R. Fong

The Durham/UKST Galaxy Redshift Survey – IV. Redshift-space distortions in the two-point correlation function

We have investigated the redshift space distortions in the optically selected Durham/UKST Galaxy Redshift Survey using the 2-point galaxy correlation function perpendicular and parallel to the observer’s line of sight, �(�,�). We present results for the real space 2-point correlation function, �(r), by inverting the optimally estimated projected correlation function, which is obtained by integration of �(�,�), and find good agreement with other real space estimates. On small, non-linear scales we observe an elongation of the constant �(�,�) contours in the line of sight direction. This is due to the galaxy velocity dispersion and is the common “Finger of God” effect seen in redshift surveys. Our result for the one-dimensional pairwise rms velocity dispersion is 1/2 = 416 ± 36kms 1 which is consistent with those from recent redshift surveys and canonical values, but inconsistent with SCDM or LCDM models. On larger, linear scales we observe a compression of the �(�,�) contours in the line of sight direction. This is due to the infall of galaxies into overdense regions and the Durham/UKST data favours a value of ( 0.6 /b)�0.5, where is the mean mass density of the Universe and b is the linear bias factor which relates the galaxy and mass distributions. Comparison with other optical estimates yield consistent results, with the conclusion that the data does not favour an unbiased critical-density universe.

THE DURHAM/UKST GALAXY REDSHIFT SURVEY - III. LARGE-SCALE STRUCTURE VIA THE TWO-POINT CORRELATION FUNCTION

ABSTRACT We have investigated the statistical clustering properties of galaxies by calculating the2-point galaxy correlation function from the Durham/UKST Galaxy Redshift Survey.This survey is magnitude limited to b J ∼ 17, contains ∼2500galaxiessampled at a rateof one on three and surveysa ∼4×10 6 (h −1 Mpc) 3 volume of space. We have empiricallydetermined the optimalmethod ofestimatingthe 2-point correlationfunction from justsuch a magnitude limited survey. Applying our methods to this survey,we find that ourredshift space results agreewell with those from previous optical surveys.In particular,we confirm the previously claimed detections of large scale power out to ∼40h −1 Mpcscales. We compare with two common models of cosmological structure formationand find that our 2-point correlation function has power significantly in excess of thestandard cold dark matter model in the 10-30h −1 Mpc region. We therefore supportthe observational results of the APM galaxy survey. Given that only the redshift spaceclustering can be measured directly we use standard modelling methods and indirectlyestimate the real space 2-point correlation function. This real space 2-point correlationfunction has a lower amplitude than the redshift space one but a steeper slope.Key words: galaxies: clusters – galaxies: general – cosmology: observations – large-scale structure of Universe.

Galaxy clustering in the Herschel Deep Field

ABSTRA C T We present a study of the angular correlation function as measured in the William Herschel Deep Field, a high galactic latitude field which has been the subject of an extensive observing campaign from optical to infrared wavelengths. It covers 50 arcmin 2 and with it we are able to investigate the scaling of the angular correlation function to B , 28; R; I , 26, K , 20 and H , 22:5: We compare our measurements to results obtained from the smaller Hubble Deep Field. To interpret our results, we use a model which correctly predicts colours, number counts and redshift distributions for the faint galaxy population. We find that at fixed separation the amplitude of v (u ) measured in BRI bandpasses is lower than the predictions of a model containing no luminosity evolution and stable clustering growth in proper coordinates. However, in the near-infrared bandpasses, our measurements are consistent with the predictions of an essentially non-evolving K-selected galaxy redshift distribution. In the range B , 27‐28 we find that our correlation amplitudes are independent of magnitude, which is consistent with the observed flattening of the number count slope and correspondingly slower increase of the cosmological volume element expected at these magnitudes. If our luminosity evolution models provide a correct description of the underlying redshift distributions (and comparisons to available observations at brighter magnitudes suggest they do), then our measurements in all bandpasses are consistent with a rapid growth of galaxy clustering O0 , e , 2 in the normal parametrization) on the sub-Mpc scales which our survey probes. We demonstrate that this rapid growth of clustering is consistent with the predictions of biased models of galaxy formation, which indicate that a rapid rate of clustering growth is expected for the intrinsically faint galaxies which dominate our survey.

New Observations of Galaxy Number Counts

A well determined galaxy number-magnitude, n(m), relation contains important information on both galaxy luminosity evolution and cosmological world models and there have therefore been many recent attempts to observationally determine the form of n(m) to faint limits, in both blue and red passbands (Kron 1978, Tyson and Jarvis 1979, Peterson et al 1979, Koo 1981, Shanks et al 1984a; hereafter SSFM). However, the observational results from different authors in different fields, particularly in the blue passband, showed a spread in the observed n(m) relation at faint blue magnitudes (B∿23m) of approximately one magnitude (see SSFM Fig. 11)., More surprisingly SSFM also found that the form of n(m) seems to be not much better determined at bright (B∿17m) magnitudes. This creates a problem for the faint count interpretation since the normalisation of the faint count models then become less certain.

