Generative deep fields : arbitrarily sized, random synthetic astronomical images through deep learning

© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.Generative Adversarial Networks (GANs) are a class of artificial neural network that can produce realistic, but artificial, images that resemble those in a training set. In typical GAN architectures these images are small, but a variant known as Spatial-GANs (SGANs) can generate arbitrarily large images, provided training images exhibit some level of periodicity. Deep extragalactic imaging surveys meet this criteria due to the cosmological tenet of isotropy. Here we train an SGAN to generate images resembling the iconic Hubble Space Telescope eXtreme Deep Field (XDF). We show that the properties of 'galaxies' in generated images have a high level of fidelity with galaxies in the real XDF in terms of abundance, morphology, magnitude distributions and colours. As a demonstration we have generated a 7.6-billion pixel 'generative deep field' spanning 1.45 degrees. The technique can be generalised to any appropriate imaging training set, offering a new purely data-driven approach for producing realistic mock surveys and synthetic data at scale, in astrophysics and beyond.Peer reviewe

Breast cancer detection using microwave holography

Breast cancer is one of the most common forms of cancer in women. X-ray mammography is the most widely used technique for early detection but has limitations. In this paper, an alternative approach for breast cancer detection using microwave imaging is presented. This is based upon microwave indirect holographic approach, central to which is the use of a synthetic reference beam. This approach has benefits in terms of simplicity and expense. Experimental results using a simple breast phantom are included to demonstrate the potential of this approach

A Test for Large-Scale Systematic Errors in Maps of Galactic Reddening

Accurate maps of Galactic reddening are important for a number of applications, such as mapping the peculiar velocity field in the nearby Universe. Of particular concern are systematic errors which vary slowly as a function of position on the sky, as these would induce spurious bulk flow. We have compared the reddenings of Burstein & Heiles (BH) and those of Schlegel, Finkbeiner & Davis (SFD) to independent estimates of the reddening, for Galactic latitudes |b| > 10. Our primary source of Galactic reddening estimates comes from comparing the difference between the observed B-V colors of early-type galaxies, and the predicted B-V color determined from the B-V--Mg_2 relation. We have fitted a dipole to the residuals in order to look for large-scale systematic deviations. There is marginal evidence for a dipolar residual in the comparison between the SFD maps and the observed early-type galaxy reddenings. If this is due to an error in the SFD maps, then it can be corrected with a small (13%) multiplicative dipole term. We argue, however, that this difference is more likely to be due to a small (0.01 mag.) systematic error in the measured B-V colors of the early-type galaxies. This interpretation is supported by a smaller, independent data set (globular cluster and RR Lyrae stars), which yields a result inconsistent with the early-type galaxy residual dipole. BH reddenings are found to have no significant systematic residuals, apart from the known problem in the region 230 < l < 310, -20 < b < 20.Comment: 8 pages, PASP, in press (Jan 1999

The Restructuring and Privatisation of British Rail: Was it really that bad?

Following the government�s decision to place Railtrack into administration (October 2001), attention has focused on what went wrong with privatisation, and how crucial network investment will be financed in future. This paper uses a social cost-benefit analysis framework to assess whether the restructuring and privatisation of British Rail has produced savings in operating costs. The paper shows that major efficiencies have been achieved, consumers have benefited through lower prices, whilst the increased government subsidy has been largely recouped through privatisation proceeds. We find that output quality has also improved (pre-Hatfield). The achievement of further savings will be key to delivering improved rail services in the future. This paper finds that a privatised structure, where shareholders demand a return on their investment, has led to significant improvements in operating efficiency - it remains to be seen whether the new regime, with a not-for-profit infrastructure owner, will deliver the same efficiency improvements

Traffic Control and Route Choice; Capacity Maximization and Stability

Peer reviewedPublisher PD

Line Emission in the Brightest Cluster Galaxies of the NOAO Fundamental Plane and Sloan Digital Sky Surveys

