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." 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." 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." 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." 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." 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." 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." 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." 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)
