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- Holopainen, Janne, et al.
(författare)
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An analytical model of surface mass densities of cold dark matter haloes - with an application to MACHO microlensing optical depths
- 2008
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 383:2, s. 720-728
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Tidskriftsartikel (refereegranskat)abstract
- The cold dark matter (CDM) scenario generically predicts the existence of triaxial dark matter haloes 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 address the biases introduced by this procedure by comparing the surface mass densities of actual N-body haloes against the widely used analytical model suggested by Navarro, Frenk and White (NFW). We conduct our analysis in the redshift range of 0.0-1.5. In cluster-sized haloes, we find that triaxiality can cause scatter in the surface mass density of the haloes up to sigma(+) = +60 per cent and sigma(-) = -70 per cent, where the 1 sigma limits are relative to the analytical NFW model given value. Subhaloes can increase this scatter to sigma(+) = +70 per cent and sigma(-) = -80 per cent. In galaxy-sized haloes, the triaxial scatter can be as high as sigma(+) = +80 per cent and sigma(-) = -70 per cent, and with subhaloes the values can change to sigma(+) = +40 per cent and sigma(-) = -80 per cent. We present 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. As an example, we discuss the impact of our results on the calculation of microlensing optical depths for massive astrophysical compact halo objects in CDM haloes.
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- Valtonen, Mauri, et al.
(författare)
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NATURAL TRANSFER OF VIABLE MICROBES IN SPACE FROM PLANETS IN EXTRA-SOLAR SYSTEMS TO A PLANET IN OUR SOLAR SYSTEM AND VICE VERSA
- 2009
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 690:1, s. 210-215
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Tidskriftsartikel (refereegranskat)abstract
- We investigate whether it is possible that viable microbes could have been transported to the Earth from planets in extra-solar systems by means of natural vehicles such as ejecta expelled by comets or asteroid impacts on such planets. The probabilities of close encounters with other solar systems are taken into account as well as the limitations of bacterial survival times inside ejecta in space, caused by radiation and DNA decay. The conclusion is that no potentially DNA/RNA life-carrying ejecta from another solar system in the general Galactic star field landed on the Earth before life already existed on the Earth, even if the microbial survival time in space is as long as tens of millions of years. However, if the Sun formed initially as a part of a star cluster, as is commonly assumed, we cannot rule out the possibility of transfer of life from one of the sister systems to us. Likewise, there is a possibility that some extra-solar planets carry life that originated in our solar system. It will be of great interest to identify the members of the Sun's birth cluster of stars and study them for evidence of planets and life on the planets. The former step may be accomplished by the GAIA mission, the latter step by the SIM and DARWIN missions. Therefore it may not be too long until we have experimental knowledge to answer the question of whether the natural transfer of life from one solar system to another has actually taken place.
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