1. The gaseous halos of spiral galaxies
Filippo Fraternali1
James Binney1
Rense Boomsma2
Tom Oosterloo3
Renzo Sancisi2,4
1 Theoretical Physics - University of Oxford (UK)
2 Kapteyn Astronomical Institute (NL)
3 ASTRON - Dwingeloo (NL)
4 INAF - Osservatorio di Bologna (I)
Filippo Fraternali (University of Oxford)

2. Inflow and outflow processes
Gas out-flow
Galactic fountain (Shapiro & Field 1976)
- Winds, SN explosions
- Gas circulation
2. Accretion from the IGM
- Companions - minor mergers (Sancisi & Van der Hulst 1988)
- Primordial gas (Oort 1970)
Thin disk
Cold gas infall
Gas accretion
Thin disk
 Study of the extra-planar (halo) gas
Filippo Fraternali (University of Oxford)

3. Outline HI observations: edge-on: NGC891 slow rotation
non-edge-on: NGC2403
slow rotation + inflow
other galaxies
Dynamical model:
model description
application to NGC891 and NGC2403
Filippo Fraternali (University of Oxford)

4. . Very similar to the Milky Way
NGC 891
. Distance: 9.5 Mpc
. Type: Sb/SBb
. Inclination ~ 90o
. LB = 8 x 1010 LO
. Non-interacting
. Very similar to the Milky Way
Filippo Fraternali (University of Oxford)

5. The gaseous halo of NGC891 Total HI maps WSRT 10 kpc
Oosterloo, Fraternali & Sancisi 2005
Sancisi & Allen 1979
Swaters et al
Filippo Fraternali (University of Oxford)

6. Extra-planar gas in NGC 891
Sancisi & Allen 1979
NH ≈ cm-2
Swaters et al. 1997
NH ≈ cm-2
Oosterloo et al. 2005
NH ≈ cm-2
Sancisi & Allen 1979
NH ≈ cm-2
Swaters et al. 1997
NH ≈ cm-2
Oosterloo et al. 2005
NH ≈ cm-2
Sancisi & Allen 1979
NH ≈ cm-2
Swaters et al. 1997
NH ≈ cm-2
Oosterloo et al. 2005
NH ≈ cm-2
200+ hours
at the WSRT
Filippo Fraternali (University of Oxford)

7. NGC891: data cube High latitude gas close to systemic velocity
Filippo Fraternali (University of Oxford)

8. NGC891: Low rotation of extra-planar gas
vrot~15 km s-1 kpc-1
Fraternali 2005
See also poster by G. Heald et al.
Filippo Fraternali (University of Oxford)

9. .Distance: 3 Mpc .Type: Sc .Inclination ~ 62 .Non-interacting
NGC 2403
.Distance: 3 Mpc
.Type: Sc
.Inclination ~ 62
.Non-interacting
.Very similar to M33
Filippo Fraternali (University of Oxford)

10. Extra-planar gas in non–edge-on galaxies
Thin disc
model
NGC2403: total HI map
Velocity field
VLA observations
HI holes
Fraternali, van Moorsel, Sancisi, Oosterloo, AJ, 2002
Filippo Fraternali (University of Oxford)

11. NGC2403: Extra-planar gas Forbidden gas 130 km/s Extra-planar gas
Thin disc
model
Conspiracy between thickness and low rotation
Fraternali, Oosterloo, Sancisi, van Moorsel 2001
Filippo Fraternali (University of Oxford)

12. Extra-planar gas and accretion
NGC2403
8 kpc
107 Mo of H I
5 kpc
Filippo Fraternali (University of Oxford)

13. NGC2403: Non circular motions
V 
Lagging halo
Thin disc
Thin disc
Extra-planar gas
Filippo Fraternali (University of Oxford)

14. Non-circular motions
Filippo Fraternali (University of Oxford)

15. Summary (observations)
Extra-planar detected up to 15 kpc from plane
Rotation lower than the disc
Global inflow motion
High velocities ( km s-1)
Link with star formation?
Evidence for accretion?
Here within 30 minutes!
Filippo Fraternali (University of Oxford)

16. 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).
Filippo Fraternali (University of Oxford)

17. NGC6946: Extra-planar gas and SF
WRST
Boomsma PhD 2005
Filippo Fraternali (University of Oxford)

18. 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).
Hints of halo gas (HI) in other galaxies:
NGC 5055 (Battaglia et al. 2005)
M33 (van der Hulst, private)
UGC 1281 (P. Kamphuis, PhD)
UGC (new WSRT observations)
HVCs in Milky Way (Wakker et al.)
HVCs in M83 and M51 (Miller & Bregman 2005)
HVCs in M31 (R. Braun et al.)
Ionised gas found and studied in several galaxies (e.g. Rand)
 Origin: fountain and/or accretion?
Filippo Fraternali (University of Oxford)

19. Dynamical models Previous works:
A barotropic [p=p(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, A&A, 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, A&A 2002)
Filippo Fraternali (University of Oxford)

20. 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
Filippo Fraternali (University of Oxford)

21. Model constraint: vertical distribution
Vkick ~ 75 km s-1
Mhalo ~2 109 M
Filippo Fraternali (University of Oxford)

22. <4 % of energy from SNe
N891: inflow/outflow
Travel times
Energy input
<4 % of energy from SNe
Filippo Fraternali (University of Oxford)

23. NGC891: Lack of low angular momentum
Fast rotating gas
NEED FOR LOW ANGULAR MOMENTUM MATERIAL
Filippo Fraternali (University of Oxford)

24. NGC2403: lagging gas 60o Thick disc Thin disc Vkick ~ 70 km s-1
Mhalo ~ M
Filippo Fraternali (University of Oxford)

25. NEED FOR INFALLING MATERIAL
NGC2403: inflow/outflow
Thin disc gas V VR Vz
Radial outflow
Extra-planar gas
NEED FOR INFALLING MATERIAL
Filippo Fraternali (University of Oxford)

26. Second-passage modelsV VR Vz V VR Vz
Filippo Fraternali (University of Oxford)

27. Summary (models)
Models reproduce the vertical extent with reasonable energy
input (<4 % SN energy)
Failure in NGC891: lack of low angular momentum
 Need for interactions or accretion
Failure in NGC2403: lack of inflow
 Need for accretion
Filippo Fraternali (University of Oxford)

28. High Velocity Clouds Forbidden gas Complex C Complex A Filament
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
Z= solar
(Tripp et at. 2003)
Wakker et al. 2003; Wakker & Van Woerden 1997
Filippo Fraternali (University of Oxford)

29. Conclusions Extra-planar gas: maybe common
up to kpc from the plane
Kinematics: Low rotation (gradient)
+ vertical motions (up to km/s)
+ overall inflow
Dynamical models:
galactic fountains alone do not reproduce the kinematics
of the extra-planar gas and require accretion from IGM
 Evolution of spiral galaxies influenced both by:
- Star formation (gas to the halo, to the outer parts...)
- Accretion of cold material
Filippo Fraternali (University of Oxford)