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Abstract The Galactic bulge is critical to our understanding of the Milky Way. However, due to the lack of reliable stellar distances, the structure and kinematics of the bulge/bar beyond the Galactic center have remained largely unexplored. Here, we present a method to measure distances of luminous red giants using a period–amplitude–luminosity relation anchored to the Large Magellanic Cloud, with random uncertainties of 10%–15% and systematic errors below 1%–2%. We apply this method to data from the Optical Gravitational Lensing Experiment to measure distances to 190,302 stars in the Galactic bulge and beyond out to 20 kpc. Using this sample, we measure a distance to the Galactic center ofR0= 8108 ± 106stat± 93syspc, consistent with direct measurements of stars orbiting Sgr A*. We cross-match our distance catalog with Gaia DR3 and use the subset of 39,566 overlapping stars to provide the first constraints on the Milky Way’s velocity field (VR,Vϕ,Vz) beyond the Galactic center. We show that theVRquadrupole from the bar’s near side is reflected with respect to the Galactic center, indicating that the bar is bisymmetric and aligned with the inner disk. We also find that the vertical heightVZmap has no major structure in the region of the Galactic bulge, which is inconsistent with a current episode of bar buckling. Finally, we demonstrate withN-body simulations that distance uncertainty plays a factor in the alignment of the major and kinematic axes of the bar, necessitating caution when interpreting results for distant stars.
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Snails across Scales: Local and Global Phase-mixing Structures as Probes of the Past and Future Milky Way
Abstract Signatures of vertical disequilibrium have been observed across the Milky Way’s (MW’s) disk. These signatures manifest locally as unmixed phase spirals inz–vzspace (“snails-in-phase”), and globally as nonzero meanzandvz, wrapping around the disk into physical spirals in thex–yplane (“snails-in-space”). We explore the connection between these local and global spirals through the example of a satellite perturbing a test-particle MW-like disk. We anticipate our results to broadly apply to any vertical perturbation. Using az–vzasymmetry metric, we demonstrate that in test-particle simulations: (a) multiple local phase-spiral morphologies appear when stars are binned by azimuthal actionJϕ, excited by a single event (in our case, a satellite disk crossing); (b) these distinct phase spirals are traced back to distinct disk locations; and (c) they are excited at distinct times. Thus, local phase spirals offer a global view of the MW’s perturbation history from multiple perspectives. Using a toy model for a Sagittarius (Sgr)–like satellite crossing the disk, we show that the full interaction takes place on timescales comparable to orbital periods of disk stars withinR≲ 10 kpc. Hence such perturbations have widespread influence, which peaks in distinct regions of the disk at different times. This leads us to examine the ongoing MW–Sgr interaction. While Sgr has not yet crossed the disk (currently,zSgr≈ −6 kpc,vz,Sgr≈ 210 km s−1), we demonstrate that the peak of the impact has already passed. Sgr’s pull over the past 150 Myr creates a globalvzsignature with amplitude ∝MSgr, which might be detectable in future spectroscopic surveys.
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- Award ID(s):
- 1715582
- PAR ID:
- 10364541
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 928
- Issue:
- 1
- ISSN:
- 0004-637X
- Format(s):
- Medium: X Size: Article No. 80
- Size(s):
- Article No. 80
- Sponsoring Org:
- National Science Foundation
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