scholarly journals Reviving old controversies: is the early Galaxy flat or round?

2020 ◽  
Vol 636 ◽  
pp. A115 ◽  
Author(s):  
P. Di Matteo ◽  
M. Spite ◽  
M. Haywood ◽  
P. Bonifacio ◽  
A. Gómez ◽  
...  
Keyword(s):  
Stellar Population ◽  
Milky Way ◽  
Galactic Disc ◽  
Chemical Abundances ◽  
First Stars ◽  
Thick Disc ◽  
Large Program ◽  
The Galaxy ◽  
Early Galaxy ◽  
Two Populations

We analysed a set of very metal-poor stars, for which accurate chemical abundances have been obtained as part of the ESO Large Program “First stars” in the light of the Gaia DR2 data. The kinematics and orbital properties of the stars in the sample show they probably belong to the thick disc, partially heated to halo kinematics, and to the accreted Gaia Sausage-Enceladus satellite. The continuity of these properties with stars at both higher ([Fe/H] >  −2) and lower metallicities ([Fe/H] <  −4.) suggests that the Galaxy at [Fe/H] ≲ −0.5 and down to at least [Fe/H] ∼ −6 is dominated by these two populations. In particular, we show that the disc extends continuously from [Fe/H] ≤ −4 (where stars with disc-like kinematics have recently been discovered) up to [Fe/H] ≥ −2, the metallicity regime of the Galactic thick disc. An “ultra metal-poor thick disc” does indeed exist, constituting the extremely metal-poor tail of the canonical Galactic thick disc, and extending the latter from [Fe/H] ∼ −0.5 up to the most metal-poor stars discovered in the Galaxy to date. These results suggest that the disc may be the main, and possibly the only, stellar population that has formed in the Galaxy at these metallicities. This would mean that the dissipative collapse that led to the formation of the old Galactic disc must have been extremely fast. We also discuss these results in the light of recent simulation efforts made to reproduce the first stages of Milky Way-type galaxies.

scholarly journals The age of the Milky Way inner stellar spheroid from RR Lyrae population synthesis

2020 ◽  
Vol 641 ◽  
pp. A96 ◽  
Author(s):  
A. Savino ◽  
A. Koch ◽  
Z. Prudil ◽  
A. Kunder ◽  
R. Smolec
Keyword(s):  
Stellar Population ◽  
Milky Way ◽  
Population Synthesis ◽  
Milky Way Galaxy ◽  
First Stars ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
The Galaxy ◽  
Stellar Halo ◽  
Lyrae Stars

The central kiloparsecs of the Milky Way are known to host an old, spheroidal stellar population, whose spatial and kinematical properties set it apart from the boxy-peanut structure that constitutes most of the central stellar mass. The nature of this spheroidal population, whether it is a small classical bulge, the innermost stellar halo, or a population of disk stars with large initial velocity dispersion, remains unclear. This structure is also a promising candidate to play host to some of the oldest stars in the Galaxy. Here we address the topic of the inner stellar spheroid age, using spectroscopic and photometric metallicities for a sample of 935 RR Lyrae stars that are constituents of this component. By means of stellar population synthesis, we derive an age-metallicity relation for RR Lyrae populations. We infer, for the RR Lyrae stars in the bulge spheroid, an extremely ancient age of 13.41 ± 0.54 Gyr and conclude they were among the first stars to form in what is now the Milky Way galaxy. Our age estimate for the central spheroid shows a remarkable agreement with the age profile that has been inferred for the Milky Way stellar halo, suggesting a connection between the two structures. However, we find mild evidence for a transition in the halo properties at rGC ∼ 5 kpc. We also investigate formation scenarios for metal-rich RR Lyrae stars, such as binarity and helium variations, and consider whether they can provide alternative explanations for the properties of our sample. We conclude that within our framework, the only viable alternative is to have younger, slightly helium-rich, RR Lyrae stars. This is a hypothesis that would open intriguing questions for the formation of the inner stellar spheroid.

