Structured outflow from a Structured outflow from a dynamo-active accretion discdynamo-active accretion disc

B. von Rekowski, A. Brandenburg,

W. Dobler, A. Shukurov

A&A 398, 825-844

Bridging the gapsBridging the gaps

Dynamo theory

Disc theory

Jet theory(Ferreira)

(Küker)

(Hawley)

Model of disc dynamo,with feedback from disc,and allowing for outflows

Do jets require external fields?Do we get dipolar fields?Are they necessary?

Our inspirationOur inspiration

• Disc modeled as b.c.

• Adiabatic EOS– Virial temperature

• Need a cool disc

• Kepler rot. only for

Ouyed & Pudritz (1997)r

GMT

R

0T

Modeling a cool discModeling a cool disc

• vertical pressure eq.

• low T high density

• Entropy lower in disc– bi-polytropic model

Vertical cross-sectionthrough the disc

z

sTh

z

0

s

Thu2

Dynamo inputDynamo input

• Local disc simulations: cyclic fields– Quadrupolar for vacuum condition– Steady dipolar field for perfect conductor b.c.

• Dynamo alpha negative– Local mean-field models: similar results

• Global mean field models: always dipolar– Bardou et al. (2001), Campbell (2001)

Structured outflowStructured outflow

Disc temperature relative to halo is free parameter:Here about 3000K

Cooler disc: more vigorous evolution

Acceleration mechanismAcceleration mechanismDisc temperatureabout 3000 K

Ratio of magneto-centrifugal forceto pressure force

Unsteady Unsteady outflow is outflow is the rulethe rule

Momentum transport from the disc into the wind

Lagrangian Lagrangian invariantsinvariants

ii Buak /)(

/)(~ 1 Bua

kBual /)(

kBhae /~

)( 221 u

Comparison with Ouyed & Pudritz (1997)Comparison with Ouyed & Pudritz (1997)

Very similar:

Alfven Mach >1

Toroidal/poloidal field ratio increases

No asymptotic collimationNo asymptotic collimation

Conical outflows similar to BN/KLConical outflows similar to BN/KL

Greenhill et al (1998)

Application: magnetic Application: magnetic contamination of galaxy clustercontamination of galaxy cluster

10,000 galaxies for 1 Gyr, 1044 erg/s each

G182

tV

cMN

F

FB sw

kin

poyntrms

Similar figure also for outflows from protostellar disc

Further experiments: interaction with magnetosphereFurther experiments: interaction with magnetosphereAlternating fieldline uploading and downloadingAlternating fieldline uploading and downloading

Star connected with the disc Star disconnected from disc

Simil ar beh avior fo und b y G

oo dso n & W

ingl ee (19 99)

ConclusionsConclusions

• Conical outflow

• Collimation requires external field– cf talk by Menard (yesterday)

• Dipolar field comes automatically