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					     UV signatures
of the „missing baryons“
      in the WHIM
                      Philipp Richter

           Institut für Physik, Universität Potsdam




                   Garching, September 2007

  B.D. Savage, K.R. Sembach, N. Lehner, T.M. Tripp, T. Fang, G.L. Bryan
UV signatures of the missing baryons in the WHIM


Census of baryons
                                                                         01




            z=4
                                                    Almost all baryons
                                                    are located in the
                                                    Lyman α forest

            z=0

                                                        < 50 % of Ωb




                    Where are all the missing baryons at z=0 ?
UV signatures of the missing baryons in the WHIM


Distribution of baryons predicted from simulations
                                                                        02




   Photoionized
 intergalactic gas
   (Ly α forest)
                                                       Warm-hot inter-
                                                     galactic gas (WHIM)




 Stars and gas in
     galaxies                                         highly ionized,
                                                      T = 105 – 107 K
UV signatures of the missing baryons in the WHIM


Intervening OVI absorbers
                                                                                     03




                                                    high-ion absorption

                                                   collisional ionization - oxygen




                                                                          +5




                                                                         300,000 K


                                                           OVI λλ1031,1037
UV signatures of the missing baryons in the WHIM


UV instruments
                                                                           04




                                             FUSE               HST STIS


                                              COS (from 2008)
UV signatures of the missing baryons in the WHIM


Intervening OVI absorbers
                                                                                               05




                                                    WHIM at T~3x105 K




                               More than 50 intervening OVI systems have been
                               detected so far in FUSE/STIS low-redshift spectra.
                                                                         (Tripp et al. 2007)
UV signatures of the missing baryons in the WHIM


Intervening OVI absorbers
                                                   06
UV signatures of the missing baryons in the WHIM


Intervening OVI absorbers
                                                                                                                                    07




                                                   Baryon content of the OVI absorbing systems :


                                                    obtain mean number density (dN/dz)OVI

                                                    assume mean metallicity (O/H) in the WHIM

                                                    determine Ωb via :                        critical …




                                                      (dN/dz)OVI ~ 18                Ωb OVI ~ 0.002 h70-1



                                                                ~ 11 percent of Ωb (WHIM)

                                                                                            (Danforth & Shull 2005; Tripp et al. 2007)
UV signatures of the missing baryons in the WHIM


Intervening OVI absorbers
                                                                                                          08




                         ~ 55 kpc




                                                                           dOVI < 800 kpc
                                                                                   (Stocke et al. 2007)
                                                   (Richter et al. 2004)
UV signatures of the missing baryons in the WHIM


Broad Lyman α absorbers (BLAs)
                                                                                                           09




                         H1821+643




                                                                   (Richter et al. 2006a)




                               About 60 intervening BLAs have been detected so
                               far in FUSE/STIS low-redshift spectra.
                                                                                    (Lehner et al. 2007)
UV signatures of the missing baryons in the WHIM


Broad Lyman α absorbers (BLAs)
                                                                                                 10




                                 HI ionization fraction (coll+photo) :


                                 Total hydrogen column density :



                                                                         (Richter et al. 2006)
UV signatures of the missing baryons in the WHIM


Broad Lyman α absorbers (BLAs)
                                                                           11




  PG 1116+215




                                                   (Sembach et al. 2004)
UV signatures of the missing baryons in the WHIM


Broad Lyman α absorbers (BLAs)
                                                                  12




       Distribution of Doppler parameters :




             HI Ly α lines get broader as the Universe evolves.
UV signatures of the missing baryons in the WHIM


Broad Lyman α absorbers (BLAs)
                                                                                                                                        13




                                                   Baryon content of the BLAs :


                                                    obtain mean number density (dN/dz)BLA

                                                    determine Ωb via :
                                                                                                         critical …




                                                     (dN/dz)BLA ~ 30               Ωb BLA ~ 0.004 h70-1



                                                                ~ 22 percent of Ωb (WHIM)

                                                                                            (Richter et al. 2006; Lehner et al. 2007)
UV signatures of the missing baryons in the WHIM


Simulations of BLAs
                                                                                                                             14




                                  BLA                                                 BLA



                                   OVI                                                   OVI




          20 Mpc h-1 cube, AMR, photo+collisional ionization, 3000 LOS , Δz=20, standard ΛCDM (Richter, Fang & Bryan 2006)
UV signatures of the missing baryons in the WHIM


Other WHIM tracers in the EUV / optical
                                                                                                         15




         EUV          Ne VIII λλ770,780; Mg X λλ609,624
                                                             (Savage et al. 2006; Richter et al. 2004)




          optical            Forbidden Fe X λ6374 and Fe XIV λ5302 transitions



                    Fe X λ6374                         Fe XIV λ5302




                   simulated WHIM filament at z=0
UV signatures of the missing baryons in the WHIM


… something is missing EVERYWHERE
                                                            16




      The „missing-something-problem“ :


          at z=0 we are missing the baryons (       WHIM)

          at z=1 we are missing the data to see wether
          there is something missing

          at z=2 we are missing the metals (       WHIM)
UV signatures of the missing baryons in the WHIM


Warm-hot gas at high z
                                                                                                                            17




                                                                             galaxy ensemble at z = 3




           10 Mpc h-1 cube, SPH, photo+collisional ionization, 1600 LOS , standard ΛCDM (Fangano, Ferrara & Richter 2007)
UV signatures of the missing baryons in the WHIM


Warm-hot gas at high z
                                                                                       18




                                                   (Fangano, Ferrara & Richter 2007)
UV signatures of the missing baryons in the WHIM


Summary
                                                                         19




         UV observations support the idea that a considerable
            fraction of the baryons at z=0 is in the WHIM.

         Intervening OVI absorbers trace the WHIM at T < 3 x 105 K,
         but ionization conditions and metallicities remain uncertain.

         Broad Lyman α absorbers (BLAs) represent an excellent
         alternative to study the WHIM at T = 105 - 106 K, but
         broadening mechanisms need to be better understood.

         Ωb OVI = 0.002 h70-1 - Ωb BLA = 0.004 h70-1

          COS on HST will greatly improve data quality and statistics
          of intervening UV WHIM absorbers.

				
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posted:10/25/2012
language:German
pages:20