When interpreted within the framework of Newtonian dynamics, the internal kinematic properties of Local Group dwarf galaxies indicate that most of these systems are completely dominated by their dark matter halos. These dwarf galaxies are therefore among the best test-benches for dark matter theories. In this review talk, I will first provide an overview of our current understanding of the...
Stellar streams are one of the most powerful tracers to determine the mass of the Milky Way and other nearby galaxies. Full 6D phase space data is necessary for us to get there. In this talk, I will discuss two ongoing spectroscopic programs to study the stellar streams in our Milky Way and highlight a few latest scientific results from these two programs. The Southern Stellar Stream...
Like any other galaxy in the universe, evidence shows that the assembly of the Milky Way is irrefutably hierarchical. The Galactic halo in particular has a nonlinear structure with a vast number of cold stellar streams with complex morphologies that prove to be a powerful test for the nature and distribution of dark matter in the halo.
In this work, we select halo main sequence stars using...
Stellar streams are sensitive probes of the Galactic potential. The likelihood of a model given stream data can only be assessed using simulations. However, comparison to simulation is challenging in a noisy 6D phase space in which even the stream paths are hard to quantify. Here we present a novel application of Self-Organizing Maps and first-order Kalman Filters to reconstruct the stream...
Providing a detailed picture of the complexity of the Sagittarius stream is an important aspect of investigating the outer Galactic halo and constraining the Milky Way potential. Several attempts have been made to model the complex structure of the Sagittarius stream. However, no model has yet been able to match all the intricate features observed for the stream, including for instance a...
The position, velocity, and chemical composition of each star provide clues to the evolutionary history of galaxies. While the Gaia mission has offered invaluable information about the Milky Way, to understand the growth of disk galaxies in the Universe we must look beyond our galaxy.
The Andromeda Galaxy (M31) is ideal for this task thanks to its proximity (making it possible for...
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 H II regions, to constrain the chemical enrichment and star formation efficiency in the thin and thicker discs of M31. The argon element is produced in larger fraction by Type Ia supernovae (SNe) than...
Recent observational efforts such as Gaia are leading us toward a new era of data abundance which offers us an incredible opportunity for discovering new physics. Thanks to recent advances in the field of machine learning, it is possible to extract valuable information from the colossal amount of data now available.
In particular, auto-differentiation allows us to get a better grasp of...
Based on Gaia Early Data Release 3 (EDR3), we estimate the proper motions for 46 dwarf galaxies of the Milky Way. The uncertainties in proper motions, determined by combining both statistical and systematic errors, are smaller by a factor 2.5, when compared with Gaia Data Release 2. We have derived orbits in four Milky Way potential models that are consistent with the MW rotation curve. ...
The ongoing merger of the Milky Way and the Large Magellanic Cloud (LMC) is deforming the dark matter haloes of both galaxies, effectively making these galaxies a local dark matter collider. Within this collider, stellar streams act as useful detectors as they are very sensitive to the gravitational potential, and span large parts of the Milky Way halo.
The Orphan-Chenab (OC) stream is...
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 (SMC) 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...
We combine Gaia EDR3 astrometry with accurate photometry and utilize a probabilistic mixture model to measure the systemic proper motion of 52 dwarf spheroidal (dSph) satellite galaxies of the Milky Way (MW). For the 46 dSphs with literature line-of-sight velocities we compute orbits in both a MW and a combined MW + Large Magellanic Cloud (LMC) potential and identify Car II, Car III, Hor I,...
The baryonic Tully-Fisher relation is a correlation between the quantity of stars and gas in a galaxy and its flat rotation speed. The relation found in external galaxies appears to hold for rotationally supported Local Group galaxies. It may also hold for some if not all of the pressure supported dwarfs. The flat rotation speed depends on dynamical mass, providing a constraint on total mass...
Determination of the mass density profiles of dwarf galaxies (and specifically whether there is a central core or cusp) provides a critical test of both the properties of dark matter (DM) and the physics of cosmological structure formation. The nearby classical dwarf spheroidal galaxies (dSphs) of the Milky Way yield some of the best dynamical constraints. While large line-of-sight velocity...
