Formation, vertex deviation, and age of the Milky Way’s bulge: input from a cosmological simulation with a late-forming bar

Debattista, Victor P.; Gonzalez, O. A.; Sanderson, Robyn E.; El-Badry, Kareem; Garrison-Kimmel, Shea; Wetzel, Andrew; Faucher-Giguère, Claude André; Hopkins, Philip F.

doi:10.1093/mnras/stz746

Cited by 45 publications

(38 citation statements)

References 97 publications

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“…the X-shape, is observed to be pronounced in metal-rich stars and weak or absent in the metal-poor ones (Ness et al 2012;Uttenthaler et al 2012;Rojas-Arriagada et al 2014). Secondly, but related to this, self-consistent chemo-hydrodynamical simulations (Debattista et al 2017(Debattista et al , 2019Athanassoula et al 2017) have predicted more pinched metallicity distributions than the density itself when viewed edge-on; this distribution has been confirmed in real galaxies (Gonzalez et al 2017). This trend is the equivalent of the metallicity dependence of the Xshape, generalised to external galaxies.…”

Section: Stellar Population Modellingmentioning

confidence: 54%

“…The resulting X-shape is better traced by the metal-rich populations, as observed. They also showed that as a consequence the metallicity distribution is more peanut-shaped than the density itself (see also Athanassoula et al 2017;Buck et al 2018;Debattista et al 2019). Such a metallicity distribution has been confirmed in the edge-on galaxy NGC 4710, which hosts a B/P bulge (Gonzalez et al 2017).…”

Section: Insights From Bulge Chemistrymentioning

confidence: 86%

“…It seems implausible that galaxies often find themselves in a state so unstable that a substantial reorganisation of their states begins immediately, and with vigour. Indeed simulations that include gas find bars forming more slowly and buckling much more gently (Berentzen et al 1998;Debattista et al 2017), even in a cosmological context (Debattista et al 2019). The consequent energy redistribution that must occur is probably milder.…”

Section: A Statistical Mechanical Viewmentioning

confidence: 99%

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Box/peanut-shaped bulges in action space

Debattista

Liddicott

Khachaturyants

et al. 2020

Monthly Notices of the Royal Astronomical Society

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We introduce the study of box/peanut (B/P) bulges in the action space of the initial axisymmetric system. We explore where populations with different actions end up once a bar forms and a B/P bulge develops. We find that the density bimodality due to the B/P bulge (the X-shape) is better traced by populations with low radial, $\rm J_{R,0}$, or vertical, $\rm J_{z,0}$, actions, or high azimuthal action, $\rm J_{\phi ,0}$. Generally populations separated by $\rm J_{R,0}$ have a greater variation in bar strength and vertical heating than those separated by $\rm J_{z,0}$. While the bar substantially weakens the initial vertical gradient of $\rm J_{z,0}$, it also drives a strikingly monotonic vertical profile of $\rm J_{R,0}$. We then use these results to guide us in assigning metallicity to star particles in a pure N-body model. Because stellar metallicity in unbarred galaxies depends on age as well as radial and vertical positions, the initial actions are particularly well suited for assigning metallicities. We argue that assigning metallicities based on single actions, or on positions, results in metallicity distributions inconsistent with those observed in real galaxies. We therefore use all three actions to assign metallicity to an N-body model by comparing with the actions of a star-forming, unbarred simulation. The resulting metallicity distribution is pinched on the vertical axis, has a realistic vertical gradient and has a stronger X-shape in metal-rich populations, as found in real galaxies.

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Section: Stellar Population Modellingmentioning

confidence: 54%

Section: Insights From Bulge Chemistrymentioning

confidence: 86%

Section: A Statistical Mechanical Viewmentioning

confidence: 99%

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Box/peanut-shaped bulges in action space

Debattista

Liddicott

Khachaturyants

et al. 2020

Monthly Notices of the Royal Astronomical Society

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“…Interestingly, none of the galaxies here exhibit the ring structures, presumed to be long-lived, seen by studies of the central regions of other spiral galaxies and the MW CMZ (Kormendy & Kennicutt 2004;Molinari et al 2011). We note the lack of strong bars in the centers of any of these FIRE galaxies at this time (m12m did develop a strong bar around z ≈ 0.2, but it does not survive to z = 0; Debattista et al 2019); without the presence of bars in these simulations at z = 0, we cannot speak to the dynamical importance of bars in producing central galactic environments similar to the MW CMZ. Other work has highlighted the potential impacts of bars in funneling gas core-ward and forming rings (Sormani et al 2015(Sormani et al , 2018.…”

