The Magellanic Stream is unique to sample the MW potential from ∼50 kpc to 300 kpc, and is also unique in constraining the LMC mass, an increasingly important question for the Local Group/Milky Way modeling. Here we compare strengths and weaknesses of the two types of models (tidal and ram-pressure) of the Magellanic Stream formation. I will present our modeling for the formation of the Magellanic System, including those of the most recent discoveries in the Stream, in the Bridge and at the outskirts of Magellanic Clouds. This model has been successful in predicting most recent observations in both properties of stellar and gas phase. It appears that it is an over-constrained model and provides a good path to investigate the Stream properties. In particular, this model requires a LMC mass significantly smaller than 1011 M⊙.

In the last two decades, some arguments have accumulated for a more important mass ratio of the Large Magellanic Cloud (LMC) to the Milky Way (MW) than was previously thought, up to a value of 10% or more. This implies that the LMC has a measurable influence on the dynamics in the MW stellar halo, including both stellar densities and kinematics, as observed by Conroy et al. (2021) and Petersen and Peñarrubia (2021). While this merger has been previously reproduced using N-body simulations (see, e.g., Garavito-Camargo et al. 2019), I exploit here the results of a recent study (Rozier et al. 2022) which aimed at modelling the merger via linear response theory (LRT). More specifically, we integrated the linearized collisionless Boltzmann-Poisson system of partial differential equations using a methodology known as the matrix method. Our results display the same large scale behaviour as state-of-the-art simulations, with a dipolar over/underdense pattern related to the reflex motion of the MW, and an overdense wake trailing behind the LMC. Using LRT, I show that the response’s self-gravity can be neglected, implying a direct proportionality between the LMC to MW mass ratio and the amplitude of the relative density variations of the MW stellar halo. However, these overdensities may also depend on other model parameters, such as the structure of the MW potential (including a dark matter component), the initial stellar halo density, as well as its internal kinematics. I focus on the latter source of degeneracy, showing how the stellar halo’s velocity anisotropy impacts its response to the LMC. Interestingly enough, it appears that the density of the dipolar response is insensitive to the stellar halo’s initial velocity anisotropy, and can therefore represent an efficient probe of the LMC to MW mass ratio.

To investigate the impact of interaction in the North-Eastern Small Magellanic Cloud (SMC) shell region, we used far-UV images from eleven observed fields obtained from the Ultra Violet Imaging Telescope. Cleaned, science-ready images were created and point spread function photometry was performed to extract photometric data. The detected FUV stars were cross-matched with the Gaia EDR3 data to select SMC stars and to obtain kinematic information. The findings from the analysis of the FUV-optical CMDs suggest a history of episodic star formation with most of the stars with age > 150 Myr, along with stars as young as 7 Myr. The spatial distribution of FUV stars shows a gradient decreasing radially outwards. We plan to perform a detailed analysis of the morphology, density, and kinematics of the young stars in this region.

We present the spatially resolved star formation history (SFH) of a shell-like structure located in the northeastern Small Magellanic Cloud (SMC). We quantitatively obtain the SFH using unprecedented deep photometric data (g ∼ 24 magnitude) from the SMASH survey and colour-magnitude diagram (CMD) fitting techniques. We consider, for the first time, the SMC’s line-of-sight depth and its optical effects on the CMDs. The SFH presents higher accuracy when a line-of-sight depth of ∼ 3 kpc is simulated.

We find young star formation enhancements at ∼150 Myr, ∼200 Myr, ∼450 Myr, ∼650 Myr, and ∼1 Gyr. Comparing the structure’s SFH with the Large Magellanic Cloud’s northern arm SFH we show strong evidence of synchronicity from at least the past ∼2.8 Gyr, possibly ∼3.5 Gyr. Our results place constraints on the orbital history of the Magellanic Clouds which, potentially, have implications on their dynamical mass estimates.

In this contribution, we present the results from proper motion measurements across the Large Magellanic Cloud (LMC) using data from the VISTA survey of the Magellanic Cloud system (VMC). Using the derived proper motions, we modelled the structure of the LMC and analysed its internal kinematics. Within the central parts of the LMC, we found observational evidence for elongated orbits parallel to the bar’s major axis, which are considered to provide the main contribution for the support of a bar structure. A peculiar kinematic structure in the outer regions of the LMC hints toward stripped material from the Small Magellanic Cloud. We further introduce an observational campaign utilising the Hubble Space Telescope to precisely measure the proper motions of star clusters within the LMC. These motions, combined with radial velocities and 3D positions will be used to trace the gravitational potential of the LMC.

I discuss circumgalactic gas flows in the extended Milky Way halo in the context of the on-going formation and evolution of the Local Group. UV absorption-line measurements, in combination with H i 21 cm observations, provide detailed information on the chemical composition, dust content, physical conditions, and large-scale kinematics of the so-called high-velocity clouds, which are believed to trace neutral and ionized gas in the gaseous halos of the Milky Way, M31, and in the intragroup medium of the Local Group. Recent results in this field and ideas for future observational studies are being presented.