The mass-anisotropy degeneracy is still one of the main issues in estimating the dark matter distribution in dwarf spheroidal galaxies, especially for the commonly used second-order Jeans analysis. We study the extension of spherical Jeans modeling by incorporating the fourth-order velocity moments under the assumption of dynamical equilibrium and a constant velocity anisotropy. The inclusion...
An accurate and unambiguous determination of the inner distribution of dark matter in dwarf spheroidal (dSph) galaxies has proven to be a challenge for a few decades now. Some of the complications include the degeneracies inherent to the dynamics of stellar systems, but also the limits of the available data (e.g., just one component of the 3D space velocities of the tracers), and the need for...
According to our currently favored cosmological framework, the Lambda- Cold Dark Matter model, galaxies like the Milky Way were built through the accretion and merger of smaller systems. In this scenario, the extended halo of the Milky Way must retain information about this process. Key to unveiling this information is our ability to trace the outermost regions of the halo by detecting and...
The ESA's astrometric mission Gaia has added an invaluable wealth of astrometric and photometric data for more than a billion stars in our Galaxy (Gaia Collaboration et al. 2018). The synergy between Gaia's third data release, EDR3, and large scale-spectroscopic surveys give us comprehensive information about individual stars in the Milky Way. To complement these data sets, we deliver new...
The combination of astrometric and chemical information from Galactic stars has revealed great detail about 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 spectroscopy data at various wavelengths, together with sophisticated dynamical models, give us the...
The wide-field spectrographs 4MOST and MOONS will enter operations in 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 nearby Local Group galaxies. Here, we provide an overview of all the planned 4MOST and MOONS surveys that focus on Local Group...
Very wide stellar binaries, with semi-major axes of hundreds of AU and larger, constitute sensitive probes of the underlying gravitational potential in which they live, having provided some of the first experimental constraints on the nature of dark matter in the Milky Way halo. As such, the detection and characterization of populations of wide binaries in nearby old dwarf galaxies could...
Our Galaxy, the Milky Way, provides us with a unique opportunity to measure the 3D shape of its dark-matter halo, thus testing the properties of the dark sector and the fundamental cosmological model. Until recently, however, these efforts have been thwarted by the scarcity of observational data, especially in the outer halo, as well as reliance on the assumption of a dynamical equilibrium,...
The Dark Energy Spectroscopic Instrument (DESI) is currently one of the most powerful instruments for wide-field multi-object spectroscopy. The synergy of DESI with current (e.g. ESA’s Gaia satellite) and future observing facilities including the Vera Rubin Observatory’s Legacy Survey of Space and Time (LSST), and the Nancy Grace Roman Space Telescope’s High Latitude Survey (HLS) will yield...
The oldest, most metal-poor stars in the Milky Way are unique probes of early star formation and the assembly of the Milky Way. The Galactic bulge region has typically been avoided in the search for metal-poor stars, because of the extremely high density of mostly metal-rich stars and the high dust extinction. The bulk of the Galactic bulge is thought to originate from the (early) Galactic...
Under the current standard scenario, galaxies such as the Milky Way (MW) are thought to have formed through repeated mergers and accretions of small galaxies due to gravitational interactions. Since the relaxation timescale of these traces in phase space is as long as more than 10 billion years, it has been theoretically suggested that they may still exist in the halo. Advances in large-scale...
The mass of the Milky Way (MW) is important to the formation and evolution of galaxy. After decades of study, the mass of dark matter halo is still open. Most studies have used dynamical tracers in the inner regions of the halo, relying on extrapolations to estimate the mass of the MW. In our study, we determine the Milky Way mass distribution from fitting dynamical models to the...
We measure the enclosed Milky Way mass profile to Galactocentric distances of $\sim70$ and $\sim50$ kpc using the smooth, diffuse stellar halo samples of Bird et al. The samples are LAMOST and 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...
Classical Cepheids are excellent tracers to estimate the rotation velocity of the galaxies because they provide better distance accuracy with less uncertainty. With stringent radial velocity from the recent Gaia DR3 and proper motion, we estimate the rotation velocity of the Milky Way galaxy for 909 Classical Cepheids. We have used a more accurate distance estimated based on the...
