the gaseous halos of spiral galaxies

Filippo Fraternali (University of Oxford) Terschelling 6 Jul 2005

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)


Thin disk

Gas out-flow

Cold gas infall

Thin disk

Gas accretion

Inflow and outflow processes

1. 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)

Study of the extra-planar (halo) gas


OutlineHI observations:

edge-on: NGC891slow rotation

non-edge-on: NGC2403slow rotation + inflow

other galaxies

Dynamical model:model descriptionapplication to NGC891 and NGC2403


NGC 891

. Distance: 9.5 Mpc

. Type: Sb/SBb

. Inclination ~ 90o

. LB = 8 x 1010 LO

. Non-interacting

. Very similar to the Milky Way


The gaseous halo of NGC891Total HI maps

Sancisi & Allen 1979 Swaters et al. 1997Oosterloo, Fraternali & Sancisi 2005

10 kpc

WSRT


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







200+ hours at the WSRT


NGC891: data cube

QuickTime™ and aVideo decompressor

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NGC891: Low rotation of extra-planar gas

Fraternali 2005

vrot~15 km s-1 kpc-1

See also poster by G. Heald et al.


NGC 2403

.Distance: 3 Mpc

.Type: Sc

.Inclination ~ 62

.Non-interacting

.Very similar to M33


Extra-planar gas in non–edge-on galaxies

NGC2403: total HI map

Fraternali, van Moorsel, Sancisi, Oosterloo, AJ, 2002

Velocity fieldThin disc model


NGC2403: Extra-planar gas

Extra-planar gas

130 km/s

Forbidden gas

Fraternali, Oosterloo, Sancisi, van Moorsel 2001

Thin disc model


Extra-planar gas and accretion

8 kp

c107 Mo of H I

5 kpc

NGC2403


NGC2403: Non circular motions

Thin disc Extra-planar gas

V

Lagging haloThin disc


Non-circular motionspurerotationpure radialinflow

rotation + outflowrotation + inflow


Summary (observations) Extra-planar detected up to 15 kpc from plane

Rotation lower than the disc

High velocities (100-200 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).


NGC6946: Extra-planar gas and SF

Boomsma PhD 2005

WRST


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 12632 (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?


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)


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

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are needed to see this picture.


Model constraint: vertical distribution

Vkick ~ 75 km s-1

Mhalo ~2 109 M


N891: inflow/outflowTravel times

Energy input <4 % of energy from SNe


NGC891: Lack of low angular momentum

Fast rotating gas

NEED FOR LOW ANGULAR MOMENTUM MATERIAL


NGC2403: lagging gas

Thin disc

Thick disc

60o

Vkick ~ 70 km s-1

Mhalo ~ 5 108 M


NGC2403: inflow/outflowThin disc gas

Extra-planar gas

Radial outflow

NEED FOR INFALLING MATERIAL

V

VR

Vz


Second-passage models

V

VR

Vz

V

VR

Vz


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 interactions or accretion


High Velocity Clouds

Complex AM 106 MO

d 8-10 kpcv 100 km s-1

Wakker et al. 2003; Wakker & Van Woerden 1997

Complex Cv 100 km s-1

If d 10 kpc M 107 MO

Low metallicity Z=0.1-0.3 solar(Tripp et at. 2003)

Forbidden gasv 100 km s-1

M 5 · 106 MO

Filamentv 80 km s-1

M 107 MO


Conclusions Extra-planar gas:

maybe common up to 10-15 kpc from the plane

Kinematics: Low rotation (gradient) + vertical motions (up to 100-200 km/s) + overall inflow

Evolution of spiral galaxies influenced both by:- Star formation (gas to the halo, to the outer parts...) - Accretion of cold material

Dynamical models: galactic fountains alone do not reproduce the kinematics of the extra-planar gas and require accretion from IGM

the gaseous halos of spiral galaxies

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