scholarly journals Galactic seismology: the evolving “phase spiral” after the Sagittarius dwarf impact

2021 ◽  
Author(s):  
Joss Bland-Hawthorn ◽  
Thor Tepper-García
Keyword(s):  
High Resolution ◽  
Total Mass ◽  
Phase Plane ◽  
Density Wave ◽  
Analytic Model ◽  
Spiral Pattern ◽  
Galactic Disc ◽  
Stellar Disc ◽  
Pattern Speed ◽  
Bending Wave

Abstract In 2018, the ESA Gaia satellite discovered a remarkable spiral pattern (“phase spiral”) in the z − Vz phase plane throughout the solar neighbourhood, where z and Vz are the displacement and velocity of a star perpendicular to the Galactic disc. In response to Binney & Schönrich’s analytic model of a disc-crossing satellite to explain the Gaia data, we carry out a high-resolution, N-body simulation (N ≈ 108 particles) of an impulsive mass (2 × 1010 M⊙) that interacts with a cold stellar disc at a single transit point. The disc response is complex since the impulse triggers a superposition of two distinct bisymmetric (m = 2) modes − a density wave and a corrugated bending wave − that wrap up at different rates. Stars in the faster density wave wrap up with time T according to φD(R, T) = (ΩD(R) + Ωo) T where φD describes the spiral pattern and ΩD = Ω(R) − κ(R)/2, where κ is the epicyclic frequency. While the pattern speed Ωo is small, it is non-zero. The slower bending wave wraps up according to ΩB ≈ ΩD/2 producing a corrugated wave. The bunching effect of the density wave triggers the phase spiral as it rolls up and down on the bending wave (“rollercoaster” model). The phase spiral emerges slowly about ΔT ≈ 400 Myr after impact. It appears to be a long-lived, disc-wide phenomenon that continues to evolve over most of the 2 Gyr simulation. Thus, given Sagittarius’ (Sgr) low total mass today (Mtot ∼ 3 × 108 M⊙ within 10 kpc diameter), we believe the phase spiral was excited by the disc-crossing dwarf some 1 − 2 Gyr before the recent transit. For this to be true, Sgr must be losing mass at 0.5-1 dex per orbit loop.

scholarly journals Possible Pattern Speeds of a Density Wave in our Galaxy

1977 ◽  
Vol 45 ◽  
pp. 279-282 ◽  
Author(s):  
Preben J. Grosbøl
Keyword(s):  
Velocity Field ◽  
Spiral Structure ◽  
Density Wave ◽  
Wave Theory ◽  
Young Stars ◽  
Spiral Pattern ◽  
Considerable Effort ◽  
Pattern Speed ◽  
Pattern Speeds ◽  
Density Wave Theory

Since the density wave theory was introduced by Lin and Shu (1964) to explain the spiral structure considerable effort has been made to detect this kind of wave in our galaxy and to determine its parameters. Observations of the distribution and velocity field of gas and young objects show the present shape and location of the spiral pattern in our galaxy but tell little about its angular velocity. It was proposed by Strömgren (1967) to estimate this important parameter by calculating the places of formation of moderately young stars for which accurate space velocities and ages are known. This was done assuming that the majority of stars is formed in spiral arms so that the stellar birthplaces would outline the position of the spiral pattern at different epochs. Later, Yuan (1969) and Wielen (1973) calculated stellar birthplaces in the spiral potential given by Lin et al. (1969). These investigations showed no disagreement with the assumed density wave, however, the number of stars was too small to verify the assumed pattern speed.

scholarly journals Radial migration in a stellar galactic disc with thick components

2018 ◽  
Vol 616 ◽  
pp. A86 ◽  
Author(s):  
A. Halle ◽  
P. Di Matteo ◽  
M. Haywood ◽  
F. Combes
Keyword(s):  
Angular Momentum ◽  
Gravitational Potential ◽  
Effective Potential ◽  
Constant Speed ◽  
Galactic Disc ◽  
Spiral Arms ◽  
Radial Migration ◽  
Stellar Disc ◽  
Local Maxima ◽  
Corotation Radius

We study how radial migration affects the stars of a galaxy with a thin stellar disc and thicker stellar components. The simulated galaxy has a strong bar and lasting spiral arms. We find that the amplitude of the churning (change in angular momentum) is similar for thin and thick components, and of limited amplitude, and that stars of all components can be trapped at the corotation of the bar. With the exception of those stars trapped at the corotation, we find that stars far from their initial guiding radius are more likely to be so due to blurring rather than churning effects. We compare the simulation to orbits integration with a fixed gravitational potential rotating at a constant speed. In the latter case, stars trapped at corotation are churned periodically outside and inside the corotation radius, with a zero net average. However, as the bar speed of the simulated galaxy decreases and its corotation radius increases, stars trapped at corotation for several Gyrs can be churned on average outwards. In this work we have studied the location of extreme migrators (stars experimenting the largest churning) and find that extreme migrators come from regions on the leading side of the effective potential local maxima.

