摘要：With an aim of probing the physical conditions and excitation mechanisms of warm molecular gas in individual star-forming regions, we performedHerschelSPIRE Fourier Transform Spectrometer (FTS) observations of 30 Doradus in the Large Magellanic Cloud. In our FTS observations, important far-infrared (FIR) cooling lines in the interstellar medium, including COJ= 4–3 toJ= 13–12, [C I] 370μm, and [N II] 205μm, were clearly detected. In combination with ground-based COJ= 1–0 andJ= 3–2 data, we then constructed CO spectral line energy distributions (SLEDs) on ~10 pc scales over a ~60 pc × 60 pc area and found that the shape of the observed CO SLEDs considerably changes across 30 Doradus. For example, the peak transitionJpvaries fromJ= 6–5 toJ= 10–9, while the slope characterized by the high-to-intermediateJratioαranges from ~0.4 to ~1.8. To examine the source(s) of these variations in CO transitions, we analyzed the CO observations, along with [C II] 158μm, [C I] 370μm, [O I] 145μm, H20–0 S(3), and FIR luminosity data, using state-of-the-art models of photodissociation regions and shocks. Our detailed modeling showed that the observed CO emission likely originates from highly compressed (thermal pressureP∕kB~ 107–109K cm−3) clumps on ~0.7–2 pc scales, which could be produced by either ultraviolet (UV) photons (UV radiation fieldGUV~ 103–105Mathis fields) or low-velocity C-type shocks (pre-shock medium densitynpre~ 104–106cm−3and shock velocityvs~ 5–10 km s−1). Considering the stellar content in 30 Doradus, however, we tentatively excluded the stellar origin of CO excitation and concluded that low-velocity shocks driven by kiloparsec-scale processes (e.g., interaction between the Milky Way and the Magellanic Clouds) are likely the dominant source of heating for CO. The shocked CO-bright medium was then found to be warm (temperatureT~ 100–500 K) and surrounded by a UV-regulated low-pressure component (P∕kB~ a few (104–105) K cm−3) that is bright in [C II] 158μm, [C I] 370μm, [O I] 145μm, and FIR dust continuum emission.
关键词：Key wordsenISM: moleculesMagellanic Cloudsgalaxies: ISMinfrared: ISM
