The evolution of the sizes and angular momentum content of galaxies in the COLIBRE simulations

TL;DR

This study uses the Colibre simulations to analyze galaxy sizes and angular momentum, comparing results to observations from redshift 0 to 4, and finds good agreement at low redshift with some discrepancies at higher redshift.

Contribution

The paper demonstrates that the Colibre simulations accurately reproduce observed galaxy size-mass and angular momentum-mass relations across a wide redshift range, highlighting their realism.

Findings

Simulations match observed size-mass relations at z=0 across various size definitions.

Reproduce the segregation of galaxy types in size-mass and angular momentum-mass planes.

At higher redshifts, simulated massive galaxies are smaller than observed, possibly due to dust attenuation effects.

Abstract

We analyse the sizes and specific angular momentum content of galaxies in the Colibre cosmological hydrodynamical simulations spanning two orders of magnitude in mass resolution. We compare the predicted size-mass and angular momentum-mass relations to a broad range of observational measurements spanning redshifts $z=0$ to $4$. At $z=0$, Colibre reproduces observed size-mass relations over the sampled mass range $10^8 \lesssim M_\star/{\rm M_\odot}\lesssim 10^{11.5}$, and for multiple size definitions, including two- and three-dimensional stellar half-mass radii, half-light radii across several wavelengths, as well as alternative measures such as baryonic half-mass radii and characteristic radii defined by stellar surface density thresholds. The simulations also recover the observed segregation of galaxies in the size-mass plane by morphological type and star formation rate, and reproduce the distinct, approximately parallel sequences followed by star-forming discs and quenched spheroids in the stellar specific angular momentum-mass plane. The angular momentum content of star-forming Colibre galaxies match that of observed systems out to $z\approx 1.5$. At higher redshifts, massive galaxies ($ 10^{9.5}\lesssim M_\star/{\rm M_\odot}\lesssim 10^{11}$) in the simulations are somewhat smaller than observed, and the separation between star-forming and passive populations in the size-mass plane is reduced relative to observations, while at lower masses the agreement remains good. This apparent discrepancy may reflect the effects of dust attenuation, which is neglected in our analysis and may preferentially obscure the central regions of observed systems. Overall, our findings highlight the close connection between galaxy size, angular momentum, and morphology over cosmic time.