scholarly journals Did Sgr cause the vertical waves in the solar neighbourhood?

2021 ◽  
Vol 503 (1) ◽  
pp. 376-393 ◽  
Author(s):  
Morgan Bennett ◽  
Jo Bovy
Keyword(s):  
Phase Space ◽  
Dwarf Galaxy ◽  
Vertical Component ◽  
Velocity Space ◽  
Solar Neighbourhood ◽  
Fast Method ◽  
Disc Galaxy ◽  
Number Count ◽  
Wave Signature ◽  
Number Counts

ABSTRACT The vertical distribution of stars in the solar neighbourhood is not in equilibrium but contains a wave signature in both density and velocity space originating from a perturbation. With the discovery of the phase-space spiral in Gaia data release (DR) 2, determining the origin of this perturbation has become even more urgent. We develop and test a fast method for calculating the perturbation from a passing satellite on the vertical component of a part of a disc galaxy. This fast method allows us to test a large variety of possible perturbations to the vertical disc very quickly. We apply our method to the range of possible perturbations to the solar neighbourhood stemming from the recent passage of the Sagittarius dwarf galaxy (Sgr), varying its mass, mass profile, and present-day position within their observational uncertainties, and its orbit within different realistic models for the Milky Way’s gravitational potential. We find that we are unable to reproduce the observed asymmetry in the vertical number counts and its concomitant breathing mode in velocity space for any plausible combination of Sgr and Milky Way properties. In all cases, either the amplitude or the perturbation wavelength of the number-count asymmetry and of the oscillations in the mean vertical velocity produced by the passage of Sgr are in large disagreement with the observations from Gaia DR2. We conclude that Sgr cannot have caused the observed oscillations in the vertical disc or the Gaia phase-space spiral.

scholarly journals Searching for cross-correlation between stochastic gravitational-wave background and galaxy number counts

2020 ◽  
Vol 500 (2) ◽  
pp. 1666-1672
Author(s):  
Kate Z Yang ◽  
Vuk Mandic ◽  
Claudia Scarlata ◽  
Sharan Banagiri
Keyword(s):  
Gravitational Wave ◽  
Cross Correlation ◽  
Sloan Digital Sky Survey ◽  
Number Count ◽  
Frequency Bands ◽  
Galaxy Count ◽  
Harmonic Decomposition ◽  
Number Counts ◽  
Gravitational Wave Background ◽  
The Universe

ABSTRACT Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) and Advanced Virgo have recently published the upper limit measurement of persistent directional stochastic gravitational-wave background (SGWB) based on data from their first and second observing runs. In this paper, we investigate whether a correlation exists between this maximal likelihood SGWB map and the electromagnetic (EM) tracers of matter structure in the Universe, such as galaxy number counts. The method we develop will improve the sensitivity of future searches for anisotropy in the SGWB and expand the use of SGWB anisotropy to probe the formation of structure in the Universe. In order to compute the cross-correlation, we used the spherical harmonic decomposition of SGWB in multiple frequency bands and converted them into pixel-based sky maps in healpix basis. For the EM part, we use the Sloan Digital Sky Survey alaxy catalogue and form healpix sky maps of galaxy number counts at the same angular resolution as the SGWB maps. We compute the pixel-based coherence between these SGWB and galaxy count maps. After evaluating our results in different SGWB frequency bands and in different galaxy redshift bins, we conclude that the coherence between the SGWB and galaxy number count maps is dominated by the null measurement noise in the SGWB maps, and therefore not statistically significant. We expect the results of this analysis to be significantly improved by using the more sensitive upcoming SGWB measurements based on the third observing run of Advanced LIGO and Advanced Virgo.

scholarly journals Gaia Data Release 2

2018 ◽  
Vol 616 ◽  
pp. A11 ◽  
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.

scholarly journals Diffusion of radial action in a galactic disc

2020 ◽  
Vol 642 ◽  
pp. A207
Author(s):  
Hervé Wozniak
Keyword(s):  
Wave Structure ◽  
Resonance Scattering ◽  
Solar Neighbourhood ◽  
Galactic Disc ◽  
Disc Galaxy ◽  
The Galaxy ◽  
Disc Region ◽  
Wave Trains ◽  
Lindblad Resonance ◽  
Radial Action

