European Workshop on Astronomical Molecules, Zwolle 2004

NGC7538-IRS1 N:modelling a maser disc

Michele Pestalozzi,M. Elitzur, J. Conway, R. Booth

European Workshop on Astronomical Molecules, Zwolle 2004

Discs in high-mass star-forming regions• Zhang et al. 1998• Cesaroni et al. 2000

• Shepherd et al. 2001

• Sandell et al. 2003

European Workshop on Astronomical Molecules, Zwolle 2004

NGC7538-IRS1N: “the” disc

Pestalozzi et al. 2004

6.7 GHz

Gaume et al. 1995Minier et al. 1998

European Workshop on Astronomical Molecules, Zwolle 2004

The data

R.A. / DEC

disp. / LOS Vel.Pestalozzi et al. 2001

Minier et al. 1998

European Workshop on Astronomical Molecules, Zwolle 2004

Comparison 6.7 / 12.2 GHz

European Workshop on Astronomical Molecules, Zwolle 2004

Assumptions:1. Keplerian rotating disc seen edge-on2. Gain per unit length between R0 and Ri:

power-law (1 / rp)3. Amplification of a continuum background (Tb ~ 104 K)

4. Maser is unsaturated

Geometry

European Workshop on Astronomical Molecules, Zwolle 2004

Model

Free parameters: h,

(3.)

(1.)

(2.,4.)

European Workshop on Astronomical Molecules, Zwolle 2004

Results

12.2 GHz

6.7 GHz

30 M(from others)1000 AU in radiush = 0.39

European Workshop on Astronomical Molecules, Zwolle 2004

The ‘kink’ Velocity

Coherence

European Workshop on Astronomical Molecules, Zwolle 2004

Important note IRAM

04191+1522

PdB, CS

Belloche et al.2002

European Workshop on Astronomical Molecules, Zwolle 2004

MASER vs Thermal emission

Advantages: • Masers allow to resolve the same linear scales further away 1 AU @ 1 kpc• Fine tracers of dynamics

European Workshop on Astronomical Molecules, Zwolle 2004

Summary• Found and modelled a disc in NGC7538

•30 M, 1000 AU radius, h=0.39

•Masers behave as thermal emission regarding optical depth

•Optimal tool to study small linear and dynamical scales at large distances

• Future: 3D modelling, outliers, satellite lines...

European Workshop on Astronomical Molecules, Zwolle 2004

Thank you