TY - JOUR
T1 - Cosmic variance and the inhomogeneous UV luminosity function of galaxies during reionization
AU - Dawoodbhoy, Taha
AU - Shapiro, Paul R.
AU - Ocvirk, Pierre
AU - Lewis, Joseph S.W.
AU - Aubert, Dominique
AU - Sorce, Jenny G.
AU - Ahn, Kyungjin
AU - Iliev, Ilian T.
AU - Park, Hyunbae
AU - Teyssier, Romain
AU - Yepes, Gustavo
N1 - Funding Information:
This material is based upon work supported by the National Science Foundation (NSF) Graduate Research Fellowship Program under Grant No. DGE-1610403. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the NSF. This research used resources of the Oak Ridge Leadership Computing Facility (OLCF) at the Oak Ridge National Lab, which is supported by the Office of Science of the US Dept. of Energy (DOE) under Contract No. DE-AC05-00OR22725. CoDa II was performed on Titan at OLCF under DOE INCITE 2016 award to Project AST031. Data analysis was performed using the computing resources from NSF XSEDE grant TG-AST090005 and the Texas Advanced Computing Center at the University of Texas at Austin. PRS acknowledges support from NASA under Grant No. 80NSSC22K175. JL acknowledges support from the German Research Foundation via the Heidelberg Cluster of Excellence STRUCTURES in the framework of Germany’s Excellence Strategy (grant EXC-2181/1-390900948). JS acknowledges support from the ANR LOCALIZATION project, grant ANR-21-CE31-0019 of the French Agence Nationale de la Recherche. KA is supported by Korea NRF-2021R1A2C1095136, NRF-2016R1A5A1013277, and RS-2022-00197685. KA also appreciates the Asia Pacific Center for Theoretical Physics for its hospitality during completion of this work. ITI was supported by the Science and Technology Facilities Council [grant numbers ST/I000976/1 and ST/T000473/1] and the Southeast Physics Network. HP was supported by the World Premier International Research Center Initiative, MEXT, Japan and JSPS KAKENHI grant No. 19K23455. GY acknowledges financial support from the Ministry of Science and Innovation/FEDER under project grant PGC2018-094975-C21.
Publisher Copyright:
© 2023 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.
PY - 2023/10
Y1 - 2023/10
N2 - When the first galaxies formed and starlight escaped into the intergalactic medium to reionize it, galaxy formation and reionization were both highly inhomogeneous in time and space, and fully coupled by mutual feedback. To show how this imprinted the UV luminosity function (UVLF) of reionization-era galaxies, we use our large-scale, radiation-hydrodynamics simulation CoDa II to derive the time- and space-varying halo mass function and UVLF, from z ≃ 6-15. That UVLF correlates strongly with local reionization redshift: earlier-reionizing regions have UVLFs that are higher, more extended to brighter magnitudes, and flatter at the faint end than later-reionizing regions observed at the same z. In general, as a region reionizes, the faint-end slope of its local UVLF flattens, and, by z = 6 (when reionization ended), the global UVLF, too, exhibits a flattened faint-end slope, 'rolling-over' at MUV ≳ -17. CoDa II's UVLF is broadly consistent with cluster-lensed galaxy observations of the Hubble Frontier Fields at z = 6-8, including the faint end, except for the faintest data point at z = 6, based on one galaxy at MUV = -12.5. According to CoDa II, the probability of observing the latter is. However, the effective volume searched at this magnitude is very small, and is thus subject to significant cosmic variance. We find that previous methods adopted to calculate the uncertainty due to cosmic variance underestimated it on such small scales by a factor of 2-4, primarily by underestimating the variance in halo abundance when the sample volume is small.
AB - When the first galaxies formed and starlight escaped into the intergalactic medium to reionize it, galaxy formation and reionization were both highly inhomogeneous in time and space, and fully coupled by mutual feedback. To show how this imprinted the UV luminosity function (UVLF) of reionization-era galaxies, we use our large-scale, radiation-hydrodynamics simulation CoDa II to derive the time- and space-varying halo mass function and UVLF, from z ≃ 6-15. That UVLF correlates strongly with local reionization redshift: earlier-reionizing regions have UVLFs that are higher, more extended to brighter magnitudes, and flatter at the faint end than later-reionizing regions observed at the same z. In general, as a region reionizes, the faint-end slope of its local UVLF flattens, and, by z = 6 (when reionization ended), the global UVLF, too, exhibits a flattened faint-end slope, 'rolling-over' at MUV ≳ -17. CoDa II's UVLF is broadly consistent with cluster-lensed galaxy observations of the Hubble Frontier Fields at z = 6-8, including the faint end, except for the faintest data point at z = 6, based on one galaxy at MUV = -12.5. According to CoDa II, the probability of observing the latter is. However, the effective volume searched at this magnitude is very small, and is thus subject to significant cosmic variance. We find that previous methods adopted to calculate the uncertainty due to cosmic variance underestimated it on such small scales by a factor of 2-4, primarily by underestimating the variance in halo abundance when the sample volume is small.
KW - cosmology: theory
KW - dark ages, reionization, first stars
KW - galaxies: high-redshift
KW - galaxies: luminosity function, mass function
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U2 - 10.1093/mnras/stad2331
DO - 10.1093/mnras/stad2331
M3 - Article
AN - SCOPUS:85168716037
SN - 0035-8711
VL - 524
SP - 6231
EP - 6246
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 4
ER -