Luminous early-type field galaxies at z∼0.4– I. Observations and redshift catalogue of 581 galaxies

We have compiled a sample of ∼ 9600 bright, i ≤18.95 , red, b _J− r >2 , candidate galaxies in an area of 220 deg². These are luminous, L > L * , field early-type galaxies with redshifts 0.3≲ z ≲0.6 . We present a redshift catalogue of a subsample of 581 targets. The galaxies were selected according to their broad-band b _J ri colours from United Kingdom Schmidt Telescope plates, and have a surface density on the sky of only ∼ 50 deg⁻². Such luminous field galaxies are virtually absent from published redshift surveys and the catalogue provides a large sample of the most luminous normal galaxies, at cosmological distances. The statistical properties of the galaxy spectra, including absorption-line and emission-line measures, are presented and a composite spectrum constructed. The nature of the sample, combined with the relatively bright apparent magnitudes, makes the galaxies suitable targets for several key investigations in galaxy evolution and cosmology.     

Galaxy groups at 0.3 ≤z≤ 0.55 – II. Evolution to z∼ 0

We compare deep Magellan spectroscopy of 26 groups at  0.3 ≤ z ≤ 0.55  , selected from the Canadian Network for Observational Cosmology 2 field survey, with a large sample of nearby groups from the 2PIGG catalogue. We find that the fraction of group galaxies with significant [O  ii ]λ3727 emission (≥5 Å) increases strongly with redshift, from ∼29 per cent in 2dFGRS to ∼58 per cent in CNOC2, for all galaxies brighter than  ∼ M _*+ 1.75  . This trend is parallel to the evolution of field galaxies, where the equivalent fraction of emission-line galaxies increases from ∼53 to ∼75 per cent. The fraction of emission-line galaxies in groups is lower than in the field, across the full redshift range, indicating that the history of star formation in groups is influenced by their environment. We show that the evolution required to explain the data is inconsistent with a quiescent model of galaxy evolution; instead, discrete events in which galaxies cease forming stars (truncation events) are required. We constrain the probability of truncation ( P _trunc) and find that a high value is required in a simple evolutionary scenario neglecting galaxy mergers  ( P _trunc≳ 0.3 Gyr⁻¹)  . However, without assuming significant density evolution, P _trunc is not required to be larger in groups than in the field, suggesting that the environmental dependence of star formation was embedded at redshifts   z ≳ 0.45  .     

Predicting the peculiar velocities of nearby PSCz galaxies using the Least Action Principle

We use the Least Action Principle to predict the peculiar velocities of PSC z galaxies inside cz =2000 km s⁻¹. Linear theory is used to account for tidal effects to cz =15 000 km s⁻¹, and we iterate galaxy positions to account for redshift distortions. As the Least Action Principle is valid beyond linear theory, we can predict reliable peculiar velocities even for very nearby galaxies (i.e., cz ≤500 km s⁻¹). These predicted peculiar velocities are then compared with the observed velocities of 12 galaxies with Cepheid distances. The combination of the PSC z galaxy survey (with its large sky coverage and uniform selection) with the accurate Cepheid distances makes this comparison relatively free from systematic effects. We find that galaxies are good tracers of the mass, even at small (≤10  h ⁻¹ Mpc) scales; under the assumption of no biasing, 0.25≤ β ≤0.75 (at 90 per cent confidence). We use the reliable predicted peculiar velocities to estimate the Hubble constant H ₀ from the local volume without 'stepping up' the distance ladder, finding a confidence range of 65–75 km s⁻¹ Mpc⁻¹ (at 90 per cent confidence).     

The redshift distribution of FIRST radio sources at 1 mJy

We present spectra for a sample of radio sources from the FIRST survey, and use them to define the form of the redshift distribution of radio sources at mJy levels. We targeted 365 sources and obtained 46 redshifts (13 per cent of the sample). We find that our sample is complete in redshift measurement to R ∼18.6, corresponding to z ∼0.2. Galaxies were assigned spectral types based on emission-line strengths. Early-type galaxies represent the largest subset (45 per cent) of the sample and have redshifts 0.15≲ z ≲0.5; late-type galaxies make up 15 per cent of the sample and have redshifts 0.05≲ z ≲0.2; starbursting galaxies are a small fraction (∼6 per cent), and are very nearby ( z ≲0.05). Some 9 per cent of the population have Seyfert 1/quasar-type spectra, all at z ≳0.8, and 4 per cent are Seyfert 2 type galaxies at intermediate redshifts ( z ∼0.2).
Using our measurements and data from the Phoenix survey (Hopkins et al.), we obtain an estimate for N ( z ) at S _1.4 GHz≥1 mJy and compare this with model predictions. At variance with previous conclusions, we find that the population of starbursting objects makes up ≲5 per cent of the radio population at S ∼1 mJy.     

