The stellar halo of the Galaxy

By A. Helmi. 2008

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Stellar halos may hold some of the best preserved fossils of the formation history of galaxies. They are a natural product of the merging processes that probably take place during the assembly of a galaxy, and hence may well be the most ubiquitous component of galaxies, independently of their Hubble type. This review focuses on our current understanding of the spatial structure, the kinematics and chemistry of halo stars in the Milky Way. In recent years, we have experienced a change in paradigm thanks to the discovery of large amounts of substructure, especially in the outer halo. I discuss the implications of the currently available observational constraints and fold them into several possible formation scenarios. Unraveling the formation of the Galactic halo will be possible in the near future through a combination of large wide field photometric and spectroscopic surveys, and especially in the era of Gaia.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/ed3442df88cba64d69de0c2ba5ee1fe327f92252

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Citations in the corpus

Using chemical tagging to redefine the interface of the Galactic disc and halo (2015, methodology): “It is spatially defined by a power-law with an index of approximately – 3.5 (e.g. Helmi 2008).”
METALLICITY EVOLUTION OF DAMPED Lyα SYSTEMS OUT TO z ∼ 5 (2012, background): “There are two primary formation scenarios for the Galactic halo stars (for a more thorough review, see Helmi (2008)).”
The GALAH survey: observational overview and Gaia DR1 companion (2016, background): “In particular, spectroscopic stellar surveys are revolutionising our understanding of Galactic structure and evolution (e.g., Helmi 2008; Rix & Bovy 2013; Hayden et al. 2014; Hayden et al. 2015; Martig et al. 2016).”
Multiple populations in globular clusters (2012, background): “4.3 Density distribution The radial distribution of halo globular clusters matches well the distribution of halo stars (Brodie & Strader 2006; Baumgardt et al. 2008; Helmi 2008).”
The GALAH survey: scientific motivation (2015, background): “It hosts some of the oldest Galactic stellar populations and is dynamically and chemically very different from the rest of the (stellar) Galaxy (Helmi 2008).”
Evidence for an Intermediate-mass Milky Way from Gaia DR2 Halo Globular Cluster Motions (2018, background): “The final component, the halo, is dominated by dark matter (DM) – only a few percent of the mass of the halo is baryonic (Helmi 2008), the exact percentage depends on the unknown total mass of DM in the halo – and it is our inability to see DM directly that gives rise to our present uncertainty in…”
KINEMATICS OF THE STELLAR HALO AND THE MASS DISTRIBUTION OF THE MILKY WAY USING BLUE HORIZONTAL BRANCH STARS (2012, background): “INTRODUCTION Understanding the formation of stellar halos gives vital insight into the formation history and the evolution of galaxies (Majewski 1993; Freeman & Bland-Hawthorn 2002; Helmi 2008).”
OXYGEN ABUNDANCES IN NEARBY FGK STARS AND THE GALACTIC CHEMICAL EVOLUTION OF THE LOCAL DISK AND HALO (2013, background): “Observations of halo streams and tidal debris heavily support the idea of early mergers (e.g., Helmi 2008; Klement 2010; Majewski et al. 2012).”
The Galaxy and its stellar halo: insights on their formation from a hybrid cosmological approach (2008, background): “The origin and structure of the stellar halo has been studied by several authors, using a variety of techniques (for a review, see Helmi 2008).”
Gaia FGK benchmark stars: Metallicity (2013, background): “Similarly, much of our knowledge about the Milky Way halo comes from these kind of studies (see review of Helmi 2008).”
Hunting for the Dark Matter Wake Induced by the Large Magellanic Cloud (2019, background): “Ultimately, the phase space information of halo tracers can inform us about the underlying DM potential, the total mass, and the accretion history of the MW (Johnston et al. 2008; Helmi 2008; Gómez et al. 2010; Carlin et al. 2016).”
THE GHOSTS SURVEY. I. HUBBLE SPACE TELESCOPE ADVANCED CAMERA FOR SURVEYS DATA (2011, background): “Galaxy halos therefore provide an unfettered view of early star formation in the universe as well as the merger history of the host system (e.g., Searle & Zinn 1978; Johnston et al. 1996; Helmi & White 1999; Bullock et al. 2001; Helmi 2008).”
Galactic stellar haloes in the CDM model (2009, methodology): “Our approach has similarities with that of De Lucia & Helmi (2008), who tag the most bound 10 per cent of particles in satellite haloes with stars.”
THE MILKY WAY TOMOGRAPHY WITH SDSS. III. STELLAR KINEMATICS (2009, background): “Of course, answers to a number of these questions are known to some extent (for excellent reviews, see Gilmore et al. 1989; Majewski 1993; Helmi 2008, for context and references, see also the first two papers in this series).”
The Galaxy in Context: Structural, Kinematic, and Integrated Properties (2016, methodology): “Previous reviews on this subject have been written by Helmi (2008), De Lucia (2012), Belokurov et al. (2013).”