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Baryonic Dark Matter An Outsider’s view

An overview of the baryonic and dark matter components in the galactic halo and their impact on rotation curves, molecular clouds, and hidden baryonic matter. Explore the CUSP AND BAR PROBLEM, Hot Clusters, and Warm Plasma in Field Galaxies.

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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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