In this talk, I will discuss the predictions of the $\Lambda$CDM model on the make-up of stellar and dark matter haloes of Milky Way-mass galaxies. I will show that the stellar haloes are made up largely of stars from massive mergers, like Gaia-Enceladus/Sausage in the Milky Way, while the same mergers also make up nearly half of the dark matter halo. Past mergers leave imprints in the...
Stellar streams are created when globular clusters or dwarf galaxies tidally disrupt in the gravitational potential of their host galaxy. These streams therefore offer a great probe to this galactic potential. Current observations show a multitude of Milky Way stellar streams to have substructure in the form of 'spurs', 'gaps' and even multiple components. These can originate from interactions...
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...
Since the chemical abundances of stars are the fossil records of the physical conditions in galaxies, they provide the key information for recovering the assembly history of galaxies. In this work, we explore the chemo-chrono-kinematics of accreted and survived dwarf galaxies by analyzing six M31/MW analogues from the HESTIA suite of cosmological hydrodynamics zoom-in simulations of the Local...
Andromeda (M31) is the nearest giant spiral galaxy to the Milky Way and the most massive member of the Local Group. It has long been recognized that M31's mass measurement is essential to understand the formation and evolution of the Local Group. I will review the different observational and modelling techniques that have developed over time to measure the mass of M31. I will discuss the the...
Proper motions (PMs) from HST and Gaia have revolutionized the field of Galactic archaeology in the Milky Way (MW). However, PM studies in and around our neighbor spiral galaxy M31 are still in their early stages with measurements being available for only a few satellites and M31 itself at the moment. Gaia can only detect some of the brightest stars in star forming regions at the distance of...
High-precision astrometric data from the Hubble Space Telescope (HST) and Gaia are revolutionizing our ability to study the Local Group. Currently, 6D phase space measurements (3-dimensional position and velocity) are available for a majority of the Milky Way’s known satellite galaxies and for four (11%) of M31’s satellite galaxies. As satellites trace the dark matter halos of their hosts,...
We present DESI observations of the stellar halo of M31 which reveal the kinematics of a recent merger in exquisite detail. Using data from less than four hours of observations by DESI survey we measure radial velocities of more than 7000 sources in M31. These observations show an intricate coherent kinematic structure in position and velocity space in M31 stellar halo. While hints of coherent...
Recent observations around the M31 have revealed many traces of past interactions with satellite galaxies. In particular, the Andromeda Giant Southern Stream (AGSS) in the halo and the double ring structure in the disc have been drawing attention. The AGSS is a giant structure extending more than 100 kpc from the center of M31 and is thought to have been formed in a collision with a satellite...
The rather intuitive concept of 'galaxy mass' is an ill-defined quantity in cosmology. First, because in an expanding, close-to-homogeneous Universe collapsed structures do not show well-defined boundaries, and second because the availability of dynamical tracers becomes very scarce in the outskirts of dark matter haloes. In this talk I will provide an overview of the timing argument, which...
The study of the dynamical mass of the Local Group requires a detailed knowledge of the velocity of its elements, in particular of the Milky Way (MW) and the Andromeda galaxy (M31). Nevertheless, a discrepancy between the proper motion of the disk of M31 and the global motion of its satellites has been identified. Moreover, recent results showing the influence of the Magellanic complex on the...
The large uncertainties on the measurement of the mass of galaxies is an important issue in modern astrophysics. For both the MW and M31, thanks to the gas rotation curve, the mass of the inner part of the haloes is well constrained. For the outer part of the haloes, we must turn to satellites galaxies as tracers. But, to use dwarf galaxies as such, it is absolutely crucial to determine the...
We estimate that the mass of the Milky Way (MW) is in the range of 2 to 15 $\times 10^{11} M_\odot$. It results from an analysis of the rotation curve (RC) from Gaia DR2 and using different profiles for baryon and dark matter (DM, including NFW & Einasto profile). The lower limit 2 $\times 10^{11} M_\odot$ corresponds to the Keplerian slope of RC at large radii. There were no major mergers in...
The formation and evolutionary history of M31 are closely related to its dynamical structures, which remain unclear due to its high inclination. Gas kinematics could provide crucial evidence for the existence of a rotating bar in M31. Using the position–velocity diagram of [O III] and H I, we are able to identify clear sharp velocity jump (shock) features with a typical amplitude over 100 km/s...
