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Baryonic Dark Matter An Outsider’s view

Baryonic Dark Matter An Outsider’s view. John Quenby Imperial College. August 27 2004. Galactic Halo: Baryons Versus Cold Dark Matter. Merrifield, 2003 Analysis Local stellar dynamics, Kuijken, Gilmore S ~70M o pc -2 Visible component S ~25M o pc -2 , stellar &

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Baryonic Dark Matter An Outsider’s view

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  1. Baryonic Dark MatterAn Outsider’s view John Quenby Imperial College August 27 2004

  2. Galactic Halo:Baryons Versus Cold Dark Matter • Merrifield, 2003 Analysis • Local stellar dynamics, Kuijken, Gilmore • S ~70Mopc-2 • Visible component • S ~25Mopc-2, stellar & • S ~15Mopc-2, interstellar (Olling, Merrifield, 2001) • So S ~30Mopc-2 can be cold dark matter. • Leads to roDM ~ 0.014Mopc-3 near sun • Also inside the solar radius, Mobaryon ~ 5.7x1010Mo from stars and ISM, while from dynamics, Mototal ~ 9.5x1010Mo • Fitting the difference as being a r~ r-a CDM to Yields a ~ 0.4 for the CDM cusp distribution

  3. CUSP AND BAR PROBLEM • Binney and Evans 2004 consider the minimum baryonic mass in the inner galaxy consistent with microlensing, putting the scale height high. • They plot circular speed observed, a gas disk plus stars including microlensing rotation curve, a cuspy DM halo curve and the combined predicted curve. • Binnie/Evans need more stars close to Galaxy plane, reducing the CDM and find Cusp a too small for most CDM simulations.

  4. Rotating bar at galaxy centre, 3 to 5 kpc long, speed w =40 → 80 km/s/kpc • Debattista et al, 2002 from OH/IR stellar velocity survey. • Bar enhances disk density but may wash out deep cusp (Weinberg, Katz, 2002) • Currently CDM and baryonic material near centre are similar mass and bar is not losing much angular momentum • Dynamics questionable

  5. Cold Molecular Clouds:The Gamma-Ray Evidence • Riley Wolfendale 1984 used COS B gammas in correlation with 12CO and H1 data to correct the molecular hydrogen column and find them of similar magnitude. • Pfeniger et al., 1994, etc, suggest cold self gravitating molecular clouds as a major dark matter component. • Ohishi et al 2004, compute gamma flux from galactic cosmic rays entering dense clouds R~1013 cm. • GEANT 4 to do attenuated emission properly. • The conventional CDM density distribution is adopted for H2

  6. DENSE CLOUD GAMMAS • Cosmic rays follow a galactic distribution It is possible to “hide” H2 from gamma ray from gamma-ray sight Hence Gammas “consistent” with all dark halo as dense clouds

  7. Plausible Physics For Dense Molecular Clouds • Paolis et al, based on Fall and Rees, 1985 • Jeans Instability due to energy release/g by pressure wave ~vs2 compared with reduction due to gravity ~Grl2 • Initial collapse. • Protogalaxy shock heats to virial T~106, proto-globular clouds form, drop to T~104 • Central AGN, etc form, UV dissociates H2. • Beyond 10 kpc UV ineffective fragmentation under Jeans and molecular formation till mainly brown dwarfs and cold clouds optically thick to own radiation occur. • So further fragmentation ceases at radii ~10-5pc. • Smooth fit of optical disk and dark halo contributions to rotation curves now natural. • Other evidence for the H2 hidden baryonic matter? • Extreme scattering events; flux change of compact radio source over weeks due perhaps to ionised cloud edge. • H2 difficult to “make”-need dust grains/high densities

  8. Local Group Halo • Suto et al 1996 suggested significant hot gas halo associated with local group. • Sidher et al 1998, using ROSAT, limited electron density from this to 1/10th the electron density of galactic Halo

  9. Galaxies Visible Baryonic Contribution • To establish the magnitude of the hidden baryonic component, construct a “known” mass budget • Mainly based on Fukugita, 2003. Note h=0.7 • Stars in high surface density galaxies are most prominent • Use an SDSS Luminosity function yielding a global luminosity density Lr = 2.3 x 108hLo(Mpc)-3 • The luminosity function weighted M/Lz ~1.5 • the IMF is flattened at 0.3Mo, yielding Wstar=0.0025 • HI 21-cm surveys give the atomic galactic gas as WHI+HeI= 6 x 10-4 • The “conventional”, CO survey based H2 contribution is WH2=1.6 x 10-4

  10. Hot Clusters • Dynamical mass from galaxy motions s8 rms within 8Mpc.h-1 spheres. • X-ray keV emission assuming hydrostatic equilibrium. • Weak gravitational lensing. • Agreement between lensing and X-ray mass distribution for very luminous galaxies - Allen et al., 2004.

