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The Large-scale Structure of the Halo of the Andromeda Galaxy. II. Hierarchical Structure in the Pan-Andromeda Archaeological Survey

McConnachie, Alan W., Ibata, Rodrigo, Martin, Nicolas, Ferguson, Annette M. N., Collins, Michelle, Gwyn, Stephen, Irwin, Mike, Lewis, Geraint F., Mackey, A. Dougal, Davidge, Tim , Arias, Veronica, Conn, Anthony, Côté, Patrick, Crnojevic, Denija, Huxor, Avon, Penarrubia, Jorge, Spengler, Chelsea, Tanvir, Nial, Valls-Gabaud, David, Babul, Arif, Barmby, Pauline, Bate, Nicholas F., Bernard, Edouard, Chapman, Scott, Dotter, Aaron, Harris, William, McMonigal, Brendan, Navarro, Julio, Puzia, Thomas H., Rich, R. Michael, Thomas, Guillaume and Widrow, Lawrence M. (2018) The Large-scale Structure of the Halo of the Andromeda Galaxy. II. Hierarchical Structure in the Pan-Andromeda Archaeological Survey The Astrophysical Journal, 868 (1).

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Abstract

The Pan-Andromeda Archaeological Survey is a survey of >400 square degrees centered on the Andromeda (M31) and Triangulum (M33) galaxies that has provided the most extensive panorama of an L͙ galaxy group to large projected galactocentric radii. Here, we collate and summarize the current status of our knowledge of the substructures in the stellar halo of M31, and discuss connections between these features. We estimate that the 13 most distinctive substructures were produced by at least 5 different accretion events, all in the last 3 or 4 Gyr. We suggest that a few of the substructures farthest from M31 may be shells from a single accretion event. We calculate the luminosities of some prominent substructures for which previous estimates were not available, and we estimate the stellar mass budget of the outer halo of M31. We revisit the problem of quantifying the properties of a highly structured data set; specifically, we use the OPTICS clustering algorithm to quantify the hierarchical structure of M31ʼs stellar halo and identify three new faint structures. M31ʼs halo, in projection, appears to be dominated by two “mega-structures,” which can be considered as the two most significant branches of a merger tree produced by breaking M31ʼs stellar halo into increasingly smaller structures based on the stellar spatial clustering. We conclude that OPTICS is a powerful algorithm that could be used in any astronomical application involving the hierarchical clustering of points. The publication of this article coincides with the public release of all PAndAS data products.

Item Type: Article
Divisions : Faculty of Engineering and Physical Sciences > Physics
Authors :
NameEmailORCID
McConnachie, Alan W.
Ibata, Rodrigo
Martin, Nicolas
Ferguson, Annette M. N.
Collins, Michellem.collins@surrey.ac.uk
Gwyn, Stephen
Irwin, Mike
Lewis, Geraint F.
Mackey, A. Dougal
Davidge, Tim
Arias, Veronica
Conn, Anthony
Côté, Patrick
Crnojevic, Denija
Huxor, Avon
Penarrubia, Jorge
Spengler, Chelsea
Tanvir, Nial
Valls-Gabaud, David
Babul, Arif
Barmby, Pauline
Bate, Nicholas F.
Bernard, Edouard
Chapman, Scott
Dotter, Aaron
Harris, William
McMonigal, Brendan
Navarro, Julio
Puzia, Thomas H.
Rich, R. Michael
Thomas, Guillaume
Widrow, Lawrence M.
Date : 20 November 2018
DOI : 10.3847/1538-4357/aae8e7
Copyright Disclaimer : © 2018. The American Astronomical Society. All rights reserved.
Uncontrolled Keywords : Catalogs – galaxies: general; galaxies: structure – Local Group
Depositing User : Diane Maxfield
Date Deposited : 17 Sep 2019 12:07
Last Modified : 17 Sep 2019 12:07
URI: http://epubs.surrey.ac.uk/id/eprint/852650

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