Structure finding in cosmological simulations: the state of affairs

The ever increasing size and complexity of data coming from simulations of cosmic structure formation demand equally sophisticated tools for their analysis. During the past decade, the art of object finding in these simulations has hence developed into an important discipline itself. A multitude of codes based upon a huge variety of methods and techniques have been spawned yet the question remained as to whether or not they will provide the same (physical) information about the structures of interest. Here we summarize and extent previous work of the ‘halo finder comparison project’: we investigate in detail the (possible) origin of any deviations across finders. To this extent, we decipher and discuss differences in halo-finding methods, clearly separating them from the disparity in definitions of halo properties. We observe that different codes not only find different numbers of objects leading to a scatter of up to 20 per cent in the halo mass and Vmax function, but also that the particulars of those objects that are identified by all finders differ. The strength of the variation, however, depends on the property studied, e.g. the scatter in position, bulk velocity, mass and the peak value of the rotation curve is practically below a few per cent, whereas derived quantities such as spin and shape show larger deviations. Our study indicates that the prime contribution to differences in halo properties across codes stems from the distinct particle collection methods and – to a minor extent – the particular aspects of how the procedure for removing unbound particles is implemented. We close with a discussion of the relevance and implications of the scatter across different codes for other fields such as semi-analytical galaxy formation models, gravitational lensing and observables in general.Fil: Knebe, Alexander. Universidad Autónoma de Madrid; EspañaFil: Pearce, Frazer R.. The University Of Nottingham; Reino UnidoFil: Lux, Hanni. The University Of Nottingham; Reino Unido. University of Oxford; Reino UnidoFil: Ascasibar, Yago. Universidad Autónoma de Madrid; EspañaFil: Behroozi, Peter. Kavli Institute for Particle Astrophysics and Cosmology; Estados Unidos. University of Stanford; Estados UnidosFil: Casado, Javier. Universidad Autónoma de Madrid; EspañaFil: Corbett Moran, Christine. Universitat Zurich; SuizaFil: Diemand, Juerg. Universitat Zurich; SuizaFil: Dolag, Klaus. Gobierno de la Republica Federal de Alemania. Max Planck Institut Fur Astrophysik; AlemaniaFil: Dominguez Tenreiro, Rosa. Universidad Autónoma de Madrid; EspañaFil: Elahi, Pascal. The University Of Nottingham; Reino Unido. Shanghai Astronomical Observatory; ChinaFil: Falck, Bridget. University of Portsmouth; Reino UnidoFil: Gottlober, Stefan. Leibniz-Institut fur Astrophysik Potsdam; AlemaniaFil: Han, Jiaxin. Shanghai Astronomical Observatory; China. Chinese Academy of Sciences; República de China. University Of Durham; Reino UnidoFil: Klypin, Anatoly. New Mexico State University; Estados UnidosFil: Lukic, Zarija. Lawrence Berkeley National Laboratory; Estados Unidos. Los Alamos National High Magnetic Field Laboratory; Estados UnidosFil: Maciejewski, Michal. Gobierno de la Republica Federal de Alemania. Max Planck Institut Fur Astrophysik; AlemaniaFil: McBride, Cameron K.. Vanderbilt University; Estados UnidosFil: Merchan, Manuel Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomia Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomia Teórica y Experimental; ArgentinaFil: Muldrew, Stuart I.. The University Of Nottingham; Reino UnidoFil: Neyrinck, Mark. University Johns Hopkins; Estados UnidosFil: Onions, Julian. The University Of Nottingham; Reino UnidoFil: Planelles, Susana. Università degli Studi di Trieste; ItaliaFil: Potter, Doug. Universitat Zurich; SuizaFil: Quilis, Vicent. Universidad de Valencia; EspañaFil: Rasera, Yann. Université Paris Diderot - Paris 7; FranciaFil: Ricker, Paul M.. University of Illinois at Urbana; Estados UnidosFil: Roy, Fabrice. Université Paris Diderot - Paris 7; FranciaFil: Ruiz, Andrés Nicolás. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomia Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomia Teórica y Experimental; ArgentinaFil: Sgró, Mario Agustín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomia Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomia Teórica y Experimental; ArgentinaFil: Springel, Volker. Heidelberg Institute for Theoretical Studies; AlemaniaFil: Stadel, Joachim. Universitat Zurich; SuizaFil: Sutter, P. M.. University of Illinois at Urbana; Estados Unidos. Ohio State University; Estados Unidos. Institut d’Astrophysique de Paris; FranciaFil: Tweed, Dylan. The Hebrew University Of Jerusalem; IsraelFil: Zemp, Marcel. Peking University; República de Chin