APM Survey Research Articles

New H-band galaxy number counts: a large local hole in the galaxy distribution

We examine H-band number counts determined using new photometry over 0.30 sq.deg. to H=19, as well as H 20 counts display a relatively constant deficit in the counts of 15-20%. We investigate various possible causes for these results: In order to address the issue of the model normalisation, we examine faint number counts for the new faint photometry presented in this work and also for the LCIRS. In each case a zeropoint is chosen to match that of the 2MASS photometry at bright magnitudes. We find a large offset between 2MASS and the LCIRS data of 0.28+/-0.01 magnitudes. Applying a consistent zeropoint, the combined faint data is in good agreement with the homogeneous model prediction used previously. We examine possible effects arising from unexpected galaxy evolution and photometric errors and find no evidence for a significant contribution from either. However, incompleteness in the 2MASS catalogue and in the faint data may have a significant contribution. Addressing the contribution from large-scale structure, we estimate the cosmic variance in the bright counts over the APM survey area and for |b|>20 expected in a LCDM cosmology using 27 LCDM mock 2MASS catalogues. Accounting for the model normalisation uncertainty and taking an upper limit for the incompleteness, the APM survey area bright counts are in line with a rare fluctuation in the local galaxy distribution of 2.5 sigma. However, the |b|>20 counts represent a 4.0 sigma fluctuation, and imply a local hole which extends over the entire local galaxy distribution and is at odds with LCDM.

2MASS constraints on the local large-scale structure: a challenge to λCDM?

We investigate the large-scale structure of the local galaxy distribution using the recently completed 2-Micron All Sky Survey (2MASS) via three techniques. First, we determine the Ks-band number counts over the 4000 deg 2 APM survey area where optical evidence for a large-scale 'local hole' has previously been detected and compare them to a non-evolving homogeneous prediction. Considering a ACDM form for the two-point angular correlation function, the observed deficiency represents a 5σ fluctuation in the galaxy distribution. We check the model normalization using faint K-band data compiled from the literature; the normalization used in this paper is in excellent agreement, although the resulting best-fitting normalization is slightly lower. Nevertheless the observed counts over the APM survey area would require the best-fitting model normalization to be lowered by 3.8σ. However, the issue is complicated by the b ≥ 20° and b ≤ -20° 2MASS counts which lie below this model normalization. Secondly, since the Ks-band counts over the APM survey area continue to suggest the possible presence of excess clustering over the ACDM prediction, we next probe the power at large scales by comparing the 2MASS and ACDM mock galaxy angular power spectra. We find a 3a excess in the 2MASS catalogue over the ACDM prediction at large scales (l ≤ 30) using a bias of b K = 1.1. However, this excess is not enough to account for the low counts over the APM survey area. Finally, in order to probe more directly whether the ACDM mocks can reproduce observed features in the galaxy distribution at large scales, we apply a counts-in-cells analysis to the 2MASS data and mock catalogues; on the assumption that the 2MASS catalogue at |b| ≥ 20° is representative, we find excellent agreement between the biased ACDM mocks and the 2MASS catalogue to 30°. The crux of the interpretation of these results appears to be whether the 2MASS volume is yet big enough to constitute a fair sample of the Universe. The number-count models based on fainter counts suggest that it may not be, although normalization uncertainties remain. It is also the case that the 2MASS depth remains comparable to the possible size of large-scale inhomogeneities. Analyses which assume the 2MASS average density is a fair sample, such as counts in cells and to a lesser extent, power spectral analysis, may return results which see less contradiction with ACDM than the number-count analysis in the APM survey area. Further progress on assessing the significance of the local hole and thus the consistency of the local galaxy distribution with ACDM will require deeper all-sky number-counts and redshift surveys in both the optical and the infrared.

Detection of the Integrated Sachs-Wolfe and Sunyaev-Zeldovich Effects from the Cosmic Microwave Background-Galaxy Correlation

We present a cross-correlation analysis of the WMAP cosmic microwave background (CMB) temperature anisotropies and the SDSS galaxy density fluctuations. We find significant detections of the angular CMB-galaxy correlation for both the flux limited galaxy sample (z~0.3) and the high redshift (z ~ 0.5) color selected sample. The signal is compatible with that expected from the integrated Sachs-Wolfe (ISW) effect at large angles (\theta > 3deg) and the Sunyaev-Zeldovich (SZ) effect at small scales (\theta < 1 deg). The detected correlation at low-z is in good agreement with a previous analysis using the APM survey (z~0.15). The combined analysis of all 3 samples yields a total significance better than 3 sigma for ISW and about 2.7 \sigma for SZ, with a Compton parameter y~10^(-6). For a given flat LCDM model, the ISW effect depends both on the value of \Omega_\Lambda and the galaxy bias b. To break this degeneracy, we estimate the bias using the ratio between the galaxy and mass auto-correlation functions in each sample. With our bias estimation, all samples consistently favor a best fit dark-energy dominated model: \Omega_\Lambda ~ 0.8, with a 2 \sigma error \Omega_\Lambda=0.69-0.86.

