The Mass of the Large Magellanic Cloud from the Three-dimensional Kinematics of Its Globular Clusters
Laura L. Watkins, Roeland P. van der Marel, Paul Bennet
Abstract
Abstract We estimate the mass of the Large Magellanic Cloud (LMC) using the kinematics of 30 LMC globular clusters (GCs). We combine proper motions measured with the Hubble Space Telescope, Gaia, or a combination of the two, from a recent study by Bennet et al. with literature line-of-sight velocities (LOSVs) to give three components of motion. With these, we derive a 3D velocity dispersion anisotropy <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>β</mml:mi> <mml:mo>=</mml:mo> <mml:mo>−</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>0.72</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1.07</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.62</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> , consistent with the GCs forming a flattened system with significant azimuthal motion. We then apply a tracer mass estimator and measure an enclosed mass <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>M</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mo><</mml:mo> <mml:mn>13.2</mml:mn> <mml:mspace width="0.25em"/> <mml:mi>kpc</mml:mi> <mml:mo stretchy="false">)</mml:mo> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>2.66</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.36</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.42</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> </mml:msup> </mml:math> M ⊙ . This is broadly consistent with results from previous studies of the LOSVs of GCs and other luminous tracers. Assuming a cosmologically constrained Navarro–Frenk–White distribution for the dark matter, this implies a virial mass <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>virial</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>1.80</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.54</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>1.05</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>11</mml:mn> </mml:mrow> </mml:msup> </mml:math> M ⊙ . Despite being an extrapolation by almost an order of magnitude in radius, this result is consistent with published estimates from other methods that are directly sensitive to the LMC’s total mass. Our results support the conclusion that the LMC is approximately <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>17</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>6</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>10</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> % of the Milky Way’s mass, making it a significant contributor to the Local Group potential.