Horseshoe-shaped brightness asymmetries of several transitional discs are thought to be caused by large-scale vortices .
Anticyclonic vortices are efficiently collect dust particles , therefore they can play a major role in planet formation .
Former studies suggest that the disc self-gravity weakens vortices formed at the edge of the gap opened by a massive planet in discs whose masses are in the range of 0.01 \leq M _ { \mathrm { disc } } / M _ { * } \leq 0.1 .
Here we present an investigation on the long-term evolution of the large-scale vortices formed at the viscosity transition of the discs ’ dead zone outer edge by means of two-dimensional hydrodynamic simulations taking disc self-gravity into account .
We perform a numerical study of low mass , 0.001 \leq M _ { \mathrm { disc } } / M _ { * } \leq 0.01 , discs , for which cases disc self-gravity was previously neglected .
The large-scale vortices are found to be stretched due to disc self-gravity even for low-mass discs with M _ { \mathrm { disc } } / M _ { * } \gtrsim 0.005 where initially the Toomre Q -parameter was \lesssim 50 at the vortex distance .
As a result of stretching , the vortex aspect ratio increases and a weaker azimuthal density contrast develops .
The strength of the vortex stretching is proportional to the disc mass .
The vortex stretching can be explained by a combined action of a non-vanishing gravitational torque caused by the vortex , and the Keplerian shear of the disc .
Self-gravitating vortices are subject to significantly faster decay than non-self-gravitating ones .
We found that vortices developed at sharp viscosity transitions of self-gravitating discs can be described by a GNG model as long as the disc viscosity is low , i.e . \alpha _ { \mathrm { dz } } \leq 10 ^ { -5 } .