Gas surface density distributions in model A+ shown at several time instances after the onset of numerical simulations (the disk forms at t = 0.1 Myr). The insets zoom in on several fragments in the disk. The yellow contour lines delineate regions with the Toomre Q-parameter smaller than unity. The red dashed line is a radial cut through the disk used later to show the vertical volume density and temperature distributions. The scale bar is in log g cm-2.