Figuring Out Gas & Galaxies in Enzo (FOGGIE). I. Resolving Simulated Circumgalactic Absorption at 2 ≤ z ≤ 2.5

Creators: Peeples, Molly S.; Corlies, Lauren; Tumlinson, Jason; O'Shea, Brian W.; Lehner, Nicolas; O'Meara, John M.; Howk, J. Christopher; Earl, Nicholas; Smith, Britton D.; Wise, John H.; Hummels, Cameron B.

Abstract

We present simulations from the new "Figuring Out Gas & Galaxies in Enzo" (FOGGIE) project. In contrast to most extant simulations of galaxy formation, which concentrate computational resources on galactic disks and spheroids with fluid and particle elements of fixed mass, the FOGGIE simulations focus on extreme spatial and mass resolution in the circumgalactic medium (CGM) surrounding galaxies. Using the Enzo code and a new refinement scheme, FOGGIE reaches spatial resolutions of 381 comoving h^(−1) pc and resolves extremely low masses (≾1–100 M⊙) out to 100 comoving h^(−1) kpc from the central halo. At these resolutions, cloud and filament-like structures giving rise to simulated absorption are smaller, and better resolved, than the same structures simulated with standard density-dependent refinement. Most of the simulated absorption arises in identifiable and well-resolved structures with masses ≾10^4 M⊙, well below the mass resolution of typical zoom simulations. However, integrated quantities such as mass surface density and ionic covering fractions change at only the ≾30% level as resolution is varied. These relatively small changes in projected quantities—even when the sizes and distribution of absorbing clouds change dramatically—indicate that commonly used observables provide only weak constraints on the physical structure of the underlying gas. Comparing the simulated absorption features to the KODIAQ (Keck Observatory Database of Ionized Absorption toward Quasars) survey of z ~ 2–3.5 Lyman limit systems, we show that high-resolution FOGGIE runs better resolve the internal kinematic structure of detected absorption and better match the observed distribution of absorber properties. These results indicate that circumgalactic medium resolution is key in properly testing simulations of galaxy evolution with circumgalactic observations.

Additional Information

© 2019 The American Astronomical Society. Received 2018 October 11; revised 2019 January 23; accepted 2019 January 26; published 2019 March 13. This study was primarily funded by the National Science Foundation via NSF AST-1517908, which helped support the contributions of L.C., B.W.O., N.L., J.O.M., and J.C.H. L.C. was additionally supported in part by HST AR #15012. B.W.O. was supported in part by NSF grants PHY-1430152, AST-1514700, and OAC-1835213, by NASA grants NNX12AC98G and NNX15AP39G, and by HST AR #14315. N.L. was also supported by NASA ADAP grant NNX16AF52G. N.E. was supported by HST AR #13919, HST GO #14268, and HST AR #14560. B.D.S. was supported by NSF AST-1615848. J.H.W. was supported by NSF grants AST-1614333 and OAC-1835213, NASA grant NNX17AG23G, and HST-AR-14326. C.B.H. was supported by HST AR #13917, HST AR #13919, and an NSF AAPF. Resources supporting this work were provided by the NASA High-End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center and were sponsored by NASA's Science Mission Directorate; we are grateful for the superb user support provided by NAS. Resources were also provided by the Blue Waters sustained-petascale computing project, which is supported by the NSF (award No. ACI 1238993 and ACI-1514580) and the state of Illinois. Blue Waters is a joint effort of the University of Illinois at Urbana-Champaign and its NCSA. This work benefited from the dancing penguin and all the things emojis on Slack. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. This research has made use of the Keck Observatory Archive (KOA), which is operated by the W. M. Keck Observatory and the NASA Exoplanet Science Institute (NExScI), under contract with the National Aeronautics and Space Administration. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. We have made extensive use of the Python libraries Astropy, a community-developed core Python package for Astronomy (The Astropy Collaboration et al. 2018, http://www.astropy.org), datashader and holoviews from Anaconda (datashader.org), pandas (McKinney 2010), and seaborn. Computations described in this work were performed using the publicly available Enzo code, which is the product of a collaborative effort of many independent scientists from numerous institutions around the world. Facilities: NASA Pleiades - , Blue Waters - , Keck (HIRES) - . Software: astropy (The Astropy Collaboration et al. 2018), Cloudy (Ferland et al. 2013), Enzo (Bryan et al. 2014), grackle (Smith et al. 2017), yt (Turk et al. 2011), Trident (Hummels et al. 2017), ytree (Smith & Lang 2018).

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