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Simulating galaxies in the reionization era with FIRE-2: morphologies and sizes


Ma, Xiangcheng; Hopkins, Philip F; Boylan-Kolchin, Michael; Faucher-Giguère, Claude-André; Quataert, Eliot; Feldmann, Robert; Garrison-Kimmel, Shea; Hayward, Christopher C; Kereš, Dušan; Wetzel, Andrew (2018). Simulating galaxies in the reionization era with FIRE-2: morphologies and sizes. Monthly Notices of the Royal Astronomical Society, 477(1):219-229.

Abstract

We study the morphologies and sizes of galaxies at z ≥ 5 using high-resolution cosmological zoom-in simulations from the Feedback In Realistic Environments project. The galaxies show a variety of morphologies, from compact to clumpy to irregular. The simulated galaxies have more extended morphologies and larger sizes when measured using rest-frame optical B-band light than rest-frame UV light; sizes measured from stellar mass surface density are even larger. The UV morphologies are usually dominated by several small, bright young stellar clumps that are not always associated with significant stellar mass. The B-band light traces stellar mass better than the UV, but it can also be biased by the bright clumps. At all redshifts, galaxy size correlates with stellar mass/luminosity with large scatter. The half-light radii range from 0.01 to 0.2 arcsec (0.05–1 kpc physical) at fixed magnitude. At z ≥ 5, the size of galaxies at fixed stellar mass/luminosity evolves as (1 + z)−m, with m ∼ 1–2. For galaxies less massive than M* ∼ 108 M⊙, the ratio of the half-mass radius to the halo virial radius is ∼10 per cent and does not evolve significantly at z = 5–10; this ratio is typically 1–5 per cent for more massive galaxies. A galaxy's ‘observed’ size decreases dramatically at shallower surface brightness limits. This effect may account for the extremely small sizes of z ≥ 5 galaxies measured in the Hubble Frontier Fields. We provide predictions for the cumulative light distribution as a function of surface brightness for typical galaxies at z = 6.

Abstract

We study the morphologies and sizes of galaxies at z ≥ 5 using high-resolution cosmological zoom-in simulations from the Feedback In Realistic Environments project. The galaxies show a variety of morphologies, from compact to clumpy to irregular. The simulated galaxies have more extended morphologies and larger sizes when measured using rest-frame optical B-band light than rest-frame UV light; sizes measured from stellar mass surface density are even larger. The UV morphologies are usually dominated by several small, bright young stellar clumps that are not always associated with significant stellar mass. The B-band light traces stellar mass better than the UV, but it can also be biased by the bright clumps. At all redshifts, galaxy size correlates with stellar mass/luminosity with large scatter. The half-light radii range from 0.01 to 0.2 arcsec (0.05–1 kpc physical) at fixed magnitude. At z ≥ 5, the size of galaxies at fixed stellar mass/luminosity evolves as (1 + z)−m, with m ∼ 1–2. For galaxies less massive than M* ∼ 108 M⊙, the ratio of the half-mass radius to the halo virial radius is ∼10 per cent and does not evolve significantly at z = 5–10; this ratio is typically 1–5 per cent for more massive galaxies. A galaxy's ‘observed’ size decreases dramatically at shallower surface brightness limits. This effect may account for the extremely small sizes of z ≥ 5 galaxies measured in the Hubble Frontier Fields. We provide predictions for the cumulative light distribution as a function of surface brightness for typical galaxies at z = 6.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Institute for Computational Science
Dewey Decimal Classification:530 Physics
Language:English
Date:11 June 2018
Deposited On:05 Mar 2019 13:42
Last Modified:17 Sep 2019 19:39
Publisher:Oxford University Press
ISSN:0035-8711
OA Status:Green
Free access at:Publisher DOI. An embargo period may apply.
Publisher DOI:https://doi.org/10.1093/mnras/sty684
Project Information:
  • : FunderSNSF
  • : Grant IDPP00P2_157591
  • : Project TitleAiming for the Parsec Scale - Star Formation and Feedback Processes in High Redshift Galaxies

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