Active galaxies

In recent years, it has become clear that the vast majority of AGNs can be explained in terms of a single unified 

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The IRAS satellite mission, launched in 1983, provided a more complete survey of disk and active galaxies containing dust than had been possible from optical observations. Follow-up measurements of redshifts and other properties led to significant results for cosmology and the discovery of many luminous star-forming and active galaxies enshrouded by dust. A typical spiral galaxy like our own... 

A diffuse X-ray background is perceived between these brilliant sources. It comes for the greater part from remote regions outside our Galaxy, probably quasars and other active galaxies. Added to these more distant emissions is a galactic component emitted by the hotter interstellar gases. 

The active galaxies of explosion supernovae are explored,it is about 14 active galaxies that there are more 20 supernovae which were detected. 

Figure 6.3. Left. The overall observed spectrum of the Coma cluster from radio to gamma-ray frequencies (see labels). Right. The constraints to the spectrum of relativistic electrons in Coma as obtained from different observation (see labels) the radio halo data (blue dashed lines) for different values of the IC magnetic field the HXR data (red solid fine with arrows), the EUV data (green solid line with arrows) and the EGRET upper limit (magenta arrow). The arrows indicate that the spectra should be considered as upper limits, because we cannot exclude that a fraction of the HXR and EUV flux is provided by active galaxies or warm gas, respectively.

More recently direct evidence for SMBHs in not obviously active galaxies has emerged. The evidence for some 40 of them is discussed in an extensive review by Kormendy and Gebhardt [16]. The strongest case is linked with the radio source Sgr A at the center of the Galaxy. A cluster of stars is observed within 0.02 pc of it, and motions of some of them with velocities up to 1350 km s 1 are seen to change in time the stars orbit the radio source in tens of years Well determined acceleration vectors for several of the stars point at... 

Figure 1. The dynamics of publications on spectropolarimeh ic observations. Gray boxes represent the total number of publications, dark grey boxes are for number of publications on active galaxies in 1989 - 2000 (from Asb onomy and Astrophysics Abstracts).

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. 

Emission lines are observed in the light from so-called active galaxies, also known as Seyfert galaxies. Emission spectra are also emitted by quasars or quasi-stellar objects (QSO). Like the absorption lines of normal galaxies these emission lines are also redshifted. 

This new instrumentation would allow detailed investigations of several fundamental astrophysical issues including the formation of the Solar System, the life and death of stars, the composition and velocity distribution of interstellar material, and the power sources of quasars and active galaxies. For example, a particularly interesting radioisotope is Ti which decays with the emission of gamma-ray lines at 68 and 78 keV, just the energies... 

Extra galactic sources like m82 may be seen out to TOMpc, thus beyond the local group. The volume of space sampled for active galaxies is considerable. One may speculate about detection of "infrared galaxies, when they exist, there is a good chance that IRAS will discover a reasonably large sample of them. 

Active galaxy A galaxy whose radiation is dominated by the emission from a localized region at the center of the galaxy. This region is thought to consist of a massive torus of gas surrounding a supermassive black hole about a few million times more massive than the sun. 

Young, S., Hough, J.H., BaUey, J.A., Axon, D.J., 8c Ward, M.J. 1993, The First Stromlo Symposium The Physics of Active Galaxies, Canberra, June 1993... 

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