scholarly journals Inside Out and Upside-Down: The Roles of Gas Cooling and Dynamical Heating in Shaping the Stellar Age-Velocity Relation

2021 ◽  
Author(s):  
Jonathan C Bird ◽  
Sarah R Loebman ◽  
David H Weinberg ◽  
Alyson M Brooks ◽  
Thomas R Quinn ◽  
...  
Keyword(s):  
Milky Way ◽  
Velocity Dispersion ◽  
Solar Neighborhood ◽  
Disk Galaxies ◽  
Low Velocity ◽  
Velocity Relationship ◽  
Gas Cooling ◽  
Multi Phase ◽  
Inside Out ◽  
Over Time

Abstract Kinematic studies of disk galaxies, using individual stars in the Milky Way or statistical studies of global disk kinematics over time, provide insight into how disks form and evolve. We use a high-resolution, cosmological zoom-simulation of a Milky Way-mass disk galaxy (h277) to tie together local disk kinematics and the evolution of the disk over time. The present-day stellar age-velocity relationship (AVR) of h277 is nearly identical to that of the analogous solar-neighborhood measurement in the Milky Way. A crucial element of this success is the simulation’s dynamically cold multi-phase ISM, which allows young stars to form with a low velocity dispersion (σbirth∼6 − 8 km s−1) at late times. Older stars are born kinematically hotter (i.e., the disk settles over time in an “upside-down” formation scenario), and are subsequently heated after birth. The disk also grows “inside-out”, and many of the older stars in the present-day solar neighborhood are present because of radial mixing. We demonstrate that the evolution of σbirth in h277 can be explained by the same model used to describe the general decrease in velocity dispersion observed in disk galaxies from z ∼ 2 − 3 to the present-day, in which the disk evolves in quasi-stable equilibrium and the ISM velocity dispersion decreases over time due to a decreasing gas fraction. Thus, our results tie together local observations of the Milky Way’s AVR with observed kinematics of high z disk galaxies.

scholarly journals The Formation of Disk Galaxies

1988 ◽  
Vol 130 ◽  
pp. 301-310
Author(s):  
K.C. Freeman
Keyword(s):  
Radial Velocity ◽  
Milky Way ◽  
Velocity Dispersion ◽  
Basic Structure ◽  
Disk Galaxy ◽  
Disk Galaxies ◽  
The Sun ◽  
Structural Components ◽  
General Review

In this talk, I will discuss a few particular topics, rather than attempting a general review of the formation of disk galaxies. First recall the basic structure and kinematics of a disk galaxy like the Milky Way. The Table below lists the four main structural components as they are presently understood, and gives typical masses, and (if known) the characteristic rotational velocities (at the sun) and the radial velocity dispersion for each component. For more details, see Freeman (1987).

scholarly journals Evolution of Abundance Gradients along the Galactic Disk

2001 ◽  
Vol 204 ◽  
pp. 419-419
Author(s):  
J. L. Hou ◽  
Nikos Prantzos ◽  
Samuel Boissier
Keyword(s):  
Milky Way ◽  
Galactic Disk ◽  
Current Data ◽  
Solar Neighborhood ◽  
Observational Constraints ◽  
Type I ◽  
Intermediate Mass Stars ◽  
Abundance Profile ◽  
Gradient Evolution ◽  
Inside Out

A detailed investigation of the abundance gradients and their evolution along the Galactic disk has recently appeared (Hou, J. L., Prantzos, N., & Boissier, S. 2000, A&A, in press; astro-ph/0007164). A chemical evolution model of S. Boissier & N. Pranzos (1999, MNRAS, 307, 857) was quite successful in reproducing the main observational constraints both in the solar neighborhood and the entire Milky Way disk. Studied elements include He, C, N, O, Ne, Mg, Al, Si, S, Ar and Fe. We use metallicity dependent yields for massive stars with and without mass loss. We find that most observed abundance profiles are correctly reproduced by massive star yields, but C and N require supplementary sources. We argue that massive, mass losing stars can totally account for the abundance profile of C, while intermediate mass stars are the main source of N. We also find that the adopted “inside-out” formation scheme for the Milky Way disk produces abundance profiles steeper in the past. Using current data on planetary nebulae of type I, II, and III, on N, Ne, S, Ar as observational constraints for gradient evolution, we find that it is difficult to conclude whether the gradient steepens or flattens with time. However, for a given interval of Galactic age, our model predicts that the corresponding abundance scatter is smaller in the inner disk than in the outer regions.

scholarly journals The turbulent environment of low-mass dense cores

2006 ◽  
Vol 2 (S237) ◽  
pp. 24-30 ◽  
Author(s):  
E. Falgarone ◽  
P. Hily-Blant ◽  
J. Pety ◽  
G. Pineau des Forêts
Keyword(s):  
Turbulent Energy ◽  
Injection Rate ◽  
Solar Neighborhood ◽  
Low Velocity ◽  
Gas Condensation ◽  
Dense Cores ◽  
Gas Cooling ◽  
Low Mass ◽  
Impulsive Heating ◽  
Turbulent Cascade