scholarly journals The Disc Origin of the Milky Way Bulge

2016 ◽  
Vol 33 ◽  
Author(s):  
P. Di Matteo
Keyword(s):  
Milky Way ◽  
Complex Structure ◽  
Galactic Bulge ◽  
Galactic Disc ◽  
Major Step ◽  
Thick Disc ◽  
Global Properties ◽  
Out Of Plane ◽  
The Galaxy ◽  
Main Components

AbstractThe Galactic bulge, that is the prominent out-of-plane over-density present in the inner few kiloparsecs of the Galaxy, is a complex structure, as the morphology, kinematics, chemistry, and ages of its stars indicate. To understand the nature of its main components—those at [Fe/H] ≳ −1 dex—it is necessary to make an inventory of the stellar populations of the Galactic disc(s), and of their borders: the chemistry of the disc at the solar vicinity, well known from detailed studies of stars over many years, is not representative of the whole disc. This finding, together with the recent revisions of the mass and sizes of the thin and thick discs, constitutes a major step in understanding the bulge complexity. N-body models of a boxy-/peanut-shaped bulge formed from a thin disc through the intermediary of a bar have been successful in interpreting a number of global properties of the Galactic bulge, but they fail in reproducing the detailed chemo-kinematic relations satisfied by its components and their morphology. It is only by adding the thick disc to the picture that we can understand the nature of the Galactic bulge.

scholarly journals Stellar multiplicity in the Milky Way Galaxy

2017 ◽  
Vol 13 (S334) ◽  
pp. 366-367
Author(s):  
E. Stonkutė ◽  
R. P. Church ◽  
S. Feltzing ◽  
J. A. Johnson
Keyword(s):  
Binary Stars ◽  
Binary Systems ◽  
Milky Way ◽  
Galactic Disc ◽  
Chemical Abundances ◽  
Milky Way Galaxy ◽  
The Galaxy ◽  
Tentative Evidence ◽  
Evolution Algorithm ◽  
Binary Evolution

AbstractWe present our models of the effect of binaries on high-resolution spectroscopic surveys. We want to determine how many binary stars will be observed, whether unresolved binaries will contaminate measurements of chemical abundances, and how we can use spectroscopic surveys to better constrain the population of binary stars in the Galaxy. Using a rapid binary-evolution algorithm that enables modelling of the most complex binary systems we generate a series of large binary populations in the Galactic disc and evaluate the results. As a first application we use our model to study the binary fraction in APOGEE giants. We find tentative evidence for a change in binary fraction with metallicity.

scholarly journals The Stellar Population of the Galactic Bulge

2009 ◽  
Vol 5 (S265) ◽  
pp. 271-278 ◽  
Author(s):  
M. Zoccali
Keyword(s):  
Galaxy Formation ◽  
Stellar Population ◽  
Milky Way ◽  
Current Knowledge ◽  
Stellar Mass ◽  
Galactic Bulge ◽  
Chemical Abundances ◽  
Massive Component ◽  
The Galaxy ◽  
Great Relevance

AbstractThe Galactic bulge is the central spheroid of our Galaxy, containing about one quarter of the total stellar mass of the Milky Way (Mbulge = 1.8 × 1010M⊙; Sofue, Honma & Omodaka 2009). Being older than the disk, it is the first massive component of the Galaxy to have collapsed into stars. Understanding its structure, and the properties of its stellar population, is therefore of great relevance for galaxy formation models. I will review our current knowledge of the bulge properties, with special emphasis on chemical abundances, recently measured for several hundred stars.

scholarly journals The Bulge-disc connection in the Milky Way

2008 ◽  
Vol 4 (S254) ◽  
pp. 145-152
Author(s):  
James Binney
Keyword(s):  
Angular Momentum ◽  
Stellar Population ◽  
Milky Way ◽  
Dark Halo ◽  
Principal Characteristics ◽  
Corotation Radius ◽  
The Galaxy

