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논문

전체
Radiative and mechanical feedback into the molecular gas in the Large Magellanic Cloud. II. 30 Doradus SCI
  • 이민영; Suzanne Madden; Franck Le Petit; 외
  • 2019-08-15
  • ASTRONOMY & ASTROPHYSICS 628 : A113-1~A113-25
With an aim of probing the physical conditions and excitation mechanisms of warm molecular gas in individual star-forming regions, we performed Herschel SPIRE 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 CO J = 4?3 to J = 13?12, [C?I] 370 μm, and [N?II] 205 μm, were clearly detected. In combination with ground-based CO J = 1?0 and J = 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 transition Jp varies from J = 6?5 to J = 10?9, while the slope characterized by the high-to-intermediate J ratio α ranges 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] 158 μm, [C?I] 370 μm, [O?I] 145 μm, H2 0?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 pressure P?kB ~ 107?109 K cm?3) clumps on ~0.7?2 pc scales, which could be produced by either ultraviolet (UV) photons (UV radiation field GUV ~ 103?105 Mathis fields) or low-velocity C-type shocks (pre-shock medium density npre ~ 104?106 cm?3 and shock velocity vs ~ 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 (temperature T ~ 100?500 K) and surrounded by a UV-regulated low-pressure component (P?kB ~ a few (104 ?105) K cm?3) t