$S^5$: Probing the Milky Way and Magellanic Clouds potentials with the 6-D map of the Orphan-Chenab stream (2211.04495v2)

Abstract: We present a 6-D map of the Orphan-Chenab (OC) stream by combining the data from Southern Stellar Stream Spectroscopic Survey ($S^5$) and {\it Gaia}. We reconstruct the proper motion, radial velocity, distance, on-sky track and stellar density along the stream with spline models. The stream has a total luminosity of $M_V=-8.2$ and metallicity of $\mathrm{[Fe/H]}=-1.9$, similar to classical Milky Way (MW) satellites like Draco. The stream shows drastic changes in its physical width varying from 200 pc to 1 kpc, but a constant line of sight velocity dispersion of 5 km/ss. Despite the large apparent variation in the stellar number density along the stream, the flow rate of stars along the stream is remarkably constant. We model the 6-D stream track by a Lagrange-point stripping method with a flexible MW potential in the presence of a moving extended Large Magellanic Cloud (LMC). This allows us to constrain the mass profile of the MW within the distance range 15.6 < r < 55.5 kpc, with the best measured enclosed mass of $(2.85\pm 0.1)\times 10^{11}\,M_\odot$ within 32.4 kpc. Our stream measurements are highly sensitive to the LMC mass profile with the most precise measurement of its enclosed mass made at 32.8 kpc, $(7.02\pm 0.9)\times10^{10}\, {\rm M}_\odot$. We also detect that the LMC dark matter halo extends to at least 53 kpc. The fitting of the OC stream allows us to constrain the past LMC trajectory and the degree of dynamical friction it experienced. We demonstrate that the stars in the OC stream show large energy and angular momentum spreads caused by LMC perturbation.

• The paper presents a comprehensive 6-D mapping of the Orphan-Chenab stream by combining Gaia and S5 data to probe galactic potentials.
• It identifies a stable 5 km/s velocity dispersion and spatial width variations that reflect the stream's response to tidal forces.
• The study constrains the enclosed mass of the Milky Way and LMC, reporting 2.85 ± 0.1×10^11 M☉ and 7.02 ± 0.9×10^10 M☉ within key radii.

Analysis of the Orphan-Chenab Stream in the Context of Galactic Dynamics

The paper "S: Probing the Milky Way and Magellanic Clouds potentials with the 6-D map of the Orphan-Chenab stream" presents an extensive analysis of the Orphan-Chenab (OC) stream to investigate the mass distributions of the Milky Way (MW) and the Large Magellanic Cloud (LMC). This paper combines data from the Southern Stellar Stream Spectroscopic Survey (S5) and the Gaia mission to produce a detailed six-dimensional map of the OC stream. The research provides new insights into the interaction between this stream and the MW and LMC, demonstrating the capabilities of stellar streams as intricate tools in mapping galactic potentials.

Key Findings and Methodologies

1. 6-D Stream Mapping: By employing a combination of data from Gaia and S5, the researchers successfully reconstructed the OC stream across its full six-dimensional parameter space, including position, velocity, and metallicity. This comprehensive mapping allows for a robust analysis of the MW's and LMC’s gravitational influences on the stream.
2. Spatial and Kinematic Characteristics: The paper notes significant variations in physical width along the stream while maintaining a nearly constant line-of-sight velocity dispersion at 5 km/s. Interestingly, despite apparent changes in stellar number density, the flow rate along the stream remains remarkably stable.
3. Mass Constraints on the MW and LMC: Through modeling the stream dynamics using a Lagrange-point stripping method, the paper constrains the mass profile of the MW within a radial distance of 15.6 to 55.5 kpc. In particular, it reports an enclosed mass of $2.85 \pm 0.1 \times 10^{11} M_\odot$ within a 32.4 kpc radius. In addition, precise measurements for the LMC's enclosed mass at 32.8 kpc, $7.02 \pm 0.9 \times 10^{10} M_\odot$, indicate that the LMC's dark matter halo extends significantly.
4. Influence of the LMC: The paper highlights the perturbations in the OC stream caused by the gravitational influence of the LMC. These perturbations lead to significant spreads in energy and angular momentum among the stream's stars, evidencing strong interactions indicative of the dynamical friction experienced by the LMC.

Theoretical and Practical Implications

• Galactic Potential Mapping: The detailed mapping of the OC stream reveals the structure of the MW halo and interactions with the LMC. The constraints on the MW mass distribution and LMC effects may refine models of galactic dynamics and halo structure in ΛCDM contexts.
• Stream Dynamics Modeling: The use of Lagrange-point stripping methods allows for the reconstruction of detailed stream trajectories under complex gravitational influences. Future work could employ similar methods on other streams to probe unknown structures or dark matter profiles further.
• Astrophysical Associations: This research suggests a robust methodology for associating streams with potential progenitors or other galactic features. The accurate mapping of streams like the OC can lead to identifying past interactions with other satellite galaxies or globular clusters.

Future Directions

The paper opens up new avenues for future research, specifically concerning the investigation of more stellar streams in detail to elaborate on the galaxies' mass and dark matter distribution. Additionally, with enhanced data from future surveys, ongoing analysis could refine the understanding of the MW's interaction with neighboring galaxies such as the LMC. As observational techniques advance, the potential for resolving the finer details of galactic dynamics and structure appears promising, providing further insights into the broader cosmological questions surrounding galaxy formation and evolution.