The study of resolved stellar populations in the nearest galaxies, or “near-field cosmology”, provides key constraints on the physics underlying galaxy formation and evolution. Deep, wide-field surveys of nearby groups of galaxies allow us to characterize the past and ongoing accretion processes shaping the halos of Milky Way-mass galaxies. This field is set to experience significant advancements with the current and future generations of state-of-the-art telescopes.

We present preliminary results from our spectroscopic survey of low-luminosity early-type galaxies in the Coma cluster conducted with the Binospec spectrograph at the 6.5 m MMT. From spatially-resolved profiles of internal kinematics and stellar population properties complemented with high-resolution images, we placed several low-luminosity dEs on the fundamental plane in the low-luminosity extension of the available literature data. We also discovered unusual kpc-sized kinematically-decoupled cores in several dwarf galaxies, which had been probably formed before these galaxies entered the cluster.

Ultra-diffuse galaxies (UDGs) are spatially extended, low surface brightness stellar systems with regular elliptical-like morphology found in large numbers in galaxy clusters and groups. Studies of the internal dynamics and dark matter content of UDGs have been hampered by their low surface brightnesses. We identified a sample of low-mass early-type post-starburst galaxies, ‘future UDGs’ in the Coma cluster still populated with young stars, which will passively evolve into UDGs in the next 5–10 Gyr. We collected deep observations for a sample of low-mass early-type galaxies in the Coma cluster using MMT Binospec, which includes present-day and future UDGs. We derived their dark matter content within a half-light radius (70–95 %) and total dynamical masses (M200 = 5.5 · 109 − 1.4·1011 M⊙) assuming the Burkert density profile and assess how different proposed evolutionary channels affect dark and visible matter in UDGs. We also discuss observational methodology of present and future UDG studies.

Triaxial dynamical models of massive galaxies observed in the ATLAS3D project can provide new insights into the complex evolutionary processes that shape galaxies. The ATLAS3D survey is ideal as the sample comprises a good mix of fast and slow rotators with vastly different mass assembly histories. We present a detailed dynamical study with our triaxial modelling code DYNAMITE, which models galaxies as a superposition of their stellar orbits. The models allow us to constrain the intrinsic shape of the stellar component, the distributions of the visible and invisible matter and the orbit distribution in these nearby early-type galaxies and to relate it with different evolutionary scenarios. Triaxial modelling is essential for these galaxies to understand their complex kinematical features.

Dwarf satellite galaxies in our Milky Way and different galaxy systems in the Local Volume appear to be arranged in thin, vast planes. It has been argued that these phase-space correlations cannot be explained to a satisfactory degree by the ΛCDM paradigm but it is unclear whether these planes in our neighborhood are statistical outliers, or if they are perhaps a common phenomenon in the Universe. Recent deep imaging surveys have significantly increased the number of known dwarf galaxies and allow us to advance such small-scale tensions beyond the Local Volume. We present our study analyzing the spatial distribution of 2210 dwarf galaxies identified in the MATLAS survey as well as results from follow-up observations with the MUSE instrument on the VLT. Spectral information for 56 of these dwarf galaxies allow for a deeper dive into their properties and for a comparison to the Local Volume dwarfs.

The number density of extragalactic 21-cm radio sources as a function of their spectral line-widths – the H i width function (H i WF) – is a tracer of the dark matter halo mass function. The ALFALFA 21-cm survey measured the H i WF in northern and southern Galactic fields finding a systematically higher number density in the north; an asymmetry which is in tension with Λ cold dark matter models which predicts the H i WF should be identical everywhere if sampled in sufficiently large volumes. We use the Sibelius-DARK N-body simulation and semi-analytical galaxy formation model GALFORM to create mock ALFALFA surveys to investigate survey systematics. We find the asymmetry has two origins: the sensitivity of the survey is different in the two fields, and the algorithm used for completeness corrections does not fully account for biases arising from spatial galaxy clustering. Once survey systematics are corrected, cosmological models can be tested against the H i WF.

It is routinely assumed that galaxy rotation curves are equal to their circular velocity curves (modulo some corrections) such that they are good dynamical mass tracers. We analysed 33 low-mass galaxies from the APOSTLE simulation suite to explore the limits of validity of this assumption. Only 3 galaxies have rotation curves similar to their circular velocity curves; the rest are undergoing a wide variety of dynamical perturbations. We assessed how many galaxies are likely to be strongly perturbed by processes in several categories: mergers/interactions, bulk gas flows, non-spherical DM halo, warps, and IGM ram pressure. Most galaxies fall into more than one of these categories; only 5/33 are not in any of them. The sum of these effects leads to an underestimation of the low-velocity slope of the baryonic Tully-Fisher relation that is difficult to avoid, and could contribute to the observed diversity in low-mass galaxy rotation curve shapes.

