The chemical and spatial variations of the bulge’s velocity ellipsoids

ABSTRACT We study the velocity ellipsoids in an N-body$+$SPH (smooth particle hydrodynamics) simulation of a barred galaxy which forms a bar with a BP bulge. We focus on the 2D kinematics, and quantify the velocity ellipses by the anisotropy, $\beta _{ij}$, the correlation, $\rho _{ij}$, and the vertex deviation, $l_{\rm v}$. We explore the variations in these quantities based on stellar age within the bulge and compare these results with the Milky Way’s bulge using data from APOGEE (Apache Point Observatory Galactic Evolution Experiment) DR16 and Gaia DR3. We first explore the variation of the model’s velocity ellipses in galactocentric velocities, $v_R$ and $v_\phi$, for two bulge populations, a (relatively) young one and an old one. The bar imprints quadrupoles on the distribution of ellipse properties, which are stronger in the young population, as expected from their stronger bar. The quadrupoles are distorted if we use heliocentric velocities $v_r$ and $v_l$. We then project these kinematics along the line of sight onto the $(l,b)$-plane. Along the minor axis $\beta _{rl}$ changes from positive at low $|b|$ to negative at large $|b|$, crossing over at lower $|b|$ in the young stars. Consequently, the vertex deviation peaks at lower $|b|$ in the young population, but reaches similar peak values in the old. The $\rho _{rl}$ is much stronger in the young stars, and traces the bar strength. The APOGEE stars split by the median $\rm [Fe/H]$ follow the same trends. Lastly, we explore the velocity ellipses across the entire bulge region in $(l,b)$ space, finding good qualitative agreement between the model and observations.

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Publication Details

Journal
Monthly Notices of the Royal Astronomical Society
Published
2025-05-30
DOI
https://doi.org/10.1093/mnras/staf887
Citations
1
Primary Topic
Stellar, planetary, and galactic studies
Type
article
Field-Weighted Citation Impact
1.15

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article

The chemical and spatial variations of the bulge’s velocity ellipsoids

Victor P. Debattista, O. A. González, Ilin Lazar, Luis M San Martin Fernandez et al.
1 citations
Monthly Notices of the Royal Astronomical Society
Stellar, planetary, and galactic studies
1.15
article

The chemical and spatial variations of the bulge’s velocity ellipsoids

Victor P. Debattista, O. A. González, Ilin Lazar, Luis M San Martin Fernandez, Steven Gough-Kelly, Á. Rojas-Arriagada, Leandro José Beraldo e Silva
article en
1 citations

Abstract

ABSTRACT We study the velocity ellipsoids in an N-body$+$SPH (smooth particle hydrodynamics) simulation of a barred galaxy which forms a bar with a BP bulge. We focus on the 2D kinematics, and quantify the velocity ellipses by the anisotropy, $\beta _{ij}$, the correlation, $\rho _{ij}$, and the vertex deviation, $l_{\rm v}$. We explore the variations in these quantities based on stellar age within the bulge and compare these results with the Milky Way’s bulge using data from APOGEE (Apache Point Observatory Galactic Evolution Experiment) DR16 and Gaia DR3. We first explore the variation of the model’s velocity ellipses in galactocentric velocities, $v_R$ and $v_\phi$, for two bulge populations, a (relatively) young one and an old one. The bar imprints quadrupoles on the distribution of ellipse properties, which are stronger in the young population, as expected from their stronger bar. The quadrupoles are distorted if we use heliocentric velocities $v_r$ and $v_l$. We then project these kinematics along the line of sight onto the $(l,b)$-plane. Along the minor axis $\beta _{rl}$ changes from positive at low $|b|$ to negative at large $|b|$, crossing over at lower $|b|$ in the young stars. Consequently, the vertex deviation peaks at lower $|b|$ in the young population, but reaches similar peak values in the old. The $\rho _{rl}$ is much stronger in the young stars, and traces the bar strength. The APOGEE stars split by the median $\rm [Fe/H]$ follow the same trends. Lastly, we explore the velocity ellipses across the entire bulge region in $(l,b)$ space, finding good qualitative agreement between the model and observations.

Monthly Notices of the Royal Astronomical SocietyVol. 540(3)
Universidad de Santiago de Chile (CL), University of Arizona (US), University of Hertfordshire (GB), University of Lancashire (GB), Millennium Institute of Astrophysics (CL), Royal Observatory (GB), Millenium Nucleus for Planet Formation (CL), UK Astronomy Technology Centre (GB)
Smithsonian Institution, U.S. Department of Energy, Alfred P. Sloan Foundation, Yale University, Carnegie Institution of Washington, Vanderbilt University, Ohio State University, University of Utah, University of Washington, Johns Hopkins University, Carnegie Mellon University, University of Notre Dame, University of Portsmouth, New Mexico State University, University of Central Lancashire, European Space Agency, York University, University of Oxford, Ministério da Ciência, Tecnologia e Inovação, Universidad Nacional Autónoma de México, Agencia Nacional de Investigación y Desarrollo, Max-Planck-Institut für Astrophysik, Max-Planck-Institut für Astronomie, Instituto de Astrofísica de Canarias, Office of Science, University of Colorado Boulder, Leibniz-Gemeinschaft, Departamento de Investigaciones Científicas y Tecnológicas, Universidad de Santiago de Chile, Lawrence Berkeley National Laboratory
Openalex Percentile: Top 19%
Stellar, planetary, and galactic studies
1.15
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