AbstractBulges come in two flavours – classical and pseudo. The principal characteristics of each flavour are summarised and their impact on discs is considered. Classical bulges probably inhibit the formation of stellar discs. Pseudobulges exchange angular momentum with stars and gas in their companion discs, and also with its embedding dark halo. Since the structure of a pseudobulge depends critically on its angular momentum, these exchanges are expected to modify the bulge. The consequences of this modification are not yet satisfactorily understood. The Galaxy has a pseudobulge. I review the manifestations of its interaction with the disc. More work is needed on the dynamics of gas near the bulge's corotation radius, and on tracing the stellar population in the inner few hundred parsecs of the Galaxy.

scholarly journals The tale of the Milky Way globular cluster NGC 6362 – I. The orbit and its possible extended star debris features as revealed by Gaia DR2

2019 ◽  
Vol 489 (4) ◽  
pp. 4565-4573
Author(s):  
Richa Kundu ◽  
José G Fernández-Trincado ◽  
Dante Minniti ◽  
Harinder P Singh ◽  
Edmundo Moreno ◽  
...  
Keyword(s):  
Milky Way ◽  
Galactic Plane ◽  
Vertical Component ◽  
Galactic Disc ◽  
Corotation Radius ◽  
Magnitude Diagram ◽  
The Galaxy ◽  
History Of ◽  
Event Based ◽  
Gaia Dr2

ABSTRACTWe report the identification of possible extended star debris candidates beyond the cluster tidal radius of NGC 6362 based on the second Gaia data release (Gaia DR2). We found 259 objects possibly associated with the cluster lying in the vicinity of the giant branch and 1–2 magnitudes fainter/brighter than the main-sequence turn-off in the cluster colour–magnitude diagram and which cover an area on the sky of ∼4.1 deg2 centred on the cluster. We traced back the orbit of NGC 6362 in a realistic Milky Way potential, using the gravpot16 package, for 3 Gyr. The orbit shows that the cluster shares similar orbital properties as the inner disc, having peri-/apogalactic distances, and maximum vertical excursion from the Galactic plane inside the corotation radius (CR), moving inwards from CR radius to visit the inner regions of the Milky Way. The dynamical history of the cluster reveals that it has crossed the Galactic disc several times in its lifetime and has recently undergone a gravitational shock, ∼15.9 Myr ago, suggesting that less than 0.1 per cent of its mass has been lost during the current disc-shocking event. Based on the cluster’s orbit and position in the Galaxy, we conclude that the possible extended star debris candidates are a combined effect of the shocks from the Galactic disc and evaporation from the cluster. Lastly, the evolution of the vertical component of the angular momentum shows that the cluster is strongly affected dynamically by the Galactic bar potential.

Recovering the origin of the lenticular galaxy NGC3115 using multi-band photometry

2019 ◽  
Vol 15 (S359) ◽  
pp. 421-423
Author(s):  
Maria Luísa Buzzo ◽  
Arianna Cortesi ◽  
Ariel Werle ◽  
Claudia Mendes de Oliveira
Keyword(s):  
Stellar Population ◽  
Galactic Nuclei ◽  
Two Phase ◽  
Thick Disc ◽  
Star Formation Activity ◽  
The Galaxy ◽  
Minor Mergers ◽  
Main Components ◽  
Baryonic Mass ◽  
Multi Band

