galaxies Article Disk Heating, Galactoseismology, and the Formation of Stellar Halos Kathryn V. Johnston 1,*,†, Adrian M. Price-Whelan 2,†, Maria Bergemann 3, Chervin Laporte 1, Ting S. Li 4, Allyson A. Sheffield 5, Steven R. Majewski 6, Rachael S. Beaton 7, Branimir Sesar 3 and Sanjib Sharma 8 1 Department of Astronomy, Columbia University, 550 W 120th st., New York, NY 10027, USA; cfl
[email protected] 2 Department of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Princeton, NJ 08544, USA;
[email protected] 3 Max Planck Institute for Astronomy, Heidelberg 69117, Germany;
[email protected] (M.B.);
[email protected] (B.S.) 4 Fermi National Accelerator Laboratory, P. O. Box 500, Batavia, IL 60510, USA;
[email protected] 5 Department of Natural Sciences, LaGuardia Community College, City University of New York, 31-10 Thomson Ave., Long Island City, NY 11101, USA; asheffi
[email protected] 6 Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, VA 22904, USA;
[email protected] 7 The Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101, USA;
[email protected] 8 Sydney Institute for Astronomy, School of Physics, University of Sydney, NSW 2006, Australia;
[email protected] * Correspondence:
[email protected]; Tel.: +1-212-854-3884 † These authors contributed equally to this work. Academic Editors: Duncan A. Forbes and Ericson D. Lopez Received: 1 July 2017; Accepted: 14 August 2017; Published: 26 August 2017 Abstract: Deep photometric surveys of the Milky Way have revealed diffuse structures encircling our Galaxy far beyond the “classical” limits of the stellar disk.