The impact of the halo spin-concentration relation on disc scaling laws

TL;DR

This paper investigates how the anti-correlation between dark matter halo spin and concentration influences galaxy scaling laws, offering insights into galaxy formation models and their secondary parameters.

Contribution

It demonstrates that the spin-concentration relation can weaken observable correlations in galaxy scaling laws, providing a new constraint for galaxy formation theories.

Findings

Anti-correlation between halo spin and concentration can reduce residual correlations.

This effect occurs only in a limited parameter space, constraining galaxy formation models.

The study offers a potential method to test secondary parameter impacts in galaxy evolution.

Abstract

Galaxy scaling laws, such as the Tully-Fisher, mass-size and Fall relations, can provide extremely useful clues on our understanding of galaxy formation in a cosmological context. Some of these relations are extremely tight and well described by one single parameter (mass), despite the theoretical existence of secondary parameters such as spin and concentration, which are believed to impact these relations. In fact, the residuals of these scaling laws appear to be almost uncorrelated with each other, posing significant constraints on models where secondary parameters play an important role. Here, we show that a possible solution is that such secondary parameters are correlated amongst themselves, in a way that removes correlations in observable space. In particular, we focus on how the existence of an anti-correlation between the dark matter halo spin and its concentration -- which is still debated in simulations -- can weaken the correlation of the residuals of the Tully-Fisher and mass-size relations. Interestingly, using simple analytic galaxy formation models, we find that this happens only for a relatively small portion of the parameter space that we explored, which suggests that this idea could be used to derive constraints to galaxy formation models that are still unexplored.