What Is The Mass Of Large Magellanic Cloud? (Cosmology)

By using stellar streams, Nora Shipp and colleagues measured the mass of Large Magellanic Cloud (LMC). They found that the mass of the LMC to be ~ 1.8 × 10¹¹ M. Their study recently appeared in Arxiv.

The mass of the Large Magellanic Cloud (LMC), the Milky Way’s largest satellite galaxy, has proven notoriously difficult to measure. Many researchers tried to directly measure the mass of the LMC from the dynamics of its star clusters and rotation curve. But, such direct dynamical tracers are only measuring the central region of a much more massive LMC halo. Another, direct dynamical tracer called stellar streams, the remnants of recently disrupted dwarf galaxies and globular clusters, measure the mass of the LMC at much larger distances.

The interaction geometry between a stream and the LMC. The blue dotted line represents a stream within an orbital plane traced by the solid black oval. The black dashed line represents the vector between the stream and the LMC at closest approach. They decompose this vector into components aligned with the angular momentum vector of the stream’s orbit (Lˆ), the radial vector between the stream and the Galactic center (ˆr), and a third perpendicular vector tangential to the stream’s orbit (Lˆ × rˆ). © Authors

Recently, a large number of stellar streams in the southern hemisphere were discovered by Dark Energy Survey (DES). Gaia then provided unprecedented measurements of proper motions of greater than 1 billion Milky Way stars, enabling the measurement of the proper motions of the DES streams. Many of these streams are close in projection to the LMC, suggesting the exciting opportunity to probe the mass of the LMC at large radii with multiple direct dynamical tracers. Such a measurement was proposed by Erkal et al., who predicted the effect of the LMC on the Tucana III (Tuc III) stream and found that the LMC could induce a substantial proper motion perpendicular to the track of the stream on the sky. They further argued that the size of this offset could be used to measure the mass of the LMC.

Now, Nora Shipp and colleagues measured the LMC mass with five streams in the Southern Galactic hemisphere, combining observations from the Southern Stellar Stream Spectroscopic Survey (S5), Gaia EDR3, and the Dark Energy Survey (DES). They found that the mass of the LMC to be ~ 1.8 × 10¹¹ M.

Table 1: LMC mass measurements and parameters of the last closest approach © authors

“This mass is compatible with previous measurements, showing that a consistent picture is emerging of the LMC’s influence on structures in the Milky Way.”

— they said.

Finally, they examined the LMC’s impact on their sample of streams. They found that the LMC’s effect depends on the relative orientation of the stream and LMC at their point of closest approach. To better understand this, they presented a simple model based on the impulse approximation and showed that the LMC’s effect depends both on the magnitude of the velocity kick imparted to the stream and the direction of this kick.

“Further study of the complexity of the Milky Way and LMC potential with a large population of stellar streams will build upon this work to reveal a more complete picture of the effect of the Milky Way’s largest satellite on our Galaxy.”

— they concluded.

Reference: Nora Shipp, Denis Erkal, Alex Drlica-Wagner, Ting S. Li, Andrew B. Pace, Sergey E. Koposov, Lara R. Cullinane, Gary S. Da Costa, Alexander P. Ji, Kyler Kuehn, Geraint F. Lewis, Dougal Mackey, Jeffrey D. Simpson, Zhen Wan, Daniel B. Zucker, Joss Bland-Hawthorn, Peter S. Ferguson, Sophia Lilleengen, S5 Collaboration, “Measuring the Mass of the Large Magellanic Cloud with Stellar Streams Observed by ${S}^5$”, Arxiv, pp. 1-23, 2021. https://arxiv.org/abs/2107.13004


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