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Title: THE VERTICAL MOTIONS OF MONO-ABUNDANCE SUB-POPULATIONS IN THE MILKY WAY DISK

Abstract

We present the vertical kinematics of stars in the Milky Way's stellar disk inferred from Sloan Digital Sky Survey/Sloan Extension for Galactic Understanding and Exploration (SDSS/SEGUE) G-dwarf data, deriving the vertical velocity dispersion, {sigma}{sub z}, as a function of vertical height |z| and Galactocentric radius R for a set of 'mono-abundance' sub-populations of stars with very similar elemental abundances [{alpha}/Fe] and [Fe/H]. We find that all mono-abundance components exhibit nearly isothermal kinematics in |z|, and a slow outward decrease of the vertical velocity dispersion: {sigma}{sub z}(z, R | [{alpha}/Fe], [Fe/H]) Almost-Equal-To {sigma}{sub z}([{alpha}/Fe], [Fe/H]) Multiplication-Sign exp (- (R - R{sub 0})/7 kpc). The characteristic velocity dispersions of these components vary from {approx}15 km s{sup -1} for chemically young, metal-rich stars with solar [{alpha}/Fe], to {approx}> 50 km s{sup -1} for metal-poor stars that are strongly [{alpha}/Fe]-enhanced, and hence presumably very old. The mean {sigma}{sub z} gradient (d{sigma}{sub z}/dz) away from the mid-plane is only 0.3 {+-} 0.2 km s{sup -1} kpc{sup -1}. This kinematic simplicity of the mono-abundance components mirrors their geometric simplicity; we have recently found their density distribution to be simple exponentials in both the z- and R-directions. We find a continuum of vertical kinetic temperatures ({proportional_to}{sigma}{sup 2}{submore » z}) as a function of ([{alpha}/Fe], [Fe/H]), which contribute to the total stellar surface-mass density approximately as {Sigma}{sub R{sub 0}}({sigma}{sup 2}{sub z}){proportional_to} exp(-{sigma}{sup 2}{sub z}). This and the existence of isothermal mono-abundance populations with intermediate dispersions (30-40 km s{sup -1}) reject the notion of a thin-thick-disk dichotomy. This continuum of disk components, ranging from old, 'hot', and centrally concentrated ones to younger, cooler, and radially extended ones, argues against models where the thicker disk portions arise from massive satellite infall or heating; scenarios where either the oldest disk portion was born hot, or where internal evolution plays a major role, seem the most viable. In addition, the wide range of {sigma}{sub z}([{alpha}/Fe], [Fe/H]) combined with a constant {sigma}{sub z}(z) for each abundance bin provides an independent check on the precision of the SEGUE-derived abundances: {delta}{sub [{alpha}/Fe]} Almost-Equal-To 0.07 dex and {delta}{sub [Fe/H]} Almost-Equal-To 0.15 dex. The slow radial decline of the vertical dispersion presumably reflects the decrease in disk surface-mass density. This measurement constitutes a first step toward a purely dynamical estimate of the mass profile of the stellar and gaseous disk in our Galaxy.« less

Authors:
 [1]; ; ;  [2];  [3]
  1. Institute for Advanced Study, Einstein Drive, Princeton, NJ 08540 (United States)
  2. Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany)
  3. National Optical Astronomy Observatory, Tucson, AZ 85719 (United States)
Publication Date:
OSTI Identifier:
22039095
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 755; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTRONOMY; ASTROPHYSICS; DENSITY; ELEMENT ABUNDANCE; GALACTIC EVOLUTION; HYDROGEN; IRON; MASS; MILKY WAY; STAR EVOLUTION; STARS

