Formation of the Galactic Stellar Halo. I. Structure and Kinematics

Bekki, Kenji

doi:10.1086/322300

Cited by 101 publications

(132 citation statements)

References 86 publications

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“…The relative lack of low-eccentricity orbits at these metallicities (see Sect. 5.7) may be due to our neglect of small-scale structure in the initial conditions; compare with Bekki & Chiba (2001). Fig.…”

Section: [Fe/h] < −1 9 ("Extreme Halo")mentioning

confidence: 83%

The formation of a disk galaxy within a growing dark halo

Samland

Gerhard

2003

A&A

126

153

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Abstract. We present a dynamical model for the formation and evolution of a massive disk galaxy, within a growing dark halo whose mass evolves according to cosmological simulations of structure formation. The galactic evolution is simulated with a new three-dimensional chemo-dynamical code, including dark matter, stars and a multi-phase ISM. The simulations start at redshift z = 4.85 with a small dark halo in a ΛCDM universe and we follow the evolution until the present epoch. The energy release by massive stars and supernovae prevents a rapid collapse of the baryonic matter and delays the maximum star formation until redshift z ≈ 1. The metal enrichment history in this model is broadly consistent with the evolution of [Zn/H] in damped Lyα systems. The galaxy forms radially from inside-out and vertically from halo to disk. As a function of metallicity, we have described a sequence of populations, reminiscent of the extreme halo, inner halo, metal-poor thick disk, thick disk, thin disk and inner bulge in the Milky Way. The first galactic component that forms is the halo, followed by the bulge, the disk-halo transition region, and the disk. At redshift z ≈ 1, a bar begins to form which later turns into a triaxial bulge. Despite the still idealized model, the final galaxy resembles present-day disk galaxies in many aspects. The bulge in the model consists of at least two stellar subpopulations, an early collapse population and a population that formed later in the bar. The initial metallicity gradients in the disk are later smoothed out by large scale gas motions induced by the bar. There is a pronounced deficiency of low-metallicity disk stars due to pre-enrichment of the disk ISM with metal-rich gas from the bulge and inner disk ("G-dwarf problem"). The mean rotation and the distribution of orbital eccentricities for all stars as a function of metallicity are not very different from those observed in the solar neighbourhood, showing that early homogeneous collapse models are oversimplified. The approach presented here provides a detailed description of the formation and evolution of an isolated disk galaxy in a ΛCDM universe, yielding new information about the kinematical and chemical history of the stars and the interstellar medium, but also about the evolution of the luminosity, the colours and the morphology of disk galaxies with redshift.

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Section: [Fe/h] < −1 9 ("Extreme Halo")mentioning

confidence: 83%

The formation of a disk galaxy within a growing dark halo

Samland

Gerhard

2003

A&A

126

153

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“…How important each of these contributions will be for a given galaxy must be driven by its size, environment and the stochastically governed individual hierarchical-merging history. Major attempts to follow these processes simultaneously have been carried out for giant ellipticals in a semianalytic model (Beasley et al 2003) and for the Milky Way in cosmological simulations (Bekki & Chiba 2001;Kravtsov & Gnedin 2005), but these are still exploratory and use prescriptive rules for star and cluster formation. However, syntheses of these approaches are developing (Bekki et al 2008), and hydrodynamic simulations of the important cases of GC formation in major mergers and in pre-galactic dwarfs are approaching the dynamical range required to resolve individual clusters (Bournaud et al 2008;Maschenko et al 2008).…”

Section: Data Versus Theory: Some Perspectivementioning

confidence: 99%

Massive star clusters in galaxies

Harris

2010

Phil. Trans. R. Soc. A.

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The ensemble of all star clusters in a galaxy constitutes its star cluster system. In this review, the focus of the discussion is on the ability of star clusters, particularly the systems of old massive globular clusters (GCs), to mark the early evolutionary history of galaxies. I review current themes and key findings in GC research, and highlight some of the outstanding questions that are emerging from recent work.

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“…Bekki & Chiba 2001;Scannapieco & Broadhurst 2001;Abadi et al 2006;Font et al 2006Font et al , 2011Tumlinson 2006;Salvadori et al 2007;Zolotov et al 2009;Brook et al 2012, to name a few), and provided different answers to the above question. According to some simulations (e.g.…”

Section: Introductionmentioning

confidence: 99%

Modeling the chemical evolution of the Galaxy halo

Brusadin¹,

Matteuccí

Romano

2013

A&A

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Context. The stellar halo provides precious information about the Galaxy in its early stages of evolution because the most metal-poor (oldest) stars in the Milky Way are found there. Aims. We study the chemical evolution and formation of the Galactic halo through the analysis of its stellar metallicity distribution function and some key elemental abundance patterns. We also test the effects of a possible Population III of zero-metal stars. Methods. Starting from the two-infall model for the Galaxy, which predicts too few low-metallicity stars, we added a gas outflow during the halo phase with a rate proportional to the star formation rate through a free parameter, λ. In addition, we considered a first generation of massive zero-metal stars in this two-infall + outflow model, adopting two different top-heavy initial mass functions and specific Population III yields. Results. The metallicity distribution function of halo stars as predicted from the two-infall + outflow model agrees well with observations when the parameter λ = 14 and the time scale for the first infall, out of which the halo formed, is not longer than 0.2 Gyr, a lower value than suggested previously. Moreover, the abundance patterns [X/Fe] vs. [Fe/H] for C, N, and α-elements O, Mg, Si, S, and Ca agree well with the observational data, as in the case of the two-infall model without outflow. If Population III stars are included, under the assumption of different initial mass functions, the overall agreement of the predicted stellar metallicity distribution function with observational data is poorer than in the case of the two-infall + outflow model without Population III. Conclusions. We conclude that it is fundamental to include both a gas infall and outflow during the halo formation to explain the observed halo metallicity distribution function in the framework of a model assuming that the stars in the inner halo formed mostly in situ. Moreover, we find that there is no satisfactory initial mass function for Population III stars that reproduces the observed halo metallicity distribution function. As a consequence, there is no need for a first generation of only massive stars to explain the evolution of the Galactic halo.

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Formation of the Galactic Stellar Halo. I. Structure and Kinematics

Cited by 101 publications

References 86 publications

The formation of a disk galaxy within a growing dark halo

The formation of a disk galaxy within a growing dark halo

Massive star clusters in galaxies

Modeling the chemical evolution of the Galaxy halo

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