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Arxiv: Knobs and dials of retrieving JWST transmission spectra. I. The importance of p-T profile complexity Published: 9/13/2024 9:00:10 PM Updated: 9/13/2024 9:00:10 PM

Paper abstract: We investigate the impact of using multipoint p-T profiles of varyingcomplexity on the retrieval of synthetically generated hot Jupiter transmissionspectra modelled after state-of-the-art observations of the hot JupiterWASP-39~b with JWST. We perform homogenised atmospheric retrievals with theTauREx retrieval framework on a sample of synthetically generated transmissionspectra, accounting for varying cases of underlying p-T profiles, cloud-toppressures, and expected noise levels. These retrievals are performed using afixed-pressure multipoint p-T prescription with increasing complexity, rangingfrom isothermal to an eleven-point profile. We evaluate the performance of theretrievals based on the Bayesian model evidence, and the accuracy of theretrievals compared to the known input parameters. We find that performingatmospheric retrievals using an isothermal prescription for thepressure-temperature profile consistently results in wrongly retrievedatmospheric parameters when compared to the known input parameters. For anunderlying p-T profile with a fully positive lapse rate, we find that atwo-point profile is sufficient to retrieve the known atmospheric parameters,while under the presence of an atmospheric temperature inversion, we find thata more complex profile is necessary. Our investigation shows that, for a dataquality scenario mirroring state-of-the-art observations of a hot Jupiter withJWST, an isothermal p-T prescription is insufficient to correctly retrieve theknown atmospheric parameters. We find a model complexity preference dependenton the underlying pressure-temperature structure, but argue that a p-Tprescription on the complexity level of a four-point profile should bepreferred. This represents the overlap between the lowest number of freeparameters and highest model preference in the cases investigated in this work.