Estimate of Current Mass of the Large Magellanic Cloud from the Orphan-Chenab Tidal Stream

TL;DR

This work uses the Orphan-Chenab Stream to bound the Large Magellanic Cloud’s mass within 30 kpc, finding a robust value near $4.93\times10^{10}$ $M_\odot$ while showing total mass estimates depend strongly on the LMC’s radial density profile. It systematically compares particle-spray and full N-body stream modeling, revealing significant biases in the former and demonstrating that MW potential choices have limited impact on the inferred inner mass. The analysis confirms the LMC’s current bound mass is well constrained, with the tidal radius around $16.9$ kpc, but emphasizes that outer halo mass remains unconstrained without a fixed radial profile; the results also show that two-component dwarf models do not materially alter the OCS path. Overall, the study highlights the importance of modeling choices in tidal-stream analyses and provides a robust inner-mew mass constraint relevant for MW dynamics and future modeling efforts.

Abstract

By fitting the tilt in the path of the Orphan-Chenab Stream (OCS), we conclude that the current mass of the Large Magellanic Cloud (LMC) within 30 kpc is $4.7$-$5.1 \times 10^{10}$ M$_\odot$. We note that the tidal radius of the LMC of this mass is 16.9 kpc, indicating that our measured mass approximates the current bound mass of the LMC. Previous measurements of the LMC mass based on fitting the observed path of the OCS through the Milky Way (MW) halo reported the total mass of the LMC. We show that because the closest approach of the LMC to the OCS, where the gravitational perturbation of the stream path is the highest, is about 20 kpc, the mass of the LMC outside of 30 kpc is not constrained and depends entirely on the assumed radial profile at large radius. Our best-fit total mass varies between $4.5 \times 10^{10}$ and $2.2 \times 10^{11}$ M$_\odot$ or more, depending on the presumed radial profile of the LMC. We also show that previous measurements of the mass of the LMC that used a particle-spray method to simulate the path of the OCS suffered from systematic error because they assumed that all particles were stripped from the dwarf galaxy at the tidal radius; N-body simulations show that particles are actually released from a range of distances from the center of mass of the OCS. In contrast, the choice of MW potential has little effect on the estimated LMC mass from the OCS.

Figures (25)

• Figure 1: Left panels: Comparison of a simulated OCS without the LMC using N-body (blue) and particle-spray (red) methods using the same parameters (summarized in Table \ref{['tab:N-body']}). Right panels: Particles in the N-body simulation that stripped from a radius of greater than 3.0 kpc from the center of the DG. Note that the stream generated by the N-body simulation is wider, and the ends of the stream in particular follow a different path through space. Also, the N-body simulation stream is slightly tilted from the stream made with the particle-spray. The N-body particles that are stripped at a distance of more than 3 kpc from the DG center (right panels) exhibit the largest departure from the particle-spray simulation.
• Figure 2: Deviation in the Galactocentric distance of the center of the particle-spray stream from the center of the N-body stream (no LMC). Note that the x-axis is Sun-centered along the stream. The upper panel shows that the particle-spray and N-body streams are tilted from each other. The lower panel shows the Galactocentric distance difference between the two simulations. This distance difference trends from the N-body simulation being farther at low $\phi_1$ to the particle-spray simulation being farther at large $\phi_1$, quantifing the stream tilt between the N-body and particle-spray simulations.
• Figure 3: Bound mass of the DG in the N-body simulation (no LMC) as a function of time. Most particles become unbound at perigalacticon, and then some particles become bound again at larger distances from the Galactic center.
• Figure 4: Eccentricity of the DG in the N-body simulation (no LMC) as a function of time. The DG shape quickly deviates from spherical, in contrast to the particle-spray which assumes a spherical DG at all times.
• Figure 5: Distance from the center of mass of the DG at which particles become unbound for the last time as a function of time (no LMC). The red line shows the tidal radius with respect to time, where the particles are released using the particle-spray. Note that the N-body simulation produces a wide variety of radii while the particle-spray method by construction assumes only one radius at a time.