Context. The stellar migration of the galactic disc stars has been invoked to explain the dispersion of stellar metallicity observed in the solar neighbourhood. Aims. We seek to identify the dynamical mechanisms underlying stellar migration in an isolated galaxy disc under the influence of a bar. Our approach is to analyse the diffusion of dynamical quantities. Methods. We extend our previous work by exploring Chirikov’s diffusion rate (and derived timescale) of the radial action JR in an idealised N-body simulation of an isolated disc galaxy. We limit our study to the evolution of the disc region well after the formation of the bar, in a regime of adiabatic evolution. Results. The JR diffusion timescale TD(JR) is less than 3 Gyr for roughly half the galaxy mass. It is always much shorter than the angular momentum diffusion timescale TD(Lz) outside the stellar bar. In the disc, ⟨TD(JR)⟩ ∼ 1 Gyr. All non-axisymmetric morphological structures that are characteristic of resonances and waves in the disc are associated to particles with TD(JR) < 3 Gyr and TD(Lz) > 10 Gyr. Short TD(JR) can be explained by the gradual de-circularisation of initially circular orbits (JR = 0) under the effect of intermittent. Inner Linblad resonance scattering by wave trains propagating in the disc, well beyond the outer Lindblad resonance of the bar (OLR). This leads to a moderate secular heating of the disc beyond the bar’s OLR for 7 Gyr, which is comparable to solar neighbourhood observations. The complex multi-wave structure, mixing permanent and intermittent modes, allows for multiple resonance overlaps.

scholarly journals Footprints of the Sagittarius dwarf galaxy in the Gaia data set

2019 ◽  
Vol 485 (3) ◽  
pp. 3134-3152 ◽  
Author(s):  
Chervin F P Laporte ◽  
Ivan Minchev ◽  
Kathryn V Johnston ◽  
Facundo A Gómez
Keyword(s):  
Phase Space ◽  
Large Scale ◽  
Dwarf Galaxy ◽  
Large Degree ◽  
Data Set ◽  
Coupled Oscillations ◽  
History Of ◽  
Bar Buckling ◽  
Gaia Dr2 ◽  
Space Volume

ABSTRACT We analyse an N-body simulation of the interaction of the Milky Way (MW) with a Sagittarius-like dSph (Sgr), looking for signatures which may be attributed to its orbital history in the phase space volume around the Sun in light of Gaia DR2 discoveries. The repeated impacts of Sgr excite coupled vertical and radial oscillations in the disc which qualitatively, and to a large degree quantitatively are able to reproduce many features in the 6D Gaia DR2 samples, from the median VR, Vϕ, V$z$ velocity maps to the local δρ($v$$z$, $z$) phase-space spiral which is a manifestation of the global disc response to coupled oscillations within a given volume. The patterns in the large-scale velocity field are well described by tightly wound spirals and vertical corrugations excited from Sgr’s impacts. We show that the last pericentric passage of Sgr resets the formation of the local present-day δρ($v$$z$, $z$) spiral and situate its formation around 500-800 Myr. As expected δρ(vz, $z$) grows in size and decreases in woundedness as a function of radius in both the Gaia DR2 data and simulations. This is the first N-body model able to explain so many of the features in the data on different scales. We demonstrate how to use the full extent of the Galactic disc to date perturbations dating from Myr to Gyr, probe the underlying potential and constrain the mass-loss history of Sgr. δρ(vz, $z$) looks the same in all stellar populations age bins down to the youngest ages which rules out a bar buckling origin.

scholarly journals Evidence for Galaxy Formation at High Redshift

2001 ◽  
Vol 204 ◽  
pp. 347-357
Author(s):  
Tom Shanks ◽  
Nigel Metcalfe ◽  
Dick Fong ◽  
Henry McCracken ◽  
Ana Campos ◽  
...  
Keyword(s):  
Galaxy Formation ◽  
Dwarf Galaxy ◽  
High Redshift ◽  
Formation Rate ◽  
Space Density ◽  
High Redshift Galaxies ◽  
Local Space ◽  
Deep Fields ◽  
Using Data ◽  
Number Counts

Metcalfe et al. (1995, 1996) have shown that galaxy counts from the UV to the near-IR are well-fitted by simple evolutionary models where the space density of galaxies remains constant with look-back time while the star-formation rate rises exponentially. We now extend these results, first by using data from the Herschel Deep Field to show that these same models give detailed fits to the faint galaxy r - i : b - r colour-colour diagram. We then use these models to predict the number counts of high redshift galaxies detected by the Lyman break technique. At z ≈ 3 there is almost exact agreement between our prediction and the data, suggesting that the space density of galaxies at z ≈ 3 may be close to its local value. At z ≈ 4 the space density of bright galaxies remains unchanged; however, the space density of dwarf galaxies is significantly lower than it is locally, suggesting that we have detected an epoch of dwarf galaxy formation at z ≈ 4. Finally, significant numbers of Lyman-break galaxy candidates are also detected at z ≈ 6 in the Hubble and Herschel Deep Fields; taking this observation together with a number of recent detections of spectroscopically confirmed z ≈ 6 galaxies suggests that the space density of bright galaxies at z ≈ 6 remains comparable to the local space density, and thus that the epoch of formation of bright galaxies may lie at yet higher redshift.

