MINDS. The Detection of <SUP>13</SUP>CO<SUB>2</SUB> with JWST-MIRI Indicates Abundant CO<SUB>2</SUB> in a Protoplanetary Disk

We present JWST-MIRI Medium Resolution Spectrometer (MRS) spectra of the protoplanetary disk around the low-mass T Tauri star GW Lup from the MIRI mid-INfrared Disk Survey Guaranteed Time Observations program. Emission from <SUP>12</SUP>CO<SUB>2</SUB>, <SUP>13</SUP>CO<SUB>2</SUB>, H<SUB>2</SUB>O, HCN, C<SUB>2</SUB>H<SUB>2</SUB>, and OH is identified with <SUP>13</SUP>CO<SUB>2</SUB> being detected for the first time in a protoplanetary disk. We characterize the chemical and physical conditions in the inner few astronomical units of the GW Lup disk using these molecules as probes. The spectral resolution of JWST-MIRI MRS paired with high signal-to-noise data is essential to identify these species and determine their column densities and temperatures. The Q branches of these molecules, including those of hot bands, are particularly sensitive to temperature and column density. We find that the <SUP>12</SUP>CO<SUB>2</SUB> emission in the GW Lup disk is coming from optically thick emission at a temperature of ~400 K. <SUP>13</SUP>CO<SUB>2</SUB> is optically thinner and based on a lower temperature of ~325 K, and thus may be tracing deeper into the disk and/or a larger emitting radius than <SUP>12</SUP>CO<SUB>2</SUB>. The derived ${N}_{{\mathrm{CO}}_{2}}$ / ${N}_{{{\rm{H}}}_{2}{\rm{O}}}$ ratio is orders of magnitude higher than previously derived for GW Lup and other targets based on Spitzer-InfraRed-Spectrograph data. This high column density ratio may be due to an inner cavity with a radius in between the H<SUB>2</SUB>O and CO<SUB>2</SUB> snowlines and/or an overall lower disk temperature. This paper demonstrates the unique ability of JWST to probe inner disk structures and chemistry through weak, previously unseen molecular features.