Data on the UBV system are presented for 14 quasistellar radio sources, 8 N galaxies,39 radio galaxies and 19 radioquiet galaxies south of +20° declination. Their positions in the two - color diagram show that the integrated colors of the radio galaxies are similar to those of the radioquiet galaxies of the same morphological type. In an absolute radio magnitude - radio index diagram a linear relation exists between M158 and ím158 Boo for radio galaxies of all classes. The QSO:s, however, do not follow this relation, and possible explanations are considered. The brightness and color distributions in the larger galaxies are described in detail. Our results are combined with other data for a discussion of the compositions of these systems. It is suggested that a fairly high amount of reddening occurs in the central regions of several galaxies, as for instance, in NGC 1068 and NGC 1316.

The question as to whether the distribution of radio loudness in active galactic nuclei (AGN) is actually bimodal has been discussed extensively in the literature. Furthermore, there have been claims that radio loudness depends on black hole mass and Eddington ratio. We investigate these claims using the low redshift broad line AGN sample of Greene & Ho 2007, which consists of 8434 objects at z < 0.35 from the Sloan Digital Sky Survey (SDSS) Fourth Data Release. We obtained radio fluxes from the Very Large Array Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) survey for the SDSS AGN. Out of the 8434 SDSS AGN, 846 have radio emission within 4" of the optical counterpart and are considered to be core emission. We also perform a systematic search for extended emission in FIRST that can be positively associated with the optical counterparts and find 51 out of the 846 previously detected core sources have extended emission that must be taken into account when calculating the total radio luminosity. Further, we find an additional 12 objects that have extended radio emission but no detectable radio core and have classic FR II type morphologies. Using these data, the question of radio bimodality and the dependence of radio-loudness on physical parameters are investigated for different subsets of the total sample. We find modest trends in the radio-loud fraction as a function of black hole mass and Eddington ratio, where the fraction of RL AGN increases for the largest black hole mass group and decreases with increasing Eddington ratio. With extended emission taken into account, we find strong evidence for a bimodal distribution in radio-loudness, where the lower radio luminosity core-only sources appear as a population separate from the extended sources with a dividing line at log(R) = 1.75. This dividing line is interesting in that it requires the radio luminosity to be 50 times the optical luminosity, ensuring that these are indeed the most RL AGN, which may have different or extreme physical conditions in their central engines when compared to the more numerous radio quiet AGN in this sample.

No description available.

>Magister Scientiae - MSc / Radio galaxies are some of the most unusual and powerful objects in the Universe and are therefore vital for so many reasons. Studies of Radio-Loud Active Galactic Nuclei (AGN) gives us the potential to enhance our understanding of the key processes leading to the ejection of material, connection to the central engine and how the jets are launched. Besides, the energetic input of these sources is thought to have an impact in the star formation history and properties of the ISM and ICM; thus by studying them, we can improve our understanding of their formation, evolution and their environment.

