The cluster environments of radio-loud AGN

Copyright IAURadio-loud AGN play an important role in galaxy evolution. We need to understand their properties, and the processes that affect their behaviour in order to model galaxy formation and development. We here present preliminary results of an investigation into the cluster environments of radio galaxies. We have found evidence of a strong correlation between radio luminosity and environment richness for low excitation radio galaxies, and no evidence of evolution of the environment with redshift. Conversely, for high excitation radio galaxies, we found no correlation with environment richness, and tentative evidence of evolution of the cluster environment

FR II radio galaxies at low frequencies I : morphology, magnetic field strength and energetics

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. ©: 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.Due to their steep spectra, low-frequency observations of FR II radio galaxies potentially provide key insights in to the morphology, energetics and spectrum of these powerful radio sources. However, limitations imposed by the previous generation of radio interferometers at metre wavelengths has meant that this region of parameter space remains largely unexplored. In this paper, the first in a series examining FR IIs at low frequencies, we use LOFAR observations between 50 and 160 MHz, along with complementary archival radio and X-ray data, to explore the properties of two FR II sources, 3C452 and 3C223. We find that the morphology of 3C452 is that of a standard FR II rather than of a double-double radio galaxy as had previously been suggested, with no remnant emission being observed beyond the active lobes. We find that the low-frequency integrated spectra of both sources are much steeper than expected based on traditional assumptions and, using synchrotron/inverse-Compton model fitting, show that the total energy content of the lobes is greater than previous estimates by a factor of around 5 for 3C452 and 2 for 3C223. We go on to discuss possible causes of these steeper than expected spectra and provide revised estimates of the internal pressures and magnetic field strengths for the intrinsically steep case. We find that the ratio between the equipartition magnetic field strengths and those derived through synchrotron/inverse-Compton model fitting remains consistent with previous findings and show that the observed departure from equipartition may in some cases provide a solution to the spectral versus dynamical age disparity.Peer reviewe

The epoch and environmental dependence of radio-loud active galaxy feedback

This thesis contains the first systematic X-ray investigation of the relationships between the properties of different types of radio-loud AGN and their large-scale environments, using samples at two distinct redshifts to isolate the effects of evolution. I used X-ray observations of the galaxy clusters hosting the radio galaxies to characterise the properties of the environments and compared them with the low-frequency radio properties of the AGN. I found a strong relationship between radio luminosity and ICM richness for lowexcitation radio galaxies (LERGs) but not for high-excitation radio galaxies (HERGs), and tentative evidence of evolution of the environment for HERGs, but not for LERGs.I then used the X-ray emission from the lobes of the FRII galaxies in the samples to calculate their internal pressures, finding them to be at slightly higher pressures than predicted by equipartition and near pressure balance with their external environment at the lobe mid-points. I made the first estimates of lower limits for lobe-tip Mach numbers for a large sample of lobes; suggesting that about half the lobe tips were driving strong shocks.Finally I verified that the correlation between LERG radio luminosity and cluster X-ray luminosity is not caused by a common correlation with black hole mass, and also found no evidence that HERG properties are affected by ICM richness, adding evidence for theories of local fuelling for HERGs. I found evidence that HERGs should have a strong relationship between jet power and radio luminosity, but that LERG jet power must be subject to factors additional to black hole mass. I also found evidence that the same mass black hole is associated with lower radio luminosities in FRI morphology galaxies than in FRIIs, perhaps as a result of the higher proton content of FRI jets leading to lower radiative efficiency

Speed and accuracy of head- and eye-based aiming systems at high vertical acceleration

BACKGROUNDThe benefits of using a head tracker in a fast jet to aim weapons and control sensor direction have been amply demonstrated, but head direction is difficult to control at high G. An experiment was conducted to assess whether aiming using the eye, rather than the head, might be advantageous.METHODSA centrifuge provided sustained accelerations of up to 8 Gz. Participating aircrew were asked to point at static targets using head- or eye-aiming, maintain the acquisition while the target was lit, and then transfer to the next target as quickly as possible. A helmet-mounted scene camera recorded the subject's view of the target board. A laser mounted by the scene camera was used for head-aiming and to determine head direction. The eye tracker camera and illuminator were also helmet-mounted. The eye and scene images were recorded and analyzed off-line.RESULTSEye-aiming acquisition times and accuracy were affected only slightly by Gz; however, both head-aiming speed and accuracy deteriorated as Gz increased. Eye-aiming was substantially faster than head-aiming at all Gz levels, but head-aiming was more accurate under these experimental conditions. Subjective ratings supported the objective data. A majority of subjects preferred eye to head as an aiming mechanism.CONCLUSIONSEye-aiming was faster and easier to use than head-aiming at all Gz levels, and particularly at high Gz