The echo of the bar buckling: Phase-space spirals in Gaia Data Release 2

We present a high-resolution numerical study of the phase-space diversity in an isolated Milky Way-type galaxy. Using a single N-body simulation (N ≈ 0.14 × 109) we explore the formation, evolution, and spatial variation of the phase-space spirals similar to those recently discovered by Antoja et al. in the Milky Way disk with Gaia Data Release 2 (DR2). For the first time in the literature we use a self-consistent N-body simulation of an isolated Milky Way-type galaxy to show that the phase-space spirals develop naturally from vertical oscillations driven by the buckling of the stellar bar. Thus, we claim that the physical mechanism standing behind the observed incomplete phase-space mixing process can be internal and not necessarily due to the perturbation induced by a massive satellite. In our model, the bending oscillations propagate outward and produce axisymmetric variations of the mean vertical coordinate and vertical velocity component of about 100 − 200 pc and 1 − 2 km s−1, respectively. As a consequence, the phase-space wrapping results in the formation of patterns with various morphologies across the disk, depending on the bar orientation, distance to the galactic center, and time elapsed since the bar buckling. Once bending waves appear, they are supported for a long time via disk self-gravity. Such vertical oscillations trigger the formation of various time-dependent phase-space spirals in the entire disk. The underlying physical mechanism implies the link between in-plane and vertical motion that leads directly to phase-space structures whose amplitude and shape are in remarkable agreement with those of the phase-space spirals observed in the Milky Way disk. In our isolated galaxy simulation, phase-space spirals are still distinguishable at the solar neighborhood 3 Gyr after the buckling phase. The long-lived character of the phase-space spirals generated by the bar buckling instability cast doubts on the timing argument used so far to get back to the time of the onset of the perturbation: phase-space spirals may have been caused by perturbations originated several gigayearrs ago, and not as recent as suggested so far.

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Gaia Data Release 2

Astronomy and Astrophysics ◽

10.1051/0004-6361/201832865 ◽

2018 ◽

Vol 616 ◽

pp. A11 ◽

Cited By ~ 157

Author(s):

◽

D. Katz ◽

T. Antoja ◽

M. Romero-Gómez ◽

R. Drimmel ◽

...

Keyword(s):

Phase Space ◽

Velocity Field ◽

Milky Way ◽

Solar Neighbourhood ◽

Galactic Centre ◽

Full Potential ◽

Galactic Disc ◽

Giant Stars ◽

Data Release ◽

Velocity Dispersions

Context. The second Gaia data release (Gaia DR2) contains high-precision positions, parallaxes, and proper motions for 1.3 billion sources as well as line-of-sight velocities for 7.2 million stars brighter than GRVS = 12 mag. Both samples provide a full sky coverage. Aims. To illustrate the potential of Gaia DR2, we provide a first look at the kinematics of the Milky Way disc, within a radius of several kiloparsecs around the Sun. Methods. We benefit for the first time from a sample of 6.4 million F-G-K stars with full 6D phase-space coordinates, precise parallaxes (σϖ∕ϖ ≤ 20%), and precise Galactic cylindrical velocities (median uncertainties of 0.9-1.4 km s-1 and 20% of the stars with uncertainties smaller than 1 km s-1 on all three components). From this sample, we extracted a sub-sample of 3.2 million giant stars to map the velocity field of the Galactic disc from ~5 kpc to ~13 kpc from the Galactic centre and up to 2 kpc above and below the plane. We also study the distribution of 0.3 million solar neighbourhood stars (r < 200 pc), with median velocity uncertainties of 0.4 km s-1, in velocity space and use the full sample to examine how the over-densities evolve in more distant regions. Results. Gaia DR2 allows us to draw 3D maps of the Galactocentric median velocities and velocity dispersions with unprecedented accuracy, precision, and spatial resolution. The maps show the complexity and richness of the velocity field of the galactic disc. We observe streaming motions in all the components of the velocities as well as patterns in the velocity dispersions. For example, we confirm the previously reported negative and positive galactocentric radial velocity gradients in the inner and outer disc, respectively. Here, we see them as part of a non-axisymmetric kinematic oscillation, and we map its azimuthal and vertical behaviour. We also witness a new global arrangement of stars in the velocity plane of the solar neighbourhood and in distant regions in which stars are organised in thin substructures with the shape of circular arches that are oriented approximately along the horizontal direction in the U − V plane. Moreover, in distant regions, we see variations in the velocity substructures more clearly than ever before, in particular, variations in the velocity of the Hercules stream. Conclusions. Gaia DR2 provides the largest existing full 6D phase-space coordinates catalogue. It also vastly increases the number of available distances and transverse velocities with respect to Gaia DR1. Gaia DR2 offers a great wealth of information on the Milky Way and reveals clear non-axisymmetric kinematic signatures within the Galactic disc, for instance. It is now up to the astronomical community to explore its full potential.

