deletions | additions       diff --git a/section_Introduction_subsection_Galaxy_Evolution__.tex b/section_Introduction_subsection_Galaxy_Evolution__.tex  index 662819a..534b61c 100644  --- a/section_Introduction_subsection_Galaxy_Evolution__.tex  +++ b/section_Introduction_subsection_Galaxy_Evolution__.tex 
...
\subsection{Galaxy Evolution: from the Big Bang to present day}  The Big Bang was is  the birth of our Universe. The early state of the Universe was hot and dense. In this era, matter was coupled to radiation, according to early models of structure formation which assumed adiabatic initial conditions. The Universe expanded and temperature decreased, this occurred approximately 380 000 years after the Big Bang at a redshift of z = 1100 and is depicted in Figure 1. It is also theorized that matter and radiation became decoupled at this same time as well. Redshift (Z) (z)  is the increase of apparent wavelength of light coming toward an observer as the result of an object moving away from the observer where $1 + z = \frac{\lambda_{\rm obs}}{\lambda_{emit}}$. The radiation is a relic of the big-bang that is still observed today; it is called the Cosmic Microwave Background (CMB). The CMB is nearly isotropic blackbody radiation which expanded and cooled and fills the universe and is now at  $T_{0}=2.725 \pm 0.002 K$. \citet{Burke_1997} state that the isotropy of the CMB implies that sections of the Universe that were never in communication with one another have similar properties at the time of observation. Observations of the CMB communicate that the post Big Bang universe is a homogeneous, isotropic expanding or contracting universe, however this is not the reality of the Universe. It has been further theorized that current structure formation originated from quantum fluctuations. These fluctuations give rise to the measured temperature and density contrast seen in the CMB and large scale structure in a homogeneous isotropic universe \cite{Mo_2009}. \citet{Burke_1997} further state that the same fluctuations would have been imprinted on the radiation that we now see as the CMB. The quantum fluctuations resulted from regions whose density was slightly higher than the mean density of the universe. These regions of higher density attracted surrounding matter through gravity. As a result, slightly-denser regions attracted matter towards them and become even denser. Low-density regions on the other hand become even less dense because matter flows away from them. This amplification of quantum fluctuations is referred to as gravitational instability \cite{Mo_2009}. The initial fluctuations were the epicenters of the newly formed clumps of matter mainly made from hydrogen helium and ionized plasma. Thus initial perturbations are the building blocks of atomic nuclei and ionized plasma which combined via recombination to form neutral atoms, there is; however, gas clouds, stars, galaxies, and other astrophysical structures.  As There is  a result, slightly-denser regions attracted significant amount of  matter towards them in the universe, which is not directly detectable. Fritz Zwicky observed using the Doppler shift  andbecome even denser. Low-density regions on  the other hand become even less dense because virial theorem that the velocity spread within a cluster of galaxies implied that there was more mass than the luminous matter accounted for. Through further experimentation it was later concluded that baryons are set in  matter flows away from them. which does not interact with light, but whose effects are observed through gravitational interactions.  This amplification non-luminous matter is called dark matter. The nature  of quantum fluctuations dark matter  is referred still unknown; however, dark matter is largely expected  to as gravitational instability be a collision-less particle  \cite{Mo_2009}. The initial fluctuations were Dark matter influences how galaxies form and even their rotation as it is  the epicenters frame upon which the visible matter is embedded. The distribution  of galaxies also depends on  the newly formed clumps distribution  of dark  matter mainly made from hydrogen helium and ionized plasma. Thus initial perturbations are in  the building blocks universe. \citet{Burke_1997} state that dark matter may be hot or cold - allowing for different levels  of atomic nuclei and ionized plasma which combined via recombination to clustering in the Universe. The Hot Dark Matter (HDM) theory allows for a hierarchy in structure formation. The theory states that large scale structure such as the distribution of galaxies  form neutral atoms, there first due to the presence of hot dark matter. Cold dark matter  is ;however , gas clouds, stars, galaxies, and other astrophysical structures. theorized to be the seed for galaxy formation.  