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T. Shanks

Publications and source records attributed to T. Shanks.

At least 73 records · Page 4Linked to original sources
arXiv2008

QSO Lensing Magnification: A Comparison of 2QZ and SDSS Results

The lensing of background QSOs by foreground galaxies is a powerful probe of the mass density of the Universe and the power spectrum of mass clustering. However, the 2dF QSO survey suggested that a strong anticorrelation effect at g<21 was seen for both galaxies and clusters which implied that galaxies are anti-biased (b~0.1) on small scales at a higher level than predicted by the standard cosmology (Myers et al., 2003, 2005) whereas results from SDSS suggested that the effect was much smaller (b~0.6) and in line with standard expectations (Scranton et al., 2005). We first cross-correlate the SDSS photo-z, g<21, 1.0<z_p<2.2 QSOs with g<21 galaxies and clusters in the same areas. These results are somewhat less negative than the results based on the 2QZ QSOs found by Myers et al. But contamination of the QSOs by low-z NELGs and QSOs can cause underestimation of the anticorrelation lensing signal. When a correction is applied to the photo-z QSO sample of Scranton et al. the anticorrelation increases and the agreement with the results of Myers et al. is improved. When we also take into account the fainter r<21 galaxy limit of Scranton et al. as opposed to g<21 for Myers et al., the two observational results appear to be in very good agreement. This therefore leaves open the question of why the theoretical interpretations are so different for these analyses. We note that the results of Guimaraes, Myers & Shanks based on mock catalogues from the LCDM Hubble Volume strongly suggest that QSO lensing at the levels detected by both Myers et al. and now Scranton et al. is incompatible with a galaxy bias of b~1 in the standard cosmological model. If the QSO lensing results are correct then the consequences for cosmology may be significant (see Shanks 2006).

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arXiv2008

QSO-LRG 2-Point Cross-Correlation Function and Redshift-Space Distorions

We have measured the bias of QSOs as a function of QSO luminosity at fixed redshift (z<1) by cross-correlating them with LRGs in the same spatial volume, hence breaking the degeneracy between QSO luminosity and redshift. We use three QSO samples from 2SLAQ, 2QZ and SDSS covering a QSO absolute magnitude range, -24.5<M_{b_J}<-21.5, and cross-correlate them with 2SLAQ (z~0.5) and AAOmega (z~0.7) photometric and spectroscopic LRGs in the same redshift ranges. The 2-D and 3-D cross-clustering measurements are generally in good agreement. Our (2SLAQ) QSO-LRG clustering amplitude (r_0=6.8_{-0.3}^{+0.1}h^{-1}Mpc) as measured from the semi-projected cross-correlation function appears similar to the (2SLAQ) LRG-LRG auto-correlation amplitude (r_0=7.45\pm0.35h^{-1}Mpc) and both are higher than the (2QZ+2SLAQ) QSO-QSO amplitude (r_0\simeq5.0h^{-1}Mpc). Our measurements show remarkably little QSO-LRG cross-clustering dependence on QSO luminosity. If anything, the results imply that brighter QSOs may be less highly biased than faint QSOs, the opposite direction expected from simple high peaks biasing models. Assuming a standard LCDM model and values for b_{LRG} measured from LRG autocorrelation analyses, we find b_Q=1.45\pm0.11 at M_{b_J}\approx-24 and b_Q=1.90\pm0.16 at M_{b_J}~-22. We also find consistent results for the QSO bias from a z-space distortion analysis of the QSO-LRG cross-clustering at z~0.55. The dynamical infall results give β_Q=0.55\pm0.10, implying b_Q=1.4\pm0.2. Thus both the z-space distortion and the amplitude analyses yield b_Q~1.5 at M_{b_J}~-23. The implied DM halo mass inhabited by QSOs at z~0.55 is \sim10^{13}h^{-1}M_{\sun}, again approximately independent of QSO luminosity.

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arXiv2007

The 2dF-SDSS LRG and QSO Survey: The LRG 2-Point Correlation Function and Redshift-Space Distortions

We present a clustering analysis of Luminous Red Galaxies (LRGs) using nearly 9 000 objects from the final catalogue of the 2dF-SDSS LRG And QSO (2SLAQ) Survey. We measure the redshift-space two-point correlation function, xi(s), at the mean LRG redshift of z=0.55. A single power-law fits the deprojected correlation function, xi(r), with a correlation length of r_0=7.45+-0.35 Mpc and a power-law slope of gamma=1.72+-0.06 in the 0.4<r<50 Mpc range. But it is in the LRG angular correlation function that the strongest evidence for non-power-law features is found where a slope of gamma=-2.17+-0.07 is seen at 1<r<10 Mpc with a flatter gamma=-1.67+-0.03 slope apparent at r<~1 Mpc scales. We use the simple power-law fit to the galaxy xi(r) to model the redshift space distortions in the 2-D redshift-space correlation function, xi(sigma,pi). We fit for the LRG velocity dispersion, w_z, Omega_m and beta, where beta=Omega_m^0.6/b and b is the linear bias parameter. We find values of w_z=330kms^-1, Omega_m= 0.10+0.35-0.10 and beta=0.40+-0.05. These high redshift results, which incorporate the Alcock-Paczynski effect and the effects of dynamical infall, start to break the degeneracy between Omega_m and beta found in low-redshift galaxy surveys. This degeneracy is further broken by introducing an additional external constraint, the value of beta(z=0.1)=0.45 from 2dFGRS, and then considering the evolution of clustering from z~0 to z_LRG~0.55. With these combined methods we find Omega_m(z=0)=0.30+-0.15 and beta(z=0.55)=0.45+-0.05. Assuming these values, we find a value for b(z=0.55)=1.66+-0.35. We show that this is consistent with a simple ``high peaks'' bias prescription which assumes that LRGs have a constant co-moving density and their clustering evolves purely under gravity. [ABRIDGED]

