scholarly journals Metallicity distribution functions using Gaia-DR1 data

2017 ◽  
Vol 12 (S330) ◽  
pp. 172-175
Author(s):  
Georges Kordopatis ◽  
Keyword(s):  
Distribution Function ◽  
Milky Way ◽  
Distribution Functions ◽  
Gaia Dr1 ◽  
The Galaxy ◽  
Vertical Changes ◽  
Metallicity Distribution

AbstractThe metallicity distribution function (MDF) of the stellar components of the Milky Way hold valuable information regarding the processes that have taken place in the evolution of our Galaxy. In this proceeding, we investigate updates concerning the MDF now that the Tycho-Gaia Astrometric Solution (TGAS) catalogue has been released and that trigonometric distances are available. In particular, vertical changes and skewness of the MDF are investigated, together with the properties of the metal-rich stars in the sample, at different positions in the Galaxy.

scholarly journals The Metallicity Distribution of the Milky Way Bulge

2016 ◽  
Vol 33 ◽  
Author(s):  
M. Ness ◽  
K. Freeman
Keyword(s):  
Distribution Function ◽  
Milky Way ◽  
Vertical Gradient ◽  
The Galaxy ◽  
Stellar Halo ◽  
Different Populations ◽  
Formation And Evolution ◽  
The Mean ◽  
Inner Region ◽  
Metallicity Distribution

AbstractThe Galactic bulge of the Milky Way is made up of stars with a broad range of metallicity, –3.0 < [Fe/H] < 1 dex. The mean of the metallicity distribution function decreases as a function of height z from the plane and, more weakly, with galactic radius RGC. The most metal-rich stars in the inner Galaxy are concentrated to the plane and the more metal-poor stars are found predominantly further from the plane, with an overall vertical gradient in the mean of the metallicity distribution function of about − 0.45 dex kpc−1. This vertical gradient is believed to reflect the changing contribution with height of different populations in the innermost region of the Galaxy. The more metal-rich stars of the bulge are part of the boxy/peanut structure and comprise stars in orbits which trace out the underlying X-shape. There is still a lack of consensus on the origin of the metal-poor stars ([Fe/H] < −0.5) in the region of the bulge. Some studies attribute the more metal-poor stars of the bulge to the thick disk and stellar halo that are present in the inner region, and other studies propose that the metal-poor stars are a distinct ‘old spheroid’ bulge population. Understanding the origin of the populations that make up the metallicity distribution function of the bulge, and identifying if there is a unique bulge population which has formed separately from the disk and halo, has important consequences for identifying the relevant processes in the formation and evolution of the Milky Way.

scholarly journals CHEMICAL CARTOGRAPHY WITH APOGEE: METALLICITY DISTRIBUTION FUNCTIONS AND THE CHEMICAL STRUCTURE OF THE MILKY WAY DISK

2015 ◽  
Vol 808 (2) ◽  
pp. 132 ◽  
Author(s):  
Michael R. Hayden ◽  
Jo Bovy ◽  
Jon A. Holtzman ◽  
David L. Nidever ◽  
Jonathan C. Bird ◽  
...  
Keyword(s):  
Chemical Structure ◽  
Milky Way ◽  
Distribution Functions ◽  
Metallicity Distribution

scholarly journals The Metallicity Distribution Function of the Halo of the Milky Way

2005 ◽  
Vol 1 (S228) ◽  
pp. 175-183 ◽  
Author(s):  
Timothy C. Beers ◽  
Norbert Christlieb ◽  
John E. Norris ◽  
Michael S. Bessell ◽  
Ronald Wilhelm ◽  
...  
Keyword(s):  
Distribution Function ◽  
Milky Way ◽  
Metallicity Distribution

scholarly journals The disc origin of the Milky Way bulge

2018 ◽  
Vol 616 ◽  
pp. A180 ◽  
Author(s):  
F. Fragkoudi ◽  
P. Di Matteo ◽  
M. Haywood ◽  
M. Schultheis ◽  
S. Khoperskov ◽  
...  
Keyword(s):  
Distribution Function ◽  
Milky Way ◽  
Chemical Properties ◽  
Stellar Populations ◽  
Solar Neighbourhood ◽  
Stellar Disc ◽  
Thick Disc ◽  
The Mean ◽  
Metallicity Distribution ◽  
Do So

