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Galaxy sizes and the galaxy–halo connection – I. The remarkable tightness of the size distributions

Galaxy sizes and the galaxy–halo connection – I. The remarkable tightness of the size distributions
Galaxy sizes and the galaxy–halo connection – I. The remarkable tightness of the size distributions
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 jstar. 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.
Galaxies: disc, Galaxies: formation, Galaxies: fundamental parameters, Galaxies: kinematics and dynamics, Galaxies: structure
0035-8711
1671-1690
Zanisi, Lorenzo
87405729-1792-4919-a0de-fc92ea450edb
Shankar, Francesco
b10c91e4-85cd-4394-a18a-d4f049fd9cdb
Lapi, Andrea
126b5f87-60fa-4a57-8b84-802d5ffb1f17
Menci, Nicola
e68473f0-6f7f-48b8-8b76-088d8752df6a
Bernardi, Mariangela
51f0929c-ba65-4d9c-a814-673442f48d75
Duckworth, Christopher
0e61d470-1393-48b5-9120-ed08644efc85
Huertas-Company, Marc
6fe27f7c-356c-448b-bcb6-c21a84bab91a
Grylls, Philip
07a63569-16b1-42c4-87fe-bda0fbc3481c
Salucci, Paolo
d09b251a-58cd-4ba6-8b51-d85edfdc5abf
Zanisi, Lorenzo
87405729-1792-4919-a0de-fc92ea450edb
Shankar, Francesco
b10c91e4-85cd-4394-a18a-d4f049fd9cdb
Lapi, Andrea
126b5f87-60fa-4a57-8b84-802d5ffb1f17
Menci, Nicola
e68473f0-6f7f-48b8-8b76-088d8752df6a
Bernardi, Mariangela
51f0929c-ba65-4d9c-a814-673442f48d75
Duckworth, Christopher
0e61d470-1393-48b5-9120-ed08644efc85
Huertas-Company, Marc
6fe27f7c-356c-448b-bcb6-c21a84bab91a
Grylls, Philip
07a63569-16b1-42c4-87fe-bda0fbc3481c
Salucci, Paolo
d09b251a-58cd-4ba6-8b51-d85edfdc5abf

Zanisi, Lorenzo, Shankar, Francesco, Lapi, Andrea, Menci, Nicola, Bernardi, Mariangela, Duckworth, Christopher, Huertas-Company, Marc, Grylls, Philip and Salucci, Paolo (2020) Galaxy sizes and the galaxy–halo connection – I. The remarkable tightness of the size distributions. Monthly Notices of the Royal Astronomical Society, 492 (2), 1671-1690. (doi:10.1093/mnras/stz3516).

Record type: Article

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 jstar. 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.

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1912.02831 - Accepted Manuscript
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Accepted/In Press date: 4 December 2019
e-pub ahead of print date: 16 December 2019
Published date: 21 February 2020
Keywords: Galaxies: disc, Galaxies: formation, Galaxies: fundamental parameters, Galaxies: kinematics and dynamics, Galaxies: structure

Identifiers

Local EPrints ID: 438710
URI: http://eprints.soton.ac.uk/id/eprint/438710
ISSN: 0035-8711
PURE UUID: fbf1b315-6e14-488d-818d-cee35ace0341

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Date deposited: 23 Mar 2020 17:30
Last modified: 08 Oct 2020 16:36

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Contributors

Author: Lorenzo Zanisi
Author: Andrea Lapi
Author: Nicola Menci
Author: Mariangela Bernardi
Author: Christopher Duckworth
Author: Marc Huertas-Company
Author: Philip Grylls
Author: Paolo Salucci

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