  11. Hot Clusters • Despite obvious merging (see Quenby et al 1999) which could reduce mass estimate, non-equilib. • Also EUV component-Lieu et al., 2004-IC scatter • Could reduce mass estimate-energetic electrons. • Wcl=0.012 for M>4.5x1013Mo and within r>200rcrit • ROSAT, Reiprich, Bohringer, 2002 • fcl,gas =0.11, Allen et al • Wcl,gas=0.0013

  12. Warm Plasma In Groups/Field Galaxies • ROSAT, Groups, 1.2x1013h<M/Mo<8.3x1013, Mulchaey et al, 1996. • (MHII/Mgrav)gr=0.022h-1.5 • Wgr=0.12 Extrapolate Bahcall-Cen, 1993, mass function. • Wgr=0.14 Dynamical, Bahcall et al, 1995. • Wgr=0.18 M/L in different galaxies, Fukugita et al., 1998. • All at h=0.7 • Average WHIIgr=0.003h-1.5 • Also states Wmass=0.15 or Wmass=0.14 Fukugita, 2003.

  13. Total Baryonic Mass • Nucleosynthesis consensus, Wbh2=0.021→0.025; • O’Mara el at; Kirkman et al.; Pettini et al • WMAP, Spergel et al, 2003, use Bond Estathiou 1984. • Thomson scatter of microwave photons in 1st CMB peak from Doppler/gravity fluctuations measures high z electron density. • Yields Wbh2=0.024

  14. Warm Plasma “Near” Galaxies • OVIll1031.92, 1037.62 doublet absorption seen towards QSOs over z range (also HI Lyman series) • Typical T≤1.2x105K and dN/dz~50 eg H1821+643; strong line, z=0.22497, weaker, z=0.22637 • Tripp, Savage, Jenkins, 2000, Wb,w>0.004h75-1 • IS THIS Wb,w JUST RELATED TO WHIIgr BUT AT LOWER T?? OR PART OF A LARGE MISSING BARYONIC COMPONENT??

  15. Z~3 Gas –To Give A Clue • Damped Lyman-a high column density absorbers increase with z; Storie-Lombardi et al, 1996 give Wneutral=0.00013→0.0007 Possible conversion to stars later. • Plasma detected by trace Lyman-a forest neutral hydrogen, Rauch el al 1997, Zhang et al 1997, Weinberg et al 1997. Need ionizing flux. • 0.006<WHII<0.04

  16. The Baryonic Mass Budget • Estimate total associated with galaxies assuming • WMAP Wb/Wm=0.178 is “universal” • Gravity lens M/Lr=170h plus SDSS Lr, give Wm,g=0.14 Fukugita, 2003. • Hence Wb,g=0.025 for galaxies total • COMBINE ALL ESTIMATES (H=0.7, z~0) • Wb,=0.044 Total Baryonic • Made up of • Wstars=0.0025 Stars • Wneutralgas,gal=0.0008 Galaxy atomic and molecular H, He. • WHII,cl=0.0013 Hot, cluster plasma • WHII,gr=0.005 Warm gas groups • Wb,w=0.004 Warm gas near “field” galaxies • Wknown=0.0136 Sum of “known” • WMISSING=0.0304 IS WHAT’S LEFT OVER

  17. Light, x : Matter,y Cen, Ostriker; Dave et al. 1999 shock heated 105-107 K low z baryon phase Ostriker et al, 2003 Light Voids ARE THE MISSING BARYONS ASSOCIATED WITH THE LYMAN-ALPHA FOREST PLASMA? BUT THERE IS MORE ASSOCIATED WITH GALAXIES THAN IS “KNOWN” WARM/COOL GAS A FEW 100kpc AWAY?

  18. Conclusions • Milky Way Baryonic Component depends on understanding Cusp/Bar dynamics near centre and cold dense molecular cloud numbers far out. • Most Baryons may be “missing”, probably in a warm or cool gas just outside galaxies or in clumps which do not shine

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