Triangulum (M33), a satellite of the Andromeda (M31) galaxy, is the only dwarf Spiral in the Local Group. With a mass ten times lower than M31’s and a star formation rate 10 times higher, M33 is the best local analog for high z galaxies. The Triangulum Extended Survey (TREX) is a large resolved stellar spectroscopic survey of M33 and its extended structures. With contiguous spectroscopic...
We review estimates of the total mass of the Local Group. High-accuracy proper motions (PMs) of M31 and other Local Group (LG) satellites have now been provided by the Gaia satellite. We revisit the timing argument to compute the total mass of the LG from the orbit of the Milky Way and M31. We discuss a number of systematic effects. The first is caused by the presence of the Large Magellanic...
I will briefly summarise the key methods for the determination of the dynamical mass and mass profiles of dwarf galaxies. I will then discuss in detail the observational challenges associated with making the necessary measurements and obtaining the necessary data, with a focus on the systematic, technical, and physical limitations of the measurement. I will review the implications of these...
The Milky Way satellite dwarf galaxy Antlia II is one of the lowest surface brightness galaxies known. It has a size comparable to the Large Magellanic Cloud, but only 10^6 solar masses of stars. We present kinematic and chemical measurements from the Southern Stellar Stream Spectroscopic Survey using the AAT/2dF, which clearly demonstrate that Antlia II is tidally disrupting. The orbit and...
Andromeda (And) XIX is a unique dwarf galaxy in the M31 system. Its large half-light radius (in excess of 3 kpc) and low surface brightness (29.3 magnitudes per square arcsecond) make it one of the most diffuse galaxies in the known Universe. In addition to its extreme structural properties, its dynamics also suggest that it sits in a low density dark matter halo that may have been shaped by...
Analysing the stellar kinematic properties of a dwarf galaxy makes it possible to investigate which internal mechanisms have shaped its evolution. Isolated dwarf galaxies with an extended star formation history, in particular, offer the opportunity to study not only star formation processes at low-mass and low-metallicity scales, but also to understand how internal kinematic properties evolve...
One particularly promising way to understand the nature of dark matter is to study the so-called core-cusp problem. Many solutions have been investigated to solve it and one possibility is that the nature of the dark matter itself is different from the successful $\Lambda$-Cold Dark Matter model. To reduce the impact of baryonic physics which obscures our ability to constrain dark matter, we...
We present kinematics and detailed chemical abundances of stars in the outskirts (out to ~8 half-light radii) of the Tucana II ultra-faint dwarf galaxy (< 10^5 Lsun; UFD) from high-resolution Magellan/MIKE spectroscopy. The Milky Way’s UFDs are “relic” galaxies (~13 Gyr old) from the early universe, making their stars unique probes of the first stages of galactic evolution. Previous...
Previous studies of Ultra-Faint Dwarfs (UFDs) show that their dynamical mass-to–light ratios are the highest values measured in any type of galaxy, implying relatively pure dark-matter halos with minimal baryonic content. Furthermore, UFDs have the lowest metallicities, oldest ages, smallest sizes, and simplest assembly histories of all galaxies. Understanding the nature of these galaxies...
Gaia has revolutionized our understanding of the Milky Way (MW) and its satellite system. However, the proper motions (PMs) of dwarf galaxies outside the MW system remain out of reach by Gaia and will remain so even with future data releases. This is problematic, as it means that our understanding of systems outside the MW will be limited and we may be basing much of our cosmological modeling...
Leo P is a poorly studied near-primordial isolated dwarf irregular galaxy at a distance of ∼ 1.6 Mpc, with an extremely low mass of ∼ 105M⊙.
From Hubble Space Telescope and Arecibo Legacy Fast observations, its characteristics show the same behaviour as expected in a low-luminosity dSph Milky Way satellite. It was defined as the “quintessential system to test theories of how the smallest...
To investigate the dynamical nature of the kinematic asymmetry in the isolated gas-rich dwarf irregular galaxy W LM in the Local Group, we first examine whether an m = 1 perturbation in the halo potential could be a mechanism creating such kinematical asymmetry.