I review methods and techniques to build mass models of disk galaxies from gas dynamics. I focus on two key steps: (1) the derivation of rotation curves using 3D emission-line datacubes from H I, CO, and/or Hαobservations, and (2) the calculation of the gravitational field from near-infrared images and emission-line maps, tracing the stellar and gas mass distributions, respectively. Mass models of nearby galaxies led to the establishment of the radial acceleration relation (RAR): the observed centripetal acceleration from rotation curves closely correlates with that predicted from the baryonic distribution at each galaxy radius, even when dark matter supposedly dominates the gravitational field. I conclude by discussing the (uncertain) location of Local Group dwarf spheroidal galaxies on the RAR defined by more massive disk galaxies.

The interplay between dark matter (DM) and baryons has long been ignored when building galaxies semi-empirically and observationally. Here I show that baryonic gravity leads to an adiabatic contraction of DM halos, which is most significant in massive galaxies. Ignoring this effect, the derived DM halos are not guaranteed in dynamical equilibrium. I present a new approach to deriving DM halos from rotation curves, which incorporates the adiabatic contraction. The compressed halos turn out super cuspy with respect to NFW halos, which require smaller baryonic contributions and less concentrated primordial halos. I also examine the semi-empirical approach to building galaxies, and find the adiabatic contraction can shift massive galaxies from the observed radial acceleration relation dramatically. Both approaches lead to super cuspy DM halos for massive galaxies, demonstrating the importance of the baryon-driven contraction, which has to be taken into account in order to make an apple-to-apple comparison with simulations.

We present a method to measure the the oblateness parameter q of the dark matter halo of gas rich galaxies that have extended HI disks. We have applied our model to a sample of 20 nearby galaxies that are gas rich and close to face-on, of which 6 are large disk galaxies, 8 have moderate stellar masses and 6 are low surface brightness (LSB) dwarf galaxies. We have used the stacked HI velocity dispersion and HI surface densities to derive q in the outer disk regions. Our most important result is that gas dominated galaxies (such as LSB dwarfs) that have M(gas)/M(baryons)>0.5 have oblate halos (q<55), whereas stellar dominated galaxies have a range of q values from 0.2 to 1.3. We also find a significant positive correlation between q and stellar mass, which indicates that galaxies with massive stellar disks have a higher probability of having halos that are spherical or slightly prolate, whereas low mass galaxies preferably have oblate halos. We briefly also discuss how the halo shape affects the disks of galaxies, especially the oblate halos.

Since the mid 70ies it is known that the dwarf galaxies around the Milky Way are arranged in a thin, polar structure. The arrangement and motion within this structure has been identified as a severe challenge to the standard model of cosmology, dubbed as the plane of satellites problem. More observational evidence for such structures has been put forward around other galaxies, such as the Andromeda galaxy, Cen A or NGC 253, among others, adding to the previously identified tensions. Solutions to the plane of satellite problem should therefore not only be tailored to the Milky Way, but need to explain all these different observed systems and environments.

Cosmological simulations predict dark matter shapes that deviate from spherical symmetry. The exact shape depends on the prescription of the simulation and the interplay between dark matter and baryons. This signature is most pronounced in the diffuse galactic haloes that can be observationally probed with planetary nebulae and globular clusters (GCs). The kinematic observations of these halo tracers support intrinsic triaxial shape for the mass generating the gravitational potential. With discrete axisymmetric modelling of GCs as the halo tracers of NGC 5128 we investigate the overall mass distribution of this nearby giant elliptical galaxy. Our modelling approach constrains c200, (M/L)*,B and inclination. We derive a preliminary M200 ∼ 1 × 1012 M⊙ and flattening qDM ∼ 1.3 indicative of prolate/triaxial halo for NGC 5128.

The Satellite Plane Problem (SPP) has been a hotly discussed topic for the past two decades. During which, a diametric discussion has begun, between papers that suggest that satellite galaxy planes represent an exception of, and papers which suggest that they are consistent with ΛCDM simulations. However, this discussion has not moved far beyond analysis and re-analysis of galaxies in the Local Group which is a roadblock in producing a more complete and robust analysis. This is motivating an effort to characterise satellite galaxy systems in the wider local universe. We present here initial results of an extensive optical survey of NGC2683 and M104, with the purpose of identifying optical elusive satellite galaxy candidates for follow up observations. These systems are among the first that will allow us to control for mechanisms which are suggested to create or otherwise explain the significance of satellite planes.

The nearby Fornax cluster (d ∼ 20 Mpc) provides an unparalleled opportunity to investigate the formation and evolution of early-type galaxies in a dense environment. Using the spectroscopic data from the ESO VLT/VIMOS spectrograph of the Fornax cluster, we have kinematically characterised the photometrically detected globular cluster (GC) candidates in the core of the cluster. We confirm a total of 777 GCs with new velocity measurements and compile the most extensive spectroscopic GC sample of 2341 objects in this environment. We used our GC radial velocity catalogue to perform dynamical mass modelling of NGC 1399, the central galaxy of the the Fornax cluster out to its 200 kpc. We find that both cusp (NFW) and core (Burkert) dark matter (DM) halo can produce the observed kinematics. Independent of the DM halo profile used, we find that inclusion of the intra-cluster GCs in mass-modelling can effect the mass-estimate.