Is the dark-matter halo spin a predictor of galaxy spin and size?

Abstract

The similarity between the distributions of spins for galaxies (λ gal ) and for dark-matter haloes (λ halo ), indicated both by simulations and observations, is naively interpreted as a one-to-one correlation between the spins of a galaxy and its host halo. This is used to predict galaxy sizes in semi-analytic models via R e ≃ λ halo R vir , where R e is the half-mass radius of the galaxy and R vir is the halo radius. Utilizing two different suites of zoom-in cosmological simulations, we find that λ gal and the λ halo of its host halo are in fact only barely correlated, especially at z 1. A general smearing of this correlation is expected based on the different spin histories, where the more recently accreted baryons through streams gain and then lose significant angular momentum compared to the gradually accumulated dark matter. Expecting the spins of baryons and dark matter to be correlated at accretion into R vir , the null correlation at the end reflects an anti-correlation between λ gal /λ halo and λ halo , which can partly arise from mergers and a compact star-forming phase that many galaxies undergo. On the other hand, the halo and galaxy spin vectors tend to be aligned, with a median cos θ = 0.6-0.7 between galaxy and halo, consistent with instreaming within a preferred plane. The galaxy spin is better correlated with the spin of the inner halo, but this largely reflects the effect of the baryons on the halo. Following the null spin correlation, λ halo is not a useful proxy for R e . While our simulations reproduce a general relation of the sort R e = AR vir , in agreement with observational estimates, the relation becomes tighter with A = 0.02(c/10) −0.7 , where c is the halo concentration, which in turn introduces a dependence on mass and redshift.

Milky Way Satellite Census. II. Galaxy–Halo Connection Constraints Including the Impact of the Large Magellanic Cloud

“…with A = 0.02, n = 1, γ = −0.7, R 0 = 1 kpc, and halo concentration c measured as a function of redshift, fits the hydrodynamic simulation results in Jiang et al (2019) with a residual scatter of ∼ 0.15 dex. This relation implies that more concentrated halos host less extended stellar systems at fixed virial radius in these simulations.…”

Probing Primordial Chirality with Galaxy Spins

“…The observational complexities require a thorough understanding of the systematics. The strong spin correlation between disk galaxies and their parent halos is confirmed in hydrodynamic simulations [24,31], so in this Letter we use halos to represent galaxies. Strong Lagrangian-Eulerian spin correlation has also been confirmed in this work and many high-resolution N -body simulations [19][20][21]23].…”

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

“…Recently, Jiang et al (2019) used cosmological hydrodynamical simulations to study the relation between the specific angular momentum of galaxies and dark matter halos and found evidence for a weak correlation, due to a combination of complex phenomena that lead to the formation of galaxies (see also Danovich et al 2015). These results are potentially very interesting since they revisit the physical basis of the MMW98 study; however, it has yet to be demonstrated whether they can reproduce the observed Fall relation since from their main result j / j h ∝ λ −1 , it would follow that j ∝ M 2/3 h -because λ ∝ j h /M 2/3 h -which is not compatible with observations of the Fall relation, unless in the case of a quasi-linear stellar-tohalo mass relation (M ∝ M h ) which is excluded by the data (Posti et al 2019a).…”