Further constraints on the evolution of Ks-selected galaxies in the GOODS/CDFS field

We have selected and analysed the properties of a sample of  2905 K_s < 21.5  galaxies in  ∼131 arcmin²  of the Great Observatories Origins Deep Survey (GOODS) Chandra Deep Field South (CDFS), to obtain further constraints on the evolution of K_s -selected galaxies with respect to the results already obtained in previous studies. We made use of the public deep multiwavelength imaging from the optical B through the infrared (IR) 4.5-μm bands, in conjunction with available spectroscopic and COMBO17 data in the CDFS, to construct an optimized redshift catalogue for our galaxy sample. We computed the K_s -band luminosity function and determined that its characteristic magnitude has a substantial brightening and a decreasing total density from   z = 0  to  〈 z 〉= 2.5  . We also analysed the colours and number density evolution of galaxies with different stellar masses. Within our sample, and in contrast to what is observed for less massive systems, the vast majority (∼85–90 per cent) of the most massive  ( M > 2.5 × 10¹¹ M_⊙)  local galaxies appear to be in place before redshift   z ∼ 1  . Around 65–70 per cent of the total assemble between redshifts   z = 1  and 3 and most of them display extremely red colours, suggesting that plausible star formation in these very massive systems should mainly proceed in obscured, short-time-scale bursts. The remaining fraction (up to ∼20 per cent) could be in place at even higher redshifts   z = 3–4  , pushing the first epoch of formation of massive galaxies beyond the limits of current near-IR surveys.     

Hubble Space Telescope imaging of the CFRS and LDSS redshift surveys – IV. Influence of mergers in the evolution of faint field galaxies from z∼1

Hubble Space Telescope images of a sample of 285 galaxies with measured redshifts from the Canada–France Redshift Survey (CFRS) and Autofib–Low Dispersion Spectrograph Survey (LDSS) redshift surveys are analysed to derive the evolution of the merger fraction out to redshifts z ∼1. We have performed visual and machine-based merger identifications, as well as counts of bright pairs of galaxies with magnitude differences δm ≤1.5 mag. We find that the pair fraction increases with redshift, with up to ∼20 per cent of the galaxies being in physical pairs at z ∼0.75–1. We derive a merger fraction varying with redshift as ∝(1+ z )^3.2±0.6, after correction for line-of-sight contamination, in excellent agreement with the merger fraction derived from the visual classification of mergers for which m =3.4±0.6. After correcting for seeing effects on the ground-based selection of survey galaxies, we conclude that the pair fraction evolves as ∝(1+ z )^2.7±0.6. This implies that an average L * galaxy will have undergone 0.8–1.8 merger events from z =1 to z =0, with 0.5 to 1.2 merger events occuring in a 2-Gyr time-span at around z ∼0.9. This result is consistent with predictions from semi-analytical models of galaxy formation. From the simple coaddition of the observed luminosities of the galaxies in pairs, physical mergers are computed to lead to a brightening of 0.5 mag for each pair on average, and a boost in star formation rate of a factor of 2, as derived from the average [O  ii ] equivalent widths. Mergers of galaxies are therefore contributing significantly to the evolution of both the luminosity function and luminosity density of the Universe out to z ∼1.     

Clustering of galaxies at 3.6 μm in the Spitzer Wide-area Infrared Extragalactic legacy survey

