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Robin Chisholm

Publications and source records attributed to Robin Chisholm.

2 recordsLinked to original sources

The Missing Black Hole in the Large Magellanic Cloud: A Dynamical Prediction for Its Present-Day Location

There are indications that the Large Magellanic Cloud (LMC) hosts a central supermassive black hole (SMBH), yet no direct detection exists: one reason is that its present-day location need not necessarily coincide with the photometric or kinematic centers. Here we frame a dynamical targeting problem and predict the present-day sky location of the LMC SMBH. We model the recent LMC-Small Magellanic Cloud (SMC) interaction, which induces a bar-disk offset, and integrate SMBH orbits within a realistic, time-dependent LMC-SMC-Milky Way (MW) potential. We show that the MW tidal field at present epoch exceeds that of the SMC by at least an order of magnitude, setting a preferred direction for coherent, vertical low-amplitude displacements, while the disk asymmetry drives in-plane offsets. Projecting onto the observed LMC frame, the mean of our predicted SMBH probability distribution is located at $(α,δ)=(80.23^{\circ},-69.55^{\circ})$, with a $1σ$ confidence ellipse having semi-major and semi-minor axes of $(a,b)=(1.34^{\circ},0.56^{\circ})$, respectively. This mean is $\sim6$ arcminutes north of the adopted dynamical center, while the mode coincides with the dynamical center and lies well within the $1σ$ confidence region. Furthermore, all literature estimates of the LMC center considered here fall within the $2σ$ confidence region. This provides a concrete, testable target for ongoing and upcoming spectroscopic surveys, transforming the search for the LMC SMBH from an unconstrained problem into a focused observational strategy.

astro-ph.GA

A Pre-Infall Magellanic Analog-Corona and Stream formation in the \textsc{HESTIA} cosmological simulations

We identify and investigate a pre-infall analog of the Large and Small Magellanic Clouds (LMC, SMC) in the HESTIA suite of constrained cosmological simulations. The system, dynamically isolated from the Local Group, evolves over ~6 Gyr and forms a multiphase warm coronal halo and a neutral gas stream via repeated tidal interactions, ~150 kpc in length. The LMC-analog's corona forms self-consistently through virial accretion and inhibits the survival of clumpy neutral structures beyond ~600 Myr. The SMC analog remains bound through to z=0, and the pair also exhibits bridge-like and leading-arm features. These results suggest that while most of the ionized Stream is formed by the LMC coronal gas, the neutral gas stream, bridge, and leading arm components of the Magellanic System can arise from dwarf-dwarf interactions prior to infall, while the survival and ionization of these features likely require additional environmental processing. Furthermore, we identify a stellar component out of phase to the neutral component of the stream, implying that if the Magellanic stellar stream exists, it may not be spatially coexistent to the dominant H I stream. This system offers a valuable pre-infall reference point for interpreting the Magellanic System and identifying analogs beyond the Local Group.

astro-ph.GA