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Table 2

Parameters for the modeling of the OH outflow.

Parameter Units Meaning Explored range (HVC)

R int pc Radius of the far-IR continuum sourcea e
T dust K Dust temperature of the far-IR continuum source 90−200
τ 100 Continuum optical depth at 100 μm along a radial (Rint) path 0.5−4
Rout/Rint Radius of the outflowing envelope relative to Rint 1.1−2.5f
v int km s-1 Gas velocity at Rintb,c 1300−1700g
v out km s-1 Gas velocity at Routb,c 100−400g
N OH cm-2 OH column density from Rint to Routb,c (0.5−5) × 1017
p f pc Limiting impact parameter for the calculation of emerging fluxes Rint − Routh
f Scaling factor d



It coincides with the inner radius of the OH envelope.


A uniform velocity gradient is adopted, so that the velocity field is given by v(r) = vint + dv/dr (r − Rint).


A constant mass-outflow rate is adopted, so that nOH × r2 × v is independent of r.


Representing either partial coverage by OH of the continuum source (a clumpy outflow, f < 1), or an ensemble of independent sources (f > 1). scales as . f is not a fitting parameter, but indicates that the modeled source size is effective. Nevertheless, we argue in Sect. 4 that f ~ 1 for the QC, and in Sect. 3.3.1 that f ≳ 0.45 for the HVC.


For a given model, Rint is fixed to give the correct absolute fluxes.


See Fig. 11.


Accelerating velocity fields have been tried as well, but they yield poor fits to both the line profiles and the flux ratios.


pf = Rout in spherical symmetry, while pf = Rint simulates an outflow directed mainly toward the observer.

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