Related papers: Was the Andromeda Stream Produced by a Disk Galaxy…
Thanks to modern sky surveys, over twenty stellar streams and overdensity structures have been discovered in the halo of the Milky Way. In this paper, we present an analysis of spectroscopic observations of individual stars from one such…
Recent observations have shown that the majority of the Andromeda galaxy's satellites are aligned in a thin plane. On the theoretical side it has been proposed that galaxies acquire their gas via cold streams. In addition, numerical…
We present the first results from our survey of stellar substructure in the outskirts of M31 using the Advanced Camera for Surveys (ACS) on board the Hubble Space Telescope. We discuss the stellar populations associated with five prominent…
The local stellar halo of the Milky Way contains the debris from several past accretion events. Here we study in detail the structure and properties of nearby debris associated with the Helmi streams, originally identified as an overdensity…
We present a quantitative measurement of the amount of clustering present in the inner $\sim30$ kpc of the stellar halo of the Andromeda galaxy (M31). For this we analyse the angular positions and radial velocities of the carefully selected…
Stars aligned in thin stream-like features (feathers), with widths of $\delta\sim1-10^{\circ}$ and lengths as large as $\Delta l\sim180^{\circ}$, have been observed towards the Anticenter of our Galaxy and their properties mapped in…
The Milky Way and Andromeda must have formed through an initial epoch of sub-structure merging. As a result of fundamental physical conservation laws tidal-dwarf galaxies (TDGs) have likely been produced. Here we show that such TDGs appear,…
Stars are born in a variety of environments that determine how they gather gas to achieve their final masses. It is generally believed that disks are ubiquitous around protostars as a result of angular momentum conservation and are natural…
Recent maps of the halo using RR Lyrae from Pan-STARRS1 have clearly depicted the spatial structure of the Sagittarius stream. These maps show the leading and trailing stream apocenters differ in galactocentric radius by a factor of two,…
An all high-latitude sky survey for cool carbon giant stars in the Galactic halo has revealed 75 such stars, of which the majority are new detections. Of these, more than half are clustered on a Great Circle on the sky which intersects the…
Growing observational evidence suggests that Class II protoplanetary disks may undergo substantial interactions with their environment in the form of late infall. This mass inflow predominantly manifests itself in the form of so-called…
The origins of most stellar streams in the Milky Way are unknown. With improved proper motions provided by Gaia EDR3, we show that the orbits of 23 Galactic stellar streams are highly clustered in orbital phase space. Based on their…
The Andromeda galaxy (M31) is the most nearby giant spiral galaxy, an opportunity to study with high resolution dynamical phenomena occurring in nuclear disks and bulges, able to explain star formation quenching, and galaxy evolution…
We study numerical simulations of satellite galaxy disruption in a potential resembling that of the Milky Way. Our goal is to assess whether a merger origin for the stellar halo would leave observable fossil structure in the phase-space…
Flat rotation curves v(r) are naturally explained by elongated (prolate) Dark Matter (DM) distributions, and we have provided competitive fits to the SPARC database. To further probe the geometry of the halo one needs out-of-plane…
Using the 100-m radio telescope at Effelsberg, we mapped a large area around the Andromeda Galaxy in the 21-cm line emission of neutral hydrogen to search for high-velocity clouds (HVCs) out to large projected distances in excess of 100…
Cold or Warm, the Dark Matter substructure spectrum must extend to objects with masses as low as $10^7 M_\odot$, according to the most recent Lyman-$\alpha$ measurements. Around a Milky Way-like galaxy, more than a thousand of these…
The recently discovered C-19 stellar stream is a collection of kinematically associated metal-poor stars in the halo of the Milky Way lacking an obvious progenitor. The stream spans an arc of ~15 degrees in the sky, and orbit-fitting…
The halo of the Milky Way has long been hypothesized to harbour significant amounts of merger debris. This view has been supported over more than a decade by wide-field photometric surveys which have revealed the outer halo to be lumpy. The…
The recently discovered, ring-like structure just outside the Galactic disk in Monoceros is detected and traced among 2MASS M giant stars. We have developed a method to recover the signature of this structure from the distance probability…