The Galactic Bulge

Barbuy, B.

doi:10.1017/pasa.2016.20

Cited by 2 publications

(2 citation statements)

References 32 publications

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“…These seemingly contradictory properties have lent support to a hybrid scenario for the MW bulge, in which the metal-rich stellar populations are part of the b/p, formed from disc material, while the metal-poor populations constitute a separate dispersion-dominated, spheroidal, classi-cal bulge component (e.g. see Babusiaux et al 2010;Rojas-Arriagada et al 2014;Barbuy 2016;Barbuy et al 2018 and references therein).…”

mentioning

confidence: 99%

Chemodynamics of barred galaxies in cosmological simulations: On the Milky Way’s quiescent merger history and in-situ bulge

Fragkoudi

Grand

Pakmor

et al. 2020

Monthly Notices of the Royal Astronomical Society

129

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We explore the chemodynamical properties of a sample of barred galaxies in the Auriga magnetohydrodynamical cosmological zoom-in simulations, which form boxy/peanut (b/p) bulges, and compare these to the Milky Way (MW). We show that the Auriga galaxies which best reproduce the chemodynamical properties of stellar populations in the MW bulge have quiescent merger histories since redshift z ∼ 3.5: their last major merger occurs at $t_{\rm lookback}\gt 12\, \rm Gyr$, while subsequent mergers have a stellar mass ratio of ≤1:20, suggesting an upper limit of a few per cent for the mass ratio of the recently proposed Gaia Sausage/Enceladus merger. These Auriga MW-analogues have a negligible fraction of ex-situ stars in the b/p region ($\lt 1{{\ \rm per\ cent}}$), with flattened, thick disc-like metal-poor stellar populations. The average fraction of ex-situ stars in the central regions of all Auriga galaxies with b/p’s is 3 per cent – significantly lower than in those which do not host a b/p or a bar. While the central regions of these barred galaxies contain the oldest populations, they also have stars younger than 5 Gyr (>30 per cent) and exhibit X-shaped age and abundance distributions. Examining the discs in our sample, we find that in some cases a star-forming ring forms around the bar, which alters the metallicity of the inner regions of the galaxy. Further out in the disc, bar-induced resonances lead to metal-rich ridges in the Vϕ − r plane – the longest of which is due to the Outer Lindblad Resonance. Our results suggest the Milky Way has an uncommonly quiet merger history, which leads to an essentially in-situ bulge, and highlight the significant effects the bar can have on the surrounding disc.

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mentioning

confidence: 99%

Chemodynamics of barred galaxies in cosmological simulations: On the Milky Way’s quiescent merger history and in-situ bulge

Fragkoudi

Grand

Pakmor

et al. 2020

Monthly Notices of the Royal Astronomical Society

129

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“…6 and 8 is that the GCs appear to follow the RRab distribution rather than the more concentrated distribution of RC in the outer region. Regretfully, there are very few GCs, and their sample is incomplete in the inner bulge (Ivanov et al 2005(Ivanov et al , 2017Borissova et al 2014;Barbuy 2016;Minniti et al 2017). Therefore, RCs become more suitable comparison targets as they are very numerous in the regions explored here.…”

Section: Comparison With Red Clump Giants and Globular Clustersmentioning

confidence: 99%

The RR Lyrae projected density distribution from the Galactic centre to the halo

Navarro

Minniti

Capuzzo-Dolcetta

et al. 2021

A&A

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The projected density distribution of type ab RR Lyrae (RRab) stars was characterised from the innermost regions of the Milky Way to the halo, with the aim of placing constraints on the Galaxy’s evolution. The compiled sample (NRRab = 64 850) stems from fundamental mode RR Lyrae variables identified by the VVV, OGLE, and Gaia surveys. The distribution is well fitted by three power laws over three radial intervals. In the innermost region (R < 2.2°) the distribution follows ΣRRab[1] ∝ R−0.94 ± 0.051, while in the external region the distribution adheres to ΣRRab[2] ∝ R−1.50 ± 0.019 for 2.2° < R < 8.0° and ΣRRab[3] ∝ R−2.43 ± 0.043 for 8.0° < R < 30.0°. Conversely, the cumulative distribution of red clump (RC) giants exhibits a more concentrated distribution in the mean, but in the central R < 2.2° the RRab population is more peaked, whereas globular clusters (GCs) follow a density power law (ΣGCs ∝ R−1.59 ± 0.060 for R < 30.0°) similar to that of RRab stars, especially when considering a more metal-poor subsample ([Fe/H] < −1.1 dex). The main conclusion emerging from the analysis is that the RRab distribution favours the star cluster infall and merger scenario for creating an important fraction (> 18%) of the central Galactic region. The radii containing half of the populations (half populations radii) are RH RRab = 6.8° (0.99 kpc), RH RC = 4.2° (0.61 kpc), and RH GCs = 11.9° (1.75 kpc) for the RRab stars, RC giants, and GCs, respectively. Finally, merely ∼1% of the stars have been actually discovered in the innermost region (R < 35 pc) out of the expected (based on our considerations) total number of RRab therein: N ∼ 1562. That deficit will be substantially ameliorated with future space missions like the Nancy Grace Roman Space Telescope (formerly WFIRST).

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The Galactic Bulge

Cited by 2 publications

References 32 publications

Chemodynamics of barred galaxies in cosmological simulations: On the Milky Way’s quiescent merger history and in-situ bulge

Chemodynamics of barred galaxies in cosmological simulations: On the Milky Way’s quiescent merger history and in-situ bulge

The RR Lyrae projected density distribution from the Galactic centre to the halo

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