2019A&A...626A.131M

Pillars and globules are the best examples of the impact of the radiation and wind from massive stars on the surrounding interstellar medium. We mapped the G287.84-0.82 cometary globule (with the Treasure Chest cluster embedded in it) in the South Pillars region of Carina (i) in [CII], 63 µm [OI], and CO(11-10) using the heterodyne receiver array upGREAT on SOFIA and (ii) in J=2-1 transitions of CO, ¹³CO, C¹⁸O, and J=3-2 transitions of H₂CO using the APEX telescope in Chile. We used these data to probe the morphology, kinematics, and physical conditions of the molecular gas and the photon-dominated regions (PDRs) in G287.84-0.82. The velocity-resolved observations of [CII] and [OI] suggest that the overall structure of the pillar (with red-shifted photoevaporating tails) is consistent with the effect of FUV radiation and winds from η Car and O stars in Trumpler 16. The gas in the head of the pillar is strongly influenced by the embedded cluster, whose brightest member is an O9.5 V star, CPD -59°2661. The emission of the [CII] and [OI] lines peak at a position close to the embedded star, while all the other tracers peak at another position lying to the northeast consistent with gas being compressed by the expanding PDR created by the embedded cluster. The molecular gas inside the globule was probed with the J=2-1 transitions of CO and isotopologs as well as H₂CO, and analyzed using a non-local thermodynamic equilibrium model (escape-probability approach), while we used PDR models to derive the physical conditions of the PDR. We identify at least two PDR gas components; the diffuse part (∼10⁴cm^–3) is traced by [CII], while the dense (n∼2-8x10⁵cm^–3) part is traced by [CII], [OI], and CO(11-10). Using the F=2-1 transition of [¹³CII] detected at 50 positions in the region, we derived optical depths (0.9-5), excitation temperatures (80-255K) of [CII], and N(C⁺) of 0.3-1x10¹⁹cm^–2. The total mass of the globule is ∼1000M_☉, about half of which is traced by [CII]. The dense PDR gas has a thermal pressure of 10⁷-10⁸K/cm³, which is similar to the values observed in other regions.