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Paul Alexander
P.Alexander@mrao.cam.ac.uk
Cavendish Astrophysics
Cosmological Evolution of Star-Forming Galaxies
Determining when and why stars formed on cosmological timescales is one of the key problems in modern astrophysics. Observations of the local Universe clearly demonstrate that very active star formation phases (starbursts) are often associated with interacting and merging galaxies and that in these systems much of the short wavelength emission is absorbed by dust and re-emitted in the IR. Earlier work has shown that the mean star-formation rate in the Universe was higher in the past, but it is the discovery of extremely luminous dusty objects at high redshift (2-5) which is challenging models of the cosmological evolution of star formation.
The
discovery of high-redshift galaxies which emit most of their power in the
far-infrared was made possible with the SCUBA instrument on the JCMT.
An early experiment used the natural lensing effects of the mass distribution
in clusters to enhance the detection rate of these very distant sources
Despite their discovery finding out more about these dusty objects is made difficult because they are very faint at almost all non-IR wavelengths. Therefore to make progress we must develop detailed models of the IR emission in order to deduce the properties of the underlying "galaxy".
We are developing a simple hierarchical model of dusty-galaxy evolution, applying it to both the high-redshift universe (as discovered in the SCUBA cluster survey) and also to the low redshift populations detected by IRAS, and ISO. Unfortunately the far-infrared emission is comparatively featureless and does not discriminate between different heating sources for the dust. We have therefore started a major observational and theoretical programme to understand the near-IR emission which is dominated by small grains and so-called PAH molecules. Observations with Michelle on UKIRT and Gemini will enable us to understand the processing history of this dust component and incorporate it in physical models of the evolving population.
A further approach is our on-going survey of the host galaxies of Gamma Ray Bursts (GRBs) with SCUBA. GRBs are highly energetic explosions which are thought to be linked to the death of high-mass stars and therefore to trace star formation throughout the universe.
Last modified: 20/1/2002