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Measuring the Stellar Halo Velocity Anisotropy With 3D Kinematics

Published online by Cambridge University Press:  09 May 2016

Emily C. Cunningham ,
Alis J. Deason ,
Puragra Guhathakurta ,
Constance M. Rockosi ,
Roeland P. van der Marel  and
S. Tony Sohn
Emily C. Cunningham
Affiliation:
Department of Astronomy & Astrophysics, UC Santa Cruz 1156 High Street, Santa Cruz, CA 95060, USA
Alis J. Deason
Affiliation:
Department of Astronomy & Astrophysics, UC Santa Cruz 1156 High Street, Santa Cruz, CA 95060, USA Physics Department, Stanford University 382 Via Pueblo Rd, Stanford, CA 94305, USA
Puragra Guhathakurta
Affiliation:
Department of Astronomy & Astrophysics, UC Santa Cruz 1156 High Street, Santa Cruz, CA 95060, USA
Constance M. Rockosi
Affiliation:
Department of Astronomy & Astrophysics, UC Santa Cruz 1156 High Street, Santa Cruz, CA 95060, USA
Roeland P. van der Marel
Affiliation:
Space Telescope Science Institute 3700 San Martin Drive, Baltimore, MD 21218, USA
S. Tony Sohn
Affiliation:
Department of Physics and Astronomy, The Johns Hopkins University Baltimore, MD 21218, USA
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Abstract

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We present the first measurement of the anisotropy parameter β using 3D kinematic information outside of the solar neighborhood. Our sample consists of 13 Milky Way halo stars with measured proper motions and radial velocities in the line of sight of M31. Proper motions were measured using deep, multi-epoch HST imaging, and radial velocities were measured from Keck II/DEIMOS spectra. We measure β = −0.3−0.9+0.4, which is consistent with isotropy, and inconsistent with measurements in the solar neighborhood. We suggest that this may be the kinematic signature of a relatively early, massive accretion event, or perhaps several such events.

Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 11 , Issue S317: The General Assembly of Galaxy Halos: Structure, Origin and Evolution , August 2015 , pp. 288 - 289
Copyright
Copyright © International Astronomical Union 2016 

References

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Cunningham, E. C., Deason, A. J., Guhathakurta, P., et al. 2016, arXiv:1602.03180Google Scholar
Deason, A. J., Belokurov, V., Evans, N. W., & Johnston, K. V. 2013a, ApJ, 763, 113Google Scholar
Deason, A. J., Van der Marel, R. P., Guhathakurta, P., Sohn, S. T., & Brown, T. M. 2013b, ApJ, 766, 24Google Scholar