scholarly journals Constraining churning and blurring in the Milky Way using large spectroscopic surveys – an exploratory study

2020 ◽  
Vol 493 (1) ◽  
pp. 1419-1433 ◽  
Author(s):  
Sofia Feltzing ◽  
J Bradley Bowers ◽  
Oscar Agertz
Keyword(s):  
Exploratory Study ◽  
Milky Way ◽  
Selection Effects ◽  
Radial Migration ◽  
Elemental Abundances ◽  
Stellar Ages ◽  
C And N ◽  
Red Giant ◽  
Future Work ◽  
Giant Branch Stars

ABSTRACT We have investigated the possibilities to quantify how much stars move in the Milky Way disc due to diffuse processes (blurring) and due to influences from spiral arms and the bar (churning). We assume that the formation radius of a star can be inferred if we know its elemental abundances and age and the metallicity profile of the interstellar medium at the time of the star’s formation. We use data for red giant branch stars from APOGEE DR14, parallaxes from Gaia, and stellar ages based on the C and N abundances. In our sample, we find that half of the stars have experienced some sort of radial migration, 10 per cent likely have suffered only from churning, and a modest 5–7 per cent have never experienced either churning or blurring making them ideal tracers of the original properties of the cool stellar disc. To arrive at these numbers, we imposed the requirement that the stars that are considered to be churned have highly circular orbits. If instead we require that the star has moved away from its formation position and at the same time that its Galactocentric radius at formation did not fall between the apo- and pericentre of its orbit today, we find that about half of the stars have undergone a radial migration. We have thus shown that it is possible to put up a framework to quantify churning and blurring. Future work includes investigations of how selection effects influence the results.

scholarly journals Neutron-capture elements in dwarf galaxies

2019 ◽  
Vol 631 ◽  
pp. A171 ◽  
Author(s):  
Á. Skúladóttir ◽  
C. J. Hansen ◽  
S. Salvadori ◽  
A. Choplin
Keyword(s):  
Neutron Capture ◽  
Milky Way ◽  
Dwarf Galaxies ◽  
Core Collapse ◽  
Chemical Abundances ◽  
Relative Contribution ◽  
History Of ◽  
Red Giant ◽  
Process Element ◽  
Giant Branch Stars

The heavy elements (Z >  30) are created in neutron (n)-capture processes that are predicted to happen at vastly different nucleosynthetic sites. To study these processes in an environment different from the Milky Way, we targeted the n-capture elements in red giant branch stars in the Sculptor dwarf spheroidal galaxy. Using ESO VLT/FLAMES spectra, we measured the chemical abundances of Y, Ba, La, Nd, and Eu in 98 stars covering the metalliticy range −2.4 < [Fe/H] < −0.9. This is the first paper in a series about the n-capture elements in dwarf galaxies, and here we focus on the relative and absolute timescales of the slow (s)- and rapid (r)-processes in Sculptor. From the abundances of the s-process element Ba and the r-process element Eu, it is clear that the r-process enrichment occurred throughout the entire chemical evolution history of Sculptor. Furthermore, there is no evidence for the r-process to be significantly delayed in time relative to core-collapse supernovae. Neutron star mergers are therefore unlikely the dominant (or only) nucleosynthetic site of the r-process. However, the products of the s-process only become apparent at [Fe/H] ≈ −2 in Sculptor, and the s-process becomes the dominant source of Ba at [Fe/H] ≳ −2. We tested the use of [Y/Mg] and [Ba/Mg] as chemical clocks in Sculptor. Similarly to what is observed in the Milky Way, [Y/Mg] and [Ba/Mg] increase towards younger ages. However, there is an offset in the trends, where the abundance ratios of [Y/Mg] in Sculptor are significantly lower than those of the Milky Way at any given age. This is most likely caused by metallicity dependence of yields from the s-process, as well as by a different relative contribution of the s-process to core-collapse supernovae in these galaxies. Comparisons of our results with data of the Milky Way and the Fornax dwarf spheroidal galaxy furthermore show that these chemical clocks depend on both metallicity and environment.

