satellite plane membership of Centaurus A's dwarf galaxies using orbital alignment constraints

The flattened, possibly co-rotating plane of satellite galaxies around Centaurus A, if more than a fortuitous alignment, adds to the pre-existing tension between the well-studied Milky Way and M31 planes and the $Λ$CDM model of structure formation. It was recently reported that the Centaurus A satellite plane (CASP) may be rotationally supported, but a further understanding of the system's kinematics is elusive in the absence of full three-dimensional velocities. We constrain the transverse velocities of 27 satellites that would rotationally stabilise the Centaurus A plane, and classify the satellites by whether their possible orbits are consistent with the CASP. Five satellites are identified to be unlikely to participate in the plane, two of which are clearly non-members. Despite their previously reported line-of-sight velocity trend suggestive of a common co-rotating motion, 17 out of 22 potential CASP members are consistent with either orbital direction within both the full range of possible kinematics as well as when limiting orbits to those within the plane. On the other hand, disregarding the 5 off-plane satellites found to be inconsistent with CASP membership enhances the significance of the CASP's line-of-sight velocity trend fivefold. Our results are robust with different mass estimates of the Centaurus A halo, and the adoption of either spherical or triaxial NFW potentials.

astro-ph.GA↗
arXiv2023

The accretion history of the Milky Way. I. How it shapes globular clusters and dwarf galaxies

Halo inhabitants are individual stars, stellar streams, star and globular clusters, and dwarf galaxies. Here we compare the two last categories that include objects of similar stellar mass, which are often studied as self-dynamical equilibrium systems. We discover that the half-light radius of globular clusters depends on their orbital pericenter and total energy, and that Milky Way (MW) tides may explain the observed correlation. We also suggest that the accretion epoch of stellar systems in the MW halo can be calibrated by the total orbital energy, and that such a relation is due to both the mass growth of the MW and dynamical friction affecting mostly satellites with numerous orbits. This calibration starts from the bulge, to Kraken, Gaia Sausage Enceladus, Sagittarius stellar systems, and finally to the new coming dwarfs, either or not linked to the vast-polar structure. The most eccentric globular clusters and dwarfs have their half-light radius scaling as the inverse of their binding energy, and this over more than two decades. This means that earlier arriving satellites are smaller due to the tidal effects of the MW. Therefore, most halo inhabitants appear to have their structural parameters shaped by MW tides and also by ram-pressure for the most recent arrivals, the dwarf galaxies. The correlations found in this study can be used as tools to further investigate the origin of globular clusters and dwarfs, as well as the assembly history of our Galaxy.

astro-ph.GA↗
arXiv2022

Incorporating baryon-driven contraction of dark matter halos in rotation curve fits

The condensation of baryons within a dark matter (DM) halo during galaxy formation should result in some contraction of the halo as the combined system settles into equilibrium. We quantify this effect on the cuspy primordial halos predicted by DM-only simulations for the baryon distributions observed in the galaxies of the SPARC database. We find that the DM halos of high surface brightness galaxies (with $Σ_{\rm eff}\gtrsim100$ $L_\odot$ pc$^{-2}$ at 3.6 $μ$m) experience strong contraction. Halos become more cuspy as a result of compression: the inner DM density slope increases with the baryonic surface mass density. We iteratively fit rotation curves to find the balance between initial halo parameters (constrained by abundance matching), compression, and stellar mass-to-light ratio. The resulting fits often require lower stellar masses than expected for stellar populations, particularly in galaxies with bulges: stellar mass must be reduced to make room for the DM it compresses. This trade off between dark and luminous mass is reminiscent of the cusp-core problem in dwarf galaxies, but occurs in more massive systems: the present-epoch DM halos cannot follow from cuspy primordial halos unless (1) the stellar mass-to-light ratios are systematically smaller than expected from standard stellar population synthesis models, and/or (2) there is a net outward mass redistribution from the initial cusp, even in massive galaxies widely considered to be immune from such effects.

astro-ph.GA↗
arXiv2022

The intervelocity of galaxy pairs in $Λ$CDM -- The observed velocity peak at ~130 km/s is not unique to MOND

Observational studies of pairs of galaxies have uncovered that their differential line-of-sight velocities indicate the presence of a peak in their three-dimensional intervelocity distribution at 130-150 km/s. It had been argued that galaxy pairs in the standard model of cosmology, $Λ$CDM, should not exhibit such an intervelocity peak, while Modified Newtonian Dynamics (MOND) predicts such a preferred intervelocity for paired galaxies. However, no direct comparison with $Λ$CDM applying the same selection criteria and methodology as the observational studies has been performed yet, placing the comparison on unsure footing. To rectify this, we investigate this potential challenge for $Λ$CDM by determining whether an analog of the observed intervelocity peak is present in galaxy pairs within the IllustrisTNG-300 cosmological simulation. We identify galaxy pairs following the observational study's selection criteria, measure their projected velocity difference, and analyse both the de-projected as well as the full velocity difference for this galaxy pair sample in the simulation. We recover a deprojected intervelocity peak at ~130 km/s for galaxy pairs selected from the simulation. The full three-dimensional velocity information available for the pairs in the simulation also reveals a clear preference for this intervelocity. The intervelocity peak among galaxy pairs does not appear to be a feature unique to MOND, but is also present in $Λ$CDM. It can thus not be claimed as a unique success of either theory over the other. Developing the galaxy pair intervelocity into a test of gravity in the low acceleration regime will require more detailed studies to identify measurable differences in the models.

astro-ph.GA↗
arXiv2022

On the Effect of the Large Magellanic Cloud on the Orbital Poles of Milky Way Satellite Galaxies

The reflex motion and distortion of the Milky Way (MW) halo caused by the infall of a massive Large Magellanic Cloud (LMC) has been demonstrated to result in an excess of orbital poles of dark matter halo particles towards the LMC orbital pole. This was suggested to help explain the observed preference of MW satellite galaxies to co-orbit along the Vast Polar Structure (VPOS). We test this idea by correcting the positions and velocities of the MW satellites for the Galactocentric-distance-dependent shifts inferred from a LMC-infall simulation. While this should substantially reduce the observed clustering of orbital poles if it were mainly caused by the LMC, we instead find that the strong clustering remains preserved. We confirm the initial study's main result with our simulation of an MW-LMC-like interaction, and use it to identify two reasons why this scenario is unable to explain the VPOS: (1) the orbital pole density enhancement in our simulation is very mild (~10% within 50-250 kpc) compared to the observed enhancement (~220-300%), and (2) it is very sensitive to the specific angular momenta (AM) of the simulation particles, with higher AM particles being affected the least. Particles in simulated dark matter halos tend to follow more radial orbits (lower AM), so their orbital poles are more easily affected by small offsets in position and velocity caused by an LMC infall than objects with more tangential velocity (higher AM), such as the observed dwarf galaxies surrounding the MW. The origin of the VPOS thus remains unexplained.

astro-ph.GA↗
arXiv2022

3D hydrodynamic simulations for the formation of the Local Group satellite planes

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 $z>1$.

astro-ph.GA↗