The power spectrum of galaxy clustering in the APM Survey

We measure the power spectrum of galaxy clustering in real space from the APM Galaxy Survey. We present an improved technique for the numerical inversion of Limber's equation that relates the angular clustering of galaxies to an integral over the power spectrum in three dimensions. Our approach is underpinned by a large ensemble of mock galaxy catalogues constructed from the Hubble volume N-body simulations. Mock catalogues are used to test for systematic effects in the inversion algorithm and to estimate the errors on our measurement. We find that we can recover the power spectrum to an accuracy of better than 15 per cent over three decades in wavenumber. A key advantage of the use of mock catalogues to infer errors is that we can apply our technique on scales for which the density fluctuations are not Gaussian, thus probing the regime that offers the best constraints on models of galaxy formation. On large scales, our measurement of the power spectrum is consistent with the shape of the mass power spectrum in the popular ‘concordance’ cold dark matter model. The galaxy power spectrum on small scales is strongly affected by non-linear evolution of density fluctuations, and, to a lesser degree, by galaxy bias. The rms variance in the galaxy distribution, when smoothed in spheres of radius 8 h−1 Mpc, is σg8= 0.96+0.17−0.20 and the shape of the power spectrum on large scales is described by a simple fitting formula with parameter Γ= 0.19+0.13−0.04 (these errors are the 1σ ranges for a two-parameter fit). We use our measurement of the power spectrum to estimate the galaxy two-point correlation function; the results are well described by a power law with correlation length r0= 5.9 ± 0.7 h−1 Mpc and slope γ= 1.61 ± 0.06 for pair separations in the range 0.1 < r/(h−1 Mpc) < 20.

The environment of active objects in the nearby Universe

We study the galaxy environment of active galaxies, radio-loud and radio-quiet quasars in the redshift range 0.1 ≤ z ≤ 0.25. We use galaxies from the APM survey in order to explore the local galaxy overdensity and the b J - R colour distribution of neighbouring galaxies of these target samples. For comparison, we perform similar analysis on samples of Abell clusters with X-ray emission, and samples of Abell clusters with richness R = 1 and 0. The projected cross-correlations show that the samples of quasars and active galaxies reside in regions of galaxy density enhancements lower than those typical of R = 0 clusters. We also find that in the nearby Universe the local galaxy overdensities of radio-loud and radio-quiet quasars are comparable. The analysis of the distribution of b J - R galaxy colour indices suggests that the environment of quasars is not strongly dominated by a population of red galaxies, characteristic of rich Abell clusters, an effect that is more clearly appreciated for our sample of radio-loud quasars.

Angular and three-dimensional correlation functions determined from the Muenster Red Sky Survey

ABSTRA C T We measure the two-dimensional galaxy ‐ galaxy correlation function from the Muenster Red Sky Survey. This survey covers a slightly larger sky area compared with the APM survey and is complete to rF , 18:3 mag ﷿zmed , 0:14fi. The large dynamic range of the survey makes it possible to examine sub-catalogues with different limiting magnitudes. The positive parts of our measured angular correlation functions (after the colour correction) show excellent agreement with those measured by Maddox, Efstathiou & Sutherland from the APM galaxy catalogue. From the measured angular correlation functions, the three-dimensional two-point correlation function j(r) is calculated. We have chosen the evolution parameter e so that the change of the correlation length r0 with the depth of the sub-catalogue is minimal. This prescription gives r0 o 5:82 ^ 0:05 h 21 Mpc and a very high, positive evolution parameter e o 2:6. The position of the point where the three-dimensional correlation function breaks away from the power law depends on the depth of the sub-catalogues: the break comes earlier for lower magnitude limits, and later for higher magnitude limits.

