H2 infrared line emission from S140: a warm PDR
نویسندگان
چکیده
ISO SWS spectra of H2 pure rotational and rovibrational transitions, as well as [Feii], and [Siii] fine structure lines were obtained for one position on the photodissociation region (PDR) adjacent to the bright rim of the S140 Hii region. The gas density is 104 cm 3 and the incident UV flux 400 at the location of the ionization front. Our PDR model analysis shows that the relative H2 line intensities are characteristic of low-density fluorescent emission and that the gas temperature is T > 500K in the partially dissociated gas. A comparison of predicted and observed fine structure line intensities permits an estimate of the abundances of Fe and Si.
منابع مشابه
Heating the Gas in Photodissociation Fronts
ISO has provided us with a new perspective on gas temperatures in photodissociation regions through measurements of line emission from rotationallyexcited levels of H2. The H2 rotational level populations provide a thermal probe, showing that gas temperatures Tgas ≈ 500 − 1000K prevail in a portion of the PDR where significant H2 is present. Such high gas temperatures were unexpected. Theoretic...
متن کاملHigh Resolution Observations of the Near - Infrared Emission from NGC 6822 Hubble
We observed Hubble V, the brightest HII region complex in the dwarf irregular galaxy NGC 6822, at near-infrared (1.8–2.4 μm) wavelengths using the Cooled Grating Spectrometer 4 (CGS4) at the United Kingdom Infra-Red Telescope (UKIRT). The line emission maps of Hubble V show the typical structure of a photo-dissociation region (PDR) where an ionized core, traced by compact He I emission (2.0587 ...
متن کاملAn ISO–SWS survey of molecular hydrogen in Starburst and Seyfert Galaxies
We present results from a survey of molecular hydrogen emission from a sample of Starburst and Seyfert galaxies carried out with the Infrared Space Observatory (ISO). Pure rotational H2 emission has been detected in a number of extragalactic objects and a variety of environments. A number of transitions from S(7) to S(0) are detected in both Starbursts and Seyferts. Using excitation diagrams we...
متن کاملPhoton Dominated Regions in Low Uv Fields: a Study of the Peripheral Region of L1204/s140
We have carried out an in-depth study of the peripheral region of the molecular cloud L1204/S140, where the far-ultraviolet radiation and the density are relatively low. Our observations test theories of photon-dominated regions (PDRs) in a regime that has been little explored. Knowledge of such regions will also help to test theories of photoionization-regulated star formation. [C II] 158 μm a...
متن کاملThe Ratio of Ortho- to Para-H2 in Photodissociation Regions
We discuss the ratio of orthoto para-H2 in photodissociation regions (PDRs). We draw attention to an apparent confusion in the literature between the ortho-to-para ratio of molecules in FUV-pumped vibrationally excited states, and the total H2 ortho-to-para abundance ratio. These ratios are not the same because the process of FUV-pumping of fluorescent H2 emission in PDRs occurs via optically t...
متن کامل