Rotation curves of the Milky Way and  external galaxies and a new mass model (F. S .Labini 9/4/2024)
Channel: Academy of Athens
Date: 09/04/2024

Francesco Sylos Labini
Enrico Fermi Research Center, Rome, Italy

Abstract:
In this presentation, I will begin by providing an overview of the Gaia data, followed by a discussion on a novel statistical deconvolution technique designed to address parallax errors. This method has been applied to data releases of the Gaia Mission, allowing us to construct maps of the three velocity components up to distances of 20 kpc (with the 2nd release) and 30 kpc (with the 3rd release). Leveraging this extended range of distance measurements, we have successfully determined the rotation curve of the Milky Way. Notably, our findings indicate a clear decline in the rotation curve up to 30 kpc, challenging previous assumptions of a flat rotation curve. These measurements have been independently confirmed by several other studies utilizing different datasets.

Next, I will introduce a new method capable of reconstructing both the circular and radial velocity fields of outer galaxies using only the velocity information along the line of sight. This innovative approach enables the reconstruction of not only the average circular and radial fields but also their variations across different regions of the galaxy. These variations, known as angular anisotropies, can then be linked to the presence of density structures such as spiral arms, bars, or satellite galaxies. This method offers a tool to determine rotation curves and represents a promising avenue for gaining insights into the dynamics and structures of outer galaxies, further enhancing our understanding of these fascinating astronomical objects.

Lastly, I will present a new mass model known as the dark matter disk model, which proposes an alternative scenario where dark matter is primarily located within the galactic disk itself. This hypothesis is supported by the observed correlation between dark matter and the distribution of neutral hydrogen (HI) gas, initially noticed by Albert Bosma in 1981. Specifically, in nearby disk galaxies, it has been observed that the ratio of the total disc surface density (derived from rotation curve measurements) to the gas surface density (measured from HI observations) remains roughly constant beyond a certain distance from the galactic center. This correlation implies that rotation curves at larger radii can be interpreted as rescaled versions of those derived from the HI gas distribution. Consequently, the dark matter is hypothesized to follow the distribution of the gas and confined to a disk, although direct observation of the dark matter distribution in this model is yet to be achieved. I will present results for a number of disk galaxies and for the Milky Way.

Relevant papers:

https://ui.adsabs.harvard.edu/abs/2024MNRAS.527.2697S/abstract 
https://ui.adsabs.harvard.edu/abs/2023ApJ...945....3S/abstract   
https://ui.adsabs.harvard.edu/abs/2023MNRAS.524.1560S/abstract 
https://ui.adsabs.harvard.edu/abs/2023ApJ...942...12W/abstract  
https://ui.adsabs.harvard.edu/abs/2020A%26A...642A..95C/abstract  
https://ui.adsabs.harvard.edu/abs/2020A%26A...634A..66L/abstract  
https://ui.adsabs.harvard.edu/abs/2019A%26A...621A..48L/abstract