I am a Professor of Physics and Head of
Astronomy in the Department of Physics at Durham University. I was previously a Professorial
Fellow
supported through a Royal Society University Research
Fellowship at Durham University. I am based
in the Institute for Computational Cosmology within the
Ogden
Centre for Fundamental Physics. My research
concentrates on the evolution of galaxies and the growth of structure in the Universe.
I use two approaches to address questions in these fields.
Firstly, I work with multiwavelength datasets to gain new insights
into galaxy formation and evolution
by contrasting the views provided by radiation
emitted in different
wavebands (in particular those in the near- and far-infrared,
submillimeter and radio). The second approach I use exploits
gravitational lensing by galaxies and clusters, especially
as viewed in imaging with the Hubble Space
Telescope, to improve the resolution and sensitivity
of observations of distant galaxies.
This has also turned out to be a very profitable method for
studying the properties of mass
concentrations in the Universe.
The following pages show a selection of images derived from my research - a brief summary can be found here, I also use these pages to distribute material to collaborators so some sections may appear a bit obscure. Information about the thesis projects of the graduate students I have worked with is given on this page.
THE DARK-SIDE OF GALAXY FORMATION
The first sensitive submillimeter surveys of the distant Universe were
completed in the late 1990's (the first deep map is shown on the left). This waveband gives access to
redshifted far-infrared emission from very dusty, active galaxies
in the distant Universe. This radiation is reprocessed UV/optical
photons which have been absorbed by dust particles, heated them
and been remitted as thermal radiation. Surveys in this waveband
demonstrated that at least half the star formation in the whole
history of the Universe has occured in highly obscured environments -
invisible to surveys in the UV/optical. Much of this activity occurs
in highly luminous systems, with star formation rates 100's to 1000's
of times more intense than our own Galaxy. These star formation rates
mean that the stellar population of a massive galaxy could be formed
in only a few 100's millions of years. Investigating the detailed properties of this
population is a very active field of study.
My research in this field is all in collaboration with various combinations of Rob Ivison,
Andrew Blain, Scott Chapman and Jean-Paul Kneib (and a host of
others).
LENSING BY CLUSTERS OF GALAXIES
A false-color Hubble Space Telescope
WFPC2 image of the gravitationally lensed "pair'' in AC114. These
two L-shaped objects are exact mirror-copies of each other and they
represent two images of a single background source at z=1.86 which is
gravitationally lensed by the foreground cluster of galaxies (more details). We
have identified a third image of the
same background galaxy, this time on the other side of the cluster
center. The cluster is sufficiently massive that it bends those
light-paths to the distant galaxy which pass close to the cluster core. By
chance this bending focuses several of these light-paths onto us and so
we observe multiple images of the background galaxy.
A number of other
multiply-imaged sources are seen in the central regions of the cluster, including
two 5-image configurations. The existence of such lensed systems
provides a direct confirmation of Einstein's General Theory of
Relativity and is one of the most direct probes of nature
of the mass in the cluster,
most of which is in the form of "dark matter''
MORE LENSING...
An HST WFPC2 image of the distant
rich cluster A2218. A plethora of faint arc-like objects are visible
around the bright central galaxy. These are images of galaxies seen
through the foreground cluster, as the light-rays from the background
galaxies traverse the cluster they are deflected by the strong
gravitational field present, causing the images to appear stretched
into "arcs''. The distorted arcs are easily recognisable and appear
concentric around the center
of the deflecting mass. More detailed analysis allows us to map the
dark matter in the lensing cluster and the distances to
the faint, background galaxies (see here),
including some of the most distant galaxies known. Images
of other lenses I've worked on with Jean-Paul
Kneib, Graham Smith and Richard Ellis are shown here.
PUTTING IT ALL TOGETHER
This is a map
in the submillimeter waveband (at around 850um)
of a 2.6 arcminute diameter field in the
rich cluster A1835 at z=0.25 (the submm
map is shown as a contour plot over a
true color optical image of the same field). The
map was made with the SCUBA
bolometer array on the 15-m JCMT, Hawaii.
