Exploring the Origins of Outer-Disk Substructures in the Milky Way

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1. Exploring the Origins of Outer-Disk Substructures in the Milky Way Anastasios Tzanidakis1, Chervin F. P. Laporte, Kathryn V. Johnston 1Columbia University, Department of Astronomy, 550 W. 120th St., New York, NY 10027 Ring Structures Diffuse Structures Figure 2— Star Count Map of Pan-STARRS1 3π Survey at the Galactic Anti-Center. The Pan-STARRS1 Survey reveals rich substructure in the Galactic halo. The following schematic represents a star count map in Galactic coordinates at the anti-center of the Milky Way. The blue fields being at 4.8-6.3 kpc, the green at 7.6-11.0 kpc and finally the more distance red fields at 14.4-17.4 kpc from the sun. Source: Slater et al. 2014. Figure 6— N-Body Simulation Particle Tracking Features. The top figure illustrates a scatter plot in Galactic coordinates of figure 2(a). The red and blue points are the “tagged” particles that we want to investigate their position in (X,Y) and (X,Z) back in time. The panels on the right, show at 3 particular timeframes the position of the tagged particles in physical space. It is evident that both populations are part of the spiral structure. Figure 2(a),2(b) — Particle Count Map of N-Body Simulations. When performing a similar density analysis on the N-Body simulations, we find a substantial resemblance in substructure between theoretical and observational data sets. The left figure is an number density plot restricted at an annulus of 15-20 kpc from the sun. At such large radii, thin ring like structures appear at high galactic latitudes. On the right figure we parametrize the distance to an annulus of 5-10 kpc to illustrate the presence of diffuse structures. The Question Figure 1 — Smooth Particle Hydrodynamic of Sagittarius Dwarf Galaxy (Sgr) Interacting with the Disk of the Milky Way. Can the interaction between the Galactic disk and the Sagittarius Dwarf Galaxy explain the origins of outer-disk substructures? Similarities in Morphology Substructures in the Milky Way Conclusions & Future Work • Both ring and diffuse structures seem to have similar creation processes. While the diffuse structures stay at closer radii, the ring structures only appear at >20 kpc radii from the sun.
 • We have shown that the dynamic interaction between Sagittarius and the Galactic disk is enough to “kick-out “ stars and create thin and diffuse substructures in the Galactic halo.
 • Looking ahead, we aim to further investigate the physics of such substructures and explain why are do they form. Such information will be vital for understanding the evolution of the Milky Way. Particle Tracing Colin T. Slater, Eric F. Bell, Edward F. Schlafly, Eric Morganson., et al. 2014, ApJ, 791. Eric Morganson, Blair Conn, Hans-Walter Rix., et al. 2016, ApJ, 825. Nicolas F. Martin, Rodrigo A. Ibata , R. Michael Rich., et al. 2014, ApJ, 787. Sagittarius Milky Way A little after the passage of Sagittarius, particles in the spiral arms create narrow substructures at radii >20 kpc and are roughly ~10 kpc above the Galactic mid-plane. References