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The True Surface Mass density of Cold Dark Matter Halos

Published online by Cambridge University Press:  01 June 2007

Janne Holopainen*
Affiliation:
Tuorla Observatory, University of Turku, Väisäläntie 20, Piikkiö, FI-21500, Finland
E. Zackrisson
Affiliation:
Tuorla Observatory, University of Turku, Väisäläntie 20, Piikkiö, FI-21500, Finland Stockholm Observatory, AlbaNova University Center, 106 91 Stockholm, Sweden Department of Astronomy and Space Physics, Box 515, SE-75120 Uppsala, Sweden
A. Knebe
Affiliation:
Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
P. Nurmi
Affiliation:
Tuorla Observatory, University of Turku, Väisäläntie 20, Piikkiö, FI-21500, Finland
P. Heinämaki
Affiliation:
Tuorla Observatory, University of Turku, Väisäläntie 20, Piikkiö, FI-21500, Finland
S. Gill
Affiliation:
Department of Astronomy, Columbia University, 550 West 120th Street, New York, NY 10027, USA
C. Flynn
Affiliation:
Tuorla Observatory, University of Turku, Väisäläntie 20, Piikkiö, FI-21500, Finland
T. Reihm
Affiliation:
Stockholm Observatory, AlbaNova University Center, 106 91 Stockholm, Sweden
*
email: jaolho@utu.fi
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Abstract

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The cold dark matter (CDM) scenario generically predicts the existence of triaxial dark matter halos which contain notable amounts of substructure. However, analytical halo models with smooth, spherically symmetric density profiles are routinely adopted in the modelling of light propagation effects through such objects. In this paper, we report the biases introduced by this procedure by comparing the surface mass densities of actual N-body halos against the widely used analytical model suggested by Navarro, Frenk and White (1996) (NFW). We conduct our analysis in the redshift range of 0.0 − 1.5.

In cluster sized halos, we find that triaxiality can cause scatter in the surface mass density of the halos up to σ+ = +60% and σ = −70%, where the 1-σ limits are relative to the analytical NFW model given value. Subhalos can increase this scatter to σ+ = +70% and σ = −80%. In galaxy sized halos, the triaxial scatter can be as high as σ+ = +80% and σ = −70%, and with subhalos the values can change to σ+ = +40% and σ = −80%.

We have developed an analytical model for the surface mass density scatter as a function of distance to the halo centre, halo redshift and halo mass. The analytical description enables one to investigate the reliability of results obtained with simplified halo models. Additionally, it provides the means to add simulated surface density scatter to analytical density profiles. We have tested our model on the calculation of microlensing optical depths for MACHOs in CDM halos.

Type
Contributed Papers
Copyright
Copyright © International Astronomical Union 2008

References

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