Forming galaxies across cosmic time: My research interests focus on understanding the processes of the formation of galaxies (large collections of stars and dark matter) through the use of large surveys and statistics. I specialize in building and fitting flexible models to images and spectroscopy of galaxies. Galaxies are complex, so these models include the full range of things that live in the night sky: stars, black holes, gas, and cosmic dust. Understanding these components better often means writing down simple or more complex (numerical) models for how the full range of the galaxy population evolves as a whole, from the Big Bang to the present day. I've harnessed millions of hours of supercomputer time running specialized code to build a more complete picture of how galaxies form and evolve. I frequently use Bayesian statistics and machine learning (AI) to interpret the massive galaxy surveys of today and tomorrow; this simultaneously speeds up our models while also allowing them to become more sophisticated and complex.
Publications
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Joel {Leja},
Pieter {van Dokkum},
Marijn {Franx},
"{Tracing Galaxies through Cosmic Time with Number Density Selection}." \apj 766 1 (2013)
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Joel {Leja},
Pieter {van Dokkum},
Marijn {Franx},
Katherine {Whitaker},
"{Reconciling the Observed Star-forming Sequence with the Observed Stellar Mass Function}." \apj 798 2 (2015)
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Joel {Leja},
Benjamin {Johnson},
Charlie {Conroy},
Pieter {van Dokkum},
Nell {Byler},
"{Deriving Physical Properties from Broadband Photometry with Prospector: Description of the Model and a Demonstration of its Accuracy Using 129 Galaxies in the Local Universe}." \apj 837 2 (2017)
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Joel {Leja},
Benjamin {Johnson},
Charlie {Conroy},
Pieter {van Dokkum},
"{Hot Dust in Panchromatic SED Fitting: Identification of Active Galactic Nuclei and Improved Galaxy Properties}." \apj 854 1 (2018)
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Joel {Leja},
Adam {Carnall},
Benjamin {Johnson},
Charlie {Conroy},
Joshua {Speagle},
"{How to Measure Galaxy Star Formation Histories. II. Nonparametric Models}." \apj 876 1 (2019)
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Joel {Leja},
Benjamin {Johnson},
Charlie {Conroy},
Pieter {van Dokkum},
Joshua {Speagle},
Gabriel {Brammer},
Ivelina {Momcheva},
Rosalind {Skelton},
Katherine {Whitaker},
Marijn {Franx},
Erica {Nelson},
"{An Older, More Quiescent Universe from Panchromatic SED Fitting of the 3D-HST Survey}." \apj 877 2 (2019)
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Joel {Leja},
Sandro {Tacchella},
Charlie {Conroy},
"{Beyond UVJ: More Efficient Selection of Quiescent Galaxies with Ultraviolet/Mid-infrared Fluxes}." \apjl 880 1 (2019)
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Joel {Leja},
Joshua {Speagle},
Benjamin {Johnson},
Charlie {Conroy},
Pieter {van Dokkum},
Marijn {Franx},
"{A New Census of the 0.2 < z < 3.0 Universe. I. The Stellar Mass Function}." \apj 893 2 (2020)
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Joel {Leja},
Joshua {Speagle},
Yuan-Sen {Ting},
Benjamin {Johnson},
Charlie {Conroy},
Katherine {Whitaker},
Erica {Nelson},
Pieter {van Dokkum},
Marijn {Franx},
"{A New Census of the 0.2< z <3.0 Universe, Part II: The Star-Forming Sequence}." arXiv e-prints (2021)
