Refiloe edited subsection_Black_holes_and_Active__.tex  over 8 years ago

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Radio galaxies are galaxies dominated by radio emissions from jets stemming from SMBHs. AGN are the small, dense and luminous components of the centers of galaxies as represented in Figure 3 and Figure 4. The majority of their energy is thought to be derived from gravitational potential energy and SMBH spin as opposed to nuclear sources within stars.  It was in the late 1940s when the connection between cosmic radio waves and synchrotron emission was established. In AGN, Bremsstrahlung,  Synchrotron and Compton  emission processes are most common. Synchrotron radiation accounts for much of the radio emissions  in AGN. The jets of an  AGN is produce synchrotron radiation  due to near-relativistic electrons spiraling around magnetic field lines.  This process produces polarized radiation in  the presence direction of propagation  of the emitting electron. The torus emits unpolarized thermal radiation. It has been theorized that the ionized disk associated with the torus produces a varying  magnetic fields. Electrons moving at near field across its surface. The varying magnetic field then induces a large electric field which accelerates particles to  relativistic speeds speeds. These particles  spiral around along the  magnetic field lines. Synchrotron emission lines and produce synchrotron radiation. Within AGN the radiation  is observable as polarized emission. Astrophysical objects emit intense radio waves through emitted by a variety of sources, where some of  the synchrotron emission. sources are thermal and others non-thermal. \cite{Burke_1997} states that the relative strength of these sources depends on the orientation of the AGN. The overall spectrum however, can be represented by a simple power law.  It is widely held that radio sources in the Universe emit by the synchrotron process at lower radio frequencies in the meter and centimeter wavelength range.\cite{Wielebinski_2006} The radio core of an AGN emits synchrotron radiation emitted through particle acceleration and collimation into a double lobed structure. These are typical traits of radio galaxies. AGN also have a pair of jets of material ejected from their core. The structure of a radio source is also determined by the interaction of its energetic jets with ionized gas which surround the host galaxy. \cite{Krawczynski_2013} also observe that the black holes in AGN accrete matter and convert the gravitational energy of the accreted matter (and possibly also the rotational energy of the black hole) into mechanical and electromagnetic energy. We also have that inside the accretion disk, a fraction of the gravitational energy of the accreted material is converted to heat and electromagnetic radiation which is then radiated away by the accretion disk. The jets are formed from a portion of the material processed through the accretion disk which escapes the accretion system as collimated and uncollimated outflows. Jet plasma velocity can be denoted by v where $v = \beta_{jet}*c \approx c $ ,and c represents the speed of light. $\Gamma_{jet}$ , the bulk Lorentz factor of the plasma is given by $ \Gamma_{jet} = (1 - (\beta_{jet})^2 )^{-1/2}$ . Emissions from the jets can be red or blue-shifted as a result of the relativistic Doppler factor $\delta_{jet} = \frac{1}{\Gamma_{jet} \times (1- \beta_{jet}\times\cos{\theta})}$  Where $\theta$ is the angle between the jet axis and the line of sight as measured in the observer frame \cite{Krawczynski_2013}. The lobes as seen in Figure 5 develop when the jets are stopped by pressure from the gas surrounding the host galaxy. The lobe structure is fairly symmetrical when viewed closer to the nucleus of the galaxy.  \cite{Burke_1997} states that the lobes derive energy from the jets, as the jets dissipate into the lobes and the total energy in the lobes can reach up to $10^{53} J$.  Released gravitational energy of stellar material falling into a supermassive black hole is believed to be the main source of the galaxy’s energy. \cite{Mo_2009} theorizes that almost all spheroidal galaxy components (i.e., ellipticals and bulges) have a SMBH with a mass which correlated with that of the host galaxy, suggesting that the formation of SMBHs is related to the formation of their host galaxies.Fanaroff and Riley classification of radio galaxies groups them into two major categories FR-I and FR-II. The two catagories are based on whether radio-galaxies have edgedarkened (FR-I) morphologies or edge-brightened (FR-II) morphologies. (http://arxiv.org/pdf/1206.6893v1.pdf) believes that these morphologies arose from the interaction of jets and the material in their surrounding environment. Spectroscopy obeservations further reveal that FR-I radio galaxy hosts s exhibit optical spectra with only absorption lines, while FR-II hosts display mixed characteristicts. Some FR-II hosts are similar to FR-Is in that they only exhibit absorption lines ,but some others have spectra with strong high ionization emission lines.  (http://arxiv.org/pdf/1212.0667v3.pdf) states that the morphology of galaxies is closely related to their luminosities. It is said that Fanaroff and Rilley noted that the morphology of radio galaxies is dependent on their luminosities.