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) b / m =0.17 (Spergel et al 03) If M M 31 '1.5M MW (cf Wilkinson & Evans 99) But L V (MW) ' 1.5£10 10 L ¯, so M * ' 3-5£10 10 M ¯ Implies most baryons missing Klypin, Zhao & Somerville (02) have M MW =10 12 M ¯ and half baryons missing

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)

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<10 19 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)

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)

Extra-planar gas in NGC 891 Sancisi & Allen 1979 N H cm -2 Swaters et al N H cm -2 Oosterloo et al N H cm -2 Sancisi & Allen 1979 N H cm -2 Swaters et al N H cm -2 Oosterloo et al N H cm -2 Sancisi & Allen 1979 N H cm -2 Swaters et al N H cm -2 Oosterloo et al N H cm -2

NGC891: Low rotation of extra-planar gas Fraternali 2005 v rot ~15 km s -1 kpc -1

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

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

NGC2403: Non circular motions Thin discExtra-planar gas V Lagging halo Thin disc

Non-circular motions

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

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

How common is halo gas? Halo gas (HI) found and studied in 7 galaxies: NGC891, N2403, N6946, N253 (Boomsma et al. 2005), N4559 (Barbieri et al. 2005), UGC7321 (Matthews & Wood 2003), NGC2613 (Irwin & Chaves 2003).

Extra-planar gas and star formation Matthews & Wood 2003, ApJ UGC 7321 ROSAT HI Optical VLA NGC ATCA Boomsma et al. 2005, A&A SFR=0.01 M yr -1 SFR>10 M yr -1

Dynamical models A barotropic [p=p( )] fluid in a gravitational field corotates ( Poincaré, 1893 ) Hydrostatic models for non-barotropic fluid show gradient in rotation velocity but also high temperatures ( Barnabé, Ciotti, Fraternali, Sancisi, A&A, submitted ) Previous works: Galactic fountain: gas circulation (disc-halo-disc) ( Shapiro & Field, ApJ 1976; Bregman, ApJ 1980 ) Ballistic models: disagreement between predicted gradient in rotation velocity and H data ( Collins, Benjamin & Rand, A&A 2002 )

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

Dynamical model Continuous flow of particles from the disc to the halo Initial conditions: distribution of kick velocities Potential: exponential discs + bulge + DM halo Integration in the (R,z) plane, then distribution along At each dt projection along the line of sight Stop at the first or second passage through the disc Pseudo-cube to be compared with HI data cube

Model constraint: vertical distribution V kick ~ 75 km s -1 M halo ~ M

N891: inflow/outflow Travel times Energy input <4 % of energy from SNe

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

NGC2403: lagging gas Thin disc Thick disc 60 o V kick ~ 70 km s -1 M halo ~ M

NGC2403: inflow/outflow Thin disc gas Extra-planar gas Radial outflow NEED FOR INFALLING MATERIAL V VRVR VzVz

Second-passage models V VRVR VzVz V VRVR VzVz

Phase-change models NGC 2403 NGC 891Fast rotating gas

Phase-change models Vertical motions

N2403: substructures

Inside view

High Velocity Clouds Complex A M 10 6 M O d 8-10 kpc v 100 km s -1 Wakker et al. 2003; Wakker & Van Woerden 1997 Complex C v 100 km s -1 If d 10 kpc M 10 7 M O Low metallicity Z= solar (Tripp et at. 2003) Forbidden gas v 100 km s -1 M 5 · 10 6 M O Filament v 80 km s -1 M 10 7 M O

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

The WHIM CDM simulations without feedback suffer from overcooling Natural solution: fast mass loss during GF Direct evidence from M outflow ' M SF (Pettini et al 01; Steidel et al 04) Also manifest connection of outflow to HVCs (NGC 6946 and …) So expect accumulation of NGC 253 Boomsma et al 05

The hot halo Munch (52) detected Ca II and Na I interstellar lines at |v-v LSR |>20 km/s even at high b Spitzer (56) argued that cold absorbing clouds must be confined by pressure p/k B '10 4 K cm -3 of gas with T' T vir At T vir, M gas = 0.52£10 9 (R max /R 0 ) M ¯ So CDM requires M>10 11 M ¯ halo to extend to R max '1Mpc

Copernicus, HST and FUSE detect absorption in C IV, O VI, etc O VI important because ionize E(O V)=114eV; O VI emission T = 3£10 5 K

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

Interaction of HVCs with WHIM Density contrast T vir /T HI ' Analogous to a transonic sprinkler Ram-pressure drag (Benjamin & Danly 97) = 21 N 19 /(n -3 v 200 ) Myr T flight ' 100 Myr Drag important

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 CHVCsPutman et al 03

Problems Fountain circulates large mass through extraplanar gas: M HI ' 5£10 8 M ¯ every 100 Myr If ejected gas loses 10% of its angular momentum, halo will become corotating if not extensive (M gas = 5£10 8 (R max /R 0 ) M ¯ ) Naively expect moving clouds to be ablated Net inflow and low Z (10% Z sun ) imply condensation prevails

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