AbstractWe perform simultaneous multi-band fitting, using the routine GALFITM, of the galaxy NGC3115, in order to recover the stellar populations of its main components (a bulge, a thin disc and a thick disc). We model 11 bands, from ultraviolet to infrared, in order to take into account the galaxy younger stellar population and the presence of the Active Galactic Nuclei (AGN). We find that the majority of the galaxy baryonic mass belongs to the thick disc, which is also the oldest galaxy component, consistent with results from the literature. Differently from previous works, we find that the bulge has the bluest colour and it is younger than the thick disc, either as a result of recent star formation activity, or AGN feedback, or white dwarf emission in an old stellar population. Finally, we propose that NGC3115 was formed either through a two-phase formation scenario, or via an outside-in quenching of an isolated spiral galaxy, whose thick disc had been heated-up via minor mergers with dwarf satellites.

scholarly journals The RAVE harvest: from the relation between abundances and kinematic of the Milky Way stars to tools for the abundance analysis of the spectra

2013 ◽  
Vol 9 (S298) ◽  
pp. 292-297
Author(s):  
Corrado Boeche ◽  
Keyword(s):  
Milky Way ◽  
Radial Velocities ◽  
Proper Motions ◽  
Chemical Abundances ◽  
Stellar Spectra ◽  
Chemical Gradients ◽  
Single Process ◽  
The Galaxy ◽  
Nearby Stars ◽  
Kinematic Information

AbstractRAVE is a spectroscopic survey of the Milky Way which collected more than 500,000 stellar spectra of nearby stars in the Galaxy. The RAVE consortium analysed these spectra to obtain radial velocities, stellar parameters and chemical abundances. These data, together with spatial and kinematic information like positions, proper motions, and distance estimations, make the RAVE database a rich source for galactic archaeology. I present recent investigations on the chemo-kinematic relations and chemical gradients in the Milky Way disk using RAVE data and compare our results with the Besançon models. I also present the code SPACE, an evolution of the RAVE chemical pipeline, which integrates the measurements of stellar parameters and chemical abundances in one single process.

The thick disc according to Gaia-ESO

2017 ◽  
Vol 12 (S330) ◽  
pp. 218-219 ◽  
Author(s):  
Louise M. Howes ◽  
Thomas Bensby
Keyword(s):  
Stellar Populations ◽  
Selection Function ◽  
Selection Effects ◽  
Galactic Disc ◽  
Thick Disc ◽  
Vertical Extent ◽  
Data Release ◽  
The Galaxy

AbstractIn the era of large spectroscopic surveys, it is vital that selection effects are taken into account when making conclusions about the stellar populations of the Galaxy. Here we use the Galactic disc sample of stars from the Gaia-ESO Survey internal data release 4 (GES iDR4), applying the published selection function to characterise the vertical extent of the chemically defined thick and thin discs.

scholarly journals Statistical Study of Globules Projected on Stellar Clouds

1958 ◽  
Vol 8 ◽  
pp. 949-950
Author(s):  
D. A. Rojkovsky
Keyword(s):  
Stellar Population ◽  
Milky Way ◽  
Statistical Study ◽  
The Other ◽  
Hot Stars ◽  
Dark Clouds ◽  
Physical Conditions ◽  
Irregular Shapes ◽  
The Galaxy ◽  
Favorable Conditions

The discovery of globules by Bok and Reilly leads to various speculation concerning their cosmogonical meaning as protostellar bodies in our galaxy.It is well known that the most favorable conditions for the discovery and study of globules are reached when they are connected with diffuse galactic nebulae (Dufay). Observations show that in this case globules possess various and generally irregular shapes. It is quite probable that these globules are connected with large dark clouds, genetically linked with bright nebulae. The number of globules in a nebula depends essentially on the peculiarity of its structure. Nevertheless the total area of the sky covered by the nebulae is relatively small and their physical conditions depending on nearby hot stars are peculiar. Consequently it is hardly possible to suppose that the properties of globules present in nebulae are the same as in the other regions of the galaxy. It is important to collect more data concerning the spatial distribution of globules, their density, sizes etc. The stellar clouds of the Milky Way give some possibility for further study in this respect. In the case of a sufficiently dense stellar field the projecting globules can be discovered as some fluctuations in the stellar population as observed on the photograph.

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