Dark-ages Reionization & Galaxy Formation Simulation I: The dynamical lives of high redshift galaxies
| Autor: | Poole, Gregory B., Angel, Paul W., Mutch, Simon J., Power, Chris, Duffy, Alan R., Geil, Paul M., Mesinger, Andrei, Wyithe, Stuart B. |
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| Rok vydání: | 2015 |
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| Druh dokumentu: | Working Paper |
| DOI: | 10.1093/mnras/stw674 |
| Popis: | We present the Dark-ages Reionization and Galaxy-formation Observables from Numerical Simulations (DRAGONS) program and Tiamat, the collisionless N-body simulation program upon which DRAGONS is built. The primary trait distinguishing Tiamat from other large simulation programs is its density of outputs at high redshift (100 from z=35 to z=5; roughly one every 10 Myr) enabling the construction of very accurate merger trees at an epoch when galaxy formation is rapid and mergers extremely frequent. We find that the friends-of-friends halo mass function agrees well with the prediction of Watson et al. at high masses, but deviates at low masses, perhaps due to our use of a different halo finder or perhaps indicating a break from "universal" behaviour. We then analyse the dynamical evolution of galaxies during the Epoch of Reionization finding that only a small fraction (~20%) of galactic halos are relaxed. We illustrate this using standard relaxation metrics to establish two dynamical recovery time-scales: i) halos need ~1.5 dynamical times following formation, and ii) ~2 dynamical times following a major (3:1) or minor (10:1) merger to be relaxed. This is remarkably consistent across a wide mass range. Lastly, we use a phase-space halo finder to illustrate that major mergers drive long-lived massive phase-space structures which take many dynamical times to dissipate. This can yield significant differences in the inferred mass build-up of galactic halos and we suggest that care must be taken to ensure a physically meaningful match between the galaxy-formation physics of semi-analytic models and the halo finders supplying their input. Comment: 15 pages, 10 figures. Accepted for publication by MNRAS |
| Databáze: | arXiv |
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