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

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, in 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 on galaxy formation models that have yet to be explored.

A tight angular-momentum plane for disc galaxies

“…Second-order effects related to the concentration of the host halo might also be relevant in determining the galaxy sizes(Posti et al 2020). L15, page 5 of 7 A&A 651,L15 (2021) …”

Dark matter and angular momentum in nearby disc galaxies

“…The same happens with R d , given the relation between the spin parameter λ of dark matter haloes and R d (e.g. Mo et al 1998;Posti et al 2020;Zanisi et al 2020), and that for galaxy discs with Sérsic profiles and flat rotation curves j * ∝ R d (Romanowsky & Fall 2012). As shown in Fig.…”

“…In theory one expects the galaxy to have a significantly larger M 200 . For example, the ΛCDM stellar-tohalo mass relation from Posti et al (2020) Fig. 4.6 shows the two resulting mass models.…”

“…We fit Eq. 5.7 using a likelihood as in P18 and Posti et al (2020), which includes a term for the orthogonal intrinsic scatter (σ ⊥ ), and we use a Markov chain Monte Carlo approach (Foreman-Mackey et al 2013) to constrain the parameters after assuming uninformative priors. We find the best-fitting parameters to be α = 0.53 ± 0.02 and β = 2.71 ± 0.02, with a perpendicular intrinsic scatter σ ⊥ = 0.15 ± 0.01.…”

“…For this, we can assume a stellar-to-halo mass relation to then find which value of f j,bar , as a function of mass, better reproduces the observed j bar − M bar relation. We adopt the empirical stellar-to-halo mass relation for disc galaxies recently derived by Posti et al (2020), by using accurate mass-decomposition models of SPARC and LITTLE THINGS galaxies (see also Read et al 2017). The relation from Posti et al (2020) follows a single power-law at all masses and deviates from relations derived with abundance matching especially at the high-mass end, where the abundance-matching relations would predict a break at around M h ∼ 10 12 M ⊙ (e.g.…”