Stellar streams unveil galactic histories through gravitational interactions, mergers, and tidal disruptions. To explore the complex morphology of streams, we use a ∼47 million halo main sequence stars catalogue using Gaia DR3 proper motion and photometry information, the combination of which renders the reduced proper motion parameter. This sample with reliable photometric distances reaches out to ∼21 kpc thereby probing much further out than would be possible using reliable Gaia parallaxes. Binned velocity moments on-sky pop up several known streams in the inner halo - particularly retrograde structures, due to the kinematic selection. We select and characterise the streams GD-1, Jhelum and Phlegethon. The faint signs of disequilibrium in the form of kinks and density variations in these thin streams will paint a more detailed picture of the existence and properties of the dark matter sub-haloes that perturb them and in turn, the mass distribution of our Galaxy.

We use oxygen and argon abundances for planetary nebulae (PNe) with low internal extinction (progenitor ages of > 4.5 Gyr) and high extinction (progenitor ages < 2.5 Gyr), as well as those of the HII regions, to constrain the chemical enrichment and star formation efficiency in the thin and thicker discs of M31. As the argon element is produced in larger fractions by Type Ia supernovae compared to oxygen, we found that the mean log(O/Ar) values of PNe as a function of their argon abundances [12 + log(Ar/H)] trace the interstellar medium (ISM) conditions at the time of birth of the M31 disc PN progenitors. Thus, the chemical enrichment and star formation effciency information encoded in the [α/Fe] versus [Fe/H] distribution of stars is also imprinted in the oxygen-to-argon abundance ratio log(O/Ar) versus argon abundance for the nebular emissions of the different stellar evolution phases. The chemical evolution model that reproduces the mean log(O/Ar) values as a function of argon abundance for the high- and low-extinction PNe requires a second infall of metal-poorer gas during a gas-rich (wet) satellite merger for the M31 disc region within 14 kpc. A strong starburst is ongoing in the intermediate radial range (14 < RGC< 18 kpc). In the outer M31 disc (RGC > 18 kpc), the log(O/Ar) versus argon abundance distribution of the younger high-extinction PNe indicates that they too were formed in a burst, though mostly from the metal-poorer gas. In M31, the thin disc is younger and less radially extended, formed stars at a higher star formation effciency, and had a faster chemical enrichment timescale than the more extended thicker disc. Both the thin and thicker discs in M31 reach similar high argon abundances (12 + log(Ar/H))∼ 6.7. The chemical and structural properties of the thin and thicker discs in M31 are thus remarkably different from those determined for the Milky Way thin and thick discs.

New large observational surveys such as Gaia are leading us into an era of data abundance, offering unprecedented opportunities to discover new physical laws through the power of machine learning. Here we present an end-to-end strategy for recovering a free-form analytical potential from a mere snapshot of stellar positions and velocities. First we show how auto-differentiation can be used to capture an agnostic map of the gravitational potential and its underlying dark matter distribution in the form of a neural network. However, in the context of physics, neural networks are both a plague and a blessing as they are extremely flexible for modeling physical systems but largely consist in non-interpretable black boxes. Therefore, in addition, we show how a complementary symbolic regression approach can be used to open up this neural network into a physically meaningful expression. We demonstrate our strategy by recovering the potential of a toy isochrone system.

We calculated the positions and velocities of 47 dwarf galaxies using a Bayesian approach. Their angular momentum distribution shows that between 36% and 57% of the dwarf galaxies are located in the Vast Polar Structure (VPOS), which could conflict with expectations for a cosmological infall of primordial dwarfs. Using four gravitational potential models with mass spans from 2.8 × 1011 M⊙ to 15 × 1011 M⊙, we find that dwarf galaxies are over-concentrated near their pericenters compared to what Kepler’s law would expect. This suggests that there may be a large number of dwarf galaxies that have not yet been discovered, or that they are not satellites of the Milky Way.

The Large Magellanic Cloud (LMC) has a complex dynamics driven by both internal and external processes. The external forces are due to tidal interactions with the Small Magellanic Cloud and the Milky Way, while internally its dynamics mainly depends on the stellar, gas, and dark matter mass distributions. Despite the overall complexity of the system, very often simple physical models can give us important insights about the main driving factors. Here we focus on the internal forces and attempt to model the proper motions of ∼ 106 stars in the LMC as measured by Gaia Data Release 3 with an axisymmetric dynamical model, based on the Jeans equations. We test both cored and cusped spherical Navarro-Frenk-White dark matter halos to fit the LMC gravitational potential. We find that this simple model is very successful at selecting a clean sample of genuine LMC member stars and predicts the geometry and orientation of the LMC with respect to the observer within the constraint of axisymmetry. Our Jeans dynamical models describe well the rotation profile and the velocity dispersion of the LMC stellar disc, however they fail to describe the motions of the LMC bar, which is a non-axisymmetric feature dominating the central region. We plan a triaxial Schwarzschild approach as a next step for the dynamical modelling of the LMC.

