Active galactic nucleus

D. E. Osterbrock and G. J. Ferland, Astrophysics of Gaseous Nebulae and Active Galactic Nuclei, University Science Books, Mill Valley, Cal., 2006, is another classic text, indispensable for studies of emission nebulae. 

We now have clear evidence of non-thermal processes in the sky. A whole panoply of violent activities is revealed to the watchful eye of our radio. X-ray and gamma-ray telescopes. Supernova remnants, pulsars, active galactic nuclei and gamma bursts emit radiation that has clearly nothing to do with thermal activity, for their spectra bear no resemblance to those of heated bodies. 

Acorn worm Acoustics Actinides Action potential Activated complex Active galactic nuclei Acupressure Acupuncture... 

V0I.693 D. Alloin, R. Johnson, P. Lira (Eds.), Physics of Active Galactic Nuclei at all Scales V0I.694 H. Schwoerer, J. Magill, B. Beleites (Eds ), Lasers and Nuclei... 

Active galactic nuclei can be readily identified both via their mid-infrared colors and as point source residuals in two-dimensional modelling. 

The idea of extracting energy from black holes has been proposed by Penrose thirtyhve years ago and followed by a cascade of energy extraction models. Nowadays it is known that from almost all Active Galactic Nuclei (AGNs) which harbour a supermassive (M > 105 x M ) Kerr black hole, focused jets of hot gas shoot into space at relativistic speed. How much energy can these jets get from the black hole or its accretion disk is a question which arises by itself. 

The catalogue of quasars and active galactic nuclei 10th edition [3], We used the BL Lac objects. Conditions magnitude < 18, the flux at 6cm > 0.17Jy, redshift> 0.1... 

Figure 32. Summary of our current knowledge of abundances at high redshift. The metallicity is plotted on the j/-axis on a log scale relative to the solar reference the latter is shown as the broken horizontal line at 0.0 and corresponds to approximately 2% of the baryons being incorporated in elements heavier than helium. The x-axis shows the typical linear dimensions of the strucures to which the abundance measurements refer, from the central regions of active galactic nuclei on scales of 10-100 pc to the intergalactic medium traced by the Lya forest on Mpc scales. Generally speaking, these typical linear scales are inversely proportional to the overdensities of the structures considered relative to the background.

Spectropolarimetry has proven to be an important tool in the development of unified theories of active galactic nuclei (AGN). Its strength is that it provides an alternative view of the inner regions of the active nucleus. This allows for the study the stracture and kinematics of both polarizing materials and the emission source. Examples of polarization spectra of two active galaxies NGC 5548 and Was 45 are given in Fig. 15. The observations of NGC 5548 were made in 1997 and Was 45 in 1999 with the 1.2m William Hershel Telescope. 

The vast majority of optical identifications in the deep ROSAT fields are active galactic nuclei (AGN), in particular quasars of medium to high z (Shanks et al. 1991). The logN logS function shows a distinct flattening at the faint end, consistent with the same evolutionary models as for QSOs in the optical waveband (Boyle et al. 1993). Thus, it seems likely that the majority of the soft (1-2 keV) X-ray background is due to unresolved AGN. 

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