The Metal-poor Metallicity Distribution of the Ancient Milky Way

Context. Large spectroscopic Galactic surveys imply a selection function in the way they performed their target selection. Aims. We investigate here the effect of the selection function on the metallicity distribution function (MDF) and 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. Methods. We use common fields between the spectroscopic surveys of APOGEE, LAMOST, RAVE (ALR) and APOGEE, RAVE, Gaia-ESO (AGR) and use two stellar population synthesis models, GALAXIA and TRILEGAL, to create mock fields for each survey. We apply the selection function in the form of colour and magnitude cuts of the respective survey to the mock fields to replicate the observed source sample. We make a basic comparison between the models to check which best reproduces the observed sample distribution. We carry out a quantitative comparison between the synthetic MDF from the mock catalogues using both models to understand the effect of the selection function on the MDF and on the vertical metallicity gradient. Results. Using both models, we find a negligible effect of the selection function on the MDF for APOGEE, LAMOST, and RAVE. We find a negligible selection function effect on the vertical metallicity gradients as well, though GALAXIA and TRILEGAL have steeper and shallower slopes, respectively, than the observed gradient. After applying correction terms on the metallicities of RAVE and LAMOST with respect to our reference APOGEE sample, our observed vertical metallicity gradients between the four surveys are consistent within 1σ. We also find consistent gradient for the combined sample of all surveys in ALR and AGR. We estimated a mean vertical metallicity gradient of − 0.241 ± 0.028 dex kpc-1. There is a significant scatter in the estimated gradients in the literature, but our estimates are within their ranges. Conclusions. We have shown that there is a negligible selection function effect on the MDF and the vertical metallicity gradients for APOGEE, RAVE, and LAMOST using two stellar population synthesis models. Therefore, it is indeed possible to combine common fields of different surveys in studies using MDF and metallicity gradients provided their metallicities are brought to the same scale.

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Chemodynamical Evolution of the Milky Way

Symposium - International Astronomical Union ◽

10.1017/s0074180900207559 ◽

2003 ◽

Vol 208 ◽

pp. 419-420 ◽

Cited By ~ 1

Author(s):

Chiaki Kobayashi ◽

Naohito Nakasato ◽

Ken'ichi Nomoto

Keyword(s):

Milky Way ◽

Metallicity Distribution

We simulate the chemodynamical evolution of the Milky Way using our GRAPE-SPH code, and reproduce the age-metallicity relation, the [O/Fe]-[Fe/H] relation, and the metallicity distribution.

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Dynamics and morphology of the Milky Way spiral arms from the metallicity distribution and radial mixing

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stx676 ◽

2017 ◽

Vol 468 (3) ◽

pp. 3615-3627 ◽

Cited By ~ 17

Author(s):

L. A. Martinez-Medina ◽

B. Pichardo ◽

A. Peimbert ◽

L. Carigi

Keyword(s):

Milky Way ◽

Spiral Arms ◽

Metallicity Distribution

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The galactic habitable zone in elliptical galaxies

International Journal of Astrobiology ◽

10.1017/s1473550412000055 ◽

2012 ◽

Vol 11 (3) ◽

pp. 157-161 ◽

Cited By ~ 12

Author(s):

Falguni Suthar ◽

Christopher P. McKay

Keyword(s):

Milky Way ◽

Planet Formation ◽

Elliptical Galaxies ◽

Extrasolar Planet ◽

Habitable Zone ◽

Milky Way Galaxy ◽

Habitable Zones ◽

Nearby Stars ◽

Host Stars ◽

Metallicity Distribution

AbstractThe concept of a Galactic Habitable Zone (GHZ) was introduced for the Milky Way galaxy a decade ago as an extension of the earlier concept of the Circumstellar Habitable Zone. In this work, we consider the extension of the concept of a GHZ to other types of galaxies by considering two elliptical galaxies as examples, M87 and M32. We argue that the defining feature of the GHZ is the probability of planet formation which has been assumed to depend on the metallicity. We have compared the metallicity distribution of nearby stars with the metallicity of stars with planets to document the correlation between metallicity and planet formation and to provide a comparison to other galaxies. Metallicity distribution, based on the [Fe/H] ratio to solar, of nearby stars peaks at [Fe/H]≈−0.2 dex, whereas the metallicity distribution of extrasolar planet host stars peaks at [Fe/H]≈+0.4 dex. We compare the metallicity distribution of extrasolar planet host stars with the metallicity distribution of the outer star clusters of M87 and M32. The metallicity distribution of stars in the outer regions of M87 peaks at [Fe/H]≈−0.2 dex and extends to [Fe/H]≈+0.4 dex, which seems favourable for planet formation. The metallicity distribution of stars in the outer regions of M32 peaks at [Fe/H]≈−0.2 dex and extends to a much lower [Fe/H]. Both elliptical galaxies met the criteria of a GHZ. In general, many galaxies should support habitable zones.

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The Metallicity Distribution Function of the Halo of the Milky Way

Proceedings of the International Astronomical Union ◽

10.1017/s1743921305005521 ◽

2005 ◽

Vol 1 (S228) ◽

pp. 175-183 ◽

Cited By ~ 5

Author(s):

Timothy C. Beers ◽

Norbert Christlieb ◽

John E. Norris ◽

Michael S. Bessell ◽

Ronald Wilhelm ◽

...