I discuss Local Group galaxies from the perspective of external galaxies that define benchmark scaling relations. Making use of this information leads to a model for the Milky Way that includes bumps and wiggles due to spiral arms. This model reconciles the terminal velocities observed in the interstellar medium with the rotation curve derived from stars, correctly predicts the gradual decline of the outer rotation curve, and extrapolates well out to 50 kpc. Rotationally supported Local Group galaxies are in excellent agreement with the baryonic Tully-Fisher relation. Pressure supported dwarfs that are the most likely to be in dynamical equilibrium also align with this relation. Local Group galaxies thus appear to be normal members of the low redshift galaxy population. There is, however, a serious tension between the dynamical masses of the Milky Way and M31 and those expected from the stellar masshalo mass relation of abundance matching.

The mass-anisotropy degeneracy is still one of the main issues in estimating the dark matter distribution in galaxies, especially for the commonly used 2nd-order Jeans analysis. We study the extension of spherical Jeans modeling by incorporating the 4th-order velocity moments under the assumption of dynamical equilibrium and a constant velocity anisotropy. Incorporating 4th -order moments allows stars’ line-of-sight velocity distribution (LOSVD), which is sensitive to the value of β, to be flexible, covering thin-tailed to heavy-tailed distributions that are inaccessible if only 2nd-order moments are used. We test our stellar dynamical modeling using mock data that resembles Draco dSph with either central NFW cusp or Burkert core. Using 500 sample stars, our simulations show that incorporating 4th-order moments improves the results. Typically, the velocity anisotropy is constrained ∼ 2 −3 times tighter, while it is ≲30% typical bias for the constraint of the dark matter inner density slope with both parameters being recovered within 1σ uncertainties.

The combination of kinematic and chemical information from Galactic stars has revealed in great detail the structure, dynamics and history of our own Galaxy. In external galaxies, it is impossible to map the distribution of individual stars, but high signal-to-noise integral field unit (IFU) spectroscopy data at various wavelengths, together with sophisticated dynamical models, give us the opportunity to gather information on the structure, dynamics and formation history of these systems. The Schwarzschild method models galaxies through the superposition of stellar orbits, and is equipped to deal with very detailed kinematic measurements, allowing us to take full advantage of high-quality IFU datasets of nearby galaxies. Here we present an implementation of this method called DYNAMITE. We provide an overview of the modelling technique, introduce applications to observations and simulations, and anticipate our future plans for DYNAMITE.

The wide-field spectrographs 4MOST and MOONS are expected to enter operations in late 2024 at the ESO Paranal Observatory. These upcoming survey facilities will play an important role in various fields over the next decade. In particular, both will host surveys aimed at observing Local Group (LG) galaxies. We describe how their scientific performances complement Gaia and other spectroscopic surveys in the field of nearby galaxy kinematics, and provide an overview of the planned surveys that focus on LG galaxy kinematics. We outline the policies for community access to data and observing time, which is different for the two instruments. The contribution concludes with a summary of the main scientific goals of MOONS and 4MOST survey science regarding the LG galaxy masses and dynamics.

We present recent results from the Pristine Inner Galaxy Survey (PIGS), which used metallicity-sensitive narrow-band CaHK photometry to identify and follow up spectroscopically thousands of ancient metal-poor candidates in the bulge. For the spectroscopic PIGS sample, we derive distances with StarHorse and compute orbital properties in a realistic potential including a bar. We find that a significant fraction of metal-poor stars is confined to the inner Galaxy (apocentre < 4 kpc), with an estimated confined fraction of 80%/50% at [Fe/H] = − 1.0/ − 2.0. We also find that the very metal-poor population has a net prograde rotation, with a υϕ ∼ 40 kms−1. It is still under discussion what the origin is of the population of very metal-poor inner Galaxy stars – it is likely a combination of in-situ and accreted stars. In future, spectroscopic observations from 4MOST will be crucial to complete our picture.

We use all the Subaru/HSC-SSP photometric data to investigate spatial substructures in the outer halo of the Milky Way. In order to effectively detect them, an isochrone-filter is created for the old, metal-poor stellar systems on the color-magnitude diagram. As a result, previously discovered stellar streams (e.g. the Orphan Stream) are detected, while a new candidate substructure is discovered toward Pisces. Based on this filter, we conclude that the progenitor is an old and metal-poor system. This kind of stellar streams are expected to be found in the next-generation observation program.

Based on RR Lyrae with accurate proper motions and classification in Gaia DR3, we determine the Milky Way mass distribution from fitting dynamical models to the gravitational force field and the Galactic rotation curve. Applying Gaussian Mixture Model to the intrinsic velocity distribution, we present the result of a multi-component kinematic model of RR Lyrae in the inner regions 5 ≲ r ≲ 20 kpc. Considering the early accretion history of the MW and thus the stellar halo may not be in equilibrium, we separate the halo population into an isotropic stellar halo and the radially-anisotropic population relevant to a merge event. With a Bayesian approach, we fit the potential model parameters, including the density flattening of the dark matter (DM) halo. Our best-fitting dynamical model suggests a nearly spherical spheroid shape of , a DM halo mass of , total MW mass of .