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Another relic bulge globular cluster: ESO 456-SC38 (Djorgovski 2)

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935726 ◽

2019 ◽

Vol 627 ◽

pp. A145 ◽

Cited By ~ 6

Author(s):

S. Ortolani ◽

E. V. Held ◽

D. Nardiello ◽

S. O. Souza ◽

B. Barbuy ◽

...

Keyword(s):

Globular Clusters ◽

Stellar Population ◽

Milky Way ◽

Galactic Center ◽

Horizontal Branch ◽

Very Old ◽

Orbital Parameters ◽

Data Release ◽

Best Fitting ◽

Bulge Formation

Context. The object ESO 456-SC38 (Djorgovski 2) is one of the globular clusters that is closest to the Galactic center. It is on the blue horizontal branch and has a moderate metallicity of [Fe/H] ∼ −1.0. It is thus similar to the very old inner bulge globular clusters NGC 6522, NGC 6558, and HP 1, and therefore appears to be part of the primeval formation stages of the Milky Way. Aims. The aim of this work is to determine an accurate distance and metallicity for ESO 456-SC38, as well as orbital parameters, in order to check similarities with other clusters in the inner bulge that have previously been well studied in terms of spectroscopy and photometry. This is a considerably fainter cluster that is contaminated by a rich stellar field; it is also quite absorbed by the dusty foreground. Methods. We analyzed ESO 456-SC38 based on HST photometry, with the filters F606W from ACS, F110W and F160W from WFC3, and photometry in V and I from FORS2 at the VLT. We combined this with identified stars that are covered by Gaia Data Release 2. Results. The isochrone fitting was carried out with the statistical Markov chain Monte Carlo method. We derive an accurate distance of d⊙ = 8.75 ± 0.12 kpc and a reddening of E(B−V) = 0.81+0.02−0.02. The best-fitting BaSTI isochrones correspond to an age of 12.70+0.72−0.69 Gyr and a metallicity of [Fe/H] = −1.11+0.03−0.03. Conclusions. ESO 456-SC38 adds to the list of moderately metal-poor globular clusters located in the inner bulge. It has a blue horizontal branch and is very old. The cluster is confined to the bulge and bar region, but it does not support the Galactic bar structure. The old stellar population represented by clusters like this has to be taken into account in models of Galactic bulge formation. Studying them also provides indications on the formation times of the globular clusters themselves.

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Hic sunt dracones: Cartography of the Milky Way spiral arms and bar resonances with Gaia Data Release 2

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936645 ◽

2020 ◽

Vol 634 ◽

pp. L8 ◽

Cited By ~ 8

Author(s):

S. Khoperskov ◽

O. Gerhard ◽

P. Di Matteo ◽

M. Haywood ◽

D. Katz ◽

...

Keyword(s):

Phase Space ◽

Milky Way ◽

Solar Radius ◽

Spiral Arms ◽

Full Phase Space ◽

Spatial Coverage ◽

Data Release ◽

Space Data ◽

First Time ◽

Stellar Density

In this paper we introduce a new method for analysing Milky Way phase-space which allows us to reveal the imprint left by the Milky Way bar and spiral arms on the stars with full phase-space data in Gaia Data Release 2. The unprecedented quality and extended spatial coverage of these data allowed us to discover six prominent stellar density structures in the disc to a distance of 5 kpc from the Sun. Four of these structures correspond to the spiral arms detected previously in the gas and young stars (Scutum-Centaurus, Sagittarius, Local, and Perseus). The remaining two are associated with the main resonances of the Milky Way bar where corotation is placed at around 6.2 kpc and the outer Lindblad resonance beyond the solar radius, at around 9 kpc. For the first time we provide evidence of the imprint left by spiral arms and resonances in the stellar densities not relying on a specific tracer, through enhancing the signatures left by these asymmetries. Our method offers new avenues for studying how the stellar populations in our Galaxy are shaped.

