Action Dynamics of the Local Supercluster

Abstract: The fully nonlinear gravitationally induced trajectories of a nearly complete set of galaxies, groups, and clusters in the Local Supercluster are constructed in a Numerical Action Method (NAM) model constrained by data from the CosmicFlows survey and various distance indicators. We add the gravity field due to inhomogeneities external to the sample sphere by making use of larger scale peculiar flow measurements. Assignments of total masses were made to find the best overall set of mutual attractions, as determined by a goodness criterion based on present day radial velocities, individually for the Virgo Cluster, M31, and the Milky Way (MW), and via a mass-to-light ratio relationship for other masses. The low median chi-square found indicates the model fits the present day velocity flow well, but a slightly high mean chi-square may indicate that some masses underwent complex orbits. The best fit, when setting the value of $H_0$ to the CosmicFlows value of 75 km/s/Mpc and the WMAP value for $\Omega_m=0.244$ consistent with that $H_0$, occurs with the following parameters: $\Omega_{orphan} = 0.077\pm0.016$, $M/L_K $= $40 \pm 2$ $L_{10}^{0.15}$ $M_\odot/L_\odot$ ($L_{10}$ is K-band luminosity in units of $10^{10} L_\odot$), a Virgo mass of $6.3\pm0.8 \times 10^{14} M_\odot$ ($M/L_K = 113\pm15 M_\odot/L_\odot$), and a mass for the MW plus M31 of $5.15\pm0.35 \times 10^{12} M_\odot$. The best constant mass-to-light ratio is $M/L_K = 58\pm3 M_\odot/L_\odot$. The Virgocentric turnaround radius is $7.3\pm0.3$ Mpc. We explain several interesting trends in peculiar motions for various regions now that we can construct the 3D orbital histories.

• The paper presents a detailed reconstruction of galaxy trajectories within the Local Supercluster using the Numerical Action Method.
• It derives precise mass estimates for the Virgo Cluster and the Milky Way-M31 pair by optimizing a goodness-of-fit to radial velocities.
• The study challenges standard spherical infall models, emphasizing the impact of external gravitational forces on local dynamics.

Analysis of the Local Supercluster Dynamics

The paper "Action Dynamics of the Local Supercluster" presents a comprehensive examination of the motion trajectories of galaxies, groups, and clusters within the Local Supercluster. Utilizing the Numerical Action Method (NAM), the study investigates the gravitationally induced paths constrained by observational data from the Cosmicflows survey. This method allows for the modeling of galaxies' trajectories, incorporating the gravitational effects of inhomogeneities external to the sample volume through peculiar velocity measurements.

Methodology and Key Results

The authors determine the total masses by optimizing a goodness-of-fit criterion based on present-day radial velocities. Noteworthy are the results indicating the Virgo Cluster's mass at $6.3\pm0.8 \times 10^{14} M_\odot$ and the combined mass of the Milky Way and M31 at $5.15\pm0.35 \times 10^{12} M_\odot$. These values are adjusted with respect to the mass-to-light ratio, set to $40 \pm 2 L_{10}^{0.15} M_\odot/L_\odot$, reflecting the variation of the mass-to-light ratio with increasing luminosity.

The analysis further establishes the Virgocentric turnaround radius at $7.3\pm0.3$ Mpc, revealing significant patterns in galaxy flow dynamics, such as the outflow from the Local Void and the substantial peculiar motions influenced by the Great Attractor. These flows illustrate the complex gravitational dynamics present within the local universe.

Theoretical Implications

The study challenges traditional spherical infall models by expanding the complexity of galaxy dynamics through NAM, providing a more nuanced understanding within the high-density regimes of the Local Supercluster. The computed models support the role of large-scale structure, including voids and external galaxies, in shaping local gravitational dynamics. This reinforces the notion that examining such systems requires considering a wider cosmic environment than previously acknowledged.

Practical Implications and Future Directions

The robust datasets utilized, especially the Cosmicflows-3 catalog, provide critical insight into the non-linear gravitational dynamics reshaping our local universe, potentially enhancing the calibration of cosmological parameters like $H_0$. The paper suggests that ongoing improvements in distance measurement accuracy, as seen in the Cosmicflows survey, will continue to refine our understanding of mass distributions and peculiar velocities.

Future investigations could expand beyond the local supercluster or incorporate more of the intricate baryonic interactions that are currently simplified in such models. Moreover, further alignment of NAM with N-body simulations could yield deeper insights into the nature of dark matter and the distribution of "orphan" matter, the intergalactic medium not associated with galaxies.

In summary, this research highlights the intricacies of the Local Supercluster's dynamics, offering a refined model that aligns theoretical predictions with observed galaxy behaviors. It provides a crucial stepping stone for further study in cosmic structure formation and dynamics, essential in the broader context of understanding the universe's evolution.