We present distances and kinematics and look at the possible populations for the blue plume (BP) stars in the Canis Major Overdensity (CMa). We conducted a medium resolution spectral survey on the BP stars (N=303) in CMa (centered at l = 238° ; b = -8°) using the data from AAOmega Spectrograph. We used a modified version of the Statistics-sensitive Non-linear Iterative Peak-clipping (SNIP) algorithm to normalize our fluxed absorption spectra. After determining the radial velocities from measurements of strong absorption features for the stars we use a Bayesian analysis of spectral feature strengths and photometric colors to determine Teff, Logg and [Fe/H]. Our procedure makes use of grid for model synthetic spectra computed using SPECTRUM with Atlas9 model atmospheres and Kurucz model colors. We determine the absolute magnitude using the stellar parameters and BaSTI isochrones and compute distances and ages for the BP stars. Our analysis of the BP stars indicates Teff ranging from 6500K to 8000K, metallicity ranging from 0.0 to -1.0 with an average of -0.5. We found for this temperature range that the surface gravity of the stars could not be well constrained. From the spatial and kinematics results we found that most of the stars are thick disk stars with a small mixture of thin disk stars. The stars are most likely a mixture of thick disk blue stragglers and normal A-type stars preferentially seen to greater depths due to the low dust extinction in this location of the Galaxy.

The work contained within this thesis Is made up primarily of two pieces Both address active galactic nuclei And the galaxies that live nearby The obscured fraction of the population Is the topic of one publication And the type-II fraction in the optical regime In chapter four this is the theme I research the vicinity overdensity Around radio galaxies in chapter three, you’ll see I reduce some spectra at redshift one But not all observations in the end got done With the spectra I have I do what I can As if all target observations had actually ran In the end I conclude with results and the theme of research to be done further downstream. The works contained herein addresses two major topics in extragalactic astrophysics, namely the Type-II AGN fraction and the Overdensity-Radio power relation. Quantifying the Type-II AGN fraction has been attempted by many works in many different observational regimes, finding rather contrasting results. Accretion onto supermassive black holes contributes between 5 per cent and 20 per cent of the luminosity of the Universe, and seems to be closely linked to star formation processes. The large uncertainty on this value is due to the ill-determined contribution from obscured accretion, namely the Type-II fraction. In Chapters 3 and 4 I address this issue from a theoretical standpoint in the X-ray regime and an observational standpoint in the optical regime respectively. In Chapter 3 I show how crude X-ray spectroscopy of partially obscured AGN can lead to catastrophic underestimations of the intrinsic X-ray luminosity of these sources. Acting over an entire population, these partial obscurers can produce an obscured AGN fraction which decreases as a function of observed luminosity. The results are consistent with observations in the X-ray vs. IR luminosity of AGN classes. In Chapter 4 I select a statistically significant sample of AGN from an unbiased 250μm galaxy sample. After spectroscopic classification I find the optical Type- II AGN fraction to be consistent across several decades in [OIII] luminosity, a common proxy for intrinsic AGN luminosity. I also investigate the relation of AGN activity to host galaxy mass, as well as star formation activity and star formation history. Probing the environments of protoclusters will help to constrain the models of structure formation in the Universe. Until now, no dataset has been big enough to probe the environments of high redshift radio galaxies at a statistical level; While many believe that the feedback processes of high luminosity radio jets will have a direct impact on star formation in the surrounding medium it has not been tested. In Chapter 2 I investigate this on an statistical level, finding no meaningful correlation between radio galaxy radio power and source overdensity in the vicinities of these sources. In Chapter 5 I discuss the reduction of a 24μm sample at redshift z ∼ 1 for direct comparison with a local 12μm sample. With only a fraction of the target sample being observed, no statistically significant results could be derived, but the objects are spectroscopically classified and spectroscopic redshifts are measured where possible. Correlations in the data set are investigated and the limitations of the sample selection strategy are discussed.