scholarly journals Young Stars far from the Galactic Plane: Runaways from Clusters

2004 ◽  
Vol 191 ◽  
pp. 121-127
Author(s):  
Christine Allen ◽  
T.D. Kinman
Keyword(s):  
Star Formation ◽  
Galactic Halo ◽  
Galactic Plane ◽  
Dynamical Evolution ◽  
Young Stars ◽  
Formation Mechanisms ◽  
Conventional View ◽  
Spiral Density Waves ◽  
Ejection Mechanism

AbstractQuite recently, a significant number of OB stars far from the galactic plane have been found, situated at z- distances ranging from several hundreds of pc to several kpc. The short lifetimes of these stars pose problems for their interpretation in terms of the standard picture of star formation. Different mechanisms have been put forward to explain the existence of these stars, either within the conventional view, or postulating star formation in the galactic halo itself. These mechanisms range from arguing that they are misidentified evolved or abnormal stars, to postulating powerful ejection mechanisms for young disk stars; in situ formation also admits several variants. We have collected from the literature a list of young stars far from the plane, for which the evidence of youth seems convincing. We discuss two possible formation mechanisms for these stars: ejection from the plane as the result of dynamical evolution of small clusters (Poveda et al. 1967) and in situ formation, via induced shocks created by spiral density waves (Martos et al. 1999). We compute galactic orbits for these stars, and identify the stars that could be explained by one or the other mechanism. We find that about 90 percent of the stars can be accounted for by the cluster ejection mechanism, that is, they can be regarded as runaway stars in the galactic halo.

Chemo-dynamical signatures in simulated Milky Way-like galaxies

2017 ◽  
Vol 12 (S330) ◽  
pp. 263-264
Author(s):  
Alessandro Spagna ◽  
Anna Curir ◽  
Marco Giammaria ◽  
Mario G. Lattanzi ◽  
Giuseppe Murante ◽  
...  
Keyword(s):  
Milky Way ◽  
Galactic Plane ◽  
Dynamical Evolution ◽  
Thin Disk ◽  
Disk Galaxy ◽  
Radial Gradient ◽  
Heating Mechanism ◽  
Disk Evolution ◽  
Inside Out

AbstractWe have investigated the chemo-dynamical evolution of a Milky Way-like disk galaxy, AqC4, produced by a cosmological simulation integrating a sub-resolution ISM model. We evidence a global inside-out and upside-down disk evolution, that is consistent with a scenario where the “thin disk” stars are formed from the accreted gas close to the galactic plane, while the older “thick disk” stars are originated in situ at higher heights. Also, the bar appears the most effective heating mechanism in the inner disk. Finally, no significant metallicity-rotation correlation has been observed, in spite of the presence of a negative [Fe/H] radial gradient.

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.

scholarly journals Rotation of B-type stars as an indicator of star formation mechanisms

1984 ◽  
Vol 105 ◽  
pp. 113-115
Author(s):  
B.N.G. Guthrie
Keyword(s):  
Star Formation ◽  
Main Sequence ◽  
Galactic Plane ◽  
Maxwellian Distribution ◽  
Formation Mechanisms ◽  
Sequence Evolution ◽  
Class V ◽  
Magnetic Braking ◽  
Normal Class

Differences in the distributions of v sin i for various samples of B-type stars may reflect different mechanisms of star formation. The overall distribution of v sin i for late B-type stars in clusters at low galactic latitudes is bimodal, but normal class V field stars may have a Maxwellian distribution of v. The spin axes of stars in tightly bound clusters may be preferentially aligned perpendicular to the galactic plane. Early B-type stars in the youngest subgroups of associations may have a Maxwellian distribution of v, but there is a prominent excess of slow rotators among stars in older subgroups and field stars. This excess cannot be entirely accounted for by tidal or magnetic braking during main-sequence evolution.

scholarly journals Large scale magnetic fields of our Galaxy

2009 ◽  
Vol 5 (H15) ◽  
pp. 450-451
Author(s):  
JinLin Han
Keyword(s):  
Star Formation ◽  
Magnetic Fields ◽  
Large Scale ◽  
Galactic Halo ◽  
Galactic Center ◽  
Galactic Plane ◽  
Galactic Disk ◽  
Zeeman Splitting ◽  
Radio Sources ◽  
Star Formation Regions

