Ian Smail
Centre for Extragalactic Astronomy, Durham University
Submm Astronomy
The Atacama Large Millimeter Array (ALMA) is the world's largest submillimetre array. ALMA sits at 5,000m in the Atacama Desert in Northern Chile, putting it above most of the atmosphere. This allows it to search for faint heat signatures at the submillimetre wave lengths of vigorous star formation in young and very distant, dust-obscured galaxies.
Specfically ALMA is perfectly positioned to exploit single-dish submillimetre survey to understand the evolution of the most luminous galaxies in the Universe ››
Gravitational Lensing
This is an image of the rich cluster of galaxies, Abell 370. There is so much mass concentrated in the central regions of this cluster that it bends the light-paths to distant, background galaxies which are seen through the cluster core. This bending distorts the apparent shape of some of these galaxies into highly elongated arcs. In the most extreme situations this bending can focus several light-paths onto the Earth and so we observe multiple images of the same background galaxy. 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''
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Multi-wavelength Astronomy
My research employs observatories across a wide range of the electromagnetic spectrum, from X-rays, through the ultraviolet, optical, near-, mid- and far-infrared and off into the sub/millimetre and radio. The photons in these wavebands have different energies and so arise from different processes. Hence comparing the views of galaxies and clusters across a range in wavelength can provide useful insights into the different physical processes occuring within them.
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Submm Galaxies
This plot shows the distances (or redshifts) of young, dusty galaxies identified at submillimetre wavelengths. These galaxies are bright in the submillimetre because the dust within them is absorbing ultraviolet star light and re-emitting it in the restframe far-infrared. The far-infrared luminosities of these galaxies imply very high rates of star formation: 1000's of stars formed each year, indicating that we are probably seeing these galaxies during an early and vigorous phase of their formation. The similarity between the redshift distribution of these submillimetre galaxies and that of Quasars (or QSOs) hints at an intimate link before the formation of these massive galaxies and the supermassive black holes they host.
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Interferometry
The Atacama Large Millimeter Array (ALMA) is the most powerful sub/millimetre interferometer on the planet. This instrument is capable of mapping the distribution of dust and molecular and atomic gas within distant submillimetre galaxies in exquisite detail. These galaxies were detected by a wide-field submillimetre survey (S2CLS) and then studied in more detail with ALMA, to precisely locate the dust-obscured starbursts occuring in these systems (shown by the crosses plotted over James Webb Space Telescope images).
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Submm Quasars
Another route to test the connection between far-infrared luminous galaxies and Quasars is to study the small fraction of Quasars which are also far-infrared luminous. Using submillimetre interferometry of Quasars detected in Herschel Space Observatory far-infrared surveys, we find that the gas content of the Quasars is less than that of submillimetre galaxies (as measured from their carbon monoxide emission, shown here). This is consistent with the expectation that the Quasars represent a later evolutionary phase in the life of high-redshift far-infrared luminous starbursts.
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Galaxy Formation
To trace the evolution of the bulk of the (less luminous) star-forming galaxies, we need to use other, more sensitive, star-formation tracers than the far-infrared emission. The most sensitive such tracer is the Hydrogen Balmer emission. Using wide-field narrow-band imaging from the UKIRT telescope we detect this emission line from star-forming galaxies lying in narrow redshift slices. This uniform selection and the large samples available enable us to trace the variation of a single star formation rate indicator over 11 billion years out to a redshift of z = 2.23. We see a strong rise in star formation back to redshift z ~ 1, with a more gradual increase beyond. This shows that most of the stars in galaxies today were formed in the last half of the age of the Universe.
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3-D Spectroscopy
The development of integral field spectrographs on large telescopes, such as KMOS on ESO's Very Large Telescope (VLT), allows Astronomers to map the internal dynamics, star formation and ISM chemistry of distant galaxies (such as the HiZELS-selected example here. These data show whether the gas and stars in these galaxies lies in a rotating disk or in the more chaotic orbits of a pressure-supported bulge. In turn this information can be used to track the evolution of galaxies and so test the importance of different mechanisms in driving their star formation and overall growth (e.g. mergers compared to more secular processes).
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I am an emeritus Professor of Physics in the Department of Physics at Durham University, based in the Centre for Extragalactic Astronomy (CEA) within the Ogden Centre for Fundamental Physics. I was the founding Director of CEA and between 2013-2018 I led the DustyGal programme supported by an ERC Advanced Investigator Grant and a Royal Society Wolfson Merit Award. I was previously a Professorial Fellow supported through a Royal Society University Research Fellowship in the Institute for Computational Cosmology, Durham University. 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. Information about the thesis projects of the graduate students I have worked with is here.
Professor Ian Smail
reverse: ku.ca.mahrud [at] liams.nai
Centre for Extragalactic Astronomy, Department of Physics, Durham University, South Road, Durham DH1 3LE
Centre for Extragalactic Astronomy, Department of Physics, Durham University, South Road, Durham DH1 3LE