In this thesis I used a sample of radio galaxies with 1.4GHz radio luminosity, S1.4 > 10mJy, with the aim of finding high-redshift radio galaxies in the Lockman Hole, ELAIS-N1, ELAISN2, XMM-LSS and CDFS using near-infrared data from the Spitzer Space Telescope, and in the VIMOS4/SSA22 field using near-infrared data from the UKIRT Infrared Deep Sky Survey Deep Extragalactic Survey (UKIDSS-DXS). I used these near-infrared data to filter out low redshift (z < 2) radio galaxies by only including sources with either a very faint identification or non-detection in the K−band or at 3.6μm. I then applied a radio selection criteria based on the compactness of the radio structure in the FIRST survey, to ensure that it was possible to correctly associate a near-infrared identification if detected. Using these filtering critera I reduced the sample from 498 to 220, and I obtained spectroscopic observations for 46 of these. I successfully measured redshifts for 22 of these. Four of these sources were found to have redshifts at z > 3, thus proving the efficiency of the selection. Using these spectroscopically identified sources I investigated the correlation between radio luminosity and Lyα emission line luminosity and showed that these radio sources lie on the same correlations as their more radio-luminous counterparts, suggesting that accretion rate on to the central supermassive black hole determines the power of the AGN, both in terms of photoionizing radiation and radio power. I also investigated the near infrared properties of the host galaxy for these sources. Studying the 3.6μm magnitude versus redshift, I found that many of the radio galaxies in our sample lie on a similar relation as other powerful radio sources studied by different methods, although in my selection there is a bias to the fainter end of the distribution, likely due to the selection bias that I impose. The selection criteria has led us to report on the discovery of the highest redshift radio galaxy ever found, however the robustness of the redshift should be confirmed by follow up spectroscopy as the source has KAB magnitude of ∼ 20.7 which is in an area of the K − z diagram which makes it consistent with both z∼ 1 (in the case of [Oii]) and z ∼ 5 (in the case of Lyα). Finally I determined the number density of high-redshift sources in my sample at different epochs and show that the SKADS simulation is consistent with our observed radio galaxy sample. Using this knowledge I go on to predict the number of sources for current and future near-infrared surveys, where the future appears very bright for this kind of work.

"July 2003." / Bibliography: p. 203-211. / xxii, 211 p. : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Investigates properties of magnetic fields in galaxy clusters via both statistical Faraday rotation measures and diffuse source polarimetry, and investigates the nature and generation mechanisms for diffuse radio emission in the ACO cluster A3667. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 2003

In this thesis I investigate the hosts and cluster environments of a sample of 41 radio galaxies between z = 0.4 and z = 0.6. I use spectroscopic data for a 24 object subsample to investigate their star formation histories via the strength of the 4000A break. I find that the higher radio luminosity or high excitation objects in the sample have evidence for young stellar populations, but the lower radio luminosity or low excitation objects do not. My investigations into the Fundamental Plane (FP) of 18 of the radio galaxies, using the same spectroscopic data as well as data from the literature, show that the Fanaroff- Riley type I objects (FRIs) lie on the FP of local radio galaxies once corrected for passive evolution but the Fanaroff-Riley type II objects (FRIIs) do not. I suggest that an evolution in the size of the host galaxies, aided by a combination of passive evolution and a mass-dependent evolution in the mass-to-light ratios, may explain the observed offsets. Finally, I use wide field multi-band imaging to investigate the cluster environments of the full z ~ 0.5 sample. I find that the environmental overdensity is positively correlated with the radio luminosity and observe a greater number of close companions around the FRIIs than the FRIs (albeit with only nine FRIs in the sample). The cluster environments of the radio galaxies with the greatest host luminosities show tentative evidence for an alignment between the major axis of a galaxy and that of its cluster, whilst there are hints that the objects with the highest radio luminosities have clusters whose major axis is aligned with the position angle of the radio jet. My results suggest a picture in which FRII type radio sources reside in particularly rich cluster environments at z ~ 0.5 but FRI type radio sources in less rich environments. The environment plays a key role in determining both the radio properties of the galaxy and the evolution of its host. The effect of the environment on the emission line properties and star formation histories of the galaxies leads to the overlap seen in the morphological and spectral properties of radio galaxies.