Keyword(s):

Distribution Function ◽

Milky Way ◽

Metallicity Distribution

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ARGOS – II. The Galactic bulge survey

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/sts305 ◽

2012 ◽

Vol 428 (4) ◽

pp. 3660-3670 ◽

Cited By ~ 90

Author(s):

K. Freeman ◽

M. Ness ◽

E. Wylie-de-Boer ◽

E. Athanassoula ◽

J. Bland-Hawthorn ◽

...

Keyword(s):

Radial Velocity ◽

Milky Way ◽

Radial Velocities ◽

Galactic Centre ◽

Red Giants ◽

Formation Processes ◽

Galactic Bulge ◽

Milky Way Galaxy ◽

Selection For ◽

Metallicity Distribution

Abstract We describe the motivation, field locations and stellar selection for the Abundances and Radial velocity Galactic Origins Survey (ARGOS) spectroscopic survey of 28 000 stars in the bulge and inner disc of the Milky Way galaxy across latitudes of b = −5° to −10°. The primary goal of this survey is to constrain the formation processes of the bulge and establish whether it is predominantly a merger or instability remnant. From the spectra (R = 11 000), we have measured radial velocities and determined stellar parameters, including metallicities and [α/Fe] ratios. Distances were estimated from the derived stellar parameters and about 14 000 stars are red giants within 3.5 kpc of the Galactic Centre. In this paper, we present the observations and analysis methods. Subsequent papers (III and IV) will discuss the stellar metallicity distribution and kinematics of the Galactic bulge and inner disc, and the implications for the formation of the bulge.

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H II REGION METALLICITY DISTRIBUTION IN THE MILKY WAY DISK

The Astrophysical Journal ◽

10.1088/0004-637x/738/1/27 ◽

2011 ◽

Vol 738 (1) ◽

pp. 27 ◽

Cited By ~ 106

Author(s):

Dana S. Balser ◽

Robert T. Rood ◽

T. M. Bania ◽

L. D. Anderson

Keyword(s):

Milky Way ◽

H Ii Region ◽

Metallicity Distribution

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HERBS I: Metallicity and alpha enhancement along the Galactic bulge minor axis

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz1104 ◽

2019 ◽

Vol 486 (3) ◽

pp. 3586-3603 ◽

Cited By ~ 2

Author(s):

L Duong ◽

M Asplund ◽

D M Nataf ◽

K C Freeman ◽

M Ness ◽

...

Keyword(s):

Milky Way ◽

High Efficiency ◽

Survey Design ◽

Minor Axis ◽

Signal To Noise ◽

Origin And Evolution ◽

Element Abundances ◽

Red Giant ◽

The Vertical Distribution ◽

Metallicity Distribution

ABSTRACT To better understand the origin and evolution of the Milky Way bulge, we have conducted a survey of bulge red giant branch and clump stars using the High Efficiency and Resolution Multi-Element Spectrograph on the Anglo–Australian Telescope. We targeted ARGOS survey stars with predetermined bulge memberships, covering the full metallicity distribution function. The spectra have signal-to-noise ratios comparable to, and were analysed using the same methods as the GALAH survey. In this work, we present the survey design, stellar parameters, distribution of metallicity, and alpha-element abundances along the minor bulge axis at latitudes b = −10°, − 7.5°, and −5°. Our analysis of ARGOS stars indicates that the centroids of ARGOS metallicity components should be located ≈0.09 dex closer together. The vertical distribution of α-element abundances is consistent with the varying contributions of the different metallicity components. Closer to the plane, alpha abundance ratios are lower as the metal-rich population dominates. At higher latitudes, the alpha abundance ratios increase as the number of metal-poor stars increases. However, we find that the trend of alpha-enrichment with respect to metallicity is independent of latitude. Comparison of our results with those of GALAH DR2 revealed that for [Fe/H] ≈ −0.8, the bulge shares the same abundance trend as the high-α disc population. However, the metal-poor bulge population ([Fe/H] ≲ −0.8) show enhanced alpha abundance ratios compared to the disc/halo. These observations point to fairly rapid chemical evolution in the bulge, and that the metal-poor bulge population does not share the same similarity with the disc as the more metal-rich populations.

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The chemistry of stars in the bar of the Milky Way

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936779 ◽

2019 ◽

Vol 632 ◽

pp. A121 ◽

Cited By ~ 4

Author(s):

C. Wegg ◽

A. Rojas-Arriagada ◽

M. Schultheis ◽

O. Gerhard

Keyword(s):

Milky Way ◽

Giant Stars ◽

Iron Abundance ◽

Red Clump ◽

Bar Formation ◽

Metallicity Distribution

We use a sample of 938 red clump giant stars located in the direction of the Galactic long bar to study the chemistry of Milky Way bar stars. Kinematically separating stars on bar orbits from stars with inner disc orbits, we find that stars on bar-like orbits are more metal rich with a mean iron abundance of ⟨[Fe/H]⟩ = +0.30 compared to ⟨[Fe/H]⟩ = +0.03 for the inner disc. Spatially selecting bar stars is complicated by a strong vertical metallicity gradient of −1.1 dex kpc−1, but we find the metallicity distribution varies in a manner consistent with our orbital selection. Our results have two possible interpretations. The first is that the most metal rich stars in the inner Galaxy pre-existed the bar, but were kinematically cold at the time of bar formation and therefore more easily captured onto bar orbits when the bar formed. The second is that the most metal rich stars formed after the bar, either directly onto the bar following orbits or were captured by the bar after their formation.

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