Dynamical imprint of interstellar gas on persistence of spiral structure in galaxies

2017 ◽  
Vol 13 (S334) ◽  
pp. 296-297
Author(s):  
Soumavo Ghosh ◽  
Chanda J. Jog
Keyword(s):  
Time Scale ◽  
Spiral Structure ◽  
Density Wave ◽  
Disk Galaxies ◽  
Interstellar Gas ◽  
Spiral Arms ◽  
Pattern Speed

AbstractThe persistence of the spiral structure in disk galaxies has long been debated. In this work, we investigate the dynamical influence of interstellar gas on the persistence of the spiral arms in disk galaxies. We show that the gas helps the spiral arms to survive for longer time-scale (~ a few Gyr). Also, we show that the addition of gas in calculation is necessary for getting a stable density wave corresponding to the observed pattern speed of the spiral arms.

scholarly journals The strange case of the peculiar spiral galaxy NGC 5474

2020 ◽  
Vol 634 ◽  
pp. A124 ◽  
Author(s):  
M. Bellazzini ◽  
F. Annibali ◽  
M. Tosi ◽  
A. Mucciarelli ◽  
M. Cignoni ◽  
...  
Keyword(s):  
Old Age ◽  
Spiral Galaxy ◽  
The Other ◽  
Spiral Pattern ◽  
Stellar Content ◽  
Peculiar Star ◽  
Space Telescope ◽  
Stellar Disc ◽  
Star Forming ◽  
The Galaxy

We present the first analysis of the stellar content of the structures and substructures identified in the peculiar star-forming galaxy NGC 5474, based on Hubble Space Telescope resolved photometry from the LEGUS survey. NGC 5474 is a satellite of the giant spiral M 101, and it is known to have a prominent bulge that is significantly off-set from the kinematic centre of the underlying H I and stellar disc. The youngest stars (age ≲ 100 Myr) trace a flocculent spiral pattern extending out to ≳8 kpc from the centre of the galaxy. On the other hand, intermediate-age (age ≳ 500 Myr) and old (age ≳ 2 Gyr) stars dominate the off-centred bulge and a large substructure residing in the south-western part of the disc (SW over-density) and they are not correlated with the spiral arms. The old age of the stars in the SW over-density suggests that this may be another signature of any dynamical interactions that have shaped this anomalous galaxy. We suggest that a fly by with M 101, generally invoked as the origin of the anomalies, may not be sufficient to explain all the observations. A more local and more recent interaction may help to put all the pieces of this galactic puzzle together.

scholarly journals New light on the corrugation phenomenon in our Galaxy

1985 ◽  
Vol 106 ◽  
pp. 175-178
Author(s):  
J. V. Feitzinger ◽  
J. Spicker
Keyword(s):  
Velocity Field ◽  
Radial Velocity ◽  
Density Wave ◽  
Radial Expansion ◽  
Spiral Pattern ◽  
Mass Model ◽  
Wave Kinematics ◽  
Spiral Arm

This investigation presents a total picture of the well-known corrugation-phenomenon for the (heliocentric) longitude range 10° ≤ 1 ≤ 240° as derived from HI-studies. For each spiral arm of the spiral pattern of Simonson (1976), we derived the centroid of the HI distribution from the 21-cm line surveys of Weaver and Williams (1974), Sinha (1979), and Westerhout and Wendlandt (1982). The three-component mass model of Rohlfs and Kreitschmann (1981) was used to derive a radial-velocity field, which was supplemented by a radial expansion field and by density-wave kinematics. This combined field served to calculated kinematic distances. The warp was taken into account according to Henderson et al. (1982) and Kulkarni et al. (1982).

scholarly journals Identifying resonances of the Galactic bar in Gaia DR2: I. Clues from action space

2020 ◽  
Vol 500 (2) ◽  
pp. 2645-2665
Author(s):  
Wilma H Trick ◽  
Francesca Fragkoudi ◽  
Jason A S Hunt ◽  
J Ted Mackereth ◽  
Simon D M White
Keyword(s):  
Action Space ◽  
Galactic Disc ◽  
Resonant Orbits ◽  
Particle Simulations ◽  
Pattern Speed ◽  
The Rich ◽  
First Time ◽  
Gaia Dr2 ◽  
Vertical Action ◽  
Lindblad Resonance

