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Published April 10, 2017 | Published + Submitted
Journal Article Open

Log-normal Star Formation Histories in Simulated and Observed Galaxies

Abstract

Gladders et al. have recently suggested that the star formation histories (SFHs) of individual galaxies are characterized by a log-normal function in time, implying a slow decline rather than rapid quenching. We test their conjecture on theoretical SFHs from the cosmological simulation Illustris and on observationally inferred SFHs. While the log-normal form necessarily ignores short-lived features such as starbursts, it fits the overall shape of the majority of SFHs very well. In particular, 85% of the cumulative SFHs are fitted to within a maximum error of 5% of the total stellar mass formed, and 99% to within 10%. The log-normal performs systematically better than the commonly used delayed-τ model, and is superseded only by functions with more than three free parameters. Poor fits are mostly found in galaxies that were rapidly quenched after becoming satellites. We explore the log-normal parameter space of normalization, peak time, and full width at half maximum, and find that the simulated and observed samples occupy similar regions, though Illustris predicts wider, later-forming SFHs on average. The ensemble of log-normal fits correctly reproduces complex metrics such as the evolution of Illustris galaxies across the star formation main sequence, but overpredicts their quenching timescales. SFHs in Illustris are a diverse population not determined by any one physical property of galaxies, but follow a tight relation, where width ∝ (peak time)^(3/2). We show that such a relation can be explained qualitatively (though not quantitatively) by a close connection between the growth of dark matter halos and their galaxies.

Additional Information

© 2017 The American Astronomical Society. Received 2017 January 9; revised 2017 March 2; accepted 2017 March 21; published 2017 April 11. We are deeply grateful to all those who shared their data with us, namely the authors of G13 (Mike Gladders, Augustus Oemler, Alan Dressler, Bianca Poggianti, and Benedetta Vulcani), Camilla Pacifici for sharing her SFHs, and the Illustris team for making their simulation public (Mark Vogelsberger, Shy Genel, Volker Springel, Debora Sijacki, Dandan Xu, Greg Snyder, Dylan Nelson, Lars Hernquist, and, in particular, Vicente Rodriguez-Gomez for his help with the merger trees). We thank Peter Behroozi, Charlie Conroy, Andrew Hearin, Lars Hernquist, Joel Leja, Camilla Pacifici, Ana-Roxana Pop, Laura Sales, Josh Speagle, and Sandro Tacchella for fruitful discussions and/or comments on a draft of this paper. B.D. gratefully acknowledges the financial support of an Institute for Theory and Computation Fellowship.

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Published - Diemer__2017_ApJ_839_26.pdf

Submitted - 1701.02308.pdf

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August 19, 2023
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