AbstractLarge-scale magnetic fields in the Galactic disk have been revealed by distributions of pulsar rotation measures (RMs) and Zeeman splitting data of masers in star formation regions, which have several reversals in arm and interarm regions. Magnetic fields in the Galactic halo are reflected by the antisymmetric sky distribution of RMs of extragalactic radio sources, which have azimuthal structure with reversed directions below and above the Galactic plane. Large-scale magnetic fields in the Galactic center probably have a poloidal and toroidal structure.

scholarly journals The origin of the first neutron star – neutron star merger

2018 ◽  
Vol 615 ◽  
pp. A91 ◽  
Author(s):  
K. Belczynski ◽  
A. Askar ◽  
M. Arca-Sedda ◽  
M. Chruslinska ◽  
M. Donnari ◽  
...  
Keyword(s):  
Star Formation ◽  
Neutron Star ◽  
Globular Clusters ◽  
Elliptical Galaxy ◽  
Binary Star ◽  
Cluster Formation ◽  
Dynamical Evolution ◽  
Compact Objects ◽  
Formation Mechanisms ◽  
Current Sensitivity

The first neutron star-neutron star (NS-NS) merger was discovered on August 17, 2017 through gravitational waves (GW170817) and followed with electromagnetic observations. This merger was detected in an old elliptical galaxy with no recent star formation. We perform a suite of numerical calculations to understand the formation mechanism of this merger. We probe three leading formation mechanisms of double compact objects: classical isolated binary star evolution, dynamical evolution in globular clusters, and nuclear cluster formation to test whether they are likely to produce NS-NS mergers in old host galaxies. Our simulations with optimistic assumptions show current NS-NS merger rates at the level of 10−2 yr−1 from binary stars, 5 × 10−5 yr−1 from globular clusters, and 10−5 yr−1 from nuclear clusters for all local elliptical galaxies (within 100 Mpc3). These models are thus in tension with the detection of GW170817 with an observed rate of 1.5−1.2+3.2 yr−1 (per 100 Mpc3; LIGO/Virgo 90% credible limits). Our results imply that either the detection of GW170817 by LIGO/Virgo at their current sensitivity in an elliptical galaxy is a statistical coincidence; that physics in at least one of our three models is incomplete in the context of the evolution of stars that can form NS-NS mergers; or that another very efficient (unknown) formation channel with a long delay time between star formation and merger is at play.

scholarly journals Origin and evolution of structure and nucleosynthesis for galaxies in the local group

2014 ◽  
Vol 29 (14) ◽  
pp. 1430012 ◽  
Author(s):  
G. J. Mathews ◽  
A. Snedden ◽  
L. A. Phillips ◽  
I.-S. Suh ◽  
J. Coughlin ◽  
...  
Keyword(s):  
Dark Matter ◽  
Local Group ◽  
Galactic Halo ◽  
Galactic Plane ◽  
Dwarf Galaxies ◽  
Gravitational Interaction ◽  
Galactic Halos ◽  
Origin And Evolution ◽  
Spiral Density Waves ◽  
Streaming Flows

The Milky Way is the product of a complex evolution of generations of mergers, collapse, star formation, supernova and collisional heating, radiative and collisional cooling, and ejected nucleosynthesis. Moreover, all of this occurs in the context of the cosmic expansion, the formation of cosmic filaments, dark matter halos, spiral density waves, and emerging dark energy. In this review we summarize observational evidence and discuss recent calculations concerning the formation, evolution nucleosynthesis in the galaxies of the Local Group (LG). In particular, we will briefly summarize observations and simulations for the dwarf galaxies and the two large spirals of the LG. We discuss how galactic halos form within the dark matter filaments that define a super-galactic plane. Gravitational interaction along this structure leads to streaming flows toward the two dominant galaxies in the cluster. These simulations and observations also suggest that a significant fraction of the Galactic halo formed as at large distances and then arrived later along these streaming flows. We also consider the insight provided by observations and simulations of nucleosynthesis both within the galactic halo and dwarf galaxies in the LG.

scholarly journals VINTERGATAN III: how to reset the metallicity of the Milky Way

2021 ◽  
Vol 503 (4) ◽  
pp. 5868-5876
Author(s):  
Florent Renaud ◽  
Oscar Agertz ◽  
Eric P Andersson ◽  
Justin I Read ◽  
Nils Ryde ◽  
...  
Keyword(s):  
Star Formation ◽  
Milky Way ◽  
Galactic Plane ◽  
First Stars ◽  
Massive Galaxies ◽  
The Galaxy ◽  
Chemical Content ◽  
Major Merger ◽  
Purely Sequential