High and Low Surface Brightness Galaxies in the Local Universe. V. Optical and H [CSC]i[/CSC] Properties

Using optical spectra of the nuclei of 250 galaxies chosen from the Automated Plate Measuring Facility (APM) survey of UK Schmidt plates, we derive synthetic B-V and V-R colors, estimates of reddening from Balmer decrements, metallicity via oxygen abundance, and star formation rate from the Hα luminosity. We also present mass-to-light ratios and gas mass fractions from 21 cm H I measurements of 238 APM survey galaxies, 101 of which also have optical spectra. This sample of galaxies spans a large range in surface brightness, from high surface brightness irregular galaxies down to the kind of low surface brightness (LSB) galaxies that are missing from most magnitude-limited catalogs. The generally blue global colors are best explained by a combination of low metallicity and active star formation, primarily because of the tremendous scatter in metallicity versus B-V. Optical spectra show the presence of G and K main-sequence stars in the nuclei of these galaxies, and the stellar mass-to-light ratios and gas mass fractions show the galaxies as a whole to be gas-rich. LSB galaxies are most likely to experience sporadic low levels of star formation over gigayear timescales.

The APM Survey for cool carbon stars in the Galactic halo -- II. The search for dwarf carbon stars

We present proper motion measurements for carbon stars found during the APM Survey for Cool Carbon Stars in the Galactic Halo (Totten & Irwin, 1998). Measurements are obtained using a combination of POSSI, POSSII and UKST survey plates supplemented where necessary by CCD frames taken at the Isaac Newton Telescope. We find no significant proper motion for any of the new APM colour-selected carbon stars and so conclude that there are no dwarf carbon stars present within this sample. We also present proper motion measurements for three previously known dwarf carbon stars and demonstrate that these measurements agree favourably with those previously quoted in the literature, verifying our method of determining proper motions. Results from a complimentary program of JHK photometry obtained at the South African Astronomical Observatory are also presented. Dwarf carbon stars are believed to have anomalous near-infrared colours, and this feature is used for further investigation of the nature of the APM carbon stars. Our results support the use of JHK photomtery as a dwarf/giant discriminator and also reinforce the conclusion that none of the new APM-selected carbon stars are dwarfs. Finally, proper motion measurements combined with extant JHK photometry are presented for a sample of previously known Halo carbon stars, suggesting that one of these stars, CLS29, is likely to be a previously unrecognised dwarf carbon star.

Spectral analysis of the Stromlo-APM Survey -- I. Spectral properties of galaxies

We analyse spectral properties of 1671 galaxies from the Stromlo—APM Survey, selected to have 15 ≤ bJ ≤ 17.15 and having a mean redshift z = 0.05. This is a representative local sample of field galaxies, so the global properties of the galaxy population provide a comparative point for analysis of more distant surveys. We measure Hα, [O ii] λ3727, [S ii] λλ6716, 6731, [N ii] λ6583 and [O i] λ6300 equivalent widths and the D4000 break index. The 5-Å-resolution spectra use an 8-arcsec slit, which typically covers 40-50 per cent of the galaxy area. We find no evidence for systematic trends depending on the fraction of galaxy covered by the slit, and further analysis suggests that our spectra are representative of integrated galaxy spectra. We classify spectra according to their Hα emission, which is closely related to massive star formation. Overall we find that 61 per cent of galaxies are Hα emitters with rest-frame equivalent widths EW(Hα) ≳2 Å. The emission-line galaxy (ELG) fraction is smaller than seen in the Canada—France Redshift Survey (CFRS) at z = 0.2, and is consistent with a rapid evolution of Hα luminosity density. The ELG fraction and EW(Hα) increase at fainter absolute magnitudes, smaller projected area and smaller D4000. In the local Universe, faint, small galaxies are dominated by star formation activity, while bright, large galaxies are more quiescent. This picture of the local Universe is quite different from that of the distant one; bright galaxies appear to show rapidly increasing activity as one moves further back in time. We find that the ratio [N ii] λ6583/Hα is anticorrelated with EW(Hα), and that the value of 0.5 commonly used to remove the [N ii] contribution from blended Hα+[N ii] λλ6548, 6583 applies only for samples with an EW distribution similar to that seen at low redshift. We show that the [O ii], [N ii], [S ii] and Hα EWs are correlated, but with large dispersions (∼50 per cent) owing to the diversity of galaxy contents sampled. Our [O ii]-Hα relation is similar to the one derived by Kennicutt, but is 10 per cent higher at 1σ significance. We show that this relation is not valid for distant, strong [O ii] emitters with blue colours, which are more numerous than locally. This relation would overestimate the individual star formation rate by ∼50 per cent for these kinds of galaxies. We find that, on average, luminous blue ELGs are likely to be enhanced in nitrogen abundance. This suggests that in faint, low-mass, late-type ELGs nitrogen is a primary element, whereas in brighter, more massive galaxies nitrogen comes from a secondary source. We also find that 4 per cent of early-type galaxies show star formation activity; this fraction seems to increase at higher redshifts.

