Far Infrared and Submillimeter Emission from Galactic and Extragalactic Photo-Dissociation Regions

Photodissociation Region (PDR) models are computed over a wide range of physical conditions, from those appropriate to giant molecular clouds illuminated by the interstellar radiation field to the conditions experienced by circumstellar disks very close to hot massive stars. These models use the most up-to-date values of atomic and molecular data, the most current chemical rate coefficients, and the newest grain photoelectric heating rates which include treatments of small grains and large molecules. In addition, we examine the effects of metallicity and cloud extinction on the predicted line intensities. Results are presented for PDR models with densities over the range n=10^1-10^7 cm^-3 and for incident far-ultraviolet radiation fields over the range G_0=10^-0.5-10^6.5, for metallicities Z=1 and 0.1 times the local Galactic value, and for a range of PDR cloud sizes. We present line strength and/or line ratio plots for a variety of useful PDR diagnostics: [C II] 158 micron, [O I] 63 and 145 micron, [C I] 370 and 609 micron, CO J=1-0, J=2-1, J=3-2, J=6-5 and J=15-14, as well as the strength of the far-infrared continuum. These plots will be useful for the interpretation of Galactic and extragalactic far infrared and submillimeter spectra observable with ISO, SOFIA, SWAS, FIRST and other orbital and suborbital platforms. As examples, we apply our results to ISO and ground based observations of M82, NGC 278, and the Large Magellenic Cloud.Comment: 54 pages, 20 figures, accepted for publication in The Astrophysical Journa

The Abundance and Emission of H2O and O2 in Clumpy Molecular Clouds

Recent observations with the Submillimeter Wave Astronomy Satellite indicate abundances of gaseous H2O and O2 in dense molecular clouds which are significantly lower than found in standard homogeneous chemistry models. We present here results for the thermal and chemical balance of inhomogeneous molecular clouds exposed to ultraviolet radiation in which the abundances of H2O and O2 are computed for various density distributions, radiation field strengths and geometries. It is found that an inhomogeneous density distribution lowers the column densities of H2O and O2 compared to the homogeneous case by more than an order of magnitude at the same A_V. O2 is particularly sensitive to the penetrating ultraviolet radiation, more so than H2O. The S140 and rho Oph clouds are studied as relevant test cases of star-forming and quiescent regions. The SWAS results of S140 can be accommodated naturally in a clumpy model with mean density of 2x10^3 cm-3 and enhancement I_UV=140 compared with the average interstellar radiation field, in agreement with observations of [CI] and 13CO of this cloud. Additional radiative transfer computations suggest that this diffuse H2O component is warm, ~60-90 K, and can account for the bulk of the 1_10-1_01 line emission observed by SWAS. The rho Oph model yields consistent O2 abundances but too much H2O, even for [C]/[O]=0.94, if I_UV<10 respectively <40 for a mean density of 10^3 respectively 10^4 cm-3. It is concluded that enhanced photodissociation in clumpy regions can explain the low H2O and O2 abundances and emissivities found in the large SWAS beam for extended molecular clouds, but that additional freeze-out of oxygen onto grains is needed in dense cold cores.Comment: To be published in ApJ

Stereotactic robot assisted implantation of multiple depth electrodes in children with therapy refractory epilepsy: significant time saving with highest accuracy

Brian Collins' Gallopers - G54 - photographed 25 August 1968

Age determination of obsidian source samples from North Queensland and New South Wales, Australia

By means of the fission track method very old obsidian samples from various Australian sites have been dated. The track fading of these samples has been corrected with the plateau age method and with the track size correction method. Ages from 85.5 Ma to 92.3 Ma have been obtained