AbstractThe signatures of intermittent dissipation of turbulent energy have been sought in the translucent environment of a low-mass dense core. Molecular line observations reveal a network of narrow filamentary structures, found on statistical grounds to be the locus of the largest velocity shears. Three independent properties of these structures make them the plausible sites of intermittent dissipation of turbulence: (1) gas there is warmer and more diluted than average, (2) it bears the signatures of a non-equilibrium chemistry triggered by impulsive heating due to turbulence dissipation, and (3) the power that these structures radiate in the gas cooling lines (mostly H2) is so large that it balances the total energy injection rate of the turbulent cascade, for a volume filling factor of only a few percents, consistent with other observations in the Solar Neighborhood. These filamentary structures may act as tiny seeds of gas condensation in diffuse molecular gas. They do not exhibit the properties of steady-state low-velocity magneto-hydrodynamic (MHD) shocks, as presently modelled.

scholarly journals Extended stellar systems in the solar neighborhood

2019 ◽  
Vol 622 ◽  
pp. L13 ◽  
Author(s):  
Stefan Meingast ◽  
João Alves ◽  
Verena Fürnkranz
Keyword(s):  
Wavelet Decomposition ◽  
Stellar Population ◽  
Main Sequence ◽  
Milky Way ◽  
Velocity Dispersion ◽  
Galactic Disk ◽  
Mass Function ◽  
Solar Neighborhood ◽  
Giant Stars ◽  
Stellar Streams

We report the discovery of a large, dynamically cold, coeval stellar stream that is currently traversing the immediate solar neighborhood at a distance of only 100 pc. The structure was identified in a wavelet decomposition of the 3D velocity space of all stars within 300 pc of the Sun. Its members form a highly elongated structure with a length of at least 400 pc, while its vertical extent measures only about 50 pc. Stars in the stream are not isotropically distributed but instead form two parallel lanes with individual local overdensities, that may correspond to a remnant core of a tidally disrupted cluster or OB association. Its members follow a very well-defined main sequence in the observational Hertzsprung–Russel diagram and also show a remarkably low 3D velocity dispersion of only 1.3 km s−1. These findings strongly suggest a common origin as a single coeval stellar population. An extrapolation of the present-day mass function indicates a total mass of at least 2000 M⊙, making it larger than most currently known clusters or associations in the solar neighborhood. We estimated the age of the stream to be around 1 Gyr based on a comparison with a set of isochrones and giant stars in our member selection and find a mean metallicity of [Fe/H] = −0.04. This structure may very well represent the Galactic disk counterpart to the prominent stellar streams observed in the Milky Way halo. As such, it constitutes a new valuable probe to constrain the Galaxy’s mass distribution.

Galactic archaeology: Understanding the metallicity gradients with chemo-dynamical models

2018 ◽  
Vol 14 (A30) ◽  
pp. 253-254
Author(s):  
I. Minchev ◽  
F. Anders ◽  
C. Chiappini
Keyword(s):  
Interstellar Medium ◽  
Milky Way ◽  
Cosmic Time ◽  
Dynamical Evolution ◽  
Disk Galaxies ◽  
Dynamical Models ◽  
Disk Formation ◽  
Recent Method ◽  
Gradient Evolution ◽  
Inside Out

AbstractRadial metallicity gradients measured today in the interstellar medium (ISM) and stellar components of disk galaxies are the result of chemo-dynamical evolution since the beginning of disk formation. This makes it difficult to infer the disk past without knowledge of the ISM metallicity gradient evolution with cosmic time. We show that abundance gradients are meaningful only if stellar age information is available. The observed gradient inversion with distance from the disk mid-plane seen in the Milky Way can be explained as the effect of inside-out disk formation and disk flaring of mono-age populations. A novel recent method is presented for constraining the evolution of the Galactic ISM metallicity with radius and time directly from the observations, while at the same time recovering the birth radii of any stellar sample with precise metallicity and age measurements.

scholarly journals The pristine dwarf-galaxy survey – III. Revealing the nature of the Milky Way globular cluster Sagittarius II

2021 ◽  
Vol 503 (2) ◽  
pp. 2754-2762
Author(s):  
Nicolas Longeard ◽  
Nicolas Martin ◽  
Rodrigo A Ibata ◽  
Else Starkenburg ◽  
Pascale Jablonka ◽  
...  
Keyword(s):  
Globular Cluster ◽  
Confidence Limit ◽  
Globular Clusters ◽  
Milky Way ◽  
Velocity Dispersion ◽  
Dwarf Galaxy ◽  
Low Velocity ◽  
Data Set ◽  
Large Size ◽  
Additional Member