The Projected Three-Point Correlation Function: Theory and Observations

We report results for the angular three-point galaxy correlation function in the APM survey and compare them with theoretical expectations. For the first time, these measurements extend to sufficiently large scales to probe the weakly non-linear regime. On large scales, the results are in good agreement with the predictions of non-linear cosmological perturbation theory, for a model with initially Gaussian fluctuations and linear power spectrum $P(k)$ consistent with that inferred from the APM survey. These results reinforce the conclusion that large-scale structure is driven by non-linear gravitational instability and that APM galaxies are relatively unbiased tracers of the mass on large scales; they also provide stringent constraints upon models with non-Gaussian initial conditions and strongly exclude the standard cold dark matter model.

Non-Gaussian Isocurvature Models

Peebles (1997) has proposed a non-Gaussian χ2isocurvature model which gives rise to early galaxy assembly at redshifts ≥ 3–4. We test whether the higher order moments (skewness and kurtosis) of such a model are compatible with the moments of the observed density field, and find that in the absence of bias these models produce moments that are much higher than those measured for the APM survey (Gaztañaga, 1994). We have applied different biasing schemes to see whether bias can bring the moments down, and find that for power law, Cen-Ostriker, and censor threshold biasing schemes (Mann et al 1997) the moments can be brought into agreement with the APM measurements only for linear bias valuesb&gt; 3. This however, would give a redshift distortion parameter, βopticai= (Ω0.6/b) &lt; 0.16 which is inconsistent with current estimates from redshift surveys of βoptical= 0.40 ± 0.12 (e.g. Peacock 1997). We conclude that for an acceptable level of bias in the schemes we have tested, the χ2isocurvature model moments disagree with current measurements of skewness and kurtosis from the APM survey.

Tidal Torques Dynamical Friction and the Structure of Clusters of Galaxies

We study the joint effect of tidal torques and dynamical friction on the collapse of density peaks solving numerically the equations of motion of a shell of barionic matter falling into the central regions of a cluster of galaxies. We calculate the evolution of the expansion parameter, a(t), of the perturbation using a coefficient of dynamical friction ηcl obtained from a clustered system and taking into account the gravitational interaction of the quadrupole moment of the system with the tidal field of the matter of the neighboring proto-galaxies. We find that the tidal torques and the dynamical friction slow down the collapse of low-v (v &lt; 3) peaks producing an observable variation of a(t) (Del Popolo &amp; Gambera 1996,1997). As consequence we have a reduction of the mass bound to collapsed perturbations and a raising of the critical threshold, δc. Besides, we have a bias of dynamical nature arises because high-density peaks preferentially collapse to form halos within which visible objects. We calculate the selection function and using it and the prescriptions given by Bardeen et al. 1986 we find a value of the coefficient of bias, b = 2.25 on clusters scales for Rf = 4h–1Mpc comparable both with that obtained from the mean mass-to-light ratio of clusters, APM survey, or from N-body simulations combined with hydrodynamical models and with the values of b given by Kauffmann et al. 1996. This means that non-radial motions and dynamical friction play a significant role in determining the bias level.

Angular correlations between LBQS and APM: weak lensing by the large-scale structure

We detect a positive angular correlation between bright, high-redshift QSOs and foreground galaxies. The QSOs are taken from the optically selected LBQS Catalogue, while the galaxies are from the APM Survey. The correlation amplitude is about a few percent on angular scales of over a degree. It is a function of QSO redshift and apparent magnitude, in a way expected from weak lensing, and inconsistent with QSO-galaxy correlations being caused by physical associations, or uneven obscuration by Galactic dust. The correlations are ascribed to the weak lensing effect of the foreground dark matter, which is traced by the APM galaxies. The amplitude of the effect found here is compared to the analytical predictions from the literature, and to the predictions of a phenomenological model, which is based on the observed counts-in-cells distribution of APM galaxies. While the latter agree reasonably well with the analytical predictions (namely those of Dolag & Bartelmann 1997, and Sanz et al. 1997), both under-predict the observed correlation amplitude on degree angular scales. We consider the possible ways to reconcile these observations with theory, and discuss the implications these observations have on some aspects of extragalactic astronomy.

