The structure of the Milky Way's bar outside the bulge

Wegg, Christopher; Gerhard, Ortwin; Portail, Matthieu

doi:10.1093/mnras/stv745

Cited by 344 publications

(407 citation statements)

References 80 publications

(144 reference statements)

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“…Most estimates agree on a bar orientation 2 of φ b = 30 • ± 10 and a pattern speed of Ω b /Ω 0 = 1.9 ± 0.1, where Ω 0 is the local standard of rest (LSR) rotation rate. A drastically different bar pattern speed has recently been suggested by the longer bar half-length measured by Wegg et al (2015), compared to previous works -r b = 5.0 ± 0.2 kpc, which places the CR 2 See Fig. 2, second panel, for the definition of the bar angle.…”

Section: The Milky Way Bar and Spiralsmentioning

confidence: 65%

Constraining the Milky Way assembly history with Galactic Archaeology

Minchev

2016

Astron Nachr

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The aim of Galactic Archaeology is to recover the evolutionary history of the Milky Way from its present day kinematical and chemical state. Because stars move away from their birth sites, the current dynamical information alone is not sufficient for this task. The chemical composition of stellar atmospheres, on the other hand, is largely preserved over the stellar lifetime and, together with accurate ages, can be used to recover the birthplaces of stars currently found at the same Galactic radius. In addition to the availability of large stellar samples with accurate 6D kinematics and chemical abundance measurements, this requires detailed modeling with both dynamical and chemical evolution taken into account. An important first step is to understand the variety of dynamical processes that can take place in the Milky Way, including the perturbative effects of both internal (bar and spiral structure) and external (infalling satellites) agents. We discuss here (1) how to constrain the Galactic bar, spiral structure, and merging satellites by their effect on the local and global disc phase-space, (2) the effect of multiple patterns on the disc dynamics, and (3) the importance of radial migration and merger perturbations for the formation of the Galactic thick disc. Finally, we discuss the construction of Milky Way chemo-dynamical models and relate to observations.

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Section: The Milky Way Bar and Spiralsmentioning

confidence: 65%

Constraining the Milky Way assembly history with Galactic Archaeology

Minchev

2016

Astron Nachr

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“…Figure 10 shows the stars on the model of the Galactic bulge of Li & Shen et al (2012), who identified an X-shaped component in the bar/boxy bulge models of Shen et al (2010) that matched the stellar observations of McWilliam & Zoccali (2010). The Shen et al (2010) model was, in turn, tailored to reproduce the kinematic data of the Bulge Radial Velocity Assay (Howard et al 2008; see also Wegg et al 2015, their Fig. 1).…”

Section: Spatial Distributionmentioning

confidence: 90%

“…Finding these metal-poor stars and ascertaining their membership with the bulge is not only of interest for the sake of reconstructing the chemical evolution of the bulge, but also has important implications for studying the morphology of the bulge. Number counts of the red clump, which led to the discoveries of, for instance, bar, boxy and X-shaped substructures (e.g., McWilliam & Zoccali 2010;Wegg et al 2015) employed certain cuts in colour-magnitude space. However, a prominent population of metal-poor, thus bluer, stars can be missed by fixed colour criteria, which could lead to biased, reconstructed spatial structures.…”

Section: Introductionmentioning

confidence: 99%

Metal-poor stars towards the Galactic bulge: A population potpourri

Koch

McWilliam

Preston

et al. 2016

A&A

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We present a comprehensive chemical abundance analysis of five red giants and two horizontal branch (HB) stars towards the southern edge of the Galactic bulge, at (l, b) ∼ (0 • ,−11 • ). Based on high-resolution spectroscopy obtained with the Magellan/MIKE spectrograph, we derived up to 23 chemical element abundances and identify a mixed bag of stars, representing various populations in the central regions of the Galaxy. Although cosmological simulations predict that the inner Galaxy was host to the first stars in the Universe, we see no chemical evidence of the ensuing massive supernova explosions: all of our targets exhibit halo-like, solar [Sc/Fe] ratios, which is in contrast to the low values predicted from Population III nucleosynthesis. One of the targets is a CEMP-s star at [Fe/H] = −2.52 dex, and another target is a moderately metal-poor ([Fe/H] = −1.53 dex) CH star with strong enrichment in s-process elements (e.g., [Ba/Fe] = 1.35). These individuals provide the first contenders of these classes of stars towards the bulge. Four of the carbon-normal stars exhibit abundance patterns reminiscent of halo star across a metallicity range spanning −2.0 to −2.6 dex, i.e., enhanced α-elements and solar Fe-peak and neutron-capture elements, and the remaining one is a regular metal-rich bulge giant. The position, distance, and radial velocity of one of the metal-poor HB stars coincides with simulations of the old trailing arm of the disrupted Sagittarius dwarf galaxy. While their highly uncertain proper motions prohibit a clear kinematic separation, the stars' chemical abundances and distances suggest that these metal-poor candidates, albeit located towards the bulge, are not of the bulge, but rather inner halo stars on orbits that make them pass through the central regions. Thus, we caution similar claims of detections of metal-poor stars as true habitants of the bulge.

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“…This is possibly due to the fact that the bar has not grown quite as much as in the Milky Way. The bar in the model has a radius of ∼ 3 kpc , while the bar in the Milky Way extends to ∼ 4.5 − 5 kpc (Wegg et al 2015). The relatively high gas inflow rate to the centre of the model, with the attendant angular momentum transport and high star formation rate, is probably the source of this slow growth.…”

Section: Caveats About the Modelmentioning

confidence: 93%

Separation of stellar populations by an evolving bar: implications for the bulge of the Milky Way

Debattista

Ness

Gonzalez

et al. 2017

Monthly Notices of the Royal Astronomical Society

157

255

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We present a novel interpretation of the previously puzzling different behaviours of stellar populations of the Milky Way's bulge. We first show, by means of pure N -body simulations, that initially co-spatial stellar populations with different in-plane random motions separate when a bar forms. The radially cooler populations form a strong bar, and are vertically thin and peanut-shaped, while the hotter populations form a weaker bar and become a vertically thicker box. We demonstrate that it is the radial, not the vertical, velocity dispersion that dominates this evolution. Assuming that early stellar discs heat rapidly as they form, then both the in-plane and vertical random motions correlate with stellar age and chemistry, leading to different density distributions for metal-rich and metal-poor stars. We then use a high-resolution simulation, in which all stars form out of gas, to demonstrate that this is what happens. When we apply these results to the Milky Way we show that a very broad range of observed trends for ages, densities, kinematics and chemistries, that have been presented as evidence for contradictory paths to the formation of the bulge, are in fact consistent with a bulge which formed from a continuum of disc stellar populations which were kinematically separated by the bar. For the first time we are able to account for the bulge's main trends via a model in which the bulge formed largely in situ. Since the model is generic, we also predict the general appearance of stellar population maps of external edge-on galaxies.

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The structure of the Milky Way's bar outside the bulge

Cited by 344 publications

References 80 publications

Constraining the Milky Way assembly history with Galactic Archaeology

Constraining the Milky Way assembly history with Galactic Archaeology

Metal-poor stars towards the Galactic bulge: A population potpourri

Separation of stellar populations by an evolving bar: implications for the bulge of the Milky Way

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