There is a long-standing debate over the origin of the metal-poor stellar populations of the Milky Way (MW) bulge, with the two leading scenarios being that these populations are either (i) part of a classical metal-poor spheroid or (ii) the same population as the chemically defined thick disc seen at the solar neighbourhood. Here we test whether the latter scenario can reproduce the observed chemical properties of the MW bulge. To do so we compare an N-body simulation of a composite (thin+thick) stellar disc – which evolves secularly to form a bar and a boxy/peanut (b/p) bulge – to data from APOGEE DR13. This model, in which the thick disc is massive and centrally concentrated, can reproduce the morphology of the metal-rich and metal-poor stellar populations in the bulge, as well as the mean metallicity and [α/Fe] maps as obtained from the APOGEE data. It also reproduces the trends, in both longitude and latitude, of the bulge metallicity distribution function (MDF). Additionally, we show that the model predicts small but measurable azimuthal metallicity variations in the inner disc due to the differential mapping of the thin and thick disc in the bar. We therefore see that the chemo-morphological relations of stellar populations in the MW bulge are naturally reproduced by mapping the thin and thick discs of the inner MW into a b/p.

scholarly journals The COMBS survey – I. Chemical origins of metal-poor stars in the Galactic bulge

2019 ◽  
Vol 488 (2) ◽  
pp. 2283-2300 ◽  
Author(s):  
Madeline Lucey ◽  
Keith Hawkins ◽  
Melissa Ness ◽  
Martin Asplund ◽  
Thomas Bensby ◽  
...  
Keyword(s):  
Stellar Population ◽  
Milky Way ◽  
Distinct Population ◽  
Elemental Abundances ◽  
The Galaxy ◽  
Stellar Halo ◽  
Kinematic Studies ◽  
Galactic Stellar Populations ◽  
Target Metal ◽  
Metallicity Distribution

ABSTRACT Chemistry and kinematic studies can determine the origins of stellar population across the Milky Way. The metallicity distribution function of the bulge indicates that it comprises multiple populations, the more metal-poor end of which is particularly poorly understood. It is currently unknown if metal-poor bulge stars ([Fe/H] <−1 dex) are part of the stellar halo in the inner most region, or a distinct bulge population or a combination of these. Cosmological simulations also indicate that the metal-poor bulge stars may be the oldest stars in the Galaxy. In this study, we successfully target metal-poor bulge stars selected using SkyMapper photometry. We determine the stellar parameters of 26 stars and their elemental abundances for 22 elements using R∼ 47 000 VLT/UVES spectra and contrast their elemental properties with that of other Galactic stellar populations. We find that the elemental abundances we derive for our metal-poor bulge stars have lower overall scatter than typically found in the halo. This indicates that these stars may be a distinct population confined to the bulge. If these stars are, alternatively, part of the innermost distribution of the halo, this indicates that the halo is more chemically homogeneous at small Galactic radii than at large radii. We also find two stars whose chemistry is consistent with second-generation globular cluster stars. This paper is the first part of the Chemical Origins of Metal-poor Bulge Stars (COMBS) survey that will chemodynamically characterize the metal-poor bulge population.

scholarly journals The Pristine Survey – VIII. The metallicity distribution function of the Milky Way halo down to the extremely metal-poor regime

2020 ◽  
Vol 492 (4) ◽  
pp. 4986-5002 ◽  
Author(s):  
K Youakim ◽  
E Starkenburg ◽  
N F Martin ◽  
G Matijevič ◽  
D S Aguado ◽  
...  
Keyword(s):  
Distribution Function ◽  
Globular Clusters ◽  
Milky Way ◽  
Current Data ◽  
Low Latitude ◽  
Chemical Enrichment ◽  
Merger Event ◽  
Low Metallicity ◽  
Metallicity Distribution ◽  
Milky Way Halo