scholarly journals The biggest splash

2020 ◽  
Vol 494 (3) ◽  
pp. 3880-3898 ◽  
Author(s):  
Vasily Belokurov ◽  
Jason L Sanders ◽  
Azadeh Fattahi ◽  
Martin C Smith ◽  
Alis J Deason ◽  
...  
Keyword(s):  
Milky Way ◽  
Large Population ◽  
Azimuthal Velocity ◽  
Causal Connection ◽  
Elemental Abundances ◽  
Eccentric Orbits ◽  
Stellar Ages ◽  
Major Merger ◽  
Nearby Stars ◽  
Rule Out

ABSTRACT Using a large sample of bright nearby stars with accurate Gaia Data Release 2 astrometry and auxiliary spectroscopy we map out the properties of the principle Galactic components such as the ‘thin’ and ‘thick’ discs and the halo. We confirm previous claims that in the Solar neighbourhood, there exists a large population of metal-rich ([Fe/H] &gt; −0.7) stars on highly eccentric orbits. By studying the evolution of elemental abundances, kinematics, and stellar ages in the plane of azimuthal velocity vϕ and metallicity [Fe/H], we demonstrate that this metal-rich halo-like component, which we dub the Splash, is linked to the α-rich (or ‘thick’) disc. Splash stars have little to no angular momentum and many are on retrograde orbits. They are predominantly old, but not as old as the stars deposited into the Milky Way (MW) in the last major merger. We argue, in agreement with several recent studies, that the Splash stars may have been born in the MW’s protodisc prior to the massive ancient accretion event which drastically altered their orbits. We cannot, however, rule out other (alternative) formation channels. Taking advantage of the causal connection between the merger and the Splash, we put constraints of the epoch of the last massive accretion event to have finished 9.5 Gyr ago. The link between the local metal-rich and metal-poor retrograde stars is confirmed using a large suite of cutting-edge numerical simulations of the MW’s formation.

scholarly journals Nucleosynthesis in the Stellar Systems ω Centauri and M22

2011 ◽  
Vol 28 (1) ◽  
pp. 28-37 ◽  
Author(s):  
G. S. Da Costa ◽  
A. F. Marino
Keyword(s):  
Globular Cluster ◽  
Total Mass ◽  
Large Range ◽  
Stellar System ◽  
Stellar Systems ◽  
Elemental Abundances ◽  
Two Systems ◽  
Red Giant ◽  
Using Data ◽  
Giant Branch Stars

AbstractThe stellar system ω Centauri (ω Cen) is well known for the large range in elemental abundances among its member stars. Recent work has indicated that the globular cluster M22 (NGC 6656) also possesses an internal abundance range, albeit substantially smallerthan that in ω Cen. Here we compare, as a function of [Fe/H], element-to-iron ratios in the two systems for a number of different elements using data from abundance analyses of red giant branch stars. It appears that the nucleosynthetic enrichment processes were very similar in these two systems despite the substantial difference in total mass.

scholarly journals Resolving the stellar halos of six massive disk galaxies beyond the Local Group

2015 ◽  
Vol 11 (S317) ◽  
pp. 222-227 ◽  
Author(s):  
Antonela Monachesi ◽  
Eric F. Bell ◽  
David J. Radburn-Smith ◽  
Roelof S. de Jong ◽  
Jeremy Bailin ◽  
...  
Keyword(s):  
Galaxy Formation ◽  
Milky Way ◽  
Local Group ◽  
Density Profiles ◽  
Galaxy Halos ◽  
The Galaxy ◽  
Stellar Halo ◽  
Red Giant ◽  
Stellar Properties ◽  
Giant Branch Stars

AbstractModels of galaxy formation in a hierarchical universe predict substantial scatter in the halo-to-halo stellar properties, owing to stochasticity in galaxies' merger histories. Currently, only few detailed observations of stellar halos are available, mainly for the Milky Way and M31. We present the stellar halo color/metallicity and density profiles of red giant branch stars out to ~60 kpc along the minor axis of six massive nearby Milky Way-like galaxies beyond the Local Group from the Galaxy Halos, Outer disks, Substructure, Thick disks and Star clusters (GHOSTS) HST survey. This enlargement of the sample of galaxies with observations of stellar halo properties is needed to understand the range of possible halo properties, i.e. not only the mean properties but also the halo-to-halo scatter, what a ‘typical’ halo looks like, and how similar the Milky Way halo is to other halos beyond the Local Group.

