Inferring (sub)millimetre dust opacities and temperature structure in edge-on protostellar discs from resolved multiwavelength continuum observations: the case of the HH 212 disc

(Sub)millimetre dust opacities are required for converting the observable dust continuum emission to the mass, but their values have long been uncertain, especially in discs around young stellar objects. We propose a method to constrain the opacity.. in edge-on discs from a characteristic optical depth tau(0),nu the density rho(0), and radius R-0 at the disc outer edge through kappa(nu)= tau(0),(nu)/(rho R-0(0)), where tau(0),nu is inferred from the shape of the observed flux along the major axis, rho(0) from gravitational stability considerations, and R-0 from direct imaging. We applied the 1D semi-analytical model to the embedded, Class 0, HH 212 disc, which has high-resolution data in Atacama Large Millimetre/submillimetre Array (ALMA) bands 9, 7, 6, and 3 and Very Large Array Ka band (lambda = 0.43, 0.85, 1.3, 2.9, and 9.1 mm). The modelling is extended to 2D through RADMC-3D radiative transfer calculations. We find a dust opacity of kappa(nu) approximate to 1.9 x 10(-2), 1.3 x 10(-2), and 4.9 x 10(-3) cm(2) g(-1) of gas and dust for ALMA bands 7, 6, and 3, respectively, with uncertainties dependent on the adopted stellar mass. The inferred opacities lend support to the widely used prescription kappa lambda = 2.3 x 10-2(1.3mm/lambda) cm(2) g(-1). We inferred a temperature of similar to 45K at the disc outer edge that increases radially inwards. It is well above the sublimation temperatures of ices such as CO and N-2, which supports the notion that the disc chemistry cannot be completely inherited from the protostellar envelope.

Automated summary

(Subtitle: English Summary) This study proposes a method to constrain dust opacities in discs around young stellar objects and finds specific values for dust opacity in ALMA bands, providing crucial insight into the distribution of dust mass in these discs.