ABSTRACT Using the cosmological zoom simulation VINTERGATAN, we present a new scenario for the onset of star formation at the metal-poor end of the low-[α/Fe] sequence in a Milky Way-like galaxy. In this scenario, the galaxy is fuelled by two distinct gas flows. One is enriched by outflows from massive galaxies, but not the other. While the former feeds the inner galactic region, the latter fuels an outer gas disc, inclined with respect to the main galactic plane, and with a significantly poorer chemical content. The first passage of the last major merger galaxy triggers tidal compression in the outer disc, which increases the gas density and eventually leads to star formation, at a metallicity 0.75 dex lower than the inner galaxy. This forms the first stars of the low-[α/Fe] sequence. These in situ stars have halo-like kinematics, similar to what is observed in the Milky Way, due to the inclination of the outer disc that eventually aligns with the inner one via gravitational torques. We show that this tilting disc scenario is likely to be common in Milky Way-like galaxies. This process implies that the low-[α/Fe] sequence is populated in situ, simultaneously from two formation channels, in the inner and the outer galaxy, with distinct metallicities. This contrasts with purely sequential scenarios for the assembly of the Milky Way disc and could be tested observationally.

scholarly journals Origin of the Galactic Halo: accretion vs. in situ formation

2017 ◽  
Vol 13 (S334) ◽  
pp. 34-37
Author(s):  
Emanuele Spitoni ◽  
Fiorenzo Vincenzo ◽  
Francesca Matteucci ◽  
Donatella Romano
Keyword(s):  
Star Formation ◽  
Neutron Capture ◽  
Time Scale ◽  
Galactic Halo ◽  
Building Blocks ◽  
The Other ◽  
Chemical Abundances ◽  
Halo Stars ◽  
In Situ Formation

AbstractWe test the hypothesis that the classical and ultra-faint dwarf spheroidal satellites of the our Galaxy have been the building blocks of the Galactic halo by comparing their [O/Fe] and [Ba/Fe] vs. [Fe/H] patterns with the ones observed in Galactic halo stars. The [O/Fe] ratio deviates substantially from the observed abundance ratios in the Galactic halo stars for [Fe/H] > -2 dex, while they overlap for lower metallicities. On the other hand, for the neutron capture elements, the discrepancy is extended at all the metallicities, suggesting that the majority of stars in the halo are likely to have been formed in situ. We present the results for a model considering the effects of an enriched gas stripped from dwarf satellites on the chemical evolution of the Galactic halo. We find that the resulting chemical abundances of the halo stars depend on the adopted infall time-scale, and the presence of a threshold in the gas for star formation.

scholarly journals Models for the dynamical evolution of the Magellanic System

2008 ◽  
Vol 4 (S256) ◽  
pp. 105-116
Author(s):  
Kenji Bekki
Keyword(s):  
Galactic Halo ◽  
Dynamical Evolution ◽  
Magellanic Clouds ◽  
Young Stars ◽  
Proper Motions ◽  
Self Consistent ◽  
The Galaxy ◽  
Formation And Evolution ◽  
Magellanic Stream ◽  
Magellanic System

AbstractI discuss the following five selected topics on formation and evolution of the LMC and the SMC based on fully self-consistent chemodynamical simulations of the Magellanic Clouds (MCs): (1) formation of bifurcated gaseous structures and young stars in the Magellanic bridge (MB), (2) formation of the Magellanic stream (MS) due to the tidal interaction between the LMC, the SMC, and the Galaxy within the last 2 Gyrs, (3) origin of the observed kinematical differences between H i gas and stars in the SMC, (4) formation of stellar structures dependent on their ages and metallicities in the LMC, and (5) a new common halo model explaining both the latest HST ACS observations on the proper motions of the LMC and the SMC and the presence of the MS in the Galactic halo. I focus exclusively on the latest developments in numerical simulations on formation and evolution of the Magellanic system.

scholarly journals Globular cluster contributions to Galactic halo assembly

2012 ◽  
Vol 10 (H16) ◽  
pp. 286-287
Author(s):  
Sarah L. Martell
Keyword(s):  
Star Formation ◽  
Globular Cluster ◽  
Second Generation ◽  
Galactic Halo ◽  
Cluster Formation ◽  
Light Element ◽  
Element Abundances ◽  
Giant Stars ◽  
Red Giant

AbstractI discuss a search for red giant stars in the Galactic halo with light-element abundances similar to second-generation globular cluster stars, and discuss the implications of such a population for globular cluster formation models and the balance between in situ star formation and accretion for the assembly of the Galactic halo.

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