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Age-metallicity-velocity relation of stars as seen by RAVE

Proceedings of the International Astronomical Union ◽

10.1017/s1743921315008522 ◽

2015 ◽

Vol 11 (S317) ◽

pp. 367-368

Author(s):

Jennifer Wojno ◽

Georges Kordopatis ◽

Matthias Steinmetz ◽

Gal Matijevič ◽

Paul J. McMillan ◽

...

Keyword(s):

Radial Velocity ◽

Large Scale ◽

Milky Way ◽

Solar Neighborhood ◽

The Past ◽

Formation History ◽

Data Release ◽

Velocity Relation ◽

History Of ◽

Made In

AbstractThroughout the past decade, significant advances have been made in the size and scope of large-scale spectroscopic surveys, allowing for the opportunity to study in-depth the formation history of the Milky Way. Using the fourth data release of the RAdial Velocity Experiment (RAVE), we study the age-metallicity-velocity space of ~ 100,000 FGK stars in the extended solar neighborhood in order to explore evolutionary processes. Combining these three parameters, we better constrain our understanding of these interconnected, fundamental processes.

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Cool Supergiants in the Solar Neighborhood

Symposium - International Astronomical Union ◽

10.1017/s0074180900045435 ◽

1991 ◽

Vol 143 ◽

pp. 341-348

Author(s):

M. Jura

Keyword(s):

Surface Density ◽

Main Sequence ◽

Milky Way ◽

Galactic Center ◽

Solar Neighborhood ◽

Main Sequence Stars ◽

Considerable Uncertainty ◽

Red Supergiants ◽

Highly Evolved

We have identified 21 mass-losing red supergiants (20 M-type, 1 G-type, L > 105 L⊙) within 2.5 kpc of the Sun. These supergiants are highly evolved descendants of main sequence stars with initial masses larger than about 20 M⊙. The surface density projected onto the plane of the Milky Way is between about 1 and 2 kpc–2. Although with considerable uncertainty, we estimate that the mass return by the M supergiants is somewhere between 1 and 3 10-5 M⊙ kpc–2 yr–1. In the hemisphere facing the galactic center there is much less mass loss from M supergiants than from W-R stars, but in the anticenter direction, the M supergiants return more mass than do the W-R stars. The duration of the M supergiant phase appears to be between 2 and 4 105 years. During this phase a star of initially at least 20 M⊙ returns perhaps 3 to 10 M⊙ into the interstellar medium.

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Spirals in galaxies

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319007051 ◽

2019 ◽

Vol 14 (S353) ◽

pp. 134-134

Author(s):

J. A. Sellwood

Keyword(s):

Phase Space ◽

Milky Way ◽

Unstable Mode ◽

Resonant Scattering ◽

Solar Neighborhood ◽

Disk Galaxies

AbstractThe venerable problem of what causes the spiral features in disk galaxies is nearing a solution. In previous work, we have shown that transient spirals in simulations result from the superposition of a few coherent waves that have many properties of modes. The new achievement presented here is a clear demonstration that the evolution of one unstable mode leads to scattering at Lindblad resonances, and the depopulation of phase space at such resonances creates a “groove” that is the cause of a new unstable mode. Thus we now understand that the cause of spiral patterns in simulations is a recurrent cycle of groove modes. In other work, we have used Gaia DR2 data, converted to action-angle variables, to identify resonant scattering features in the Solar neighborhood that closely resemble those seen in the simulations, suggesting that the mechanism that causes spirals in simulations may also be at work in the Milky Way.

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Numerical Study on Particle Distribution in Longitudinal Phase Space and Beam Current Profile using Compact Electron Beam Simulator for Heavy Ion Inertial Fusion

IEEJ Transactions on Power and Energy ◽

10.1541/ieejpes.137.344 ◽

2017 ◽

Vol 137 (5) ◽

pp. 344-348

Author(s):

Takashi Kikuchi ◽

Yasuo Sakai ◽

Jun Hasegawa ◽

Kazuhiko Horioka ◽

Kazumasa Takahashi ◽

...

