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

Ma, Xiangcheng and Hopkins, Philip F. and Boylan-Kolchin, Michael and Faucher-Giguère, Claude-André and Quataert, Eliot and Feldmann, Robert and Garrison-Kimmel, Shea and Hayward, Christopher C. and Kereš, Dušan and Wetzel, Andrew (2018) Simulating galaxies in the reionization era with FIRE-2: morphologies and sizes. Monthly Notices of the Royal Astronomical Society, 477 (1). pp. 219-229. ISSN 0035-8711.

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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_star~10^8 M_sun, the ratio of the half-mass radius to the halo virial radius is ~10% and does not evolve significantly at z = 5-10; this ratio is typically 1-5% 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.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Hopkins, Philip F.0000-0003-3729-1684
Boylan-Kolchin, Michael0000-0002-9604-343X
Quataert, Eliot0000-0001-9185-5044
Feldmann, Robert0000-0002-1109-1919
Hayward, Christopher C.0000-0003-4073-3236
Kereš, Dušan0000-0002-1666-7067
Wetzel, Andrew0000-0003-0603-8942
Additional Information:© 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2018 March 12. Received 2018 March 12; in original form 2017 September 30. Published: 15 March 2018. We acknowledge the anonymous referee for useful comments that help improve this manuscript. We thank Rychard Bouwens, Brian Siana, James Bullock, and Eros Vanzella for helpful discussion. The simulations used in this paper were run on XSEDE computational resources (allocations TG-AST120025, TG-AST130039, TG-AST140023, and TG-AST140064). The analysis was performed on the Caltech compute cluster “Zwicky” (NSF MRI award #PHY-0960291). Support for PFH was provided by an Alfred P. Sloan Research Fellowship, NASA ATP Grant NNX14AH35G, and NSF Collaborative Research Grant #1411920 and CAREER grant #1455342. MBK acknowledges support from NSF grant AST-1517226 and from NASA grants NNX17AG29G and HSTAR-12836, HST-AR-13888, HST- AR-13896, and HST-AR-14282 from the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS5-26555. CAFG was supported by NSF through grants AST-1412836, AST-1517491, AST-1715216 and CAREER award AST-1652522, by NASA through grant NNX15AB22G, and by STScI through grant HST-AR-14562.001. EQ was supported by NASA ATP grant 12-APT12- 0183, a Simons Investigator award from the Simons Foundation, and the David and Lucile Packard Foundation. RF acknowledges financial support from the Swiss National Science Foundation (grant no 157591). SGK was supported by NASA through Einstein Postdoctoral Fellowship grant number PF5-160136 awarded by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for NASA under contract NAS8-03060. DK was supported by NSF grant AST-1412153, funds from the University of California, San Diego, and a Cottrell Scholar Award from the Research Corporation for Science Advancement. AW was supported by NASA through grants HST-GO-14734 and HST-AR-15057 from STScI.
Funding AgencyGrant Number
Alfred P. Sloan FoundationUNSPECIFIED
Simons FoundationUNSPECIFIED
David and Lucile Packard FoundationUNSPECIFIED
Swiss National Science Foundation (SNSF)157591
NASA Einstein FellowshipPF5-160136
Research CorporationUNSPECIFIED
Subject Keywords:galaxies: evolution, galaxies: formation, galaxies: high-redshift, cosmology: theory
Record Number:CaltechAUTHORS:20171031-184920974
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Official Citation:Xiangcheng Ma, Philip F Hopkins, Michael Boylan-Kolchin, Claude-André Faucher-Giguère, Eliot Quataert, Robert Feldmann, Shea Garrison-Kimmel, Christopher C Hayward, Dušan Kereš, Andrew Wetzel; Simulating galaxies in the reionization era with FIRE-2: morphologies and sizes, Monthly Notices of the Royal Astronomical Society, Volume 477, Issue 1, 11 June 2018, Pages 219–229,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:82825
Deposited By: Joy Painter
Deposited On:01 Nov 2017 12:59
Last Modified:26 Apr 2018 16:09

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