ABSTRACT The Pristine survey uses narrow-band photometry to derive precise metallicities down to the extremely metal-poor regime ($ \rm [Fe/H] \lt -3$), and currently consists of over 4 million FGK-type stars over a sky area of $\sim 2500\, \mathrm{deg}^2$. We focus our analysis on a subsample of ∼80 000 main-sequence turn-off stars with heliocentric distances between 6 and 20 kpc, which we take to be a representative sample of the inner halo. The resulting metallicity distribution function (MDF) has a peak at $ \rm [Fe/H] =-1.6$, and a slope of Δ(LogN)/$\Delta \rm [Fe/H] = 1.0 \pm 0.1$ in the metallicity range of $-3.4\; \lt\; \rm [Fe/H]\; \lt -2.5$. This agrees well with a simple closed-box chemical enrichment model in this range, but is shallower than previous spectroscopic MDFs presented in the literature, suggesting that there may be a larger proportion of metal-poor stars in the inner halo than previously reported. We identify the Monoceros/TriAnd/ACS/EBS/A13 structure in metallicity space in a low-latitude field in the anticentre direction, and also discuss the possibility that the inner halo is dominated by a single, large merger event, but cannot strongly support or refute this idea with the current data. Finally, based on the MDF of field stars, we estimate the number of expected metal-poor globular clusters in the Milky Way halo to be 5.4 for $ \rm [Fe/H]\; \lt\; -2.5$ and 1.5 for $ \rm [Fe/H]\; \lt\; -3$, suggesting that the lack of low-metallicity globular clusters in the Milky Way is not due simply to statistical undersampling.

scholarly journals The effects of the selection function on metallicity trends in spectroscopic surveys of the Milky Way

2017 ◽  
Vol 13 (S334) ◽  
pp. 345-346
Author(s):  
G. Nandakumar ◽  
M. Schultheis ◽  
M. Hayden ◽  
A. Rojas-Arriagada ◽  
G. Kordopatis ◽  
...  
Keyword(s):  
Distribution Function ◽  
Stellar Population ◽  
Milky Way ◽  
Selection Function ◽  
Population Synthesis ◽  
Stellar Population Synthesis ◽  
Metallicity Distribution

AbstractWe investigate here the effect of the selection function on the metallicity distribution function (MDF) as well as on the vertical metallicity gradient by studying similar lines-of-sight using four different spectroscopic surveys (APOGEE, LAMOST, RAVE and Gaia-ESO) which have different targeting strategies and therefore different selection functions. We create mock fields for each survey using two stellar population synthesis models, GALAXIA and TRILEGAL. The effects of the selection function are studied in detail by applying the selection function to the two models and comparing the MDF as well as vertical metallicity gradients of the selected sources with that of the underlying sample. We find a negligible selection function effect on the MDF as well as on the vertical metallicity gradients for APOGEE, RAVE and LAMOST, and estimate a mean vertical metallicity gradient of -0.241±0.028 dex kpc−1.

scholarly journals Structure and Kinematics of the Stellar Halos and Thick Disks of the Milky Way Based on Calibration Stars from SDSS DR7

2009 ◽  
Vol 5 (S265) ◽  
pp. 267-270
Author(s):  
D. Carollo ◽  
T. C. Beers ◽  
M. Chiba ◽  
J. E. Norris ◽  
K. C. Freeman ◽  
...  
Keyword(s):  
Milky Way ◽  
Thick Disk ◽  
Sloan Digital Sky Survey ◽  
Spatial Density ◽  
Density Profiles ◽  
Sky Survey ◽  
Likelihood Analysis ◽  
The Galaxy ◽  
Kinematic Information ◽  
Metallicity Distribution

AbstractThe structure and kinematics of the recognized stellar components of the Milky Way are explored, based on well-determined atmospheric parameters and kinematic quantities for 32360 “calibration stars” from the Sloan Digital Sky Survey (SDSS) and its first extension, (SDSS-II), which included the sub-survey SEGUE: Sloan Extension for Galactic Understanding and Exploration. Full space motions for a sub-sample of 16920 stars, exploring a local volume within 4 kpc of the Sun, are used to derive velocity ellipsoids for the inner- and outer-halo components of the Galaxy, as well as for the canonical thick-disk and proposed metal-weak thick-disk populations. This new sample of calibration stars represents an increase of 60% relative to the numbers used in a previous analysis. A Maximum Likelihood analysis of a local sub-sample of 16920 calibration stars has been developed in order to extract kinematic information for the major Galactic components (thick disk, inner halo, and outer halo), as well as for the elusive metal-weak thick disk (MWTD). We measure velocity ellipsoids for the thick disk, the MWTD, the inner halo, and the outer halo, demonstrate that the MWTD may be a component that is kinematically and chemically independent of the canonical thick disk (and put limits on the metallicity range of the MWTD), and derive the inferred spatial density profiles of the inner/outer halo components. We also present evidence for tilts in the velocity ellipsoids for stars in our sample as a function of height above the plane, for several ranges in metallicity, and confirm the shift of the observed metallicity distribution function (MDF) from the inner-halo to the outer-halo dominated sample.

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