By fitting a theoretical rotational velocity associated with an m = 1 perturbation in the halo potential model to the observed...
The chemical abundance patterns exhibited by stars in Ultra-Faint Dwarf (UFD) galaxies can provide a wealth of information about the evolutionary history of UFDs, including what dynamical history the stars in a UFD may have experienced. Of particular interest are stars in the outer regions of UFDs because they may hold evidence of tidal stripping, mergers, or other mechanisms; and because of...
In the hierarchical clustering scenario based on the $\Lambda$ cold dark matter ($\Lambda$CDM) model, sub-galactic dark matter halos (subhalos) are of crucial importance in building up the larger structures via merging processes. Moreover, dwarf galaxies around the Milky Way (MW) are ideal sites for studying the nature of dark matter since they are dark-matter-dominated systems.
We...
The unusually low velocity dispersion and large sizes of `feeble giant' galaxies, such as Crater II or Antlia II, pose a challenge to our understanding of dwarf galaxies in the Lambda Cold Dark Matter (LCDM) cosmogony. Their low velocity dispersions suggest either a dark halo mass much lower than the minimum expected from hydrogen cooling limit arguments, or one that is in the late stages of...
Dwarf galaxies play a key role in probing the dynamics of the Milky Way, the history of star formation in the Local Group, and the accretion and retention of gas in dark matter halos at the smallest scales of galaxy formation. In this work, we use the Ultraviolet Near-Infrared Optical Northern Survey (UNIONS), the deepest, widest photometric survey ever carried out in the northern hemisphere,...
The dwarf spheroidal galaxies (dSphs) in the Local Group are excellent test beds for probing the properties of dark matter and its role in galaxy formation.
These galaxies are sufficiently close that it is possible to measure line-of-sight velocities for large samples of resolved stars. This kinematic information enables us to study the structural properties of their dark matter...
Dwarf galaxies are valuable laboratories for dynamical studies related to dark matter and galaxy evolution, yet it is currently unknown just how extended their stellar components are. Each satellite orbiting within the Milky Way’s (MW’s) gravitational potential may undergo tidal stripping by the host galaxy, or alternatively, may themselves have accreted yet smaller systems whose debris...
Gaia EDR3 has provided proper motions of Milky Way (MW) dwarf galaxies with an unprecedented accuracy, which allows us to investigate their orbital properties. We found that the total energy and angular momentum of MW dwarfs are much larger than that of MW K-giant stars, Sagittarius stream stars and globular clusters. It suggests that many MW dwarfs have recently infall into the Milky Way...
Dwarf satellite galaxies around Andromeda (M31) and the Milky Way form thin, coherently rotating planes argued to be in tension with expectations from the cold-dark-matter (CDM) model of cosmology. For M31, this disagreement is compounded by a prominent asymmetry in its satellite distribution; over 80% of its dwarfs lie in the hemisphere facing the Milky Way. To a degree, lopsided dwarf galaxy...
The discussion "dark matter vs. modified gravity" has not been resolved yet. It was proposed that dynamical friction could be used to discriminate between the two alternatives. Analytic calculations indicate that, with modified gravity, globular clusters (GCs) of low-mass galaxies experience much stronger dynamical friction than in the equivalent system with Newtonian gravity and dark matter....
In this talk I will present our results on environmental secular evolution processes that affect satellite galaxies as they enter their hosts.
Our approaches consist of global statistical analysis of satellites, and the modelling of detailed observations. For the latter approach we study distant gas rich dwarf satellites like Leo T and Phoenix, which are entering the Milky Way. Both...
Low-mass or dwarf galaxies are particularly compelling laboratories for star formation quenching because they are highly susceptible to quenching effects from both internal stellar feedback and external environment. We explore the role of ram pressure in the environmental regulation of gas content and quenching of low-mass galaxies in zoom-in hydrodynamic simulations of Milky Way (MW) mass...
Ultra-faint dwarf galaxies (UFDs) are often found in large numbers in close proximity to the Milky Way and other massive spiral galaxies. As such, their projected stellar ellipticity and extended light distributions are often thought to owe to tidal forces. I discuss the projected stellar ellipticities and faint stellar outskirts of isolated ultra-faints, drawn from the `Engineering Dwarfs at...
