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One of the generic predictions of modern cosmological models is that large galaxies should have experienced many mergers with smaller galaxies at some point in their past. Debris from such encounters will leave spatially distinct…

Astrophysics · Physics 2007-05-23 James E. Taylor

Aims. Several kinematic and chemical substructures have been recently found amongst Milky Way halo stars with retrograde motions. It is currently unclear how these various structures are related to each other. This Letter aims to shed light…

Astrophysics of Galaxies · Physics 2019-11-13 Helmer H. Koppelman , Amina Helmi , Davide Massari , Adrian M. Price-Whelan , Tjitske K. Starkenburg

We use the Bullock & Johnston suite of simulations to study the density profiles of L*-type galaxy stellar haloes. Observations of the Milky Way and M31 stellar haloes show contrasting results: the Milky Way has a `broken' profile, where…

Astrophysics of Galaxies · Physics 2015-06-11 A. J. Deason , V. Belokurov , N. W. Evans , K. V. Johnston

The Milky Way (MW) stellar halo, containing debris from past accretion events, serves as a fossil record of hierarchical mass assembly. Due to their distinct properties, RR Lyrae stars (RRLs) serve as excellent tracers for identifying and…

Astrophysics of Galaxies · Physics 2026-04-29 T. Muraveva , L. Monti , D. Massari , M. De Leo , A. Garofalo , G. Clementini , E. Ceccarelli , U. Michelucci

In the Milky Way, recent progress in the exploration of its assembly history is driven by the tremendous amount of high-quality data delivered by Gaia, which has revealed a number of substructures potentially linked to several ancient…

This paper explores the mapping between the observable properties of a stellar halo in phase- and abundance-space and the parent galaxy's accretion history in terms of the characteristic epoch of accretion and mass and orbits of progenitor…

We combine the Siding Spring Survey of RR Lyrae stars with the Southern Proper Motion Catalog 4, in order to detect and kinematically characterize overdensities in the inner halo of the Milky Way. We identify one such overdensity above the…

Astrophysics of Galaxies · Physics 2015-09-09 D. I. Casetti-Dinescu , D. A. Nusdeo , T. M. Girard , V. I. Korchagin , W. F. van Altena

The Milky Way halo was predominantly formed by the merging of numerous progenitor galaxies. However, our knowledge of this process is still incomplete, especially in regard to the total number of mergers, their global dynamical properties…

An analytical model predicting the growth rates, the absolute growth times and the saturation values of the magnetic field strength within galactic haloes is presented. The analytical results are compared to cosmological MHD simulations of…

Cosmology and Nongalactic Astrophysics · Physics 2015-06-04 Alexander M. Beck , Harald Lesch , Klaus Dolag , Hanna Kotarba , Annette Geng , Federico A. Stasyszyn

We present low frequency observations at $315$ and $745$ MHz from the upgraded Giant Metrewave Radio Telescope (uGMRT) of the edge-on, nearby galaxy NGC $4631$. We compare the observed surface brightness profiles along the minor axis of the…

Astrophysics of Galaxies · Physics 2022-02-09 Aditi Vijayan , K. S. Dwarakanath , Biman B. Nath , Ruta Kale

Iorio et al. (2018) mapped out the Milky Way halo using a sample of RR Lyrae stars drawn from a cross-match of Gaia with 2MASS. We investigate the significant residual in their model which we constrain to lie at Galactocentric radii…

Astrophysics of Galaxies · Physics 2018-11-28 D. Boubert , V. Belokurov , D. Erkal , G. Iorio

Our Galaxy is thought to have undergone an active evolutionary history dominated by star formation, the accretion of cold gas, and, in particular, mergers up to 10 gigayear ago. The stellar halo reveals rich fossil evidence of these…

The Milky Way's (MW) inner stellar halo contains an [Fe/H]-rich component with highly eccentric orbits, often referred to as the "last major merger." Hypotheses for the origin of this component include Gaia-Sausage/Enceladus (GSE), where…

Astrophysics of Galaxies · Physics 2024-05-09 Thomas Donlon , Heidi Jo Newberg , Robyn Sanderson , Emily Bregou , Danny Horta , Arpit Arora , Nondh Panithanpaisal

With the use of a detailed Milky Way nonaxisymmetric potential, observationally and dynamically constrained, the effects of the bar and the spiral arms in the Galaxy are studied in the disc and in the stellar halo. Especially the trapping…

Astrophysics of Galaxies · Physics 2016-10-31 Edmundo Moreno , Barbara Pichardo , William Schuster

Many of the Milky Way's accreted substructures have been discovered and studied in the space of energy $E$, and angular momentum components $L_z$ and $L_{\bot}$. In a static axisymmetric system, these quantities are (reasonable…

Astrophysics of Galaxies · Physics 2025-08-27 Hanneke C. Woudenberg , Amina Helmi

Longitude-velocity (l-V) diagrams of H I and CO gas in the inner Milky Way have long been known to be inconsistent with circular motion in an axisymmetric potential. Several lines of evidence suggest that the Galaxy is barred, and gas flow…

Astrophysics · Physics 2008-11-26 Benjamin J. Weiner , J. A. Sellwood

We continue our series of papers on phase-space distributions of stars in the Milky Way based on photometrically derived metallicities and Gaia astrometry, with a focus on the halo-disk interface in the local volume. To exploit various…

Astrophysics of Galaxies · Physics 2023-07-26 Deokkeun An , Timothy C. Beers , Young Sun Lee , Thomas Masseron

The assembly process of our Galaxy can be retrieved using the motions and chemistry of individual stars. Chemo-dynamical studies of the nearby halo have long hinted at the presence of multiple components such as streams, clumps, duality and…

Astrophysics of Galaxies · Physics 2018-11-14 Amina Helmi , Carine Babusiaux , Helmer H. Koppelman , Davide Massari , Jovan Veljanoski , Anthony G. A. Brown

Fast radio bursts offer the opportunity to place new constraints on the mass and density profile of hot and ionized gas in galactic haloes. We test here the X-ray emission and dispersion measure predicted by different gas profiles for the…

Astrophysics of Galaxies · Physics 2020-06-03 Laura C. Keating , Ue-Li Pen