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					Proper motion surveys
          and the
 Galactic dark matter

    Bertrand Goldman
 N.M.S.U. – N.A.S.A./Ames
                  Summary
• White dwarfs contribution to the Galactic
  halo
  – Constraints from proper motion surveys
     (EROS 2 proper motion survey)
  – Some positive results
• SNAP surveys
  – Halo white dwarfs
  – Brown dwarfs
            Why white dwarfs?
• Microlensing results towards the Magellanic Clouds
   – MACHO positive signal: 20%, ≈0.5 Mo
   – EROS 20% upper limits
• Various indirect constraints
   – C and N pollution (Brook et al. 2003)
   – D and He pollution (Fields et al. 2000)
   – TeV rays surviving the progenitors’ redshifted light
              (Graff et al. 2000)




                                    Alcock et al, 2001
         Why not white dwarfs?
• No strong direct
  constraints:
                                  disk WD LF
   – HWD LF depends on
     cooling function, WD
     mass and progenitors’
     IMF
     (bias toward high masses
     makes WD cooler)           vtan >250km/s
   – Liebert et al, 1998            WD LF




                                          Chabrier, 1999
      EROS 2 proper motion survey
• Uses the EROS 2
  two-broad band,
  wide-field imager
  1º2, 2x 32 Mpix
• 250º 2 over five years,
  mid and high Galactic latitudes
• Data shared with the nearby
  SNe search program
          EROS 2 proper motion survey
                         results
• no candidate
       95% CL limits
• Color-dependent when
  combining both bands
•   7% for MV =17 to
  30% for MV =18
• if 5+% DA WDs,
   age > 14 Gyr

                                   Goldman et al, 2002
    Other proper motion surveys
• Several other failed to detect halo WDs
   – Knox et al, 1999 (stacked plates)
   – Crézé et al, 2004 (CFHT 12k)
• Other reported halo white dwarf discoveries:
   – Ibata et al, 2001: ≈10% (2 confirmed fast, cool WDs
                                           in survey plates)
   – Oppenheimer et al. 2001 (and Salim et al. 2003):
                          1–2% of the halo
     uncertainties on the nature of those objects:
     young (Hansen, 2001); thick disk dynamics and contamination (Reylé et
     al, Reid et al, Flynn et al, 2001)
            SNAP contribution
• Detection of 14 Gyr white dwarfs, in most bands,
  high above the Galactic plan:
  1,500 pc with proper motion (deep fields)
  3,000 pc by color, flattening measurement
  thousands of WDs if halo is made of 1% WDs
• WD LF of the thick disk to the end
      with height distribution
• LSST will also solve these questions

             Using the Chabrier et al, 1999 cooling functions
                  Brown dwarfs
• 8 detection in two or more bands of
  Teff = 300 K BDs (9 MJ @ 5 Gyr, or 4 MJ @ 1 Gyr)
     375 pc3 with proper motion and parallaxes
   6,000 pc3 with the deep field surveys
  12,500 pc3 with a 500º2 wide field survey
• Detection of Teff = 220K planets
       (5 MJ @ 5 Gyr, or 2 MJ @ 1 Gyr)
  in the deep surveys up to 15pc (5pc3)
                                Using the Baraffe et al, 2003 models
• WISE would do better

				
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posted:8/23/2012
language:English
pages:9