There is a significant amount Galaxies are formed from the mergers  of matter stellar material which result  in the universe, which is not directly detectable. Fritz Zwicky observed using the Doppler shift formation of systems of billions of stars, gas  and the virial theorem dust, held together by gravitational attraction. It has been shown  that under appropriate conditions,  the velocity spread process of gravitational collapse  within a cluster of galaxies implied that there was more mass than gaseous cloud,  the luminous matter accounted for. Through further experimentation cloud, or some part of  it was later concluded that baryons were set in matter which does not interact with light, but whose effects are observed through gravitational interactions. This non-luminous matter is called dark matter. The nature becomes unstable and begins to collapse if it lacks sufficient gaseous pressure support to balance the force  of dark matter is still unknown; however, dark matter gravity. The cloud  is largely expected to be stable for sufficiently small mass (at  a collisionless particle \cite{Mo_2009}. Dark matter influences how galaxies form given temperature  and even their rotation as it is the frame upon which radius), but once  the visible matter Jeans mass (a critical mass)  is embedded. The distribution of galaxies also depends on exceeded,  the distribution cloud begins a process  of dark matter in runaway contraction until an external unbalanced force can impede  the universe. \citet{Burke_1997} state collapse. \citet{Loeb_2010} states  that when an object above the Jeans mass collapses, the  dark matter may be hot or cold - allowing for different levels forms a halo inside  of clustering in which  the Universe. The Hot Dark Matter (HDM) theory allows for a hierarchy in structure formation. The theory states that large scale structure such as collapsed matter cools, condenses to  the distribution center  of galaxies the dark matter halo, and eventually  form first due stars. Dark matter is weakly interacting and is thus unable  to cool. Consequently,  the presence emergent structure  of hot a galaxy becomes one in which a central core that is occupied by stars and cold gas which is enclosed by  dark matter. Cold dark matter is theorized to be \citet{Loeb_2010} further states that a centrifugal force associated with  the seed for rotation of the galaxy’s center prevents the gas from collapsing into the center and forming a black hole. The gas later forms stars and a  galaxy formation. is born.  Galaxies are formed from the mergers of stellar material which result in the formation of systems of billions of stars, gas and dust, held together by gravitational attraction. It has been shown that under appropriate conditions, the process of gravitational collapse within a gaseous cloud, the cloud, or some part of it becomes unstable and begins to collapse if it lacks sufficient gaseous pressure support to balance the force of gravity. The cloud is stable for sufficiently small mass (at a given temperature and radius), but once the Jeans mass (a critical mass) is exceeded, the cloud begins a process of runaway contraction until an external unbalanced force can impedes the collapse. \citet{Loeb_2010} states that when an object above the Jeans mass collapses, the dark matter forms a halo inside of which the collapsed matter cools, condense to the center of the dark matter halo, and eventually form stars. Dark matter is weakly interacting and is thus unable to cool. Consequently the emergent structure of a galaxy becomes one in which a central core that is occupied by stars and cold gas which is enclosed by dark matter. \citet{Loeb_2010} further states that a centrifugal force associated with the rotation of the galaxy’s center prevents the gas from collapsing into the center and forming a black hole. The gas later forms stars and a galaxy is born.  Radiative cooling, star formation and supernova explosions processes that are also integral to the formation of a galaxy while processes such as accretion of gas, and galaxy mergers, govern the galaxy’s structure. These sets of processes together drive the formation and evolution of galaxies \cite{Ceverino_2009}.  Dark matter halos grow in hierarchy in the sense that larger halos are formed through the merging of smaller predecessors. Figure 2 illustrates the formation of a dark matter halo. From this hierarchical model, it can been seen that present formation and evolution of galaxies has its roots in the Big Bang.   Radiative cooling, star formation and supernova explosions processes that are also integral to the formation of a galaxy while processes such as accretion of gas, and galaxy mergers, govern the galaxy’s structure. These sets of processes together drive the formation and evolution of galaxies \cite{Ceverino_2009}.  \citet{Fanaroff_1974} classification of radio galaxies groups them into two major categories FR-I categories, FR-I,  and FR-II. The two categories are based on whether radio-galaxies have edge-darkened (FR-I) morphologies or edge-brightened (FR-II) morphologies. \citet{Saripalli_2012} believes that these morphologies arose from the interaction of jets (as depicted in Figure 4)and 4) and  the material in their surrounding environment. Spectroscopy observations further reveal that FR-I radio galaxy hosts exhibit optical spectra with only absorption lines, while FR-II hosts display mixed characteristics. 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. \citet{Singal_2014} states that the morphology of galaxies is closely related to their luminosities. It is said that \citet{Fanaroff_1974} noted that the morphology of radio galaxies is dependent on their luminosities. Since luminosity is in turn related to redshift, it is easy to confuse the effects due to luminosity as those due to redshift. \citet{Singal_2014} further discovered that FR-I and FR-II morphology is dependent only on luminosity and not redshift. \citet{Fanaroff_1974} observed that the luminosity of FR-I galaxies falls below a threshold luminosity at 1.4 GHz $ L_{1.4} = 2 \times 10^{25} W Hz^{-1}sr^{−1}$ . Studies have also shown that through optical observations we find most FR-II sources at find that at redshift ∼ 0.2 − 0.3 FR-II sources (\cite{Belsole_2007} , and references therein).