Galaxy sizes and the galaxy-halo connection - I. The remarkable tightness of the size distributions
Abstract
The mass and structural assembly of galaxies is a matter of intense debate. Current theoretical models predict the existence of a linear relationship between galaxy size (Re) and the host dark matter halo virial radius (Rh). By making use of semi-empirical models compared to the size distributions of central galaxies from the Sloan Digital Sky Survey, we provide robust constraints on the normalization and scatter of the Re-Rh relation. We explore the parameter space of models in which the Re-Rh relation is mediated by either the spin parameter or the concentration of the host halo, or a simple constant the nature of which is in principle unknown. We find that the data require extremely tight relations for both early-type and late-type galaxies (ETGs, LTGs), especially for more massive galaxies. These constraints challenge models based solely on angular momentum conservation, which predict significantly wider distributions of galaxy sizes and no trend with stellar mass, if taken at face value. We discuss physically motivated alterations to the original models that bring the predictions into better agreement with the data. We argue that the measured tight size distributions of SDSS disc galaxies can be reproduced by semi-empirical models in which the Re-Rh connection is mediated by the stellar specific angular momenta j(star). We find that current cosmological models of galaxy formation broadly agree with our constraints for LTGs, and justify the strong link between Re and jstar that we propose, however the tightness of the Re-Rh relation found in such ab initio theoretical models for ETGs is in tension with our semi-empirical findings.
Citation
Zanisi , L , Shankar , F , Lapi , A , Menci , N , Bernardi , M , Duckworth , C , Huertas-Company , M , Grylls , P & Salucci , P 2020 , ' Galaxy sizes and the galaxy-halo connection - I. The remarkable tightness of the size distributions ' , Monthly Notices of the Royal Astronomical Society , vol. 492 , no. 2 , pp. 1671-1690 . https://doi.org/10.1093/mnras/stz3516
Publication
Monthly Notices of the Royal Astronomical Society
Status
Peer reviewed
ISSN
0035-8711Type
Journal article
Description
L.Z. acknowledges support from the Science and Technologies Facilities Council and from the Royal Astronomical Society. F.S. acknowledges partial support from a Leverhulme Trust Research Fellowship and from the European Union’s Horizon 2020 programme under the AHEAD project (grant agreement 654215). A.L. acknowledges PRIN MIUR 2017 prot. 20173ML3WW002, Opening the ALMA window on the cosmic evolution of gas, stars, and supermassive black holes.Collections
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