My Ph.D. has been composed of work involving the use of far–IR and submm observations of AGN. During this time it has focused on the in- terplay between AGN and their host galaxies and cluster environments. Understanding the role of AGN, and how they affect the evolution of both their host galaxies and surrounding environments, is a pressing concern in cosmological models of the universe, affecting as they do the chemical makeup, star formation rate, and morphology of their host galaxies. In Chapter 2, we focus on attempting to determine whether there is an inherent physical difference between Broad Absorption Line Quasars and non–BAL QSOs using Herschel observations taken at 250, 350 and 500 μm as part of the H–ATLAS (Eales et al. 2010) survey. BAL QSOs have been considered the most visible form of AGN feedback, and therefore are a prime starting point for understanding how galaxy evolution may be affected by the presence of an AGN. By using matched samples of 50 BAL and 329 non–BAL QSOs, we create weighted stacks at each wavelength, finding similar far–IR flux–densities for each sample within the errors. By SED modelling using a simple modified black body (Hildebrand 1983) fit to Mrk 231 and IZw1, we derive likely upper and lower limits for the BAL and non–BAL QSOs in each wavelength, again finding they are consistent within the errors. A bevy of statistical tests run on either population similarly finds no evidence to reject the null hypothesis they are drawn from the same parent population. These results would imply that HiBAL QSOs can be unified with ordinary QSOs within a simple orientation dependent scheme. We cannot make the same distinction for LoBALs or FeLoBALs, which the literature suggests may well be a separate evolutionary phase. In Chapter 3, we determine whether the presence of an AGN correlates to an overdensity of star–forming galaxies in the FIR, as has been found at shorter wavelengths (Falder et al. 2010). For the SHAGs study, 171 AGN were observed and selected at z∼1. By using observations at 250 μm, we are able to trace close to the peak of the grey–body SED created by reprocessing by dust of radiation from young O and B stars. Following data reduction, we determine number counts and correct for completeness within a 1Mpc radius of the central AGN. We find an overdensity on the order of around 0.4 sources per AGN, implying a degree of activity already significantly lower than at higher redshifts. This overdensity appears to be somewhat different between RL AGN and RQQ within 1Mpc. A cor- relation is found between radio luminosity and star formation overdensity, consistent with a stronger dependence found by Falder et al. (2010) at 3.6 μm, and there also appears to be a correlation between stellar mass and star formation overdensity for radio–loud QSOs. The galaxies in the environs of the AGN have LIRG–level luminosities, and are likely the pro- genitors of modern day S0 galaxies, whose population increases steadily from z∼1 to the present day (Postman et al. 2005; Smith et al. 2005). Our work with SCUBA–2, presented in Chapter 4, follows on from a prior sample of X–ray–absorbed QSOs (Stevens et al. 2005). This new sample is composed of more highly–absorbed X–ray QSOs and covers a larger area than the initial sample, so is ideal for an analysis of source counts around AGN at high–redshift. Data from the JCMT have been reduced, and completeness corrections and flux corrections applied to catalogues to determine the number counts around AGN. A comparison background, created using data from the Cosmology Legacy Survey has been used to derive comparison counts. The AGN have been investigated, yet none are detected above 3 at 850 μm, in contrast to the original sample. This may suggest that star formation in their host galaxies has been suppressed. Upon stacking in redshift and BAL classification, no difference in flux– density is apparent and the sources studied here have a similar stacked submm output to an unabsorbed QSO sample created for the original X– ray absorbed QSOs. However, over half of the sources here are BAL QSOs in contrast to the original absorbed QSO sample which contained only 1 BAL QSO. From the work in Chapter 2, one might expect BAL and non–BAL QSOs to have similar flux–densities. We argue that the sources studied in this thesis have likely undergone rapid evolution owing to a strong outflow, and as such star formation has been suppressed sufficiently that the submm emission is below the confusion noise. BAL winds may still be present, but essentially, the show is already over. A similar mechanism may already have occurred in unabsorbed QSOs if all QSOs pass through an X–ray–absorbed phase. With regard to source counts, we find that there is tentative evidence for an overdensity of sources around these AGN. The SFRs of the companion sources have been calculated using several greybody analogues, all of which imply a high degree of activity, suggesting these fields will evolve to become some of the most massive regions at the present epoch, in keeping with current theories of SMGs and high–redshift clusters.

