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Realistic mock observations of the sizes and stellar mass surface densities of massive galaxies in FIRE-2 zoom-in simulations

Parsotan, T. and Cochrane, R. K. and Hayward, C. C. and Anglés-Alcázar, D. and Feldmann, R. and Faucher-Giguère, C. A. and Wellons, S. and Hopkins, P. F. (2021) Realistic mock observations of the sizes and stellar mass surface densities of massive galaxies in FIRE-2 zoom-in simulations. Monthly Notices of the Royal Astronomical Society, 501 (2). pp. 1591-1602. ISSN 0035-8711.

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The galaxy size–stellar mass and central surface density–stellar mass relationships are fundamental observational constraints on galaxy formation models. However, inferring the physical size of a galaxy from observed stellar emission is non-trivial due to various observational effects, such as the mass-to-light ratio variations that can be caused by non-uniform stellar ages, metallicities, and dust attenuation. Consequently, forward-modelling light-based sizes from simulations is desirable. In this work, we use the SKIRT  dust radiative transfer code to generate synthetic observations of massive galaxies (⁠M∗∼10¹¹M⊙ at z = 2, hosted by haloes of mass M_(halo)∼10^(12.5)M⊙⁠) from high-resolution cosmological zoom-in simulations that form part of the Feedback In Realistic Environments project. The simulations used in this paper include explicit stellar feedback but no active galactic nucleus (AGN) feedback. From each mock observation, we infer the effective radius (R_e), as well as the stellar mass surface density within this radius and within 1kpc (Σ_e and Σ₁, respectively). We first investigate how well the intrinsic half-mass radius and stellar mass surface density can be inferred from observables. The majority of predicted sizes and surface densities are within a factor of 2 of the intrinsic values. We then compare our predictions to the observed size–mass relationship and the Σ₁−M⋆ and Σ_e−M⋆ relationships. At z ≳ 2, the simulated massive galaxies are in general agreement with observational scaling relations. At z ≲ 2, they evolve to become too compact but still star forming, in the stellar mass and redshift regime where many of them should be quenched. Our results suggest that some additional source of feedback, such as AGN-driven outflows, is necessary in order to decrease the central densities of the simulated massive galaxies to bring them into agreement with observations at z ≲ 2.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper ItemData
Parsotan, T.0000-0002-4299-2517
Cochrane, R. K.0000-0001-8855-6107
Hayward, C. C.0000-0003-4073-3236
Anglés-Alcázar, D.0000-0001-5769-4945
Feldmann, R.0000-0002-1109-1919
Faucher-Giguère, C. A.0000-0002-4900-6628
Wellons, S.0000-0002-3977-2724
Hopkins, P. F.0000-0003-3729-1684
Additional Information:© 2020 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( Accepted 2020 December 1. Received 2020 November 28; in original form 2020 September 21. Published: 05 December 2020. We thank the anonymous reviewer for detailed suggestions that helped improve the content and clarity of the paper. This work was initiated as a project for the Kavli Summer Program in Astrophysics held at the Center for Computational Astrophysics of the Flatiron Institute in 2018. The programme was co-funded by the Kavli Foundation and the Simons Foundation. We thank them for their generous support. TP would like to thank all of the participants of the summer programme including Marius Ramsoy, Ulrich Steinwandel, and Daisy Leung for stimulating discussion. TP acknowledges funding from the Future Investigators in NASA Earth and Space Science and Technology (FINESST) Fellowship, NASA grant 80NSSC19K1610. RKC acknowledges funding from the John Harvard Distinguished Science Fellowship and thanks Sandro Tacchella for helpful discussions. The Flatiron Institute is supported by the Simons Foundation. DAA was supported in part by NSF grant AST-2009687. RF acknowledges financial support from the Swiss National Science Foundation (grant number 157591). CAFG was supported by the NSF through grants AST-1517491, AST-1715216 and CAREER award AST-1652522, by NASA through grant 17-ATP17-0067, by STScI through grant HST-AR-14562.001, and by a Cottrell Scholar Award from the Research Corporation for Science Advancement. SW was supported by the CIERA Postdoctoral Fellowship Program (Center for Interdisciplinary Exploration and Research in Astrophysics, Northwestern University) and by an NSF Astronomy and Astrophysics Postdoctoral Fellowship under award AST-2001905. The simulations were run using XSEDE (TG-AST160048, TG-AST140023), supported by NSF grant ACI-1053575, and Northwestern University’s compute cluster ‘Quest’, as well as using NASA HEC allocations SMD-16-7561 and SMD-17-1204. Support for PFH was provided by NSF Collaborative Research Grants 1715847 and 1911233, NSF CAREER grant 1455342, NASA grants 80NSSC18K0562, JPL 1589742. Numerical calculations were run on the Caltech compute cluster ‘Wheeler,’ allocations FTA-Hopkins supported by the NSF and TACC, and NASA HEC SMD-16-7592. The data used in this work were, in part, hosted on facilities supported by the Scientific Computing Core at the Flatiron Institute. This research has made use of the SVO Filter Profile Service, supported from the Spanish MINECO through grant AyA2014-55216. Data Availability: The data underlying this article will be shared on reasonable request to the corresponding author. Additional data including simulation snapshots, initial conditions, and derived data products are available at
Group:Astronomy Department, TAPIR
Funding AgencyGrant Number
Kavli FoundationUNSPECIFIED
Simons FoundationUNSPECIFIED
John Harvard Distinguished Science FellowshipUNSPECIFIED
Swiss National Science Foundation (SNSF)157591
Cottrell Scholar of Research CorporationUNSPECIFIED
Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA)UNSPECIFIED
Northwestern UniversityUNSPECIFIED
Texas Advanced Computing Center (TACC)UNSPECIFIED
Ministerio de Economía, Industria y Competitividad (MINECO)AyA2014-55216
Subject Keywords:radiative transfer – galaxies: formation
Issue or Number:2
Record Number:CaltechAUTHORS:20210211-133104724
Persistent URL:
Official Citation:T Parsotan, R K Cochrane, C C Hayward, D Anglés-Alcázar, R Feldmann, C A Faucher-Giguère, S Wellons, P F Hopkins, Realistic mock observations of the sizes and stellar mass surface densities of massive galaxies in FIRE-2 zoom-in simulations, Monthly Notices of the Royal Astronomical Society, Volume 501, Issue 2, February 2021, Pages 1591–1602,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:108009
Deposited By: Tony Diaz
Deposited On:11 Feb 2021 22:17
Last Modified:11 Feb 2021 22:17

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