A timing constraint on the (total) mass of the Large Magellanic Cloud

This paper explores the effect of the LMC on the mass estimates obtained from the timing argument. We show that accounting for the presence of the LMC systematically lowers the Local Group mass ($M_{rm LG}$) derived from the relative motion of the Milky Way--Andromeda pair. Motivated by this result we apply a Bayesian technique devised by Pe~narrubia et al. (2014) to simultaneously fit (i) distances and velocities of galaxies within 3~Mpc and (ii) the relative motion between the Milky Way and Andromeda derived from HST observations, with the LMC mass ($M_{rm LMC}$) as a free parameter. Our analysis returns a Local Group mass $M_{rm LG}=2.64^{+0.42}_{-0.38}times 10^{12}M_odot$ at a 68% confidence level. The masses of the Milky Way, $M_{rm MW}=1.04_{-0.23}^{+0.26}times 10^{12}M_odot$, and Andromeda, $M_{rm M31}=1.33_{-0.33}^{+0.39}times 10^{12}M_odot$, are consistent with previous estimates that neglect the impact of the LMC on the observed Hubble flow. We find a (total) LMC mass $M_{rm LMC}=0.25_{-0.08}^{+0.09}times 10^{12}M_odot$, which is indicative of an extended dark matter halo and supports the scenario where this galaxy is just past its first pericentric approach. Consequently, these results suggest that the LMC may induce significant perturbations on the Galactic potential.

Signatures of minor mergers in Milky Way-like disc kinematics: Ringing revisited

By means of N-body simulations we study the response of a galactic disc to a minor merger event. We find that non-self-gravitating, spiral-like features are induced in the thick disc. As we have shown in a previous work, this ringing also leaves an imprint in velocity space (the u-v plane) in small spatial regions, such as the solar neighbourhood. As the disc relaxes after the event, clumps in the u-v plane get closer with time, allowing us to estimate the time of impact. In addition to confirming the possibility of this diagnostic, here we show that in a more realistic scenario, the in-fall trajectory of the perturber gives rise to an azimuthal dependence of the structure in phase-space. We also find that the space defined by the energy and angular momentum of stars is a better choice than velocity space, as clumps remain visible even in large local volumes. This makes their observational detection much easier since one need not be restricted to a small spatial volume. We show that information about the time of impact, the mass of the perturber, and its trajectory is stored in the kinematics of disc stars.

On the identification of merger debris in the {it Gaia} Era

We model the formation of the Galactic stellar halo via the accretion of satellite galaxies onto a time-dependent semi-cosmological galactic potential. Our goal is to characterize the substructure left by these accretion events in a close manner to what may be possible with the {it Gaia} mission. We have created a synthetic {it Gaia} Solar Neighbourhood catalogue by convolving the 6D phase-space coordinates of stellar particles from our disrupted satellites with the latest estimates of the {it Gaia} measurement errors, and included realistic background contamination due to the Galactic disc(s) and bulge. We find that, even after accounting for the expected observational errors, the resulting phase-space is full of substructure. We are able to successfully isolate roughly 50% of the different satellites contributing to the `Solar Neighbourhood by applying the Mean-Shift clustering algorithm in energy-angular momentum space. Furthermore, a Fourier analysis of the space of orbital frequencies allows us to obtain accurate estimates of time since accretion for approximately 30% of the recovered satellites.