J/ApJ/894/34 Metallicity gradient from SDSS & SMSS in halo stars (Dietz+, 2020)
The metallicity gradient and complex formation history of the outermost halo
of the Milky Way.
Dietz S.E., Yoon J., Beers T.C., Placco V.M.
<Astrophys. J., 894, 34-34 (2020)>
=2020ApJ...894...34D 2020ApJ...894...34D (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way; Stars, halo; Abundances, [Fe/H]; Radial velocities;
Proper motions; Rotational velocities; Optical
Keywords: Milky Way Galaxy; Milky Way evolution; Milky Way formation
Milky Way dynamics; Milky Way stellar halo; Stellar populations
Population II stars; Stellar kinematics; Metallicity; Galaxy structure
Abstract:
We present an examination of the metallicity distribution function of
the outermost stellar halo of the Galaxy based on an analysis of both
local (within 4kpc of the Sun, ∼16500 stars) and non-local
(∼21700 stars) samples. These samples were compiled using
spectroscopic metallicities from the Sloan Digital Sky Survey (SDSS)
and photometric metallicities from the SkyMapper Southern Survey (SMSS).
We detect a negative metallicity gradient in the outermost halo
(r>35kpc from the Galactic center), and find that the frequency of
very metal-poor ([Fe/H]<-2.0) stars in the outer-halo region reaches
up to ∼60% in our most distant sample, commensurate with previous
theoretical predictions. This result provides clear evidence that the
outer-halo formed hierarchically. The retrograde stars in the
outermost halo exhibit a roughly constant metallicity, which may be
linked to the accretion of the Sequoia progenitor. In contrast,
prograde stars in the outermost halo exhibit a strong
metallicity-distance dependence, indicating that they likely
originated from the accretion of galaxies less massive than the
Sequoia progenitor galaxy.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 185 10078 *SDSS DR15 ex-situ sample
table2.dat 193 13958 SMSS (Cat. II/358) ex-situ sample
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Note on table1.dat: This dataset has been cut to contain only
local (<4kpc from the Sun), halo (Rapo>10kpc, Zmax>3kpc),
low-uncertainty (absolute Rapo uncertainty <10kpc) stars from SDSS DR15
(see text for more details).
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See also:
V/147 : The SDSS Photometric Catalogue, Release 12 (Alam+, 2015)
II/358 : SkyMapper Southern Sky Survey. DR1.1 (Wolf+, 2018)
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
I/347 : Distances to 1.33 billion stars in Gaia DR2 (Bailer-Jones+, 2018)
J/AJ/119/2866 : Proper motions of metal-poor stars (Beers+, 2000)
J/AJ/137/4377 : List of SEGUE plate pairs (Yanny+, 2009)
J/ApJ/714/663 : Stellar density map of the Milky Way (de Jong+, 2010)
J/ApJ/788/180 : Very metal-poor stars in the Milky Way's halo (Carollo+, 2014)
J/ApJ/795/52 : Red giant star sample from SDSS (Chen+, 2014)
J/A+A/577/A81 : Deep SDSS Optical Spectroscopy. II. (Fernandez-Alvar+, 2015)
J/ApJ/816/80 : The SEGUE K giant survey. III. Galactic halo (Janesh+, 2016)
J/ApJ/833/20 : Carbon-enhanced metal-poor (CEMP) star abundances (Yoon+, 2016)
J/AJ/156/18 : APOGEE:Binary companions of evolved stars (Price-Whelan+, 2018)
J/MNRAS/478/4513 : GALAH Survey DR2 (Buder+, 2018)
J/ApJS/238/16 : LAMOST-DR3 very metal-poor star catalog (Li+, 2018)
J/ApJ/891/39 : LAMOST DR3 very metal-poor stars in Galactic halo (Yuan+, 2020)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- MJD [51609/57520] MJD of the observation
7- 10 I4 --- Plate Plate number
12- 14 I3 --- Fiber Fiber ID
16- 27 F12.9 [-] [Fe/H] [-3.63/0.34] Metallicity
29- 41 F13.9 deg RAdeg Right Ascension, decimal degrees (J2000)
43- 55 F13.9 deg DEdeg Declination, decimal degrees (J2000)
57- 67 F11.6 mas/yr pmRA [-149/160] Proper motion in ra
69- 76 F8.6 mas/yr e_pmRA [0.018/3] Error on pmRA
78- 87 F10.5 mas/yr pmDE [-191/112] Proper motion in dec
89- 96 F8.6 mas/yr e_pmDE [0.019/3] Error on pmDE
98-110 F13.8 km/s RV [-597/499] Radial velocity
112-121 F10.7 km/s e_RV [0.3/20] Error on RV
123-133 F11.9 kpc Dist [0.1/4] Distance (heliocentric)
135-145 F11.9 kpc e_Dist [0.001/0.8] Error on distance
147-160 F14.9 km/s Vphi [-403/375] Rotational velocity (galactocentric)
162-172 F11.8 kpc Rapo [10/83.4] Apocentric radius (G1)
174-185 F12.9 kpc Zmax [3/82.3] Maximum vertical extent
from Galactic plane (G1)
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 9 I9 --- ObjID [4833/318781654] SMSS object ID
( in Simbad)
11- 22 F12.9 [-] [Fe/H] [-3.78/0.6] Metallicity
24- 33 F10.6 deg RAdeg Right Ascension, decimal degrees (J2000)
35- 44 F10.6 deg DEdeg Declination, decimal degrees (J2000)
46- 59 F14.9 mas/yr pmRA [-102/71] Proper motion in ra
61- 71 F11.9 mas/yr e_pmRA [0/2.2] Error on pmRA
73- 86 F14.9 mas/yr pmDE [-108/34] Proper motion in dec
88- 98 F11.9 mas/yr e_pmDE [0/2.3] Error on pmDE
100-113 F14.9 km/s RV [-504/616] Radial velocity
115-126 F12.9 km/s e_RV [0/54] Error on RV
128-139 F12.9 kpc Dist [0.4/40] Distance (heliocentric)
141-151 F11.9 kpc e_Dist [0.002/6] Error on distance
153-166 F14.9 km/s Vphi [-451/455] Rotational velocity (galactocentric)
168-179 F12.8 kpc Rapo [10/112] Apocentric radius (G1)
181-193 F13.9 kpc Zmax [3/109] Maximum vertical extent
from Galactic plane (G1)
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Global notes:
Note (G1): Orbital values have been calculated using the Stackel potential
developed by Sommer-Larsen & Zhen (1990MNRAS.242...10S 1990MNRAS.242...10S). Uncertainties
on orbital values have been calculated via a Markov Chain Monte Carlo
sampling method (see text for more details).
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 10-Sep-2021