For a general, non-technical (and more colourful!) overview of my research interests, click here
I lead A&A group research in cosmology and have a strong
interest in cosmological applications of gravitational wave astronomy, using
ground- and space-based laser interferometric detectors -- particularly
LISA. I also work on stellar
astrophysics applications of gravitational
lensing.
A common theme to almost all of my research is how to get the best out of
sparse and noisy datasets -- particularly using the methodology of Bayesian
inference. Listed below are brief summaries
of my past and present research topics, together with links to some of
my published work.
| Distance Estimation and Malmquist Bias
For a number of years I have studied intensively the impact of observational selection effects - known generically in the literature as Malmquist bias - on galaxy distance indicators. This topic was the central theme of my PhD thesis (one of the last of the pre-latex era!) supervised at Glasgow by John Simmons, and continues to spawn a number of research papers and review articles. |
The Galaxy Density and Velocity Fields
Another major theme of my research has been the reconstruction of the large-scale density and velocity field from galaxy redshift and redshift distance surveys. With John Simmons, Andrew Newsam and Stephane Rauzy, I have developed various techniques for eliminating systematic biases from the reconstructed fields, with application to e.g. POTENT and VELMOD. Recently I wrote an invited review of this topic. |
| Estimating the Hubble Parameter
With Stephane Rauzy, Simon Goodwin and John Gribbin, I have developed a powerful, robust statistical technique for estimating the Hubble parameter from redshift-distance data. This method is fully non-parametric and circumvents completely the problem of Malmquist bias corrections. We have applied it using HST calibrating galaxies to obtain improved estimates from galaxy linear diameters and Tully-Fisher data, and are currently extending the method to other indicators. |
Testing Velocity Field Models
With Stephane Rauzy I have developed a robust method for comparing velocity field models with galaxy peculiar velocity estimates. The method makes minimal assumptions about the galaxy luminosity function and spatial distribution, and is completely free from Malmquist bias. We have applied it to estimate the linear bias parameter from MarkIII and IRAS data. With Kenton D'Mellow we are extending the method to develop diagnostics of large scale bulk flow motions. |
| Optimal Representation of the Density Field
With Elke Schumacher and Stephane Rauzy I have developed a new orthogonalisation procedure to deal with the effects of an angular mask and radial selection function, in determining the galaxy density field from e.g. the PSCz survey. With Kenton D'Mellow we are extending the method to deal with redshift space distortions. |
Cepheids as Distance Indicators
With Shashi Kanbur and Nial Tanvir I am studying methods to improve the accuracy and calibration of Cepheid variables as extragalactic distance indicators. This work has focussed on the physical properties of Cepheids at maximum light and applied principal component analysis to reconstruct Cepheid light curves from sparse and noisy data. We have also recently applied principal component analysis to Cepheid light curves as a more effective probe of their physical properties. |
| Building Galaxy Models
With Gail Penny, Amr El-Zant and Alejandro Gonzalez I have developed a new algorithm for building self-consistent density potential pairs in galaxy disk-halo models. This method uses Monte Carlo integration and dynamical systems theory to map more efficiently the phase space structure of orbits in the disk-halo models. I will soon begin work with Lyndsay Fletcher and Iain Hannah applying the method to trace chaotic trajectories in solar flare modelling. |
Testing Models of the Galaxy Luminosity Function
With Stephane Rauzy and Kenton D'Mellow I have developed a new, robust method for reconstructing the galaxy LF from redshift survey data, combining the statistical efficiency of maximum likelihood with the efficacy of goodness-of-fit tests. We are adapting the method to develop diagnostics of luminosity evolution, and with David Valls-Gabaud we are adapting it to study the stellar LF derived from Hipparcos data. |
| Microlensing of Extended Sources - I
With Helen Bryce and David Valls-Gabaud I am investigating the use of gravitational microlensing as a probe of stellar atmosphere models and a means of "gravitationally imaging" stellar photospheres. We are studying the photometric and spectroscopic signatures of e.g. starspots on cool giants, lensed by point and fold caustic events, and investigating the sensitivity of microlensing as a test of "Next Generation" atmosphere models, using data from monitoring programs such as PLANET. |
Microlensing of Extended Sources - II
With Helen Bryce and Rico Ignace I am studying the spectroscopic signatures of extended source microlensing events as a diagnostic of cirucmstellar envelopes and stellar winds. Microlensing can, for example, discriminate between rotating and expanding winds from the shape of emission line profiles. We have also developed a general procedure for inverting the emission profiles of lines of arbitrary optical depth in e.g. supernovae ejecta undergoing homologous expansion. |
| Non-Standard Cosmological Models
With Mariusz Dabrowski I have investigated the compatibility of non-uniform pressure Stephani model universes with high-redshift surpernovae data, exploring the relation between the geometry of the Universe and the "exotic matter" source of the pressure. With Barry Suprenant I am now developing general non-parametric techniques for inferring the equation of state of exotic matter from supernovae data. |
Improving the Tully-Fisher Relation
With Paolo Salucci and Massimo Persic I have studied methods for improving the accuracy and physical basis of spiral galaxy distance indicators, by incorporating rotation curve shape information into the conventional Tully-Fisher relation. Using the "Universal Rotation Curve" model, we explored the impact of shape information on the TF relation for the Mathewson spirals sample. |
| Statistical Properties of X-Ray Binaries
With Rob Fender I have investigated a very interesting property of a large sample of persistent Galactic X-Ray binary sources: their apparent brightnesses are well-fitted by a rather narrow luminosity function, which places strong statitistical constraints on the possible role of relativistic beaming for these systems. |
Estimating Open Cluster Distances
With Mark O' Dell and Andrew Collier Cameron I developed a powerful new method for estimating open cluster distances from studying the rotational modulation - due to starspots - of rapidly rotating G dwarfs. This work has also led to studies of photometric modulation as a stellar activity indicator, and a probe of the starspot distribution. |
| Cosmochronology
With Khalil Chamcham I have studied the impact of dynamical threshold star formation models on age estimates of the galactic disk, asking the questions: do threshold models result in a significant delay before the onset of star formation in the solar neighbourhood, and how does this affect age estimates for the galaxy? |
The Age of the Universe
With the late Roger Tayler I wrote an invited review of the Age of the Universe, assessing constraints on this parameter from cosmology and stellar evolution, and addressing what (at least at that time!) cosmologists identified as the "Age Paradox" of globular clusters appearing to be older than the Universe. |
Click here to see a brief CV and complete list of publications