TY - JOUR
T1 - Orbits of massive satellite galaxies - I. A close look at the Large Magellanic Cloud and a new orbital history for M33
AU - Patel, Ekta
AU - Besla, Gurtina
AU - Sohn, Sangmo Tony
N1 - Funding Information: EP is supported by the National Science Foundation through the Graduate Research Fellowship Programme funded by Grant Award No. DGE-1143953. This research was also funded through a grant for HST programme AR-12632. Support for AR-12632 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. Orbital model calculations were performed with the El Gato cluster at the University of Arizona, which is funded by the National Science Foundation through Grant No. 1228509. The Illustris simulations were run on the Odyssey cluster supported by the FAS Science Division Research Computing Group at Harvard University. Many thanks to Vicente Rodriguez-Gomez for useful discussions related to Illustris and the associated merger trees. The authors would also like to acknowledge Oleg Gnedin and Mary Putman whose private correspondences have further contributed to our understanding of previous orbital analyses. Finally, we thank Mike Boylan-Kolchin, Roeland van der Marel, Nicolas Garavito, Paul Torrey, Dennis Zaritsky, Nitya Kallivayalil, Daniel Stark, Benjamin Weiner, Erik Tollerud, and Beth Willman for stimulating discussions that have contributed to this paper. Publisher Copyright: © 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.
PY - 2017/2/1
Y1 - 2017/2/1
N2 - The MilkyWay (MW) and M31 both harbour massive satellite galaxies, the Large Magellanic Cloud (LMC) and M33, which may comprise up to 10 per cent of their host's total mass. Massive satellites can change the orbital barycentre of the host-satellite system by tens of kiloparsec and are cosmologically expected to harbour dwarf satellite galaxies of their own. Assessing the impact of these effects crucially depends on the orbital histories of the LMC and M33. Here, we revisit the dynamics of theMW-LMC system and present the first detailed analysis of the M31-M33 system utilizing high-precision proper motions and statistics from the dark-matter-only Illustris cosmological simulation.With the latest Hubble Space Telescope proper motion measurements of M31, we reliably constrain M33's interaction history with its host. In particular, like the LMC, M33 is either on its first passage (tinf < 2 Gyr ago) or if M31 is massive (≥2 × 1012 M⊙), it is on a long-period orbit of about 6 Gyr. Cosmological analogues of the LMC and M33 identified in Illustris support this picture and provide further insight about their host masses. We conclude that, cosmologically, massive satellites such as the LMC and M33 are likely completing their first orbits about their hosts. We also find that the orbital energies of such analogues prefer an MW halo mass ~1.5 × 1012 M⊙ and an M31 halo mass ≥1.5 × 1012 M⊙. Despite conventional wisdom, we conclude it is highly improbable that M33 made a close (< 100 kpc) approach to M31 recently (tperi < 3 Gyr ago). Such orbits are rare (< 1 per cent) within the 4σ error space allowed by observations. This conclusion cannot be explained by perturbative effects through four-body encounters amongst the MW, M31, M33, and the LMC. This surprising result implies that we must search for a new explanation for M33's strongly warped gas and stellar discs.
AB - The MilkyWay (MW) and M31 both harbour massive satellite galaxies, the Large Magellanic Cloud (LMC) and M33, which may comprise up to 10 per cent of their host's total mass. Massive satellites can change the orbital barycentre of the host-satellite system by tens of kiloparsec and are cosmologically expected to harbour dwarf satellite galaxies of their own. Assessing the impact of these effects crucially depends on the orbital histories of the LMC and M33. Here, we revisit the dynamics of theMW-LMC system and present the first detailed analysis of the M31-M33 system utilizing high-precision proper motions and statistics from the dark-matter-only Illustris cosmological simulation.With the latest Hubble Space Telescope proper motion measurements of M31, we reliably constrain M33's interaction history with its host. In particular, like the LMC, M33 is either on its first passage (tinf < 2 Gyr ago) or if M31 is massive (≥2 × 1012 M⊙), it is on a long-period orbit of about 6 Gyr. Cosmological analogues of the LMC and M33 identified in Illustris support this picture and provide further insight about their host masses. We conclude that, cosmologically, massive satellites such as the LMC and M33 are likely completing their first orbits about their hosts. We also find that the orbital energies of such analogues prefer an MW halo mass ~1.5 × 1012 M⊙ and an M31 halo mass ≥1.5 × 1012 M⊙. Despite conventional wisdom, we conclude it is highly improbable that M33 made a close (< 100 kpc) approach to M31 recently (tperi < 3 Gyr ago). Such orbits are rare (< 1 per cent) within the 4σ error space allowed by observations. This conclusion cannot be explained by perturbative effects through four-body encounters amongst the MW, M31, M33, and the LMC. This surprising result implies that we must search for a new explanation for M33's strongly warped gas and stellar discs.
KW - Galaxies: evolution
KW - Galaxies: kinematics and dynamics
KW - Galaxy: fundamental parameters
KW - Local Group
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U2 - 10.1093/mnras/stw2616
DO - 10.1093/mnras/stw2616
M3 - Article
SN - 0035-8711
VL - 464
SP - 3825
EP - 3849
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 4
ER -