Disks, Tori, and Cocoons: Emission and Absorption Diagnostics of AGN Environments

One of the most important problems in the study of active galaxies is understanding the detailed geometry, physics, and evolution of the central engines and their environments. The leading models involve an accretion disk and torus structure around a central dense object, thought to be a supermassive black hole. Gas found in the environment of AGN is associated with different structures: molecular accretion disks, larger scale atomic tori, ionized and neutral "cocoons" in which the nuclear regions can be embedded. All of them can be studied at radio wavelengths by various means. Here, we summarize the work that has been done to date in the radio band to characterize these structures. Much has been learned about the central few parsecs of AGN in the last few decades with contemporary instruments but the picture remains incomplete. In order to be able to define a more accurate model of this region, significant advances in sensitivity, spectral and angular resolution, and bandpass stability are required. The necessary advances will only be provided by the Square Kilometer Array and we discuss the possibilities that these dramatic improvements will open for the study of the gas in the central region of AGN.Comment: To appear in "Science with the Square Kilometer Array," eds. C. Carilli and S. Rawlings, New Astronomy Reviews (Elsevier: Amsterdam); 17 pages, 7 figures (four of them in separate gif/tif files) The full paper with high resolution images can be downloaded from http://www.astron.nl/~morganti/Papers/AGNenvironment.ps.g

Active Galactic Nuclei at the Crossroads of Astrophysics

Over the last five decades, AGN studies have produced a number of spectacular examples of synergies and multifaceted approaches in astrophysics. The field of AGN research now spans the entire spectral range and covers more than twelve orders of magnitude in the spatial and temporal domains. The next generation of astrophysical facilities will open up new possibilities for AGN studies, especially in the areas of high-resolution and high-fidelity imaging and spectroscopy of nuclear regions in the X-ray, optical, and radio bands. These studies will address in detail a number of critical issues in AGN research such as processes in the immediate vicinity of supermassive black holes, physical conditions of broad-line and narrow-line regions, formation and evolution of accretion disks and relativistic outflows, and the connection between nuclear activity and galaxy evolution.Comment: 16 pages, 5 figures; review contribution; "Exploring the Cosmic Frontier: Astrophysical Instruments for the 21st Century", ESO Astrophysical Symposia Serie

Water, Nitrogen and Ion Balance in the African Treefrog \u3cem\u3eChiromantis petersi\u3c/em\u3e Boulenger (Anura: Rhacophoridae), With Comments on the Structure of the Integument

Physiological and anatomical investigations were carried out on Chiromantis petersi, an African rhacophorid treefrog, with the following results: 1. The minimum rate of evaporative water loss (EWL) was 0.41±0.25 mg/g.h. 2. The maximum rate of water uptake in dehydrated frogs averaged 75% body weight/h in the first 10 min of rehydration. 3. The low EWL correlates with the unique structure of the chromatophore units of the dorsum, the sides and the gular region. 4. The high rates of water uptake correlate with the structure of the verrucae hydrophilica of the abdominal and femoral surfaces. These verrucae are not unique to this species. 5. When denied water and force-fed mealworms for 30 days, plasma osmotic concentrations increased from 210 mosM to 384 mosM, with Na+, Cl− and urea contributing most to the increase. 6. The ratio of urinary K+∶Na+ excretion is 3∶1. 7. Excretion totaled 155 mg N/kg·day with 97% as uric acid, 2% as ammonia and 1% as urea. 8. Since urea accumulated in the body at the rate of 58.5±6.1 mg N/kg·day, total nitrogen production was 213 mg N/kg·day. Uric acid formed 70% thereof. 9. Chiromantis petersi is capable of surviving without free water for prolonged periods and is as well adapted to its xeric environment as are many desert reptiles