We measure the enclosed Milky Way (MW) mass profile to Galactocentric distances of ∼70 and ∼50 kpc using the smooth, diffuse stellar halo samples of Bird et al. The samples are Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) and Sloan Digital Sky Survey/Sloan Extension for Galactic Understanding and Exploration (SDSS/SEGUE) K giants (KG) and SDSS/SEGUE blue horizontal branch (BHB) stars with accurate metallicities. The 3D kinematics are available through LAMOST and SDSS/SEGUE distances and radial velocities and Gaia DR2 proper motions. Two methods are used to estimate the enclosed mass: 3D spherical Jeans equation and Evans et al. tracer mass estimator (TME). We remove substructure via the Xue et al. method based on integrals of motion. We evaluate the uncertainties on our estimates due to random sampling noise, systematic distance errors, the adopted density profile, and non-virialization and non-spherical effects of the halo. The tracer density profile remains a limiting systematic in our mass estimates, although within these limits we find reasonable agreement across the different samples and the methods applied. Out to ∼70 and ∼50 kpc, the Jeans method yields total enclosed masses of 4.3±0.95 (random) ±0.6 (systematic) ×1011 M⊙ and 4.1±1.2 (random) ±0.6 (systematic) ×1011 M⊙ for the KG and BHB stars, respectively. For the KG and BHB samples we find a dark matter virial mass of (random) ±0.083 (systematic) ×1012 M⊙ and (random) ±0.15 (systematic) ×1012 M⊙, respectively.

Understanding the origin of the stellar streams around the Milky Way can be of great relevance to learn about the history of the Milky Way and the formation of its substructures. A previous study on the Milky Way streams (Pawlowski et al. 2012) showed that many of these (7 out of 14) present a similar orientation to that of the disk of satellite galaxies (DoS) and the young globular clusters of the Milky Way. This suggests that the DoS, the young globular clusters and a large fraction of the Milky Way streams have a correlated origin. The authors proposed that these substructures could have formed as a result of a past interaction between the Milky Way and the Andromeda galaxy. In this work, we revise the distribution of the orbital poles of the Milky Way streams in light of the latest stream dataset, which includes a total of 97 streams.

Andromeda (M 31) is the nearest giant spiral galaxy to our Milky Way, and, over the past few decades, has been dubbed the most massive member of the Local Group. I explore the evolution of the measured mass of M 31 over the past ∼80 years, reviewing the different observational and modelling techniques that have developed over time to measure its mass. I discuss the best present-day constraints of the mass of M 31 and the consistency of different techniques.

The field of Galactic archaeology in the Milky Way (MW) has been significantly transformed by the advent of proper motions (PMs), but PM studies are still in their early stages in the M31 system. Measuring PMs in the M31 system poses a challenge for Gaia, limiting HST and JWST as the only reliable options. PM measurements of M31 satellites enable the estimation of M31’s total mass, examination of the dynamical stability of the Great Plane of Andromeda, and establishing connections to M31 substructures. We have successfully measured the PMs of NGC 147 and NGC 185 using multiepoch HST imaging data. Recently, we have obtained second-epoch HST imaging data for seven additional satellites through the HST program GO-16273. We present preliminary results from the PM measurements of these galaxies along with the implications. Finally, we discuss the future prospects of measuring PMs at the distance of M31.

We investigate the possible link between the Andromeda Giant Stream (AGS) and the 10 kpc ring structure using N-body/SPH simulations of a minor merger between the M31 and a satellite galaxy with a mass of 1010 M⊙. The simulation result successfully matches the observed features of the AGS and the 10 kpc ring concurrently. The simulation reproduced the observations, showing that the stars are smoothly distributed in the galactic disk, and the gas is shaped in a ring-like structure. In addition, we demonstrate the spatial metallicity distribution of the merger remnant, assuming the metallicity gradient of the progenitor galaxy. The result remarkably captures the observed features in the AGS exhibiting non-uniform metallicity distribution perpendicular to the AGS axis. These results indicate that a minor merger with a massive dwarf galaxy is capable of simultaneously forming the AGS and the 10 kpc ring.

We use the rotation curve from Gaia data release (DR) 3 to estimate the mass of the Milky Way. We consider an Einasto density profile to model the dark matter component. We extrapolate and obtain a dynamical mass at 112 kpc. This lower-mass Milky Way is consistent with the significant declining rotation curve, and can provide new insights into our Galaxy and halo inhabitants.

We have identified the velocity jump (shock) features in the inner 20′ × 10′ region of M31 using the data of [O III] and H I. The identified shock features are found primarily on the leading side of the potential bar, displaying a typical pattern of bar-driven gas inflow. The shock features provide independent evidence for M31 being a barred galaxy. Our preliminary gas simulations with a barred potential of M31 can reproduce these shock features.

The Triangulum Extended (TREX) Survey is a spectroscopic survey† that targets resolved stars of all ages throughout the disk of Triangulum (M33). We summarize the first results from the TREX Survey, including the discovery of a kinematically hot, halo-like population throughout M33’s inner disk in both the old and intermediate-age populations and evidence that the youngest stars have been dynamically heated. We also discuss the implications for our understanding of M33’s dynamical history in the context of recent results from the Panchromatic Hubble Andromeda Treasury: Triangulum Extended Region (PHATTER) Survey.