Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.atnf.csiro.au/research/LVmeeting/magsys_pres/ishiyama.pdf Дата изменения: Mon Jul 16 03:18:46 2007 Дата индексирования: Tue Oct 2 17:44:01 2012 Кодировка: Поисковые слова: dwarf spheroidal

Statistical Study of Substructure Pair Histories

Tomoaki Ishiyama
( University of Tokyo )

Toshiyuki Fukushige
( K & F Computing Research Co. )

Elizabeth and Frederick White Conference on the Magellanic System 16 to 17 July 2007 The CSIRO Australia Telescope National Facility


Table of Contents


Motivation


How do the Magellanic Clouds orbit ? Murai and Fujimoto (1980)



Simulation Model and Analysis


Cosmological N-body Simulation



Results and Discussions Summary




Motivation


How do the Magellanic Clouds orbit ? Murai and Fujimoto (1980)


Modeling the orbits of the Clouds. Motion of the Magellanic Clouds was integrated backward in time. Initial condition is combinations of present position and velocity of the Clouds ( more than 1000 in the range of observational error). Magellanic Clouds could be bound orbit over the Hubble time.








The model of Murai and Fujimoto (1980)



Motion of the Magellanic Clouds is integrated backward in time. Similar Method : Gardiner et al. (1994), Yoshizawa and Noguchi (2003), Bekki and Chiba (2005), Connors et al. (2006) The equations do not include




dynamical friction between the Clouds tidal-deformation and tidal-stripping of the Clouds merger history of the Milky Way.

Cosmological N-body Simulation includes all of these effects.


Our Approach


Cosmological N-body Simulation


Dark matter in phase space is represented by N particles. Particles are evolved forward in time using Newton's law from the early Universe to present. 1012 M , >200km/s) ( > 108 M ) from a and track these z=0





Find host halos( > and substructures the simulation dat orbit from z=1 to



Investigate how many substructure close pairs exist at present and their histories.


Cosmological N-body Simulation


Density fluctuation in the early Universe is generated by GRAFIC package ( Bertshinger 2001) based on the CDM model.


N=5123 in 21.4Mpc cubic box.

The SMC size substructures are m=3.0x106 M : mass per particle. resolved.



The gravitational forces was computed using parallel TreePM code (Yoshikawa and Fukushige 2005) . Calculation of the gravitational forces was accelerated using GRAPE-6A, a special-purposed computer for gravitational N-body simulations. A leapfrog integrator was used with adaptive time steps.










Substructure Pair Histories


Average number of pair per host halo at z=0. If the separation of two substructures is less than 50kpc, we define them pair.


galaxy group scale halo 55.7 giant galaxy scale halo 7.1 galaxy scale halo 3.7



Average number of pair formed before z=0.33 per host halo.


galaxy group scale halo 1.0 giant galaxy scale halo 0.13 galaxy scale halo 0.0


Evolution of the Magellanic Clouds


If the host halos and substructures similar to the Milky Way and the Magellanic Clouds were picked out......


Pair formed before z=0.33 was not found. Average number of pair formed after z=0.33 per host halo


top 2 massive substructures 0.0 top 5 massive substructures 0.10 all substructures 3.1







A galaxy close pair like the Magellanic Clouds can exist in the CDM context, but it might have formed recently (z<0.33).


Recent study


The 3D velocities of the Magellanic Clouds are higher than previously estimated ( Kallivayalil et al. 2006a,b). Besla et al. (2007) calculated the orbital evolution of the Clouds using these proper motion. They suggested a first passage scenario, which is the Clouds are currently on their first passage about the Milky Way.





Our result is consistent with their results.


Summary


We followed dark matter halos formation using cosmological N-body simulation, and the evolution of the halos and substructures from z=1 to z=0 A galaxy close pair like the Magellanic Clouds can exist in the CDM context, but it might have formed recently (z<0.33).