Gas in the Local Group

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 ) MLG4.81012M (Kahn
  Woltjer 59 ff)
• ?b/?m0.17 (Spergel et al 03)
• If MM31'1.5MMW (cf Wilkinson Evans 99)
• But LV(MW) ' 1.51010L, so M ' 3-51010M
• Implies most baryons missing
• Klypin, Zhao Somerville (02) have MMW1012M
  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 Nlt1019 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
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
NGC2403 Extra-planar gas
Forbidden gas
130 km/s
Extra-planar gas
Fraternali, Oosterloo, Sancisi, van Moorsel 2001
11
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
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).

16
Extra-planar gas and star formation
17
Dynamical models
Previous works

• A barotropic pp(r) 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, AA,
  submitted)

• 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, AA 2002)

18
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, AA 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 z0
• lt4 of SN energy needed

19
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

20
Model constraint vertical distribution
Vkick 75 km s-1 Mhalo 2 109 M?
21
N891 inflow/outflow
Travel times
Energy input lt4 of energy from SNe
22
NGC 891 Lack of low angular momentum
Fast rotating gas
?NEED FOR LOW ANGULAR MOMENTUM MATERIAL
23
NGC2403 lagging gas
Vkick 70 km s-1 Mhalo 5 108 M?
24
NGC2403 inflow/outflow
Radial outflow
?NEED FOR INFALLING MATERIAL
25
Second-passage models
V?
VR
Vz
V?
VR
Vz
26
Phase-change models
NGC 2403
NGC 891
Fast rotating gas
27
Phase-change models
Vertical motions
28
N2403 substructures
29
Inside view
30
High Velocity Clouds
Forbidden gas ?v ? 100 km s-1 M ? 5 106 MO
Complex C ?v ? 100 km s-1 If d ? 10 kpc
M ? 107 MO
Complex A M ? 106 MO d ? 8-10 kpc ?v ? 100 km s-1
Filament ?v ? 80 km s-1 M ? 107 MO
Low metallicity Z0.1-0.3 solar (Tripp et at.
2003)
Wakker et al. 2003 Wakker Van Woerden 1997
31
Summary (models)

• Models reproduce the vertical extent with
  reasonable energy
• input (lt4 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

32
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 _at_

33
The hot halo

• Munch (52) detected Ca II and Na I interstellar
  lines at v-vLSRgt20 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 0.52109 (Rmax/R0) M
• So ?CDM requires Mgt1011M halo to extend to
  Rmax'1Mpc

34

• 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 _at_ T 3105 K

35
HI emission O VI absorption
Sembach et al 02

• Consistent with O VI at interface of HI and WHIM
• Possible evidence that O VI expanding relative to
  HI

36
Interaction of HVCs with WHIM

• Density contrast Tvir/THI' 100-104
• Analogous to a transonic sprinkler
• Ram-pressure drag (Benjamin Danly 97)
• ? 21 N19/(n-3v200) Myr
• Tflight ' 100 Myr
• Drag important

37
Evidence for drag

• Structure of leading arm
  of Magellanic stream
• Head-tail structure of HVCs (Bruns
  et al 01)
• Z lt Z for complex C

HVC
CHVCs
Putman et al 03
38
Problems

• Fountain circulates large mass through
  extraplanar gas MHI ' 5108 M every 100 Myr
• If ejected gas loses 10 of its angular momentum,
  halo will become corotating if not extensive
  (Mgas 5108 (Rmax/R0) M)
• Naively expect moving clouds to be ablated
• Net inflow and low Z (10 Zsun) imply
  condensation prevails

39
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 gt 1Mpc