摘要
Constraining ionization and excitation processes in protoplanetary disks is essential for understanding the chemical structure and evolution of disk material, shaping planet formation pathways. We present JWST/NIRSpec integral-field-unit observations of the edge-on disk Oph 163131, which reveal an unusual rovibrational H2 spectrum dominated by the 1-0 O(2) line (2.627 mu m), with suppressed higher-J emission despite excitation to v = 2 and 3. This vibrationally hot, rotationally cold H2 emission is spatially extended, broadly following the molecular disk traced by CO(J = 2-1), with emission increasing above and below a thin midplane dark lane and extending radially beyond similar to 200 au, where near-IR scattered-light emission is no longer dominant. We interpret the observed H2 emission as arising from nonthermal excitation in cold, dense outer-disk gas, where collisions depopulate higher-J rotational levels within each vibrational manifold prior to emission, producing the characteristic "v-hot, J-cold" spectrum. We consider both ultraviolet irradiation and cosmic-ray excitation as contributors to the H2 emission and find that their combined action, together with collisional deexcitation of high-J level populations, broadly reproduces the observed line ratios and morphology. Within this framework, we infer a rather high effective cosmic-ray ionization rate of similar to(1-10) & times; 10-15 s-1 in the presence of a moderate UV field (chi UV = 100-1000, in Draine units). These results for disks, together with the recent findings by Bialy et al. for the lower-density starless core B68, highlight the potential of ro-vibrational H2 emission as a novel probe of cosmic-ray ionization.