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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…

Astrophysics of Galaxies · Physics 2022-03-14 Emma Dodd , Amina Helmi , Helmer H. Koppelman

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…

Astrophysics of Galaxies · Physics 2019-05-01 Helmer H. Koppelman , Amina Helmi , Davide Massari , Sebastian Roelenga , Ulrich Bastian

Stellar streams are particularly sensitive probes of the mass distribution of galaxies. In this work, we focus on the Helmi Streams, the remnants of an accreted dwarf galaxy orbiting the inner Milky Way. We examine in depth their peculiar…

Astrophysics of Galaxies · Physics 2024-11-20 Hanneke C. Woudenberg , Amina Helmi

We aim to determine unique features that characterise the past evolution of the progenitor of the Helmi streams through the analysis of star formation histories (SFHs). From the 5D {\it Gaia} EDR3 dataset, we extracted local samples of…

Astrophysics of Galaxies · Physics 2022-12-21 T. Ruiz-Lara , A. Helmi , C. Gallart , F. Surot , S. Cassisi

Stellar streams have proven to be powerful tools for measuring the Milky Way's gravitational potential and hence its dark matter halo. In the coming years, Vera Rubin, Euclid, ARRAKIHS, and NGRST will uncover a plethora of streams around…

Astrophysics of Galaxies · Physics 2024-02-22 Madison Walder , Denis Erkal , Michelle Collins , David Martinez-Delgado

The advent of Gaia's 2nd data release in combination with large spectroscopic surveys are revolutionizing our understanding of the Galaxy. Thanks to these and the knowledge accumulated thus far, a more mature picture of the evolution of the…

Astrophysics of Galaxies · Physics 2020-08-18 Amina Helmi

The phase-space structure of our Galaxy holds the key to understand and reconstruct its formation. The Lambda-CDM model predicts a richly structured phase-space distribution of dark matter and (halo) stars, consisting of streams of…

Astrophysics of Galaxies · Physics 2015-05-19 Rainer J. Klement

We study the formation of the Milky Way's halo in a $\Lambda$CDM cosmology by scaling down a high resolution simulation of the formation of a cluster of galaxies. We determine how much phase-space substructure is left over from the objects…

Astrophysics · Physics 2009-09-25 Amina Helmi , Simon D. M. White , Volker Springel

We analyse the dynamical properties of substructures in a high-resolution dark matter simulation of the formation of a Milky Way-like halo in a $\Lambda$CDM cosmology. Our goal is to shed light on the dynamical peculiarities of the Milky…

Astrophysics · Physics 2008-03-11 Yang-Shyang Li , Amina Helmi

Galactic rotation curves are often considered the first robust evidence for the existence of dark matter. However, even in the presence of a dark matter halo, other galactic-scale observations, such as the Baryonic Tully-Fisher Relation and…

Astrophysics of Galaxies · Physics 2019-10-23 Mariangela Lisanti , Matthew Moschella , Nadav Joseph Outmezguine , Oren Slone

The massive galaxies in the young universe, ten billion years ago, formed stars at surprising intensities. Although this is commonly attributed to violent mergers, the properties of many of these galaxies are incompatible with such events,…

In this contribution we discuss the expected properties of our halo if our Galaxy had been built from mergers of smaller systems. Using both analytic arguments and high-resolution simulations, we find that the Galactic halo in the Solar…

Astrophysics · Physics 2007-05-23 Amina Helmi

Dynamically cold stellar streams are ideal probes of the gravitational field of the Milky Way. This paper re-examines the question of how such streams might be used to test for the presence of "missing satellites" -the many thousands of…

Astrophysics of Galaxies · Physics 2015-05-20 Joo Heon Yoon , Kathryn V. Johnston , David W. Hogg

Stellar streams from disrupted globular clusters are excellent probes of dark matter (DM) subhalos. Observed Milky Way streams display a remarkable diversity of features: spurs, gaps, kinks, cocoons, and density variations, many attributed…

Simulations of tidal streams show that close encounters with dark matter subhalos induce density gaps and distortions in on-sky path along the streams. Accordingly, observing disrupted streams in the Galactic halo would substantiate the…

Astrophysics of Galaxies · Physics 2017-07-26 Emily Sandford , Andreas H. W. Kuepper , Kathryn V. Johnston , Juerg Diemand

Narrow stellar streams in the Milky Way halo are uniquely sensitive to dark-matter subhalos, but many of these subhalos may be tidally disrupted. I calculate the interaction between stellar and dark-matter streams using analytical and…

Astrophysics of Galaxies · Physics 2016-03-30 Jo Bovy

In the cold dark matter model of structure formation, galaxies are assembled hierarchically from mergers and the accretion of subclumps. This process is expected to leave residual substructure in the Galactic dark halo, including partially…

Astrophysics · Physics 2009-11-06 D. Stiff , L. M. Widrow , J. Frieman

Aiming at discriminating different gravitational potential models of the Milky Way, we perform tests based on the kinematic data powered by the Gaia DR2 astrometry, over a large range of $(R,z)$ locations. Invoking the complete form of…

Astrophysics of Galaxies · Physics 2022-12-07 Yongda Zhu , Hai-Xia Ma , Xiao-Bo Dong , Yang Huang , Tobias Mistele , Bo Peng , Qian Long , Tianqi Wang , Liang Chang , Xi Jin

The halo of the Milky Way galaxy hosts multiple dynamically coherent substructures known as stellar streams that are remnants of tidally disrupted systems such as globular clusters (GCs) and dwarf galaxies (DGs). A particular case is that…

Milgromian Dynamics (MOND) has been particularly successful in predicting scaling relations for galactic systems, namely the baryonic Tully-Fisher for spirals, the Faber-Jackson for ellipticals and the Radial Acceleration Relation for…

Cosmology and Nongalactic Astrophysics · Physics 2025-11-20 Nikolaos Samaras
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