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Gas in the Local Group

Gas in the Local Group. James Binney & Filippo Fraternali Oxford University. Outline. Missing baryons Infall and HVCs Extraplanar gas in external galaxies The hot halo Conclusions. Missing baryons. Negative v los of M31 ) M LG =4.8 £ 10 12 M ¯ (Kahn & Woltjer 59 ff)

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Gas in the Local Group

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  1. Gas in the Local Group James Binney & Filippo Fraternali Oxford University

  2. Outline • Missing baryons • Infall and HVCs • Extraplanar gas in external galaxies • The hot halo • Conclusions

  3. Missing baryons • Negative vlos of M31 ) MLG=4.8£1012M¯ (Kahn & Woltjer 59 ff) • b/m=0.17 (Spergel et al 03) • If MM31'1.5MMW (cf Wilkinson & Evans 99) • But LV(MW) ' 1.5£1010L¯, so M* ' 3-5£1010M¯ • Implies most baryons missing • Klypin, Zhao & Somerville (02) have MMW=1012M¯ and half baryons missing

  4. Still infalling? • Muller Oort & Raimond (63) found HI at highly anomalous velocities • HVCs mapped at ever higher sensitivity !Leiden-Dwingeloo (Hartman & Burton 1997) & HIPASS (Barnes et al 01) surveys • Are HVCs distant & massive? (Oort 70; Blitz et al 99) • Efforts to detect massive extragalactic clouds in other groups repeatedly failed (Pisano & Wilcots 03) • Clouds usually have detectable H emission (Tufte et al 02; Putman et al 03)

  5. Extraplanar gas • Some HVCs associated with LG galaxies (Magellanic Stream; Andromeda clouds) • Most are within MW and of low mass (Westmeier 03) • Extend to N<1019 cm-2 at which HI hard to detect (Hoffman et al 04; Richter et al 05) • Significant covering factor • Have complex shapes (Richter et al 05) • Local clouds show net infall v ' 50 km/s (de Heij et al 02; Wakker 04)

  6. Outside view • Counterparts of HVCs now studied in external galaxies • (M101: van der Hulst & Sancisi; NGC 5668: Schulman et al 94-6; NGC 891, NGC 2403: Swaters et al 97 ! Fraternali, Oosterloo & Sancisi 04)

  7. Extra-planar gas in NGC 891 • Sancisi & Allen 1979 NH ≈ 5 1020 cm-2 • Swaters et al. 1997 NH ≈ 7 1019 cm-2 • Oosterloo et al. 2005 NH ≈ 1.7 1019 cm-2 • Sancisi & Allen 1979 NH ≈ 5 1020 cm-2 • Swaters et al. 1997 NH ≈ 7 1019 cm-2 • Oosterloo et al. 2005 NH ≈ 1.7 1019 cm-2 • Sancisi & Allen 1979 NH ≈ 5 1020 cm-2 • Swaters et al. 1997 NH ≈ 7 1019 cm-2 • Oosterloo et al. 2005 NH ≈ 1.7 1019 cm-2

  8. vrot~15 km s-1 kpc-1 NGC891: Low rotation of extra-planar gas Fraternali 2005

  9. NGC 2403 .Distance: 3 Mpc .Type: Sc .Inclination ~ 62 .Non-interacting .Very similar to M33

  10. Thin disc model NGC2403: Extra-planar gas Forbidden gas 130 km/s Extra-planar gas Fraternali, Oosterloo, Sancisi, van Moorsel 2001

  11. Thin disc Lagging halo V NGC2403: Non circular motions Thin disc Extra-planar gas

  12. Non-circular motions

  13. NGC 6946: Extra-planar gas and SF WRST Boomsma PhD 2005

  14. Summary (observations) Extra-planar detected up to 15 kpc from plane Rotation lower than the disc Global inflow motion High velocities (100-200 km s-1) Link with star formation? Evidence for accretion?

  15. Fountain model(Shapiro & Field, ApJ 1976; Bregman, ApJ 1980) New work (Fraternali & B 05): • Clouds ejected from circular orbits with distributions in v,  • Clouds move ballistically as in Collins, Benjamin & Rand, A&A 02, but may not be visible until zmax or rmax • Axisymmetry exploited to build pseudo-data cube • Clouds return to disk on first or second passage through z=0 • <4% of SN energy needed

  16. Model constraint: vertical distribution Vkick ~ 75 km s-1 Mhalo ~2 109 M

  17. NGC 891: Lack of low angular momentum Fast rotating gas NEED FOR LOW ANGULAR MOMENTUM MATERIAL

  18. Thick disc 60o Thin disc NGC2403: lagging gas Vkick ~ 70 km s-1 Mhalo ~ 5 108 M

  19. Thin disc gas Extra-planar gas V VR Vz NGC2403: inflow/outflow Radial outflow NEED FOR INFALLING MATERIAL

  20. Second-passage models V VR Vz V VR Vz

  21. Phase-change models NGC 2403 NGC 891 Fast rotating gas

  22. Inside view

  23. Summary (models) • Models reproduce the vertical extent with reasonable energy input (<4 % SN energy) • Failure in NGC891: lack of low angular momentum • Need for drag • Failure in NGC2403: lack of inflow • Need for accretion Seen from inside, a successful cloud model would look like HVC population But must reverse outflow and diminish rotation

  24. The WHIM NGC 253 Boomsma et al 05 • CDM simulations without feedback suffer from “overcooling” • Natural solution: fast mass loss during GF • Direct evidence from Moutflow' MSF (Pettini et al 01; Steidel et al 04) • Also manifest connection of outflow to HVCs (NGC 6946 and …) • So expect accumulation of gas @

  25. The hot halo • Munch (52) detected Ca II and Na I interstellar lines at |v-vLSR|>20 km/s even at high b • Spitzer (56) argued that cold absorbing clouds must be confined by pressure p/kB'104 K cm-3 of gas with T' Tvir • At Tvir, Mgas= 0.52£109 (Rmax/R0) M¯ • So CDM requires M>1011M¯ halo to extend to Rmax'1Mpc

  26. Copernicus, HST and FUSE detect absorption in C IV, O VI, etc • O VI important because ionize E(O V)=114eV; O VI emission peaks @ T = 3£105 K

  27. HI emission & O VI absorption • Consistent with O VI at interface of HI and WHIM • Possible evidence that O VI expanding relative to HI Sembach et al 02

  28. Interaction of HVCs with WHIM • Density contrastTvir/THI' 100-104 • Analogous to a transonic sprinkler • Ram-pressure drag (Benjamin & Danly 97) •  = 21 N19/(n-3v200) Myr • Tflight' 100 Myr • Drag important

  29. Evidence for drag • Structure of leading arm of Magellanic stream • Head-tail structure of HVCs (Bruns et al 01) • Z < Z¯ for complex C HVC Putman et al 03 CHVCs

  30. Problems • Fountain circulates large mass through extraplanar gas: MHI' 5£108 M¯ every 100 Myr • If ejected gas loses 10% of its angular momentum, halo will become corotating if not extensive (Mgas= 5£108 (Rmax/R0) M¯) • Naively expect moving clouds to be ablated • Net inflow and low Z (10% Zsun) imply condensation prevails

  31. Conclusions •  CDM predicts that most baryons are hidden • Observations of external groups & galaxies show that HVCs lie at 10 – 100 kpc distances • HVCs are generated by star formation • The basic fountain model does not reproduce: lag in rotation & net infall • Much evidence for interaction of HI with WHIM • Likely that lag & infall result from interaction with WHIM • LCDM predicts that WHIM contains bulk of LG baryons & extends to > 1Mpc

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