Keyword(s):

Electron Beam ◽

Phase Space ◽

Particle Distribution ◽

Numerical Study ◽

Heavy Ion ◽

Beam Current ◽

Inertial Fusion ◽

Current Profile ◽

Longitudinal Phase

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A Statistical Estimation of the Occurrence of Extraterrestrial Intelligence in the Milky Way Galaxy

Galaxies ◽

10.3390/galaxies9010005 ◽

2021 ◽

Vol 9 (1) ◽

pp. 5

Author(s):

Xiang Cai ◽

Jonathan H. Jiang ◽

Kristen A. Fahy ◽

Yuk L. Yung

Keyword(s):

Statistical Estimation ◽

Milky Way ◽

Galactic Center ◽

Model Simulation ◽

Temporal Variations ◽

Extraterrestrial Intelligence ◽

Milky Way Galaxy ◽

The Galaxy ◽

Peak Location ◽

Intelligent Life

In the field of astrobiology, the precise location, prevalence, and age of potential extraterrestrial intelligence (ETI) have not been explicitly explored. Here, we address these inquiries using an empirical galactic simulation model to analyze the spatial–temporal variations and the prevalence of potential ETI within the Galaxy. This model estimates the occurrence of ETI, providing guidance on where to look for intelligent life in the Search for ETI (SETI) with a set of criteria, including well-established astrophysical properties of the Milky Way. Further, typically overlooked factors such as the process of abiogenesis, different evolutionary timescales, and potential self-annihilation are incorporated to explore the growth propensity of ETI. We examine three major parameters: (1) the likelihood rate of abiogenesis (λA); (2) evolutionary timescales (Tevo); and (3) probability of self-annihilation of complex life (Pann). We found Pann to be the most influential parameter determining the quantity and age of galactic intelligent life. Our model simulation also identified a peak location for ETI at an annular region approximately 4 kpc from the galactic center around 8 billion years (Gyrs), with complex life decreasing temporally and spatially from the peak point, asserting a high likelihood of intelligent life in the galactic inner disk. The simulated age distributions also suggest that most of the intelligent life in our galaxy are young, thus making observation or detection difficult.

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Remarkable Symmetries in the Milky Way Disc's Magnetic Field

Publications of the Astronomical Society of Australia ◽

10.1071/as10045 ◽

2011 ◽

Vol 28 (2) ◽

pp. 171-176 ◽

Cited By ~ 15

Author(s):

P. P. Kronberg ◽

K. J. Newton-McGee

Keyword(s):

Magnetic Structure ◽

Large Scale ◽

Milky Way ◽

Galactic Center ◽

Galactic Plane ◽

Galactic Disk ◽

Field Structure ◽

Field Pattern ◽

Close Coupling ◽

Sign Change

AbstractWe apply a new, expanded compilation of extragalactic source Faraday rotation measures (RM) to investigate the broad underlying magnetic structure of the Galactic disk at latitudes ∣b∣ ≲15° over all longitudes l, where our total number of RMs is comparable to those in the combined Canadian Galactic Plane Survey (CGPS) at ∣b∣ < 4° and the Southern Galactic Plane (SGPS) ∣b∣<1.5°. We report newly revealed, remarkably coherent patterns of RM at ∣b∣≲15° from l∼270° to ∼90° and RM(l) features of unprecedented clarity that replicate in l with opposite sign on opposite sides of the Galactic center. They confirm a highly patterned bisymmetric field structure toward the inner disc, an axisymmetic pattern toward the outer disc, and a very close coupling between the CGPS/SGPS RMs at ∣b∣≲3° (‘mid-plane’) and our new RMs up to ∣b∣∼15° (‘near-plane’). Our analysis also shows the vertical height of the coherent component of the disc field above the Galactic disc's mid-plane—to be ∼1.5 kpc out to ∼6 kpc from the Sun. This identifies the approximate height of a transition layer to the halo field structure. We find no RM sign change across the plane within ∣b∣∼15° in any longitude range. The prevailing disc field pattern and its striking degree of large-scale ordering confirm that our side of the Milky Way has a very organized underlying magnetic structure, for which the inward spiral pitch angle is 5.5°±1° at all ∣b∣ up to ∼12° in the inner semicircle of Galactic longitudes. It decreases to ∼0° toward the anticentre.

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