Gas Density Perturbations Induced by One or More Forming Planets in the AS 209 Protoplanetary Disk as Seen with ALMA

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The formation of planets occurs within protoplanetary disks surrounding young stars, resulting in perturbation of the gas and dust surface densities. Here, we report the first evidence of spatially resolved gas surface density (Σg) perturbation towards the AS~209 protoplanetary disk from the optically thin C18O (J=2−1) emission. The observations were carried out at 1.3~mm with ALMA at a spatial resolution of about 0.3\arcsec × 0.2\arcsec (corresponding to 38 × 25 au). The C18O emission shows a compact ($\le60 au),centrallypeakedemissionandanouterringpeakingat140 au,consistentwiththatobservedinthecontinuumemissionand,itsazimuthallyaveragedradialintensityprofilepresentsadeficitthatisspatiallycoincidentwiththepreviouslyreporteddustmap.Thisdeficitcanonlybereproducedwithourphysicothermochemicaldiskmodelbylowering\Sigma_{gas}$ by nearly an order of magnitude in the dust gaps. Another salient result is that contrary to C18O, the DCO+ (J=3−2) emission peaks between the two dust gaps. We infer that the best scenario to explain our observations (C18O deficit and DCO+ enhancement) is a gas perturbation due to forming-planet(s), that is commensurate with previous continuum observations of the source along with hydrodynamical simulations. Our findings confirm that the previously observed dust gaps are very likely due to perturbation of the gas surface density that is induced by a planet of at least 0.2~MJupiter in formation. Finally, our observations also show the potential of using CO isotopologues to probe the presence of saturn mass planet(s).

ISM: molecules, planet-disk interactions, protoplanetary disks
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Astrophysical Journal
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American Astronomical Society
European Research Council (341137)
Science and Technology Facilities Council (ST/N000927/1)