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The evolution of galaxy number density at z < 8 and its implications

Conselice, Christopher J.; Wilkinson, Aaron; Duncan, Kenneth; Mortlock, Alice

Authors

Christopher J. Conselice

Aaron Wilkinson

Kenneth Duncan

Alice Mortlock



Abstract

The evolution of the number density of galaxies in the universe, and thus also the total number of galaxies, is a fundamental question with implications for a host of astrophysical problems including galaxy evolution and cosmology. However there has never been a detailed study of this important measurement, nor a clear path to answer it. To address this we use observed galaxy stellar mass functions up to z _ 8 to determine how the number densities of galaxies changes as a function of time and mass limit. We show that the increase in the total number density of galaxies (_T), more massive than M∗ = 106 M⊙ , decreases as _T _ t−1, where t is the age of the universe. We further show that this evolution turns-over and rather increases with time at higher mass lower limits of M∗ > 107 M⊙ . By using the M∗ = 106 M⊙ lower limit we further show that the total number of galaxies in the universe up to z = 8 is 2.0+0.7 −0.6 × 1012 (two trillion), almost a factor of ten higher than would be seen in an all sky survey at Hubble Ultra-Deep Field depth. We discuss the implications for these results for galaxy evolution, as well as compare our results with the latest models of galaxy formation. These results also reveal that the cosmic background light in the optical and near-infrared likely arise from these unobserved faint galaxies. We also show how these results solve the question of why the sky at night is dark, otherwise known as Olbers’ paradox.

Citation

Conselice, C. J., Wilkinson, A., Duncan, K., & Mortlock, A. (2016). The evolution of galaxy number density at z < 8 and its implications. Astrophysical Journal, 830(2), https://doi.org/10.3847/0004-637X/830/2/83

Journal Article Type Article
Acceptance Date Jul 14, 2016
Publication Date Oct 14, 2016
Deposit Date Jan 4, 2017
Publicly Available Date Jan 4, 2017
Journal Astrophysical Journal
Print ISSN 0004-637X
Electronic ISSN 1538-4357
Publisher American Astronomical Society
Peer Reviewed Peer Reviewed
Volume 830
Issue 2
DOI https://doi.org/10.3847/0004-637X/830/2/83
Keywords Galaxies: Evolution, Formation, Structure, Morphology, Classification
Public URL http://eprints.nottingham.ac.uk/id/eprint/39568
Publisher URL http://iopscience.iop.org/article/10.3847/0004-637X/830/2/83/meta
Copyright Statement Copyright information regarding this work can be found at the following address: http://eprints.nottingham.ac.uk/end_user_agreement.pdf

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Copyright Statement
Copyright information regarding this work can be found at the following address: http://eprints.nottingham.ac.uk/end_user_agreement.pdf





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