Galaxy Number‐Counts to B = 28m

Counting the number of galaxies as a function of their apparent brightness is one of the fundamental cosmological tests, providing an important probe of both the geometry and evolutionary history of the Universe. CCD detectors have in recent years enabled astronomers to explore magnitude limits undreamed of a decade or so ago, and where important constraints can be placed on the allowable combinations of q 0 and evolution. Recent work has shown that the B-band counts keep rising with a power-law distribution, with a fivefold excess in the number of galaxies at B = 26.5 over that expected from simple non-evolving models. Indeed, it has been suggested that the total numbers of galaxies already seen may be too high for a q 0 = 0.5 universe, assuming there is a redshift cut-off in the galaxy distribution caused either by galaxies having strong Lyman limit systems or a low redshift of formation. As q 0 = 0.5 is favoured by theoretical arguments, it is important to see if the behaviour of the counts at even fainter magnitudes can be reconciled with a high density universe. Most published counts are unreliable faintward of B ≈ 26, as the incompleteness corrections required become comparable in size to the data. We have now extended the counts to B ∼ 28, using a ∼ 24 hour CCD exposure taken on the 2.5 m Isaac Newton telescope (INT) on La Palma, together with a ∼ 10 hour exposure on a small part of this field taken using the 4.2 m William Herschel Telescope (WHT).

The Durham/UKST Galaxy Redshift Survey

We are currently engaged in a long-term project to make a redshift survey of ~ 4000 galaxies based on the Durham/ROE Southern Galaxy Catalogue (Collins et al., 1988) which is a COSMOS survey of the 2D distribution of b j > 20.5m galaxies over 60 UK Schmidt Telescope (UKST) fields. The current programme makes further use of the UKST in conjunction with FLAIR, a fibre-coupled spectroscopy system. The ultimate aim is to map the 3D distribution of galaxies over all 60 high galactic latitude fields by making a 1-in-3 random sampled redshift survey of b j ≲ 16.75m galaxies. We are currently able to observe 61 galaxies simultaneously per 5° x 5° field using the Durham dual CCD camera coupled to 2 FLAIR spectrographs.

Galaxy Clustering to B = 27m

The angular two-point correlation function, ω(θ), for galaxies can be used as a probe of their redshift distribution N(z) and, therefore, of galaxy luminosity evolution. Without redshift data, we can still observe the projection onto the two-dimensional sky of the three-dimensional clustering of galaxies. The autocorrelation of this projected distribution is described by ω(θ). Observations have indicated that ω(θ) follows a o(su2010;0,8 power-law (Peebles 1980) and that the index of the power-law remains approximately constant to the faintest limits of photographic surveys (Jones, Shanks & Fong 1987).

The Clustering and Evolution of Optically-Selected QSOs

We are in the process of compiling a large catalogue of faint (B < 20.9 mag), UVX selected QSOs with complete spectroscopic identification using the fibre optic (FOCAP) system at the Anglo-Australian Telescope. From the 220 QSOs thus far identified we find that QSO evolution is most simply parameterised by a uniform increase in luminosity towards higher redshifts. We also find evidence for strong QSO clustering at scales < 10h−1 Mpc.

Correlation Analyses of Galaxy Clustering to B ~ 24

Estimates of the angular two-point galaxy correlation function, w(θ), are presented as obtained from COSMOS machine measurements of 1.2m UK Schmidt telescope (UKST) and 4m Anglo-Australian telescope (AAT) plates. The UKST plates cover an area of sky of ~ 170 square degrees, some four times larger than any previous study to these depths. The new estimate of w(θ) shows a break from its -0.8 power law behaviour at a scale corresponding to a spatial separation of 3h−1Mpc, (where h = Hubble’s constant in units of 100 Kms−1Mpc−l) in agreement with the earlier results of Shanks et al (1980).

Dark matter in voids

The theory of the formation of large‐scale structure in the universe through the action of gravitational instability imply the existence of substantial amounts of baryonic dark matter, of the order of 50% of the total baryon content in the universe, in the ‘‘voids’’ or under‐dense regions seen in the large‐scale distribution of galaxies. We discuss also the large‐scale structure of dark matter expected in voids and the present and future possibilities for the observation of this baryonic dark matter in ‘‘voids.’’