Limit on the LMC mass from a census of its satellites (1907.09484v1)

Abstract: We study the orbits of ultra-faint dwarf galaxies in the combined presence of the Milky Way and LMC and we find 6 dwarfs which were likely accreted with the LMC (Car 2, Car 3, Hor 1, Hyi 1, Phe 2, Ret 2), in addition to the SMC, representing strong evidence of dwarf galaxy group infall. This procedure depends on the gravitational pull of the LMC, thus allowing us to place a lower bound on the Cloud's mass of $M_{\rm LMC} > 1.24\times10^{11} M_\odot$. This mass estimate is validated by applying the technique to a cosmological zoom-in simulation of a Milky Way-like galaxy with an LMC analogue where we find that while this lower bound may be overestimated, it will improve in the future with smaller observational errors. We apply this technique to dwarf galaxies lacking radial velocities and find that Eri 3 has a broad range of radial velocities for which it has a significant chance ($> 0.4$) of having being bound to the Cloud. We study the non-Magellanic classical satellites and find that Fornax has an appreciable probability of being an LMC satellite if the LMC is sufficiently massive. In addition, we explore how the orbits of the Milky Way satellites change in the presence of the LMC and find a significant change for several objects. Finally, we find that the LMC satellites are slightly smaller than the Milky Way satellites at a fixed luminosity, possibly due to the different tidal environments they have experienced.

Limit on the LMC Mass from a Census of its Satellites

In the paper conducted by Erkal and Belokurov, the authors investigate the accretion history of ultra-faint dwarf galaxies within the context of their association with the Large Magellanic Cloud (LMC). This research aims to elucidate the hierarchical structure formation within our Local Group by assessing the gravitational influence exerted by the LMC on its satellite companions. The focal point of this research is to establish a lower bound on the mass of the LMC by examining the binding energies of its satellite galaxies.

Methodology and Key Findings

The paper utilizes a novel backwards orbital integration technique to identify satellites that were accreted with the LMC. By rewinding the trajectories of these satellites, the authors endeavor to ascertain whether these objects were energetically bound to the LMC five billion years ago. This approach is grounded on utilizing precise astrometric data derived from Gaia DR2, which has vastly improved the understanding of the dynamical properties of these satellite galaxies.

The authors identify six ultra-faint dwarfs—Car 2, Car 3, Hor 1, Hyi 1, Phe 2, Ret 2—along with the Small Magellanic Cloud (SMC) as likely accreted companions of the LMC. This demarcation represents compelling evidence for dwarf galaxy group infall and corroborates prior findings envisaging the infall of galaxy groups around the Milky Way. Through these examinations, Erkal and Belokurov establish a lower bound for the mass of the LMC at $M_{\rm LMC} > 1.24\times10^{11} M_\odot$.

The research further explores satellite galaxies lacking radial velocities and employs its binding-energy-focused technique to evaluate potential associativity. Notably, Eridanus 3 emerges as a candidate that could be bound to the LMC, given a broad range of plausible radial velocities.

Theoretical and Practical Implications

The implication of the LMC mass estimation serves multiple astrophysical research fronts. The delineation of a lower LMC mass offers insights into the dark matter distribution and total mass within the local volume occupied by the Milky Way and its satellites. The identified LMC satellite galaxies enable deeper probes into the physics underpinning dwarf galaxy formation and evolution. Moreover, these findings emphasize the necessity to incorporate the LMC's gravitational influence when modeling the Milky Way dynamics and, by extension, the dynamics of its satellite system.

Speculative Outlook

Future developments in observational astrophysics, particularly with Gaia's subsequent data releases, are likely to refine this mass estimate further by reducing observational errors. The paper’s methodology provides a reliable framework to accurately classify LMC satellites despite varied observational qualities. This approach expands prospects for research into understanding Hierarchical formation more intricately within our galactic neighborhood.

In conclusion, the research by Erkal and Belokurov contributes significantly to the broader narrative of galactic evolution and satellite system dynamics. The mass estimations and satellite classification established within their work not only augment the understanding of the LMC's historical dynamics but also set a precedent for approaching galaxy-satellite interaction models with improved precision and reliability.