Numerous observations in recent years have shown that the satellite galaxies orbiting our local galaxies tend to align their orbits in one or two thin planes around the host galaxy. This has been observed in local galaxies, Andromeda and Centaurus A, and our own Milky Way. Numerical simulations in a cosmological context find these planes to be rare or short-lived leading to tension between...
Prolate rotation in galaxies (rotation around the major axis) is a rare phenomenon in the Universe. The effect has been exclusively attributed to past major mergers and thus studies of prolate-rotating systems can help us better understand the hierarchical process of galaxy evolution. Dynamical studies of such galaxies is important to find their gravitational potential profile, total mass, and...
Recent panoramic maps of the Magellanic system have revealed a wealth of low-surface-brightness stellar substructures surrounding both the Large and Small Magellanic Clouds (LMC/SMC); clear evidence of tidal interactions between the two Clouds, as well as with the Milky Way. However, the interaction history of the Magellanic system beyond the most recent LMC/SMC close passage remains poorly...
The Magellanic Bridge is a tidally-stripped structure located between the Magellanic Clouds and contains hundreds of stellar clusters and associations, which can help understanding the origin and evolution of the entire Magellanic Clouds-Milky Way (MW) system. Two main competing models describe the formation of the pair LMC-SMC: the LMC captured the SMC about 2 Gyr ago and they are in a bound...
Observational studies have identified several sub-structures in different regions of the Magellanic Clouds (MCs). One such interesting sub-structure in the Small Magellanic Cloud (SMC) is a dual population of intermediate-age giant stars which are spatially and kinematically distinct. Comparisons with simulations suggest that the foreground population might be tidally stripped from the SMC...
The Large Magellanic cloud(LMC) and Small Magellanic cloud(SMC) are the nearest interacting dwarf galaxies in the local group. And Magellanic clouds(MCs) have had interactions with each other as well as with the Milky Way. These interactions have triggered star formation in both galaxies, resulting in the formation of star clusters. Thus a comprehensive analysis of cluster population in MCs...
The Small Magellanic Cloud (SMC), as one of the nearest galaxies to us, provides a superb laboratory for studying its stellar populations in exquisite detail. We collected the largest sample of SMC red giant branch (RGB) stars (~6000) observed using the AAOmega spectrograph fed by the Two Degree Field (2dF) multi-object system at the Anglo-Australian Telescope of the Siding Spring Observatory...
Dark matter halo properties are well studied in cosmological simulations but are very challenging to estimate from observations. The dark matter halo density profile of galaxies from observations has been modeled previously using multiple probes that trace the dark matter potential, however, the angular momentum distribution of the dark matter halos is still a subject of debate. In this study,...
The Magellanic Stream is the most spectacular example of a gaseous stream in the local Universe. In this review I will discuss the Stream's importance for many areas of Galactic astronomy, summarize key unanswered questions, and identify future observations and simulations needed to resolve them.
The Large Magellanic Cloud (LMC) is the largest of the dwarf galaxies orbiting the Milky Way (MW). It sits in a very interesting niche within the Local Group (LG), being both sufficiently different in mass than the MW to be an interesting comparison and sufficiently massive to be a major player in the MW's recent history and present state. In particular, it is massive enough to have a...
The Magellanic Stream is unique to sample the MW potential from ~50kpc to 300
kpc, and is also unique in constraining the LMC mass, an increasingly important
question for the Local Group/Milky Way modeling. I will compare on the
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...
The OC stream is a dwarf galaxy stream and is one of the longest and best-measured streams in the Galaxy, spanning over 200 degrees on the sky. It extends from the inner Milky Way ($\sim$15 kpc) to the outer halo ($\sim$60 kpc), giving us a great tool with which to measure our Galaxy's dark matter halo. In addition, portions of the stream pass remarkably close to the LMC ($\sim$5 kpc),...
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, of about 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 *et...
The ongoing interaction of the Large Magellanic Cloud (LMC) and Milky Way (MW) allows for constraint of the mass (and profile) of both. Through comparison of models of the interaction and 6d halo star data, we determined that the LMC is currently both pulling the MW stellar disc away from the barycentre of the MW at 30 km/s, as well as inducing a measurable distortion in the outer halos of...