We examine the optical emission line properties of Brightest Cluster Galaxies (BCGs) selected from two large, homogeneous datasets. The first is the X-ray selected National Optical Astronomy Observatory Fundamental Plane Survey (NFPS), and the second is the C4 catalogue of optically selected clusters built from the Sloan Digital Sky Survey Data Release ~3 (SDSS DR3). Our goal is to better understand the optical line emission in BCGs with respect to properties of the galaxy and the host cluster. Throughout the analysis we compare the line emission of the BCGs to that of a control sample made of the other bright galaxies near the cluster centre. Overall, both the NFPS and SDSS show a modest fraction of BCGs with emission lines (~15%). No trend in the fraction of emitting BCGs as a function of galaxy mass or cluster velocity dispersion is found. However we find that, for those BCGs found in cooling flow clusters, 71^{+9}_{-14}% have optical emission. Furthermore, if we consider only BCGs within 50kpc of the X-ray centre of a cooling flow cluster, the emission-line fraction rises further to 100^{+0}_{-15}%. Excluding the cooling flow clusters, only ~10% of BCGs are line emitting, comparable to the control sample of galaxies. We show that the physical origin of the emission line activity varies: in some cases it has LINER-like line ratios, whereas in others it is a composite of star-formation and LINER-like activity. We conclude that the presence of emission lines in BCGs is directly related to the cooling of X-ray gas at the cluster centre.Comment: Accepted for publication in MNRAS. 13 pages mn2e style with 7 figures and 2 table

Ages and metallicities of faint red galaxies in the Shapley Supercluster

We present results on the stellar populations of 232 quiescent galaxies in the Shapley Supercluster, based on spectroscopy from the AAOmega spectrograph at the AAT. The key characteristic of this survey is its coverage of many low-luminosity objects (sigma ~ 50 km/s), with high signal-to-noise (~45 per Angstrom). Balmer-line age estimates are recovered with ~25% precision even for the faintest sample members. We summarize the observations and absorption line data, and present correlations of derived ages and metallicities with mass and luminosity. We highlight the strong correlation between age and alpha-element abundance ratio, and the anti-correlation of age and metallicity at fixed mass, which is shown to extend into the low-luminosity regime.Comment: Four pages, three figures; To appear in Proceedings of IAU Symp. 245 "Formation and Evolution of Galaxy Bulges", (Oxford, July 16-20 2007), Eds. Martin Bureau, Lia Athanassoula, and Beatriz Barbu

Big Bang Nucleosynthesis with Independent Neutrino Distribution Functions

We have performed new Big Bang Nucleosynthesis calculations which employ arbitrarily-specified, time-dependent neutrino and antineutrino distribution functions for each of up to four neutrino flavors. We self-consistently couple these distributions to the thermodynamics, the expansion rate and scale factor-time/temperature relationship, as well as to all relevant weak, electromagnetic, and strong nuclear reaction processes in the early universe. With this approach, we can treat any scenario in which neutrino or antineutrino spectral distortion might arise. These scenarios might include, for example, decaying particles, active-sterile neutrino oscillations, and active-active neutrino oscillations in the presence of significant lepton numbers. Our calculations allow lepton numbers and sterile neutrinos to be constrained with observationally-determined primordial helium and deuterium abundances. We have modified a standard BBN code to perform these calculations and have made it available to the community.Comment: 9 pages, 5 figure

Problems in merging Earth sensing satellite data sets

Satellite remote sensing systems provide a tremendous source of data flow to the Earth science community. These systems provide scientists with data of types and on a scale previously unattainable. Looking forward to the capabilities of Space Station and the Earth Observing System (EOS), the full realization of the potential of satellite remote sensing will be handicapped by inadequate information systems. There is a growing emphasis in Earth science research to ask questions which are multidisciplinary in nature and global in scale. Many of these research projects emphasize the interactions of the land surface, the atmosphere, and the oceans through various physical mechanisms. Conducting this research requires large and complex data sets and teams of multidisciplinary scientists, often working at remote locations. A review of the problems of merging these large volumes of data into spatially referenced and manageable data sets is presented