ABSTRACT We present a new spectroscopic study of the faint Milky Way satellite Sagittarius II. Using multiobject spectroscopy from the Fibre Large Array Multi-Element Spectrograph, we supplement the data set of Longeard et al. with 47 newly observed stars, 19 of which are identified as members of the satellite. These additional member stars are used to put tighter constraints on the dynamics and the metallicity properties of the system. We find a low velocity dispersion of $\sigma _\mathrm{v}^\mathrm{SgrII} = 1.7 \pm 0.5$ km s−1, in agreement with the dispersion of Milky Way globular clusters of similar luminosity. We confirm the very metal-poor nature of the satellite ([Fe/H]$_\mathrm{spectro}^\mathrm{SgrII} = -2.23 \pm 0.07$) and find that the metallicity dispersion of Sgr II is not resolved, reaching only 0.20 at the 95 per cent confidence limit. No star with a metallicity below −2.5 is confidently detected. Therefore, despite the unusually large size of the system (r$_h = 35.5 ^{+1.4}_{-1.2}$ pc), we conclude that Sgr II is an old and metal-poor globular cluster of the Milky Way.

Spirals in galaxies

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.

Motions of neutral hydrogen at high latitudes

1967 ◽  
Vol 31 ◽  
pp. 265-278 ◽  
Author(s):  
A. Blaauw ◽  
I. Fejes ◽  
C. R. Tolbert ◽  
A. N. M. Hulsbosch ◽  
E. Raimond
Keyword(s):  
Surface Density ◽  
Velocity Dispersion ◽  
Neutral Hydrogen ◽  
Hydrogen Gas ◽  
High Latitudes ◽  
Low Velocity

Earlier investigations have shown that there is a preponderance of negative velocities in the hydrogen gas at high latitudes, and that in certain areas very little low-velocity gas occurs. In the region 100° <l< 250°, + 40° <b< + 85°, there appears to be a disturbance, with velocities between - 30 and - 80 km/sec. This ‘streaming’ involves about 3000 (r/100)2solar masses (rin pc). In the same region there is a low surface density at low velocities (|V| < 30 km/sec). About 40% of the gas in the disturbance is in the form of separate concentrations superimposed on a relatively smooth background. The number of these concentrations as a function of velocity remains constant from - 30 to - 60 km/sec but drops rapidly at higher negative velocities. The velocity dispersion in the concentrations varies little about 6·2 km/sec. Concentrations at positive velocities are much less abundant.

Linking Identity Politics and Foreign Policy

2018 ◽  
Author(s):  
Lisel Hintz
Keyword(s):  
Foreign Policy ◽  
Identity Politics ◽  
Relevant Literature ◽  
Process Tracing ◽  
Theoretical Argument ◽  
Change Over Time ◽  
Inside Out ◽  
Domestic Level ◽  
Over Time

This chapter provides clear definitions of the concepts the book uses and the theory of inside-out identity contestation it develops. The chapter defines competing identity proposals as suggested understandings of the national self that prescribe and proscribe specific behaviors and red lines as particularly intolerable points of contention among supporters of various proposals. It then argues that identity hegemony is the goal of these supporters, and contestation is the process by which the contours of identity debates change over time in supporters’ efforts to achieve hegemony. The chapter briefly reviews relevant literature to carve out space for the book’s theoretical argument: when supporters of a proposal are blocked at the domestic level, they take their fight “outside” through the use of international institutional conditionality, transnational activist networks, and/or diasporic politics. The chapter also discusses the methodology of intertextual analysis and process tracing employed in the study.

scholarly journals Probing non-spherical dark halos in the Galactic dwarf satellites

2013 ◽  
Vol 9 (S298) ◽  
pp. 411-411
Author(s):  
Kohei Hayashi ◽  
Masashi Chiba
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Milky Way ◽  
Velocity Dispersion ◽  
Line Of Sight ◽  
Spherical Structure ◽  
Spherical Models ◽  
Galactic Satellites ◽  
Best Fitting

AbstractWe construct axisymmetric mass models for dwarf spheroidal (dSph) galaxies in the Milky Way to obtain realistic limits on the non-spherical structure of their dark halos. This is motivated by the fact that the observed luminous parts of the dSphs are actually non-spherical and cold dark matter models predict non-spherical virialized dark halos on sub-galactic scales. Applying these models to line-of-sight velocity dispersion profiles along three position angles in six Galactic satellites, we find that the best fitting cases for most of the dSphs yield not spherical but oblate and flattened dark halos. We also find that the mass of the dSphs enclosed within inner 300 pc varies depending on their total luminosities, contrary to the conclusion of previous spherical models. This suggests the importance of considering non-spherical shapes of dark halos in dSph mass models.

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