We investigate the clustering of galaxies selected in the 3.6 μm band of the Spitzer Wide-area Infrared Extragalactic (SWIRE) legacy survey. The angular two-point correlation function is calculated for 11 samples with flux limits of S _3.6≥ 4–400 μJy, over an 8 deg² field. The angular clustering strength is measured at >5σ significance at all flux limits, with amplitudes of A = (0.49–29) × 10⁻³ at 1°, for a power-law model, A θ^−0.8. We estimate the redshift distributions of the samples using phenomological models, simulations and photometric redshifts, and so derive the spatial correlation lengths. We compare our results with the Galaxies In Cosmological Simulations (GalICS) models of galaxy evolution and with parametrized models of clustering evolution. The GalICS simulations are consistent with our angular correlation functions, but fail to match the spatial clustering inferred from the phenomological models or the photometric redshifts. We find that the uncertainties in the redshift distributions of our samples dominate the statistical errors in our estimates of the spatial clustering. At low redshifts (median z ≤ 0.5), the comoving correlation length is approximately constant,   r ₀= 6.1 ± 0.5  h ⁻¹  Mpc, and then decreases with increasing redshift to a value of 2.9 ± 0.3  h ⁻¹ Mpc for the faintest sample, for which the median redshift is z ∼ 1. We suggest that this trend can be attributed to a decrease in the average galaxy and halo mass in the fainter flux-limited samples, corresponding to changes in the relative numbers of early- and late-type galaxies. However, we cannot rule out strong evolution of the correlation length over  0.5 < z < 1  .     

A 98 per cent spectroscopically complete sample of the most powerful equatorial radio sources at 408 MHz

A new sample of very powerful radio galaxies is defined from the Molonglo Reference Catalogue, according to the criteria S _408 MHz>5 Jy, −30°≤ δ ≤10° and | b |≥10°. The sample is selected to have similar properties to the northern 3CR revised sample, and to be visible to a combination of existing northern telescopes such as the Very Large Array radio interferometer and large southern hemisphere telescope facilities. The sample contains 178 sources, of which spectroscopic redshifts are available in the literature for 128. For the remaining 50 sources, new radio imaging, optical imaging and spectroscopic observations are presented to identify the host galaxies and determine their redshifts. With these new observations the total sample is 100 per cent optically identified and redshifts are available for 174 (98 per cent) of the sources. The sample consists of one starburst galaxy, one Seyfert galaxy, 127 radio galaxies and 49 quasars. Basic properties of the sample, such as the distributions of the quasar and radio-galaxy populations in redshift and their locations on the radio power versus linear size ( P − D ) diagram, show no significant differences from the revised 3CR sample. The equatorial location and the high spectroscopic completeness of this sample make it a valuable resource for detailed studies of the nature and environments of these important objects with the new generation of southern hemisphere telescopes.     

A sample of galaxies near the South Celestial Pole

This paper reports the results of a modest redshift survey carried out, at generally low Galactic latitudes, in the vicinity of the South Celestial Pole. Target galaxies were selected as a 'representative' sample of underlying large-scale structures. Dimensions, approximate magnitudes and radial velocity measurements, are reported for 336 galaxies. Two obvious Seyfert 1 galaxies, one probably Seyfert 1 and three Seyfert 2 galaxies have been discovered. The redshifts are used to supplement existing data and serve to map southern voids and features out to 25 000 km s⁻¹ in the region  270° < l < 330°, 0° > b > −45°  . Three distinct superclusters and twenty apparent voids are tentatively identified. One Void, at   l = 300°, b =−20°, cz = 16 000 km s⁻¹  , with a diameter of 6000 km s⁻¹, is as large as any yet mapped. It appears as part of a general underdense region.     

Radio galaxies in the 2SLAQ Luminous Red Galaxy survey – II. The stellar populations of radio-loud and radio-quiet LRGs

We present an analysis of the optical spectra of a volume-limited sample of 375 radio galaxies at redshift  0.4 < z < 0.7  from the 2dF-SDSS (Sloan Digital Sky Survey) Luminous Red Galaxy (LRG) and QSO (quasi-stellar object) (2SLAQ) redshift survey. We investigate the evolution of the stellar populations and emission-line properties of these galaxies. By constructing composite spectra and comparing with a matched sample of radio-quiet sources from the same survey, we also investigate the effect on the galaxy of the presence of an active nucleus.
The composite spectra, binned by redshift and radio luminosity, all require two components to describe them, which we interpret as an old and a younger population. We found no evolution with redshift of the age of the younger population in radio galaxies, nor were they different from the radio-quiet comparison sample. Similarly, there is no correlation with radio power, with the exception that the most powerful radio sources  ( P _1.4 > 10²⁶  W Hz⁻¹) have younger stars and stronger emission lines than the less powerful sources. This suggests that we have located the threshold in radio power where strong emission lines 'switch on', at radio powers of around 10²⁶ W Hz⁻¹. Except for the very powerful radio galaxies, the presence of a currently active radio active galactic nucleus (AGN) does not appear to be correlated with any change in the observed stellar population of a luminous red galaxy at   z ∼ 0.5  .     