Warps, Waves, and Phase Spirals in the Milky Way

2019 ◽  
Vol 14 (S353) ◽  
pp. 65-70
Author(s):  
Lawrence M. Widrow ◽  
Keir Darling ◽  
Haochuan Li
Keyword(s):  
Milky Way ◽  
Dynamic Mode Decomposition ◽  
Galactic Centre ◽  
Dynamic Mode ◽  
Vertical Force ◽  
Disc Galaxy ◽  
Stellar Disc ◽  
Mode Decomposition ◽  
Number Counts ◽  
Galactic Warp

AbstractThe stellar disc of the Milky Way exhibits clear departures from planarity, the most conspicuous manifestation being the Galactic Warp but also includes an apparent corrugation pattern in number counts around 15kpc from the Galactic centre, a wave like pattern in the vertical velocities of stars as a function of guiding radius, asymmetries about the midplane in both number counts and bulk motions, and phase spirals in the z–vz projection of the local stellar distribution function. We discuss the physics of these phenomena and, in particular, suggest a possible avenue for inferring the vertical force in the Solar Neighbourhood from phase spirals. We apply Dynamic Mode Decomposition, a technique widely used in the realm of fluid mechanics, to simulations of disc galaxy simulations. This method appears to be particularly well-suited to the study of nonlinear processes such as the coupling of warps and spirals, first discussed by Masset and Tagger.

Star formation history and dynamical evolution of the solar neighbourhood

2017 ◽  
Vol 13 (S334) ◽  
pp. 310-311
Author(s):  
Andreas Just ◽  
Kseniia Sysoliatina
Keyword(s):  
Star Formation ◽  
Galactic Plane ◽  
Dynamical Evolution ◽  
Star Formation History ◽  
Solar Neighbourhood ◽  
Data Set ◽  
Disc Model ◽  
Formation History ◽  
Number Counts ◽  
Good Agreement

AbstractWe used our detailed analytic local disc model to compare predictions in number counts, colour distribuitons and kinematics with a data set extracted from a combination of TGAS and RAVE catalogues. We find generally a very good agreement with some deviations close to the Galactic plane.

Time asymptotic statistics of the Vlasov equation

1977 ◽  
Vol 17 (3) ◽  
pp. 553-569 ◽  
Author(s):  
Georg Knorr
Keyword(s):  
Phase Space ◽  
Electric Field ◽  
Vlasov Equation ◽  
Reasonable Agreement ◽  
Initial Conditions ◽  
Velocity Space ◽  
Expectation Values ◽  
Asymptotic Statistics ◽  
Field Spectrum

A statistical description of the Vlasov equation is made possible by truncation of phase space in the velocity co-ordinates and writing the equation in terms of Fourier components in configuration and velocity space. Invariants of the resulting nonlinear turbulence equations are discussed. Expectation values and in particular an electric field spectrum of the form (β+ ακ2)-1 are derived. α and β are constants; α is always positive; β may be negative, depending on the initial conditions of the plasma. The spectrum is in reasonable agreement with available experiments and simulations.

Quantum Velocity Space Distributions

1969 ◽  
Vol 24 (9) ◽  
pp. 1431 ◽  
Author(s):  
J.G. Gilson
Keyword(s):  
Quantum Mechanics ◽  
Phase Space ◽  
Present Author ◽  
Fluid Phase ◽  
Velocity Space ◽  
Two Fluid

Abstract In a recent paper 1 , the present author has shown that it is possible to reformulate Schrödinger quantum mechanics in terms of a two fluid phase space or velocity space struc-ture. The distribution which has played a central role in this work, except that the function y(ri, r2) has not before now been introduced into its prescription, has the form m (x, 11 vi, ^2) =

scholarly journals Galaxy clusters as intrinsic alignment tracers: present and future

2020 ◽  
Vol 500 (4) ◽  
pp. 5561-5569
Author(s):  
C J G Vedder ◽  
N E Chisari
Keyword(s):  
Large Scale ◽  
Signal To Noise Ratio ◽  
Sloan Digital Sky Survey ◽  
Line Of Sight ◽  
Expected Number ◽  
Number Count ◽  
Sky Survey ◽  
Redshift Survey ◽  
Number Counts ◽  
The Universe

ABSTRACT Galaxies and clusters embedded in the large-scale structure of the Universe are observed to align in preferential directions. Galaxy alignment has been established as a potential probe for cosmological information, but the application of cluster alignments for these purposes remains unexplored. Clusters are observed to have a higher alignment amplitude than galaxies, but because galaxies are much more numerous, the trade-off in detectability between the two signals remains unclear. We present forecasts comparing cluster and galaxy alignments for two extragalactic survey set-ups: a currently available low-redshift survey (Sloan Digital Sky Survey, SDSS) and an upcoming higher redshift survey (Legacy Survey of Space and Time, LSST). For SDSS, we rely on the publicly available redmapper catalogue to describe the cluster sample. For LSST, we perform estimations of the expected number counts while we extrapolate the alignment measurements from SDSS. Clusters in SDSS have typically higher alignment signal-to-noise ratio (S/N) than galaxies. For LSST, the cluster alignment signals quickly wash out with redshift due to a relatively low number count and a decreasing alignment amplitude. Nevertheless, a potential strong suit of clusters is in their interplay with weak lensing: intrinsic alignments can be more easily isolated for clusters than for galaxies. The S/N of cluster alignment can in general be improved by isolating close pairs along the line of sight.

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