This is one of the deepest submillimeter map of the distant Universe ever
taken and it shows a number of submm sources detected. These
objects are seen in the submm because the dust within them is
absorbing UV and optical star-light and re-emitting it in
the restframe far-infrared. The far-infrared luminosities
can be used to infer the star-formation rates (as most of the
UV radiation comes from massive stars which don't live very long).
The high rates (1000's of stars formed each year)
indicate that we are probably seeing the formation of massive
galaxies. Optical surveys are generally insensitive to this population,
as shown by the relative insignificance of the optical counterparts
to the submm sources in this field - even though more stars are
being formed in the two brightest submm sources than in all the
other galaxies visible in this field.
These data were acquired in collaboration with Rob Ivison, Andrew Blain and
Jean-Paul Kneib (see here). A review of this project can be found in this paper, while
more details can be found here and in
the papers or the press release, as well as further examples of our
maps.
NOT-SO-LENSED FAINT GALAXIES
A real color (VRI) representation of one of the deepest ground-based
images of the sky ever taken. This is a 2×1 arcminute section of
a deep pointing obtained in 0.5 arcsecond seeing with the 10-m Keck Telescope, Mauna Kea. The
faintest objects visible have magnitudes of R=27 (60 billion times
fainter than the star Vega). There are over 300 galaxies brighter than
R=27 in this small patch of sky, equivalent to 30,000,000,000 over the
whole sky. The analysis of the faint galaxy counts from these data is
presented here,
while in this paper use the data to
study the clustering of faint galaxies. These images have also been
used to constrain faint star counts in our galaxy, as is discussed here. Similar material has provided constraints on the large scale structure of the
universe from weak gravitational
lensing, more
clustering of faint galaxies and the masses of galaxies from their
lensing effect on the shapes of other, background galaxies (more details).
LOOKING AT THE LENSES
Here we see a 0.5 Mpc region in the core of a rich cluster of galaxies
viewed as it was 6 billion years ago. The wide variety of galaxy morphologies and large fraction of
disturbed and interacting blue galaxies are in contrast to that
observed in similar clusters today, where the clusters are deficient in
star-forming spiral galaxies. The conclusion is that the galaxy
populations in clusters has changed significantly over the last third
of the lifetime of the Universe, a process which may be driven by the
growth of the clusters. This decline in the numbers of star-forming
spiral galaxies is connected with a increase in the numbers of S0
galaxies (disk galaxies with little or no on-going star-formation) in
the clusters. We conclude that the morphological transformation of this
population is one of the main processes in forming the galaxy populations
we see in clusters today. In contrast to the strong evolution seen
in the disk galaxies in high-density regions, the
luminous spheroidal or
elliptical galaxies appear to have changed little in the last
5-10 billion years. This supports the suggestion
that the submm-bright
galaxies seen with the SCUBA camera are the progenitors
of the earliest phase of the formation of these luminous ellipticals.
More details of these data are available in
the US at this site and in Europe from here. Some more images from this
project are shown here.
Other projects I am undertaking
to study the nature of galaxies in distant clusters
and groups are detailed on this page.
SOME USEFUL AND EDUCATIONAL THINGS...
A page listing useful information for Postgraduates in Astronomy at Durham is given here. If you have any suggestions for further information to be added to this page please email me.
I've been playing about with the ADS email query to automatically search (every month) the last month's journals for articles of interest. Instructions on how to do this can be found on this page. A few useful rules for working in Observational Cosmology are given here. While this page gives a list of telescope deadlines.
Finally, I've written a couple of Java-based labs for use on the Web. These are based on the needs of the Astronomy courses at Durham, but they might be of interest to others too. If you want to have a play then follow this link. If you'd like to use or adapt the labs yourself email me and I can provide the Java source.
Last Modified: whenever...
Professor Ian Smail,
ian.smail [at] durham.ac.uk
Institute for Computational Cosmology, Department of Physics, Durham University, South Road, Durham DH1 3LE
Tel: +44-191-334-3605/ Mobile: +44-775-383-2658 / Secretary:
+44-191-334-3772 (lindsay.borrero [at] durham.ac.uk) / FAX: +44-191-334-3645