Photometric redshifts for weak lensing tomography from space: the role of optical and near infrared photometry

We study in detail the photometric redshift requirements needed for tomographic weak gravitational lensing in order to measure accurately the dark energy equation of state. In particular, we examine how ground-based photometry  ( u , g , r , i , z , y )  can be complemented by space-based near-infrared (near-IR) photometry  ( J , H )  , e.g. onboard the planned DUNE satellite. Using realistic photometric redshift simulations and an artificial neural network photo- z method we evaluate the figure of merit for the dark energy parameters  ( w ₀, w _a )  . We consider a DUNE -like broad optical filter supplemented with ground-based multiband optical data from surveys like the Dark Energy Survey, Pan-STARRS and LSST. We show that the dark energy figure of merit would be improved by a factor of 1.3–1.7 if IR filters are added onboard DUNE . Furthermore we show that with IR data catastrophic photo- z outliers can be removed effectively. There is an interplay between the choice of filters, the magnitude limits and the removal of outliers. We draw attention to the dependence of the results on the galaxy formation scenarios encoded into the mock galaxies, e.g. the galaxy reddening. For example, very deep u -band data could be as effective as the IR. We also find that about  10⁵–10⁶  spectroscopic redshifts are needed for calibration of the full survey.     

Clustering of luminous red galaxies – II. Small-scale redshift-space distortions

This is the second paper of a series where we study the clustering of luminous red galaxies (LRG) in the recent spectroscopic Sloan Digital Sky Survey (SDSS) data release, DR6, which has 75 000 LRG covering over  1 Gpc³  h ⁻³  for  0.15 < z < 0.47  . Here, we focus on modelling redshift-space distortions in  ξ(σ, π)  , the two-point correlation in separate line-of-sight and perpendicular directions, at small scales and in the line-of-sight. We show that a simple Kaiser model for the anisotropic two-point correlation function in redshift space, convolved with a distribution of random peculiar velocities with an exponential form, can describe well the correlation of LRG on all scales. We show that to describe with accuracy the so-called 'fingers-of-God' (FOG) elongations in the radial direction, it is necessary to model the scale dependence of both bias b and the pairwise rms peculiar velocity σ₁₂ with the distance. We show how both quantities can be inferred from the  ξ(σ, π)  data. From   r ≃ 10 Mpc  h ⁻¹  to   r ≃ 1 Mpc  h ⁻¹  , both the bias and σ₁₂ are shown to increase by a factor of 2: from   b = 2  to 4 and from  σ₁₂= 400  to  800 km s⁻¹  . The latter is in good agreement, within a 5 per cent accuracy in the recovered velocities, with direct velocity measurements in dark matter simulations with  Ω_m= 0.25  and  σ₈= 0.85  .     

The evolution of [O ii] emission from cluster galaxies

We investigate the evolution of the star formation rate in cluster galaxies. We complement data from the Canadian Network for Observational Cosmology 1 (CNOC1) cluster survey  (0.15 < z < 0.6)  with measurements from galaxy clusters in the Two-degree Field (2dF) galaxy redshift survey  (0.05 < z < 0.1)  and measurements from recently published work on higher-redshift clusters, up to almost   z = 1  . We focus our attention on galaxies in the cluster core, i.e. galaxies with   r < 0.7  h ⁻¹₇₀ Mpc  . Averaging over clusters in redshift bins, we find that the fraction of galaxies with strong [O  ii ] emission is ≲20 per cent in cluster cores, and the fraction evolves little with redshift. In contrast, field galaxies from the survey show a very strong increase over the same redshift range. It thus appears that the environment in the cores of rich clusters is hostile to star formation at all the redshifts studied. We compare this result with the evolution of the colours of galaxies in cluster cores, first reported by Butcher and Oemler. Using the same galaxies for our analysis of the [O  ii ] emission, we confirm that the fraction of blue galaxies, which are defined as galaxies 0.2 mag bluer in the rest-frame B – V than the red sequence of each cluster, increases strongly with redshift. Because the colours of galaxies retain a memory of their recent star formation history, while emission from the [O  ii ] line does not, we suggest that these two results can best be reconciled if the rate at which the clusters are being assembled is higher in the past, and the galaxies from which it is being assembled are typically bluer.     

