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Semi-analytic Models based on Millennium II Haloes

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					Semi-analytic Models based on
    Millennium II Haloes


                        富坚


                                1
   Introduction to Millennium II Simulation
• Michael Boylan-Kolchin et al. 2009
• The comparison between Millennium I and Millennium II: higher
  resolution
                       Millennium I           Millennium II     Mini-Millennium II
 Particle number                      21603                           4323
   Particle Mass      8.6×108M☉h-1            6.8×106 M☉h-1       8.6×108M☉h-1
     Box size           500 h-1 Mpc            100 h-1 Mpc         100 h-1 Mpc
 Output snapshots      64 snapshots                      68 snapshots
                    Between z=0 and 127               Between z=0 and 127
Minimum halo mass     1.7×1010M☉h-1           1.4×108M☉h-1       1.7×1010M☉h-1

• Mini-Millennium II: same resolution as Millennium I but same box
  size as Millennium II
• http://www.g-vo.org/MyMillennium3/ sql queries for Millennium
  II halo tree data
                                                                                 2
The halo mass functions between MI and
            MII simulations




                                         3
           The semi-analytic models
• The L-Galaxies models based on
  Millennium I haloes by De Lucia et
  al. 2007                              Stellar mass function
                                       from L-Galaxies at z=0
• The inconsistency for the merger
  history of haloes smaller than
  Mhalo~1011 M☉ at z=0
• Resolution effect for galaxies
  smaller than M* ~109.5 M☉
• Both the results based on
  Millennium I and II haloes predict
  too much small galaxies

                                                            4
               The semi-analytic models
• The models by Guo Qi et al. 2010 aims to solve the
  problem of too much small galaxies from the model results
• The changes to L-Galaxies model:
  1.supernova feedback recipes
  ESN  0.5òhalo m*vSN
                      2
                                 òhalo : the proportion of sn energy to reheat the gas
  mreheat  òdisk m*     disk cold gas  halo hot gas
  meject  2  ESN  Ereheat  / vvir
                                     2


              2
             vSN
   òhalo m* 2  mreheat        halo hot gas  ejected gas if meject  0
             vvir
  De Lucia's recipe: òhalo =0.35 and òdisk =3.5 are constants.
  Guo's recipe:
  òdisk  ò 0.5   vmax / 70km s 1         òhalo   0.5   vmax / 70km s 1  
                                        1                                           2
                                            
            
                                                        
                                                                                         
                                                                                          
  ò  6.5   0.32 1   2  3.5                                                             6
                 The semi-analytic models
• The changes to L-Galaxies model:
  2. reincorporation recipe
   mreincorporate        mejected
                                      ejected gas reincorporated back into halo
         t                  halo
                            tdyn
   De Lucia's recipe:   0.5
                                       vvir
   Guo Qi's recipe:    0                            0  0.3
                                     220 km/s

  3. other changes
     gas stripping, satellite disruption
     disk size recipes
        gas,*  r   0 exp  r / Rd gas,* 
                        gas,*
                                                     Trace the change of angular
                          J gas,*                    momentum in gas infall, star
        Rd gas,* 
                     2M gas,*vdisk                   formation, bulge formation, galaxy
                                                     merger etc…                          7
                          The mass functions at z=0 from Guo Qio’s model compared to the
                                                observational results
                     0


                     -1
       




                     -2
    




                     -3
   




                     -4
                                 Obreschow et al. 2009
                                 results based on MI haloes
                     -5          results based on MII haloes


                     -6
                           8.5       9        9.5     10       10.5
                                           
                                               
                                            

                                                                                     8
H2 formation and star formation processes
         in Millennium II haloes
• Migrate my previous codes based on Millennium I
  haloes to Millennium II haloes
• Include the multiple ring
• Include the H2 formation processes to get HI and H2
  components in Millennium II simulation
• Star formation rate SFR   H
                             2


• Get the redshift evolution of gas (neutral and
  molecular), i.e. MZ relation as a function of z


                                                        9
Inconsistency for the results from different halo resolutions




                                                                10
 The reason for the inconsistency from different
                 halo resolutions
• No gas consumption or metal production in small haloes
  based on Millennium simulation
• The H2 proportional star formation law is more sensitive
  to the gas metallicity than Guo Qi and De Lucia’s recipe
                    SFR  M gas  M crit
• Inconsistency: earlier star formation processes in
  Millennium II scenario
   metallicity → H2 → star formation → gas consumption
• Possible solution:
  decrease the H2 formation rate in small galaxies/haloes
  change the supernova feedback                              12
Thank you!



             13

				
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posted:11/28/2012
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