Low Surface Brightness Galaxies in the Local Universe. III. Implications for the Field Galaxy Luminosity Function

We present a luminosity function for low surface brightness (LSB) galaxies identified in the APM survey of Impey et al 1996. These galaxies have central surface brightnesses in B in the range 22 < mu < 25. Using standard maximum-likelihood estimators, we determine that the best-fit Schechter function parameters for this luminosity function (LF) are alpha = -1.42, M* = -18.34, and phi* = 0.0036, assuming H_0 = 100. We compare these results to those of other recent studies and find that surveys which do not take account of the observation selection bias imposed by surface brightness are missing a substantial fraction of the galaxies in the local universe. Under our most conservative estimates, our derivation of the LF for LSB galaxies suggests that the CfA redshift survey has missed at least one third of the local galaxy population. This overlooked fraction is not enough by itself to explain the large number of faint blue galaxies observed at moderate redshift under no-evolution models, but it does help close the gap between local and moderate-redshift galaxy counts.

Large-scale fluctuations in the distribution of galaxies

The null hypothesis that the three dimensional power spectrum measured from the APM Survey is consistent with the one dimensional power spectrum measured from the pencil beams surveys of Broadhurst et al and of Szalay et al is tested. The external estimates of the mean power that we make are sensitive to details of the model for the survey geometry and to the assumed level of the distortion of the pattern of galaxy clustering caused by peculiar motions. We find that the measured 3D clustering of galaxies can account for the presence of peaks in the one dimensional power spectrum, but is less successful in recovering the detailed appearence of the observations. We find no strong evidence for any additional large scale structure in the deep pencil beams beyond that recovered from the APM Survey. We conclude therefore that it is unlikey that large scale structure can be responsible for the steep local number counts of bright galaxies.

Testing Ansatze for quasi-non-linear clustering: the linear APM power spectrum

We compare the accuracy of published formulae that transform the linear perturbation theory power spectrum into the nonlinear regime against the results of an ensemble of large N-body simulations. We find that the modified transformation given by Jain, Mo and White (1995) performs well for initial fluctuations that have a power law power spectrum, but is less succesful for scale dependent spectra. The inverse transformation to obtain the linear power spectrum is applied to the APM Galaxy Survey power spectrum measured by Baugh \& Efstathiou (1993). The resulting linear spectrum is used to generate the initial density fluctuations in an N-body simulation, which is evolved to match the measured APM amplitude on large scales. We find very good agreement between the final power spectrum of the simulation and the measured APM power spectrum. However, the higher moments for the particle distribution only match the ones recovered from the APM Survey on large scales, $R \simgt 10 \mpc$. On small scales, $R \simlt 10 \mpc$, the APM estimations give smaller amplitudes, indicating that non-gravitational effects, such as biasing, are important on those scales. Our approach can be used to constrain a model of how light from galaxies traces the underlying mass distribution.

High-order correlations of peaks and haloes: a step towards understanding galaxy biasing

We develop an analytic model for the hierarchical correlation amplitudes is the jth order connected moment of counts in spheres of radius R) of density peaks and dark matter haloes in the quasi-linear regime. The statistical distributions of density peaks and dark matter haloes within the initial density field (assumed Gaussian) are determined by the peak formalism of Bardeen et al. and by an extension of the Press-Schechter formalism, respectively. Modifications of these distributions caused by gravitationally induced motions are treated using a spherical collapse model. We test our model against results for S3,g(R) and S4,g(R) from a variety of N-body simulations. The model works well for peaks even on scales where the second moment of mass is significantly greater than unity. The model also works successfully for haloes that are identified earlier than the time when the moments are calculated. Because haloes are spatially exclusive at the time of their identification, our model is only qualitatively correct for haloes identified at the same time as the moments are calculated. For currently popular initial density spectra, the values of Sj,g at R ∼ 10 h−1 Mpc are significantly smaller for both haloes and peaks than those for the mass, unless the linear bias parameterb [defined by for large R] is comparable to or less than unity. The Sj,g depend only weakly on b for large b but increase rapidly with decreasing b at b ∼1. Thus if galaxies are associated with peaks in the initial density field, or with dark haloes formed at high redshifts, a measurement of Sj,g in the quasi-linear regime should determine whether galaxies are significantly biased relative to the mass. We use our model to interpret the observed high-order correlation functions of galaxies and clusters. We find that if the values of Sj,gfor galaxies are as high as those given by the APM survey, then APM galaxies should not be significantly biased.

