giordano de marzo | Francesco Sylos Labini

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Francesco Sylos Labini, Giordano De Marzo, and Matteo Straccamore

Citation Francesco Sylos Labini et al 2025 ApJ 988 122

DOI 10.3847/1538-4357/adc71c

Abstract

Observations of the line-of-sight (LOS) component of emitter velocities in galaxies are valuable for reconstructing their two-dimensional (2D) velocity fields, albeit requiring certain assumptions. A common one is that radial flows can be neglected in the outer regions of galaxies, while their geometry can be deformed by a warp. A specular approach assumes that galactic disks are flat but allows for the presence of radial flows. This approach enables the reconstruction of 2D velocity maps that encompass both the transversal and radial velocity fields. Through the study of velocity fields in toy disk models, we find that the presence of warps is manifested as a dipolar correlation between the two velocity components obtained by assuming a flat disk. This shows that the analysis of angular velocity anisotropies provides an effective tool for breaking the degeneracy between warps and radial flows. We have applied these findings to the analysis of velocity fields of the galaxies from the THINGS sample and M33. Many of these galaxies exhibit such a dipolar correlation, indicating the presence of warps. However, we have found that the warp alone cannot explain all variations in the velocity field, suggesting that intrinsic perturbations are common. Furthermore, we have observed that the spatial distribution of the LOS velocity dispersion may correlate with both velocity components, providing independent evidence of nontrivial velocity fields. These findings offer a robust approach to reconstructing the velocity fields of galaxies, allowing us to distinguish between the presence of warps and complex velocity structures by assessing their relative amplitude.

Francesco Sylos Labini, Giordano De Marzo, Matteo Straccamore, Sébastien Comerón

Monthly Notices of the Royal Astronomical Society, Volume 527, Issue 2, January 2024, Pages 2697–2717, https://doi.org/10.1093/mnras/stad3278

(https://arxiv.org/abs/2310.15673)

We show that the rotation curves of 16 nearby disc galaxies in the THINGS sample and the Milky Way can be described by the NFW halo model and by the Bosma effect at approximately the same level of accuracy. The latter effect suggests that the behavior of the rotation curve at large radii is determined by the rescaled gas component and thus that dark matter and gas distributions are tightly correlated. By focusing on galaxies with exponential decay in their gas surface density, we can normalize their rotation curves to match the exponential thin disc model at large enough radii. This normalization assumes that the galaxy mass is estimated consistently within this model, assuming a thin disc structure. We show that this rescaling allows us to derive a new version of the Tully-Fisher (TF) relation, the Bosma TF relation that nicely fit the data. In the framework of this model, the connection between the Bosma Tully-Fisher (TF) relation and the baryonic TF relation can be established by considering an additional empirical relation between the baryonic mass and the total mass of the disc, as measured in the data.