The Diversity of Spiral Galaxies Explained

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Frosst, Matt
galaxies: haloes , galaxies: structure , dark matter , Astrophysics - Astrophysics of Galaxies , Astrophysics - Cosmology and Nongalactic Astrophysics
I have assembled a collection of galaxy rotation curves and g-,r-,i-, and z-band light profiles for a representative sample of 391 spiral galaxies and integrated it with an extensive catalog of galaxy structural properties compiled by Courteau’s research group. This large catalog is used to investigate the drivers of diversity in galaxy structural parameters and explore the claims and origin of the diversity of rotation curve shapes of galaxies, originally presented by Oman et al. (2015). Multiple methods to characterize the shapes of galaxy rotation curves and stellar mass profiles are applied to the compiled observational datasets and NIHAO simulated galaxies in order to determine the origin of the galaxy diversity. We show that the inner slope of a rotation curve is highly correlated with baryon-dominated parameters, as opposed to dark matter dominated parameters. The inner slope of the rotation curve most strongly correlates with Σ1, the stellar mass density measured within 1 kpc, and the (g−r)1kpc colour measured at 1 kpc. Galaxies with the largest inner slopes often appear to host an active galactic nucleus (AGN) and are less likely to host a bar, both likely due to the impact of AGNs on the gas kinematics of the inner regions of the galaxy. Diversity of rotation curves is reflected by a scatter in the maximum circular velocity, Vmax, that is three times larger for baryon-dominated systems than dark matter-dominated systems. This broad range of Vmax is not reproduced by numerical simulations of galaxies (e.g., NIHAO). With this thesis, we have verified that the diversity in spiral galaxy properties is largely driven by the baryons within these galaxies. This finding is most relevant for simulators and dark matter theorists alike.
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