The History of Starburst Galaxies

Dusty galaxies with luminosities in excess of 10 L⊙ have been detected out to redshifts z ∼ 1 by the Infrared Space Observatory (ISO), and to higher redshifts using millimetre(mm)and submm-wave cameras on ground-based telescopes. The integrated properties of these more distant galaxies are also constrained by measurements of the intensity of the submm-wave background radiation. While it is generally unclear whether their energy is released by gravitational accretion or by star formation, circumstantial evidence favours star formation. Unless these high-redshift galaxies are extremely massive, which is not expected from standard models of galaxy evolution, this luminosity cannot be sustained for more than a fraction of a Hubble time, and so they are undergoing some sort of ‘bursting’ behaviour. The interpretation and analysis of this population is discussed, and the key observations for deriving a robust history of their evolution, which is likely to be the history of starburst activity, are highlighted. 1 The Evolution of Luminous Dusty Galaxies From observations of low-redshift dusty galaxies using the IRAS satellite [28] close to the peak of their restframe spectral energy distributions (SEDs), it is known that a similar amount of energy in the local Universe is produced by stars in dust-enshrouded and dust-free environments. The comoving luminosity density of dusty galaxies is also known to evolve strongly, from the slope of the faint counts of IRAS galaxies at 60μm [3], which provide information to z ≃ 0.2. ISO observations at both shorter [13] and longer [19] wavelengths confirm that strong evolution continues to z ∼ 1. At longer wavelengths, the redshifted emission from very luminous, highredshift dusty galaxies can be detected in the mm and submm wavebands. Independent surveys made using the 450/850-μm SCUBA camera at the JCMT [27] have determined the counts of high-redshift dusty galaxies. 1.2-mm surveys using the MAMBO detector array at the IRAM 30-m telescope [8] have detected a similar population of galaxies. In three cases, the detection of CO emission from gas located at the position and redshift of a suspected optical identification (at z = 1.06, 2.55 and 2.80) [15] provides absolute confirmation of the identification. Extremely deep VLA radio images of the survey fields can be used to impose constraints on the redshifts and SEDs of the detected galaxies [10,26]. It is likely that the detected galaxies are at z̄ ≃ 2 − 3, and there are very few plausible low-redshift (z ≤ 1) counterparts. The counts and redshift distributions of these distant dusty galaxies can be used to constrain models of galaxy evolution at high redshifts.