The Data-Driven Approach to Spectroscopic Analyses

2018 ◽  
Vol 35 ◽  
Author(s):  
M. Ness
Keyword(s):  
Galaxy Formation ◽  
Milky Way ◽  
Galactic Disk ◽  
Data Driven ◽  
Chemical Compositions ◽  
Giant Stars ◽  
Stellar Ages ◽  
Data Driven Approach ◽  
Red Giant

AbstractI review the data-driven approach to spectroscopy, The Cannon, which is a method for deriving fundamental diagnostics of galaxy formation of precise chemical compositions and stellar ages, across many stellar surveys that are mapping the Milky Way. With The Cannon, the abundances and stellar parameters from the multitude of stellar surveys can be placed directly on the same scale, using stars in common between the surveys. Furthermore, the information that resides in the data can be fully extracted, this has resulted in higher precision stellar parameters and abundances being delivered from spectroscopic data and has opened up new avenues in galactic archeology, for example, in the determination of ages for red giant stars across the Galactic disk. Coupled with Gaia distances, proper motions, and derived orbit families, the stellar age and individual abundance information delivered at the precision obtained with the data-driven approach provides very strong constraints on the evolution of and birthplace of stars in the Milky Way. I will review the role of data-driven spectroscopy as we enter the era where we have both the data and the tools to build the ultimate conglomerate of galactic information as well as highlight further applications of data-driven models in the coming decade.

scholarly journals The AMBRE project: a study of Li evolution in the Galactic thin and thick discs

2017 ◽  
Vol 606 ◽  
pp. A132 ◽  
Author(s):  
N. Prantzos ◽  
P. de Laverny ◽  
G. Guiglion ◽  
A. Recio-Blanco ◽  
C. C. Worley
Keyword(s):  
Milky Way ◽  
Asymptotic Giant Branch ◽  
Red Giants ◽  
Asymptotic Giant Branch Stars ◽  
Radial Migration ◽  
Stellar Sources ◽  
Stellar Envelopes ◽  
Giant Branch Stars ◽  
Simple Picture

Context. Recent observations suggest a double-branch behaviour of Li/H versus metallicity in the local thick and thin discs. This is reminiscent of the corresponding O/Fe versus Fe/H behaviour, which has been explained as resulting from radial migration in the Milky Way disc. Aims. We study here the role of radial migration in shaping these observations. Methods. We use a semi-analytical model of disc evolution with updated chemical yields and parameterised radial migration. We explore the cases of long-lived (red giants of a few Gy lifetime) and shorter-lived (asymptotic giant branch stars of several 108 yr) stellar sources of Li, as well as those of low and high primordial Li. We show that both factors play a key role in the overall Li evolution. Results. We find that the observed two-branch Li behaviour is only directly obtained in the case of long-lived stellar Li sources and low primordial Li. In all other cases, the data imply systematic Li depletion in stellar envelopes, thus no simple picture of the Li evolution can be obtained. This concerns also the reported Li/H decrease at supersolar metallicities.

scholarly journals Exploring the vertical age structure of the Galactic disc

2015 ◽  
Vol 11 (S319) ◽  
pp. 113-113
Author(s):  
Luca Casagrande
Keyword(s):  
Age Structure ◽  
Milky Way ◽  
High Redshift ◽  
Age Distribution ◽  
Galactic Disc ◽  
High Redshift Galaxies ◽  
Giant Stars ◽  
Stellar Ages ◽  
Red Giant ◽  
Stellar Properties