In this thesis I use X-ray observations to study the cores and extended structures of radio-loud AGN, to determine their structure, accretion properties and the impact they have on their surroundings. I use new Chandra data and archival XMM-Newton observations ofMarkarian 6 to look for evidence of emission from shocked gas around the external radio bubbles, using spatially resolved regions in Chandra and spectral analysis of the XMM data. The results show that the bubbles in Mrk 6 are indeed driving a shock into the halo of the host galaxy, with a Mach number of 3.9. I also find that the spectrum of the AGN has a variable absorbing column, which changes from 8 × 1021 atoms cm−2 to 3 × 1023 atoms cm−2 on short timescales (2-6 years). This is probably caused by a clump of gas close to the central AGN, passing in front of us at the moment of the observation. Using new and archival Chandra observations of the Circinus galaxy, I match them to pre-existing radio, infrared and optical data to study the kpc-scale emission. As for Mrk 6, I find that the radio bubbles in Circinus are driving a shock into the interstellar medium of the host galaxy, with Mach numbers M 2.7–3.6 and M 2.8–5.3 for the W and E shells respectively. Comparing the results with those we previously obtained for Centaurus A, NGC 3801 and Mrk 6, I show that the total energy in the lobes (thermal+kinetic) scales approximately with the radio power of the parent AGN. The spatial coincidence between the X-ray and edge-brightened radio emission in Circinus resembles the morphology of some SNR shocks, a parallel that has been expected for AGN, but has never been observed before. I investigate what underlying mechanisms both types of systems may have in common, arguing that, in Circinus, the edge-brightening in the shells may be accounted for by a B field enhancement caused by shock compression, but do not preclude some local particle acceleration. I also carry out a systematic study of the X-ray emission from the cores in the 0.02 < z < 0.7 2Jy sample, using Chandra and XMM-Newton observations. I combine the results with the mid-IR, optical emission line and radio luminosities, and compare them with those of the 3CRR sources, to show that the low-excitation objects in our sample show all the signs of radiatively inefficient accretion. I study the effect of the jet-related emission on the various luminosities, confirming that it is the main source of soft X-ray emission for our sources. I also find strong correlations between the accretion-related luminosities, and identify several sources whose optical classification is incompatible with their accretion properties. I derive the bolometric and jet kinetic luminosities for the sample and find a difference in the total Eddington rate between the low and high-excitation populations, with the former peaking at 1 per cent and the latter at 20 per cent Eddington. There is, however, an overlap between the two, indicating that a simple Eddington switch may not be possible. The apparent independence of jet kinetic power and radiative luminosity in the highexcitation population in our plots allows us to test the hypothesis in which jet production and radiatively efficient accretion are in fact independent processes that can coexist in high-excitation objects.

Active galactic nuclei (AGN) jets are energetic phenomena where twin jets of plasma emerge perpendicular to the plane of the accretion disk surrounding supermassive black holes in galactic centers. Radio-loud jets are largely divided into classes based on the angle of observation (blazars versus radio galaxies), spectral line widths (Flat Spectrum Radio Quasars/FSRQs versus BL Lac objects/BL Lacs), and location of the synchrotron peak frequency in their spectral energy distribution (high-spectral peaked/HSP, intermediate-spectral peaked/ISP, or low-spectral peaked/LSP).<br><br>The linear fractional polarization of the radio emission and the direction of the polarization plan (electric vector position angle, "EVPA'') can be measured, providing information on the properties of the jets' magnetic field. This study uses and describes some processing of data from the MOJAVE program, taken with the VLBA at 15 GHz, to investigate the polarization behavior of 387 AGN. <br><br>The most polarized jets have good alignment between the EVPA and the local jet direction, and higher stability in both fractional polarization and the EVPA. This characterization best describes BL Lacs, which are notably different from FSRQs. HSP BL Lacs have lower fractional polarization than LSP BL Lacs, with fractional polarization partially dependent on apparent jet speeds. These results have supported a scenario where HSP BL Lacs and LSP BL Lacs are similar objects with differing relativistic beaming factors, while FSRQs and BL Lacs as a class have inherent differences in the makeup of their magnetic fields.