The APM Galaxy Survey -- III. An analysis of systematic errors in the angular correlation function and cosmological implications

We present measurements of the angular two-point galaxy correlation function, $w(theta)$, from the APM Galaxy Survey. The performance of various estimators of $w$ is assessed using simulated galaxy catalogues and analytic arguments. Several error analyses show that residual plate-to-plate errors do not bias our estimates of $w$ by more than $10^{-3}$. Direct comparison between our photometry and external CCD photometry of over 13,000 galaxies from the Las Campanas Deep Redshift Survey shows that the rms error in the APM plate zero points lies in the range 0.04-0.05 magnitudes, in agreement with our previous estimates. We estimate the effects on $w$ of atmospheric extinction and obscuration by dust in our Galaxy and conclude that these are negligible. We use our best estimates of the systematic errors in the survey to calculate corrected estimates of $w$. Deep redshift surveys are used to determine the selection function of the APM Galaxy Survey, and this is applied in Limber's equation to compute how $w$ scales as a function of limiting magnitude. Our estimates of $w$ are in excellent agreement with the scaling relation, providing further evidence that systematic errors in the APM survey are small. We explicitly remove large-scale structure by applying filters to the APM galaxy maps and conclude that there is still strong evidence for more clustering at large scales than predicted by the standard scale-invariant cold dark matter (CDM) model. We compare the APM $w$ and the three dimensional power spectrum derived by inverting $w$, with the predictions of scale-invariant CDM models. We show that the observations require $Gamma=Omega_0 h$ in the range 0.2-0.3 and are incompatible with the value $Gamma=0.5$ of the standard CDM model.

The real-space correlation function measured from the APM Galaxy Survey

We present a determination of the real space correlation function for galaxies in the APM Survey, with magnitudes in the range $17 < b_J < 20$. We recover a power law form for the correlation function $\xi(r) = (r/4.5)^{-1.7}$ on scales $r < 4 Mpc/h$, for a flat universe and clustering that is fixed in comoving coordinates.If we assume that clustering evolves according to linear perturbation theory, we obtain $\xi(r) = (r/5.25)^{-1.7}$. We recover a shoulder feature in $\xi(r)$ for scales $4 < r < 25 Mpc/h$, with the correlation function rising above the power law, before becoming consistent with zero around $r > 40 Mpc/h$. The form we obtain for $\xi(r)$ is smooth on large scales, allowing a determination of the distortions in the correlation function in redshift space, caused by the peculiar motions of galaxies to be made. Comparing the real space correlation function with the measurement of the redshift space correlation function by Loveday et al (1995), we find that a value for $omega^{0.6}/b$ (where $\omega$ is the density parameter of the universe and b is the bias factor between the density of light and mass) of unity is ruled out at the 2 sigma level.

The real-space power spectrum of IRAS galaxies on large scales and the redshift distortion

Galaxy redshift surveys contain valuable cosmological information on the power spectrum of galaxy clustering, but the information is not easily obtained because of distortion of the map arising from the use of redshift as a distance indicator. The distortion arises because of peculiar velocities, the magnitude of which depends on the mean density of the Universe. Using a spherical transform of the data which correctly accounts for the radial nature of the distortion, we calculate simultaneously the real-space power spectrum and the distortion, for the near-all-sky Infrared Astronomical Satellite (IRAS) 1.2-Jy survey. For the distortion, we find |$\beta=1.04\pm0.3$|⁠, where |$\beta\equiv\Omega^{0.6}_0/b$|⁠, and b is the IRAS linear bias parameter. We constrain the power spectrum on large scales with wavenumbers 0.01 ≲ k ≲ 0.1 h Mpc−1 where the ‘distant-observer’ Fourier approximation should not be used. Power is not convincingly detected at wavenumbers less than 0.03 h Mpc−1, but the power spectrum is consistent with a change in slope from the k−1.5 behaviour observed on smaller scales to Zeldovich spectrum on large scales. In the wavenumber range considered, we find somewhat less power than in the optically selected APM survey.