The vast multidimensional data observed in the Local Group (LG) provide us with the unique opportunity of comparing the properties of the LG with their simulated analogs in cosmological simulations. In such a comparison it has been found that the observed kinematic properties of satellite galaxies in the LG are very unusual when compared to cosmological simulations. In both the Milky Way and...
The Small Magellanic Cloud (SMC) is one of the nearest, gas-rich interacting dwarf satellites of the Milky Way and the companion of the Large Magellanic Cloud (LMC). The interactions with the LMC and/or with the Milky Way play a significant role in the evolution of the SMC. With its widespread star formation and low metallicity, the SMC is one of the best test beds to study star formation and...
Recent measurements of a high mass for the LMC imply the LMC should host a massive Magellanic Corona, a collisionally ionized, warm-hot gaseous halo at the virial temperature $\sim10^{5.4}$ K initially extending out to the virial radius (100 - 130 kpc). Such a primordial Magellanic Corona would have shaped and fed the formation of the Magellanic Stream (e.g. Lucchini et al. 2020). Now, we have...
I present work on a spatially resolved, global star-formation history (SFH) of the Small Magellanic Cloud (SMC). I use the unprecedented deep photometric data (g~24 magnitude) from the Survey of the MAgellanic Stellar History (SMASH) survey utilising the Dark Energy Camera (DECAm) on the NOAO Blanco 4 m Telescope. The SFH is quantitatively obtained using colour-magnitude diagram (CMD) fitting...
One major source of disequilibrium in the Milky Way is its most massive satellite, the LMC. Kinematics of distant halo tracers show a velocity dipole in the Milky Way halo, which has been interpreted using N-body simulations as the LMC inducing a reflex motion in the Milky Way disk. In this talk, I discuss applying this framework to more realistic halos comprised of substructure from the...
The Large and Small Magellanic Clouds (LMC and SMC) are the largest and most luminous dwarf satellite companions of the Milky Way. Due to their close proximity, they provide a unique opportunity to study the dynamics of their resolved stellar populations in unparalleled detail. Within the last years, high-precision proper motion measurements of stars within the Magellanic Clouds had a...
In this talk, I will discuss recent UV absorption-line measurements of large-scale gas flows in the Local Group with particular emphasis on the relation between LG galaxy kinematics and CGM/IGrM gas dynamics. New results from an HST/COS all-sky survey of gas in the Milky Way's CGM and the Local Group IGrM will be presented and compared with predictions from the HESTIA simulations .
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. In this talk, I will present an overview of how 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...
Ultra-diffuse galaxies (UDGs) are spatially extended, low surface brightness stellar systems with regular elliptical-like morphology found in a wide range of environments. Studies of the internal dynamics and dark matter content of UDGs that would elucidate their formation and evolution have been hampered by their low surface brightnesses. We identified a sample of low-mass early-type...
In the coming decade, thousands of stellar streams will be observed in the halos of external galaxies with the Nancy Grace Roman Space Telescope, the Euclid Space Telescope, and the Vera C. Rubin Observatory. Stellar streams form when a dwarf galaxy or a cluster of stars is torn apart due to an underlying galactic potential, leaving behind a swath of thousands of stars that exhibit coherent,...
Understanding the mass assembly of galaxies is one of the big open questions in astronomy. A dynamical analysis of galaxies of the ATLAS3D survey provides new clues about the galaxy evolution process of galaxies as the sample comprises a good mix of fast and slow rotators with very different growing scenarios. Slow rotators are thought to accrete about 50 per cent of their stellar mass from...
Dwarf galaxies are regarded as the oldest and most numerous galaxy type in the Universe, responsible for the formation of the higher mass galaxies we see today. While we know a lot about the properties of dwarfs in the Local Group as well as selected nearby groups and clusters, our understanding of these galaxies beyond the Local Volume is comparatively poor. The properties probed by this...
It has long been speculated that Blue Compact Dwarf galaxies (BCDs) are formed through the interaction between low-mass gas-rich galaxies, but due to a lack of evidence, this possibility has rarely been explored. We study a sample of compact star-forming dwarf galaxies that are selected from a merging dwarf galaxy catalog. We present a detailed study of their spectroscopic and structural...