ABSTRACT Action space synthesizes the orbital information of stars and is well suited to analyse the rich kinematic substructure of the disc in the second Gaia data release's radial velocity sample. We revisit the strong perturbation induced in the Milky Way disc by an m = 2 bar, using test particle simulations and the actions (JR, Lz, Jz) estimated in an axisymmetric potential. These make three useful diagnostics cleanly visible. (1) We use the well-known characteristic flip from outward to inward motion at the outer Lindblad resonance (OLR; l = +1, m = 2), which occurs along the axisymmetric resonance line (ARL) in (Lz, JR), to identify in the Gaia action data three candidates for the bar’s OLR and pattern speed Ωbar: 1.85Ω0, 1.20Ω0, and 1.63Ω0 (with ∼0.1Ω0 systematic uncertainty). The Gaia data is therefore consistent with both slow and fast bar models in the literature, but disagrees with recent measurements of ∼1.45Ω0. (2) For the first time, we demonstrate that bar resonances – especially the OLR – cause a gradient in vertical action 〈Jz〉 with Lz around the ARL via ‘Jz-sorting’ of stars. This could contribute to the observed coupling of 〈vR〉 and 〈|vz|〉 in the Galactic disc. (3) We confirm prior results that the behaviour of resonant orbits is well approximated by scattering and oscillation in (Lz, JR) along a slope ΔJR/ΔLz = l/m centred on the l:m ARL. Overall, we demonstrate that axisymmetrically estimated actions are a powerful diagnostic tool even in non-axisymmetric systems.

scholarly journals THE SHOCK-INDUCED STAR FORMATION SEQUENCE RESULTING FROM A CONSTANT SPIRAL PATTERN SPEED

2014 ◽  
Vol 790 (2) ◽  
pp. 118 ◽  
Author(s):  
Eric E. Martínez-García ◽  
Ivânio Puerari
Keyword(s):  
Star Formation ◽  
Spiral Pattern ◽  
Pattern Speed

Microstructure, Mass and Chemical Analysis with 8 to 44 Angstrom X-Radiation

1958 ◽  
Vol 2 ◽  
pp. 117-155 ◽  
Author(s):  
Burton L. Henke
Keyword(s):  
High Resolution ◽  
Chemical Analysis ◽  
Mass Distribution ◽  
Total Mass ◽  
Biological Research ◽  
Chemical Information ◽  
Analysis Method ◽  
X Ray

AbstractThe requirement of ultrasoft x-radiation (10 to 100A) for high resolution microradiographic analysis is established. Optimum methods are described for obtaining structure, mass distribution and mass-chemical information for microscopic sample regions as small as a few square microns and for total mass as small as a few micro-micrograms. The details of the techniques and of the instrumentation which are used in high resolution microradiographic analysis are presented.There has been a considerable amount of work reported on low magnification microradiography (up to 100 diameters) using conventional x-ray wavelengths.Relatively little work has been done in high resolution microradiography and with ultra soft x-radiation. Nearly all which has been reported has been in application to biological research where the need for such an analysis method seems to be greatest at this time. Outstanding among this work has been that of Engstrom and his co-workers.Much of the material which is presented in the present paper is intended as a supplement to that presented in the works of Engstrom and Lindstrom and with an emphasis upon the quantitative aspects of microradiographic analysis, using ultrasoft x-radiation.

scholarly journals A Spectroscopic Search for Hot (B-Type) Post-AGB Stars

1993 ◽  
Vol 155 ◽  
pp. 360-360 ◽  
Author(s):  
E.S. Conlon
Keyword(s):  
High Resolution ◽  
Model Atmosphere ◽  
Agb Stars ◽  
Young Population ◽  
Atmospheric Parameters ◽  
Galactic Disc ◽  
Low Resolution ◽  
Signal To Noise ◽  
Queen's University

At Queen's University, we have been undertaking a spectroscopic programme to elucidate the nature of faint blue stars at high galactic latitudes. We have identified approximately 50 that appear to spectroscopically identical (even at high resolution and signal-to-noise) to normal young Population I B-type stars in the galactic disc. However, we have also found seven faint objects () that were previously classified as Population I on the basis of photometry and/or low resolution spectroscopy; careful model atmosphere analyses of high resolution spectra now indicate that they have non-Population I compositions. Their derived atmospheric parameters are coincident with theoretical post-AGB evolutionary tracks and thus together with their peculiar composition, they would appear to be hot evolved post-AGB objects.

scholarly journals Gas Response to a Rotating Stellar Bar

1978 ◽  
Vol 3 (3) ◽  
pp. 234-236
Author(s):  
M. P. Schwarz
Keyword(s):  
Spiral Galaxies ◽  
Fast Rate ◽  
Density Wave ◽  
Wave Theory ◽  
Finite Amplitude ◽  
Spiral Waves ◽  
Galactic Rotation ◽  
Spiral Pattern ◽  
Density Wave Theory ◽  
Gas Response

The arms in spiral galaxies cannot be material arms for then they would wind up on a time scale of one galactic rotation, or a few times 108 years. The large number of spirals suggests that the spiral pattern must persist for about 1010 years (or be continually rejuvenated). The density wave theory treats the spiral pattern as a wave phenomenon, thus overcoming this problem. Much work has been done studying small amplitude oscillations in flat stellar discs. Self-consistent spiral modes have been found, but they are not stable and grow at a fast rate. Numerical simulations of thin stellar discs, such as those of Hohl (1971), which can handle finite amplitude waves, have been more successful. Spiral waves form initially but evolve into a steady state rotating bar. It seems therefore, that a long-lived spiral cannot be formed in stars alone.

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