Models and observational predictions of dust traps in protoplanetary discs

This manuscript investigates the impact of key dust evolution parameters-disc viscosity, fragmentation velocity, and the initial gas disc critical radius-on dust retention and trapping in protoplanetary discs. Using models with and without pressure bumps, combined with radiative transfer simulations, images of the dust continuum emission at (sub-)millimeter wavelengths, their fluxes and observed disc sizes are presented. For discs without pressure bumps (smooth discs), significant dust mass can only be retained over Myr timescales when dust fragmentation velocities are low ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>v</mml:mi> <mml:mi>frag</mml:mi></mml:msub> <mml:mo>=</mml:mo> <mml:mn>1</mml:mn></mml:math> m s^-1) and with viscosity values of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>α</mml:mi> <mml:mo>=</mml:mo> <mml:msup><mml:mn>10</mml:mn> <mml:mrow><mml:mo>-</mml:mo> <mml:mn>3</mml:mn></mml:mrow> </mml:msup> </mml:math> . For such a combination of fragmentation velocity and viscosity the synthetic images show a bright inner emission follow by a shallow emission with potential gaps if they are present in the gas profile as well. At higher fragmentation velocities ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>v</mml:mi> <mml:mi>frag</mml:mi></mml:msub> <mml:mo>=</mml:mo> <mml:mn>5</mml:mn></mml:math> -10 m s^-1), most dust is lost due to radial drift at million-year timescales unless pressure traps are present, in which case dust masses can increase by orders of magnitude and structures are observed in synthetic images. The viscosity parameter strongly shapes observable features, with low <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>α</mml:mi></mml:math> producing sharper, potentially asymmetric inner wall cavities in inclined discs due to optically thick emission. High <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>α</mml:mi></mml:math> favors the appearance of shoulders around the predominant rings that dust trapping produces. However, distinguishing between different fragmentation velocities observationally remains challenging. The inferred dust disc sizes from synthetic observations do not always correspond directly to dust model sizes or to the location of pressure bumps. Finally, we discuss implications for pebble fluxes and the delivery of volatiles to the inner disc. These results emphasize the strong degeneracies among dust evolution parameters and highlight the need for multi-wavelength, high-resolution observations to disentangle the processes shaping the formation of planets and planetary embryos in protoplanetary discs.