The number density of extragalactic 21-cm radio sources as a function of their spectral line-widths -- the HI width function (HI WF) -- is in principle a sensitive tracer of the dark matter halo mass function (HMF). The Λ cold dark matter model predicts that the HMF should be identical everywhere provided it is sampled in sufficiently large volumes, implying that the same should be true of the...
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. I will present the results of an unconventional, visualisation-driven analysis of 33 low-mass field galaxies from the APOSTLE suite of galaxy formation simulations exploring the limits of the validity of this assumption. Only...
Galaxy clusters are the largest gravitationally bound structures in the Universe. Numerical simulations provide detailed scenarios on how they assemble and evolve over the lifetime of the Universe, but observational evidences supporting these predictions are still elusive. Galaxy populations in nearby clusters are dominated by dwarf stellar systems, and the number of these galaxies continues...
In this talk I will review techniques and idiosyncrasies in building mass models of disk galaxies using cold gas dynamics. I will particularly focus on HI disks, which are generally more extended than stellar disks, so they allow tracing galaxy dynamics out to the most dark-matter-dominated regions. The combination of HI observations and near-infrared photometry, tracing the distribution of...
The gravitational interaction between dark matter (DM) and baryons has long been ignored when building galaxies semi-empirically and observationally. In this talk, I will show that the baryonic gravity leads to an adiabatic contraction of DM halos, ignoring which would result in the built galaxies that are not in a dynamic equilibrium and hence cannot exist in reality. We propose a new...
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 dwarf galaxies. We have used the stacked HI velocity...
One of the primary hurdles in pushing dark matter constraints to dwarf scales the uncertainty in the stellar-mass--halo-mass (SMHM) relation. Results from simulations differ by two orders of magnitude at halo masses < 10^10 solar masses, and none can match observations. Moreover, there is no consensus on the amount of scatter. To address these uncertainties, I used high-resolution...
Recent large photometric, astrometric, and spectroscopic surveys have enabled the first systematic observations of Milky Way stellar streams in 6D. At the same time, cutting edge cosmological simulations are now at resolutions that allow for the study of dwarf galaxy streams around Milky Way-like hosts. In this talk, I will present the discovery and characterization of a population of 6D...
The plane-of-satellites problem is one of the most severe small-scale challenges for the standard Λ cold dark matter (ΛCDM) cosmological model: Several dwarf galaxies around the Milky Way and Andromeda co-orbit in thin, planar structures. A similar case has been identified around the nearby elliptical galaxy Centaurus A (Cen A). We studied the satellite system of Cen A with line-of-sight...
The mass content of the Universe is dominated by non-baryonic dark matter, according to the Lambda Cold Dark Matter cosmology interpretation of observational evidence. However, not all observations agree with the theory and many predictions remain difficult to investigate. In particular, simulations predict that the shapes of the most massive dark matter haloes deviate from spherical symmetry....
Since the early 2000s satellite dwarf galaxies of the Local Group and more recently, the nearby Centaurus A/M83 group, have been known to show morphological characteristics and spatial distributions that do not match predictions from ΛCDM simulations. In particular, satellite dwarf galaxies inhabiting the Local Group and the Centaurus A/M83 group appear to be co-rotating in confined disks...
Cosmological simulations have been used to understand the formation of structure in the LCDM paradigm on small and large scales. Most simulations start with unconstrained Gaussian initial conditions, and therefore generically do not produce good analogues of the Local Group at present day. While constrained simulations exist, these have difficulty in precisely satisfying all our observational...
The satellite galaxy systems of the Milky Way (MW) and M31 both show a very thin kinematically coherent structure or satellite plane. It has previously been shown that each plane is in 3.55σ tension with ΛCDM expectations, which combined with the similar structure around Centaurus A falsifies the model at 5.3σ confidence. In this talk, I will present hydrodynamical simulations of the MW and...
The Fornax cluster provides an unparalleled opportunity to investigate the formation and evolution of early-type galaxies in a dense environment. Using the spectroscopic data from the Visible Multi-Object Spectrograph at Very Large Telescope (VLT/VIMOS) from the FVSS survey, we have kinematically characterised the photometrically detected globular cluster (GC) candidates in the core of the...