Citation Formats

Bovy, Jo, Rix, Hans-Walter, Hogg, David W, Zhang, Lan, Beers, Timothy C, and Lee, Young Sun, E-mail: bovy@ias.edu. THE VERTICAL MOTIONS OF MONO-ABUNDANCE SUB-POPULATIONS IN THE MILKY WAY DISK. United States: N. p., 2012. Web. doi:10.1088/0004-637X/755/2/115.
Bovy, Jo, Rix, Hans-Walter, Hogg, David W, Zhang, Lan, Beers, Timothy C, & Lee, Young Sun, E-mail: bovy@ias.edu. THE VERTICAL MOTIONS OF MONO-ABUNDANCE SUB-POPULATIONS IN THE MILKY WAY DISK. United States. https://doi.org/10.1088/0004-637X/755/2/115
Bovy, Jo, Rix, Hans-Walter, Hogg, David W, Zhang, Lan, Beers, Timothy C, and Lee, Young Sun, E-mail: bovy@ias.edu. Mon . "THE VERTICAL MOTIONS OF MONO-ABUNDANCE SUB-POPULATIONS IN THE MILKY WAY DISK". United States. https://doi.org/10.1088/0004-637X/755/2/115.
@article{osti_22039095,
title = {THE VERTICAL MOTIONS OF MONO-ABUNDANCE SUB-POPULATIONS IN THE MILKY WAY DISK},
author = {Bovy, Jo and Rix, Hans-Walter and Hogg, David W and Zhang, Lan and Beers, Timothy C and Lee, Young Sun, E-mail: bovy@ias.edu},
abstractNote = {We present the vertical kinematics of stars in the Milky Way's stellar disk inferred from Sloan Digital Sky Survey/Sloan Extension for Galactic Understanding and Exploration (SDSS/SEGUE) G-dwarf data, deriving the vertical velocity dispersion, {sigma}{sub z}, as a function of vertical height |z| and Galactocentric radius R for a set of 'mono-abundance' sub-populations of stars with very similar elemental abundances [{alpha}/Fe] and [Fe/H]. We find that all mono-abundance components exhibit nearly isothermal kinematics in |z|, and a slow outward decrease of the vertical velocity dispersion: {sigma}{sub z}(z, R | [{alpha}/Fe], [Fe/H]) Almost-Equal-To {sigma}{sub z}([{alpha}/Fe], [Fe/H]) Multiplication-Sign exp (- (R - R{sub 0})/7 kpc). The characteristic velocity dispersions of these components vary from {approx}15 km s{sup -1} for chemically young, metal-rich stars with solar [{alpha}/Fe], to {approx}> 50 km s{sup -1} for metal-poor stars that are strongly [{alpha}/Fe]-enhanced, and hence presumably very old. The mean {sigma}{sub z} gradient (d{sigma}{sub z}/dz) away from the mid-plane is only 0.3 {+-} 0.2 km s{sup -1} kpc{sup -1}. This kinematic simplicity of the mono-abundance components mirrors their geometric simplicity; we have recently found their density distribution to be simple exponentials in both the z- and R-directions. We find a continuum of vertical kinetic temperatures ({proportional_to}{sigma}{sup 2}{sub z}) as a function of ([{alpha}/Fe], [Fe/H]), which contribute to the total stellar surface-mass density approximately as {Sigma}{sub R{sub 0}}({sigma}{sup 2}{sub z}){proportional_to} exp(-{sigma}{sup 2}{sub z}). This and the existence of isothermal mono-abundance populations with intermediate dispersions (30-40 km s{sup -1}) reject the notion of a thin-thick-disk dichotomy. This continuum of disk components, ranging from old, 'hot', and centrally concentrated ones to younger, cooler, and radially extended ones, argues against models where the thicker disk portions arise from massive satellite infall or heating; scenarios where either the oldest disk portion was born hot, or where internal evolution plays a major role, seem the most viable. In addition, the wide range of {sigma}{sub z}([{alpha}/Fe], [Fe/H]) combined with a constant {sigma}{sub z}(z) for each abundance bin provides an independent check on the precision of the SEGUE-derived abundances: {delta}{sub [{alpha}/Fe]} Almost-Equal-To 0.07 dex and {delta}{sub [Fe/H]} Almost-Equal-To 0.15 dex. The slow radial decline of the vertical dispersion presumably reflects the decrease in disk surface-mass density. This measurement constitutes a first step toward a purely dynamical estimate of the mass profile of the stellar and gaseous disk in our Galaxy.},
doi = {10.1088/0004-637X/755/2/115},
url = {https://www.osti.gov/biblio/22039095}, journal = {Astrophysical Journal},
issn = {0004-637X},
number = 2,
volume = 755,
place = {United States},
year = {2012},
month = {8}
}