Galaxy groups at 0.3 ≤z≤ 0.55 – I. Group properties

The evolution of galaxies in groups may have important implications for the evolution of the star formation history of the Universe, since many processes which operate in groups may suppress star formation and the fraction of galaxies in bound groups grows rapidly between   z = 1  and the present day. In this paper, we present an investigation of the properties of galaxies in galaxy groups at intermediate redshift  ( z ∼ 0.4)  . The groups were selected from the Canadian Network for Observational Cosmology Redshift Survey (CNOC2) redshift survey as described by Carlberg et al., with further spectroscopic follow-up undertaken at the Magellan telescope in order to improve the completeness and depth of the sample. We present the data for the individual groups, and find no clear trend in the fraction of passive galaxies with group velocity dispersion and group concentration. We stack the galaxy groups in order to compare the properties of group galaxies with those of field galaxies at the same redshift. The groups contain a larger fraction of passive galaxies than the field, this trend being particularly clear for galaxies brighter than   M _{B J} < −20  in the higher velocity dispersion groups. In addition, we see evidence for an excess of bright passive galaxies in the groups relative to the field. In contrast, the luminosity functions of the star-forming galaxies in the groups and the field are consistent. These trends are qualitatively consistent with the differences between group and field galaxies seen in the local Universe.     

The Australia Telescope 20-GHz (AT20G) Survey: the Bright Source Sample

The Australia Telescope 20-GHz (AT20G) Survey is a blind survey of the whole southern sky at 20 GHz (with follow-up observations at 4.8 and 8.6 GHz) carried out with the Australia Telescope Compact Array from 2004 to 2007.
The Bright Source Sample (BSS) is a complete flux-limited subsample of the AT20G Survey catalogue comprising 320 extragalactic     ) radio sources south of  δ=−15°  with      Jy. Of these, 218 have near simultaneous observations at 8 and 5 GHz.
In this paper we present an analysis of radio spectral properties in total intensity and polarization, size, optical identifications and redshift distribution of the BSS sources. The analysis of the spectral behaviour shows spectral curvature in most sources with spectral steepening that increases at higher frequencies (the median spectral index α, assuming   S ∝ν^α  , decreases from  α^8.6_4.8= 0.11  between 4.8 and 8.6 GHz to  α²⁰_8.6=−0.16  between 8.6 and 20 GHz), even if the sample is dominated by flat spectra sources (85 per cent of the sample has  α²⁰_8.6 > −0.5)  . The almost simultaneous spectra in total intensity and polarization allowed us a comparison of the polarized and total intensity spectra: polarized fraction slightly increases with frequency, but the shapes of the spectra have little correlation. Optical identifications provided an estimation of redshift for 186 sources with a median value of 1.20 and 0.13, respectively, for QSO and galaxies.     

A photometric study of the field around the candidate recoiling/binary black hole SDSS J092712.65+294344.0

We present a photometric far-ultraviolet (FUV) to K _s-band study of the field around quasar SDSS J092712.65+294344.0. The SDSS spectrum of this object shows various emission lines with two distinct redshifts, at   z = 0.699  and 0.712. Because of this peculiar spectroscopic feature, this source has been proposed as a candidate recoiling or binary black hole. A third alternative model involves two galaxies moving in the centre of a rich galaxy cluster. Here, we present a study addressing the possible presence of such a rich cluster of galaxies in the SDSS J092712.65+294344.0 field. We observed the  3.6 × 2.6  arcmin² field in the K _s band and matched the near-infrared data with the FUV and near-ultraviolet images in the Galaxy Evolution Explorer archive and the ugriz observations in the SDSS. From various colour–colour diagrams, we were able to classify the nature of 32 sources, only 6–11 of which have colours consistent with galaxies at   z ≈ 0.7  . We compare these numbers with the surface density of galaxies, stars and quasars and the expectations for typical galaxy clusters both at low and high redshift. Our study shows that the galaxy cluster scenario is in clear disagreement with the new observations.     

The Durham/UKST Galaxy Redshift Survey — V. The catalogue

We present the radial velocities and blue, optical magnitudes for all of the galaxies within the Durham/UKST Galaxy Redshift Survey. This catalogue consists of ∼2500 galaxy redshifts to a limiting apparent magnitude of B _J⋍17 mag, covering a ∼1500-deg² area around the South Galactic Pole. The galaxies in this survey were selected from the Edinburgh/Durham Southern Galaxy Catalogue and were sampled, in order of apparent magnitude, at a rate of one galaxy in every three. The spectroscopy was performed at the 1.2-m UK Schmidt Telescope in Australia using the FLAIR multi-object spectrograph. We show that our radial velocity measurements made with this instrument have an empirical accuracy of ±150 km s⁻¹. The observational techniques and data reduction procedures used in the construction of this survey are also discussed. This survey demonstrates that the UKST can be used to make a three-dimensional map of the large-scale galaxy distribution, via a redshift survey to b _J⋍17 mag, over a wide area of the sky.     