Section: Two Morphological Classes Of Fire-cmzsmentioning

confidence: 46%

Fiery Cores: Bursty and Smooth Star Formation Distributions across Galaxy Centers in Cosmological Zoom-in Simulations

Orr

Hatchfield

Battersby

et al. 2021

ApJL

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We present an analysis of the R  1.5 kpc core regions of seven simulated Milky Way-mass galaxies, from the FIRE-2 (Feedback in Realistic Environments) cosmological zoom-in simulation suite, for a finely sampled period (Δt = 2.2 Myr) of 22 Myr at z ≈ 0, and compare them with star formation rate (SFR) and gas surface density observations of the Milky Way's Central Molecular Zone (CMZ). Despite not being tuned to reproduce the detailed structure of the CMZ, we find that four of these galaxies are consistent with CMZ observations at some point during this 22 Myr period. The galaxies presented here are not homogeneous in their central structures, roughly dividing into two morphological classes; (a) several of the galaxies have very asymmetric gas and SFR distributions, with intense (compact) starbursts occurring over a period of roughly 10 Myr, and structures on highly eccentric orbits through the CMZ, whereas (b) others have smoother gas and SFR distributions, with only slowly varying SFRs over the period analyzed. In class (a) centers, the orbital motion of gas and star-forming complexes across small apertures (R  150 pc, analogously |l| < 1°in the CMZ observations) contributes as much to tracers of star formation/dense gas appearing in those apertures, as the internal evolution of those structures does. These asymmetric/bursty galactic centers can simultaneously match CMZ gas and SFR observations, demonstrating that time-varying star formation can explain the CMZ's low star formation efficiency.

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“…In many cases, authors assume a certain initial metallicity distribution and test the impact of the further secular evolution (e.g., Martel et al 2013;Martinez-Valpuesta & Gerhard 2013;Di Matteo et al 2013). The alternative approach is to trace stellar populations in hydrodynamical simulations with star formation and feedback (e.g., Grand et al 2016;Debattista et al 2017Debattista et al , 2019Tissera et al 2016Tissera et al , 2017Tissera et al , 2019Taylor & Kobayashi 2017).…”

Section: Origins Of the Spatial Trendsmentioning

confidence: 99%

Unravelling stellar populations in the Andromeda Galaxy

Gajda

Gerhard

Blaña

et al. 2021

A&A

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To understand the history and formation mechanisms of galaxies, it is crucial to determine their current multidimensional structure. In this work, we focus on the properties that characterise stellar populations, such as metallicity and [α/Fe] enhancement. We devised a new technique to recover the distribution of these parameters using spatially resolved, line-of-sight averaged data. Our chemodynamical method is based on the made-to-measure framework and results in an N-body model for the abundance distribution. Following a test on a mock data set we found that the radial and azimuthal profiles were well-recovered, however, only the overall shape of the vertical profile matches the true profile. We applied our procedure to spatially resolved maps of mean [Z/H] and [α/Fe] for the Andromeda Galaxy, using an earlier barred dynamical model of M 31. We find that the metallicity is enhanced along the bar, with a possible maxima at the ansae. In the edge-on view, the [Z/H] distribution has an X shape due to the boxy/peanut bulge; the average vertical metallicity gradient is equal to −0.133 ± 0.006 dex kpc−1. We identify a metallicity-enhanced ring around the bar, which also has relatively lower [α/Fe]. The highest [α/Fe] is found in the centre, due to the classical bulge. Away from the centre, the α-overabundance in the bar region increases with height, which could be an indication of a thick disc. We argue that the galaxy assembly resulted in a sharp peak of metallicity in the central few hundred parsecs and a more gentle negative gradient in the remaining disc, but no [α/Fe] gradient. The formation of the bar leads to the re-arrangement of the [Z/H] distribution, causing a flat gradient along the bar. Subsequent star formation close to the bar ends may have produced the metallicity enhancements at the ansae and the [Z/H] enhanced lower-α ring.

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Formation, vertex deviation, and age of the Milky Way’s bulge: input from a cosmological simulation with a late-forming bar

Cited by 45 publications

References 97 publications

Box/peanut-shaped bulges in action space

Box/peanut-shaped bulges in action space

Fiery Cores: Bursty and Smooth Star Formation Distributions across Galaxy Centers in Cosmological Zoom-in Simulations

Unravelling stellar populations in the Andromeda Galaxy

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