The Aemulus Project. II. Emulating the Halo Mass Function

• Published in: The Astrophysical journal Vol. 872; no. 1; pp. 53 - 63
• Main Authors: McClintock, Thomas, Rozo, Eduardo, Becker, Matthew R., DeRose, Joseph, Mao, Yao-Yuan, McLaughlin, Sean, Tinker, Jeremy L., Wechsler, Risa H., Zhai, Zhongxu
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 10-02-2019; IOP Publishing; Institute of Physics (IOP)
• Subjects: Astronomical models; ASTRONOMY AND ASTROPHYSICS; Astrophysics; Clusters; Computer simulation; Cosmic microwave background; Cosmology; Emulators; Error analysis; Initial conditions; large-scale structure of universe; methods: numerical; methods: statistical; Model accuracy; Parameter uncertainty; Red shift; Simulation
• ISSN: 0004-637X; 1538-4357; 1538-4357
• DOI: 10.3847/1538-4357/aaf568

Existing models for the dependence of the halo mass function on cosmological parameters will become a limiting source of systematic uncertainty for cluster cosmology in the near future. We present a halo mass function emulator and demonstrate improved accuracy relative to state-of-the-art analytic models. In this work, mass is defined using an overdensity criteria of 200 relative to the mean background density. Our emulator is constructed from the Aemulus simulations, a suite of 40 N-body simulations with snapshots from z = 3 to z = 0. These simulations cover the flat wCDM parameter space allowed by recent cosmic microwave background, baryon acoustic oscillation and SNe Ia results, varying the parameters w, m, b, 8, Neff, ns, and H0. We validate our emulator using five realizations of seven different cosmologies, for a total of 35 test simulations. These test simulations were not used in constructing the emulator, and were run with fully independent initial conditions. We use our test simulations to characterize the modeling uncertainty of the emulator, and introduce a novel way of marginalizing over the associated systematic uncertainty. We confirm nonuniversality in our halo mass function emulator as a function of both cosmological parameters and redshift. Our emulator achieves better than 1% precision over much of the relevant parameter space, and we demonstrate that the systematic uncertainty in our emulator will remain a negligible source of error for cluster abundance studies through at least the LSST Year 1 data set.