arXiv subjects

Pierre-Antoine Oria

Publications and source records attributed to Pierre-Antoine Oria.

4 recordsLinked to original sources

arXiv2024

Typhon: a polar stream from the outer halo raining through the Solar neighborhood

We report on the discovery in the Gaia DR3 astrometric and spectroscopic catalog of a new polar stream that is found as an over-density in action space. This structure is unique as it has an extremely large apocenter distance, reaching beyond 100 kpc, and yet is detected as a coherent moving structure in the Solar neighborhood with a width of $\sim 4$ kpc. A sub-sample of these stars that was fortuitously observed by LAMOST has a mean spectroscopic metallicity of $\langle {\rm [Fe/H]}\rangle = -1.60^{+0.15}_{-0.16}$ dex and possesses a resolved metallicity dispersion of $σ({\rm [Fe/H]}) = 0.32^{+0.17}_{-0.06}$ dex. The physical width of the stream, the metallicity dispersion and the vertical action spread indicate that the progenitor was a dwarf galaxy. The existence of such a coherent and highly radial structure at their pericenters in the vicinity of the Sun suggests that many other dwarf galaxy fragments may be lurking in the outer halo.

astro-ph.GA↗

arXiv2022

Antaeus: a retrograde group of tidal debris in the Milky Way's disk plane

We present the discovery of a wide retrograde moving group in the disk plane of the Milky Way using action-angle coordinates derived from the \textit{Gaia} DR3 catalog. The structure is identified from a sample of its members that are currently almost at the pericenter of their orbit and are passing through the Solar neighborhood. The motions of the stars in this group are highly correlated, indicating that the system is probably not phase mixed. With a width of at least 1.5 kpc and with a probable intrinsic spread in metallicity, this structure is most likely the wide remnant of a tidal stream of a disrupted ancient dwarf galaxy (age $\sim 12$ Gyr, $\langle {\rm [Fe/H]} \rangle \sim -1.74$). The structure presents many similarities (e.g. in energy, angular momentum, metallicity, and eccentricity) with the Sequoia merging event. However, it possesses extremely low vertical action $J_z$ which makes it unique even amongst Sequoia dynamical groups. As the low $J_z$ may be attributable to dynamical friction, we speculate that the these stars may be the remnants of the dense core of the Sequoia progenitor.

astro-ph.GA↗

arXiv2022

Revisiting a disky origin for the faint branch of the Sagittarius stellar stream

We investigate ways to produce the bifurcation observed in the stellar stream of the Sagittarius dwarf galaxy (Sgr). Our method consists in running $N$-body simulations of Sgr falling into the Milky Way for the last 3~Gyr, with added test particles on disk orbits that span a wide range of initial positions, energies, and angular momenta. We find that particles that end up in the faint branch are predominantly high angular momentum particles that can all originate from a single plane within the progenitor, nearly perpendicular both to the orbital plane of the progenitor and to the Milky Way stellar disk. Their original configuration at the start of the simulation corresponds to spiral features already present 3~Gyr ago, which could be, e.g., the result of a disk-like component being tidally perturbed, or the tidal tails of a satellite being disrupted within Sgr. We then run a simulation including the self-gravity of this disky component. Despite the remaining ambiguity of its origin, this disk component of the Sgr dwarf with spiral over-densities provides a first step towards a working model to reproduce the observed faint branch of the bifurcated Sgr stream.

astro-ph.GA↗

arXiv2022

On the Effect of the Large Magellanic Cloud on the Orbital Poles of Milky Way Satellite Galaxies

The reflex motion and distortion of the Milky Way (MW) halo caused by the infall of a massive Large Magellanic Cloud (LMC) has been demonstrated to result in an excess of orbital poles of dark matter halo particles towards the LMC orbital pole. This was suggested to help explain the observed preference of MW satellite galaxies to co-orbit along the Vast Polar Structure (VPOS). We test this idea by correcting the positions and velocities of the MW satellites for the Galactocentric-distance-dependent shifts inferred from a LMC-infall simulation. While this should substantially reduce the observed clustering of orbital poles if it were mainly caused by the LMC, we instead find that the strong clustering remains preserved. We confirm the initial study's main result with our simulation of an MW-LMC-like interaction, and use it to identify two reasons why this scenario is unable to explain the VPOS: (1) the orbital pole density enhancement in our simulation is very mild (~10% within 50-250 kpc) compared to the observed enhancement (~220-300%), and (2) it is very sensitive to the specific angular momenta (AM) of the simulation particles, with higher AM particles being affected the least. Particles in simulated dark matter halos tend to follow more radial orbits (lower AM), so their orbital poles are more easily affected by small offsets in position and velocity caused by an LMC infall than objects with more tangential velocity (higher AM), such as the observed dwarf galaxies surrounding the MW. The origin of the VPOS thus remains unexplained.

astro-ph.GA↗