Tim Pearson
Senior Research Associate, Astronomy, Caltech
Research
My research interests include radio interferometry and its
application to observations of active galactic nuclei and the
cosmic microwave background radiation.
The Cosmic Microwave Background Radiation
Together with Professor Tony Readhead and Dr Steven Padin, I am
working on a project to design, construct and operate a
ground-based radio interferometer array, called the Cosmic
Background Imager, to measure the very small brightness
fluctuations in the 2.7 K cosmic microwave background radiation, a
relic of the early, hot universe. In the standard models for the
formation of structure (galaxies and clusters) in the universe, the
angular power spectrum of these fluctuations carries information
that should allow us to measure the major cosmological parameters
(such as the density parameter, the baryon fraction, and the
expansion rate of the universe) with high precision.
Active Galaxies and Quasars
Very-Long-Baseline Interferometry (VLBI) is a technique that can
make images of astronomical radio sources with milli-arcsecond
resolution - the highest resolution obtainable in any wave band -
corresponding to scales of only a few light-years in high-redshift
quasars. With such high resolution, we can see changes in the
structure of the emitting regions on time-scales of a year or less.
VLBI was pioneered at Caltech using ad hoc networks of antennas
around the world, including the 40-meter antenna at the Owens
Valley Radio Observatory, and special-purpose correlators in
Pasadena to process the signals recorded on magnetic tape. The ad
hoc networks are now superseded by the Very Long Baseline Array
(VLBA), operated by the National
Radio Astronomy Observatory. This dedicated array provides data
of high quality and much more observing time, and makes possible
many exciting new observations such as the imaging of polarization
from the jets of active galaxies and quasars. In collaboration with
colleagues at Caltech, Jodrell Bank (England), and elsewhere, I am
using VLBI to make images in several radio wave bands of the
structure of the nuclei of active galaxies and quasars. We have
concentrated on large, complete samples so that we can make a
useful statistical study. Among the discoveries we have made are
that most active nuclei contain well-collimated, one-sided radio
jets and that many show apparent ``superluminal'' expansion. Both
these phenomena are consistent with highly relativistic ejection of
material along a jet pointed almost directly toward the observer.
These discoveries have led to the widespread acceptance of the idea
that the ``central engine'' in these objects is associated with a
very massive black hole, and to the development of ``unified
theories'' of active galaxies and quasars, in which the primary
difference between quasars and radio galaxies is in their
orientation relative to the observer. A recent discovery is a group
of compact symmetrical objects which are apparently not dominated
by relativistic motion; these are almost certainly young objects
(about 1000 years old) and they illuminate the early stages of the
evolution of radio galaxies and quasars.
Gravitational Lensing
The gravitational field of intervening galaxies can distort or
split the images of distant galaxies and quasars. I am part of a
world-wide group conducting the Cosmic Lens All-Sky Survey (CLASS):
a search for new such ``gravitational lenses.'' Observations of
gravitational lenses can place strong constraints on the Hubble
constant and other cosmological parameters. We have made images of
about 10,000 flat-spectrum radio sources, using the Very Large
Array and other telescopes, and we identify lenses by looking for
achromatic splitting of the images into double or more complex
structures. This project has already found several new lensed
systems and many promising candidates.
Software
In my spare time, I develop and maintain a subroutine library
for creation of scientific graphics which is used by astronomers
and other scientists worldwide.
Publications
A complete list of my published
papers, including links to online abstracts or text where
available.