Power spectrum shape from peculiar velocity data

We constrain the velocity power spectrum shape parameter Γ in linear theory using the nine bulk flow and shear moments estimated from four recent peculiar velocity surveys. For each survey, a likelihood function for Γ was found after marginalizing over the power spectrum amplitude  σ₈Ω^0.6_m  using constraints obtained from comparisons between redshift surveys and peculiar velocity data. In order to maximize the accuracy of our analyses, the velocity noise σ_* was estimated directly for each survey. A statistical analysis of the differences between the values of the moments estimated from different surveys showed consistency with theoretical predictions, suggesting that all the surveys investigated reflect the same large-scale flows. The peculiar velocity surveys were combined into a composite survey yielding the constraint  Γ= 0.13^+0.09_−0.05  . This value is lower than, but consistent with, values obtained using redshift surveys and cosmic microwave background data.     

Topology and geometry of the CfA2 redshift survey

We analyse the redshift space topology and geometry of the nearby Universe by computing the Minkowski functionals of the Updated Zwicky Catalogue (UZC). The UZC contains the redshifts of almost 20 000 galaxies, is 96 per cent complete to the limiting magnitude m _Zw=15.5, and includes the Center for Astrophysics (CfA) Redshift Survey (CfA2). From the UZC we can extract volume-limited samples reaching a depth of 70  h ⁻¹ Mpc before sparse sampling dominates. We quantify the shape of the large-scale galaxy distribution by deriving measures of planarity and filamentarity from the Minkowski functionals. The nearby Universe shows a large degree of planarity and a small degree of filamentarity. This quantifies the sheet-like structure of the Great Wall, which dominates the northern region (CfA2N) of the UZC. We compare these results with redshift space mock catalogues constructed from high-resolution N -body simulations of two cold dark matter (CDM) models with either a decaying massive neutrino ( τ CDM) or a non-zero cosmological constant (ΛCDM). We use semi-analytic modelling to form and evolve galaxies in these dark matter‐only simulations. We are thus able, for the first time, to compile redshift space mock catalogues which contain galaxies, along with their observable properties, rather than dark matter particles alone. In both models the large-scale galaxy distribution is less coherent than the observed distribution, especially with regard to the large degree of planarity of the real survey. However, given the small volume of the region studied, this disagreement can still be a result of cosmic variance, as shown by the agreement between the ΛCDM model and the southern region of CfA2.     

The SCUBA HAlf Degree Extragalactic Survey (SHADES) – VII. Optical/IR photometry and stellar masses of submillimetre galaxies

We present estimates of the photometric redshifts, stellar masses and star formation histories of sources in the Submillimetre Common-User Bolometer Array (SCUBA) HAlf Degree Extragalactic Survey (SHADES). This paper describes the 60 SCUBA sources detected in the Lockman Hole covering an area of ∼320 arcmin². Using photometry spanning the B band to 8 μm, we find that the average SCUBA source forms a significant fraction of its stars in an early period of star formation and that most of the remainder forms in a shorter more intense burst around the redshift it is observed. This trend does not vary significantly with source redshift. However, the sources show a clear increase in stellar mass with redshift, consistent with downsizing. In terms of spectral energy distribution types, only two out of the 51 sources we have obtained photometric redshifts for are best fitted by a quasar-like spectrum, with approximately 80 per cent of the sources being best fitted with late-type spectra (Sc, Im and starburst). By including photometry at 850 μm, we conclude that the average SCUBA source is forming stars at a rate somewhere between 6 and 30 times the rate implied from the rest-frame optical in a dust obscured burst and that this burst creates 15–65 per cent of the total stellar mass. Using a simplistic calculation, we estimate from the average star formation history that between one in five and one in 15 bright  ( L _*+ 2 < L _optical < L _*− 1 mag)  galaxies in the field over the interval  0 < z < 3  will at some point in their lifetime experience a similar energetic dusty burst of star formation. Finally, we compute the evolution of the star formation rate density and find it peaks around   z ∼ 2  .