AbstractWhile in external or high-redshift galaxies we can only measure integrated stellar properties at best, the Milky Way offers us the unique opportunity to study its individual baryonic components, including stars. We use oscillations measured in red giant stars by the Kepler satellite to derive stellar ages and explore the vertical age structure across few kpc of the Milky Way disc. We find that old stars dominate at increasing Galactic heights, whereas closer to the plane a rich zoology of ages exists. The age distribution of stars shows a smooth distribution over the last 10 Gyr, which together with a flat age-metallicity relation is consistent with a quiescent evolution for the Milky Way disc since a redshift of about two.

scholarly journals Towards an Improved Model of the Galaxy

1998 ◽  
Vol 11 (1) ◽  
pp. 570-570
Author(s):  
Johan Holmberg ◽  
Lennart Lindegren ◽  
Chris Flynn
Keyword(s):  
Three Dimensional ◽  
Direct Determination ◽  
Galactic Structure ◽  
Open Clusters ◽  
Selection Effects ◽  
Observational Errors ◽  
Red Giant ◽  
Improved Model ◽  
First Time ◽  
Hr Diagram

We use the Hipparcos survey to derive an improved model of the local galactic structure. The availability of parallaxes for all the stars permits direct determination of stellar distributions, eliminating the basic indeterminacy of classical methods based on star counts. Hipparcos gives for the first time a truly three-dimensional view of the solar vicinity, and a complete, homogeneous and highly accurate set of magnitudes and colours. This means that new techniques can be applied in the treatment of the data which place strong constraints on a model that tries to describe the local Galactic structure. Here we investigate how well a static model of low complexitycan describe the Hipparcos observations. The interpretation of the Hipparcos data is complicated by various observational errors and selection effects that are hard to treat correctly. We do not try to correct the data, but instead use a model and subject this model to the same observational errors and selection effects. A model catalogue is created that can be compared with the observed catalogue directly in the observational domain, thereby eliminating the effects from various biases. Many features in the HR diagram are for the first time seen in field stars thanks to Hipparcos, such as the slanted red giant clump, previously seen in rich old open clusters such as Berkeley 18. This and other features ofthe observed HR diagram are well reproduced by the model thanks to the rather detailed modelling of the joint Mv/B — V distribution. Actually, separate distributions were derived for the three different components, disk, thick disk and halo, using the kinematic characteristics of the components to discriminate between them.

scholarly journals Shaping Disk Galaxy Stellar Populations via Internal and External Processes

2012 ◽  
Vol 10 (H16) ◽  
pp. 372-372
Author(s):  
Rok Roškar
Keyword(s):  
Galaxy Formation ◽  
Stellar Population ◽  
Milky Way ◽  
Stellar Populations ◽  
Radial Migration ◽  
Disk Formation ◽  
Process Understanding ◽  
History Of ◽  
Nearby Galaxies ◽  
Gas Accretion

AbstractIn recent years, effects such as the radial migration of stars in disks have been recognized as important drivers of the properties of stellar populations. Radial migration arises due to perturbative effects of disk structures such as bars and spiral arms, and can deposit stars formed in disks to regions far from their birthplaces. Migrant stars can significantly affect the demographics of their new locales, especially in low-density regions such as in the outer disks. However, in the cosmological environment, other effects such as mergers and filamentary gas accretion also influence the disk formation process. Understanding the relative importance of these processes on the detailed evolution of stellar population signatures is crucial for reconstructing the history of the Milky Way and other nearby galaxies. In the Milky Way disk in particular, the formation of the thickened component has recently attracted much attention due to its potential to serve as a diagnostic of the galaxy's early history. Some recent work suggests, however, that the vertical structure of Milky Way stellar populations is consistent with models that build up the thickened component through migration. I discuss these developments in the context of cosmological galaxy formation.

Sign in / Sign up

Export Citation Format

Share Document