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arXiv2007

Anomalous SZ Contribution to 3 Year WMAP Data

We first show that the new WMAP 3 year data confirm the detection by Myers et al 2004 of an extended SZ signal centred on 606 Abell (ACO) clusters with richness class, R>1. Our results also show SZ decrements around APM and 2MASS groups at increased significance than previously detected. We then follow the approach of Lieu et al 2006 and compare the stacked WMAP results for the decrement in 31 clusters with ROSAT X-ray profiles where Lieu et al found on average less SZ decrement in the WMAP 1 year data than predicted. We confirm that in the 3 year data these same clusters again show less SZ decrement than the X-ray data predicts. We then analysed the WMAP results for the 38 X-ray clusters with OVRO/BIMA measured SZ decrements as presented by Bonamente et al 2006. We again find that the average decrement is measured to be significantly less (5.5 sigma) than predicted by the Chandra X-ray data. Thus while we confirm the original detection of an extended SZ effect by Myers et al 2004, these X-ray comparisons may now suggest that the central SZ amplitudes detected by WMAP may actually be lower than expected. One possible explanation is that there is contamination of the WMAP SZ signal by radio sources in the clusters but we argue that this appears implausible. We then consider the possibility that the SZ decrement has been lensed away by foreground galaxy groups. Such a model predicts that the SZ decrement should depend on cluster redshift. A reduction in the SZ decrement with redshift is suggested from the ACO cluster sample and also from comparing the samples of Lieu et al 2006 and Bonamente et al 06. However, the mass power-spectrum would require a far higher amplitude than currently expected if lensing was to explain the SZ deficit in high redshift clusters.

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arXiv2007

The Effect of Lensing on the Large-Scale CMB Anisotropy

We first compare the CMB lensing model of Seljak (1996) with the empirical model of Lieu & Mittaz (2005) to determine if the latter approach implies a larger effect on the CMB power-spectrum. We find that the empirical model gives significantly higher results for the magnification dispersion, assuming standard cosmological parameters. However, when the empirical foreground model is modelled via correlation functions and used in the Seljak formalism, the agreement is considerably improved. Thus we conclude that the main difference may be in the assumed foregrounds. We then discuss a foreground mass distribution which gives a lensing dispersion which is constant with angle. In Seljak's formalism, we show this can lead to a smoothing of the CMB power-spectrum which may be able to move the first acoustic peak to smaller l, if the mass clustering amplitude is high enough. Evidence for such a high amplitude comes from the QSO magnification results of Myers et al (2003, 2005) who suggest that foreground galaxy groups may be more massive than expected, implying that Omega_m ~ 1 and strong galaxy anti-bias. We then show that an inflationary model with neither CDM nor a cosmological constant and that predicts a primordial first peak at l=330 may fit the first acoustic peak of the WMAP data. This fit may be regarded as somewhat contrived since it also requires high redshift reionisation at the upper limit of what is allowed by the WMAP results. But given the finely-tuned nature of the standard LCDM model, the contrivance may be small in comparison and certainly the effect of lensing and other foregrounds may still have a considerable influence on the cosmological interpretation of the CMB.

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arXiv2006

The 2dF-SDSS LRG and QSO Survey: QSO clustering and the L-z degeneracy

We combine the QSO samples from the 2dF QSO Redshift Survey (2QZ) and the 2dF-SDSS LRG and QSO Survey (2SLAQ) in order to investigate the clustering of z~1.4 QSOs and measure the correlation function. The clustering signal in z-space, projected along the sky direction, is similar to that previously obtained from 2QZ alone. By fitting the z-space correlation function and lifting the degeneracy between beta and Omega_m_0 by using linear theory predictions, we obtain beta(z=1.4) = 0.60+-0.12 and Omega_m_0=0.25+-0.08, implying a value for the QSO bias, b(z=1.4)=1.5+-0.2. We further find that QSO clustering does not depend strongly on luminosity at fixed redshift. This result is inconsistent with the expectation of simple `high peaks' biasing models where more luminous, rare QSOs are assumed to inhabit higher mass haloes. The data are more consistent with models which predict that QSOs of different luminosities reside in haloes of similar mass. We find that halo mass does not evolve strongly with redshift nor depend on QSO luminosity. We finally investigate how black hole mass correlates with luminosity and redshift and ascertain the relation between Eddington efficiency and black hole mass. Our results suggest that QSOs of different luminosities may contain black holes of similar mass.

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arXiv2006

The evolution of host mass and black hole mass in QSOs from the 2dF QSO Redshift Survey

We investigate the relation between the mass of super-massive black holes (Mbh) in QSOs and the mass of the dark matter halos hosting them (Mdh). We measure the widths of broad emission lines (Mgii lambda 2798, Civ lambda 1549) from QSO composite spectra as a function of redshift. These widths are then used to determine virial black hole mass estimates. We compare our virial black hole mass estimates to dark matter halo masses for QSO hosts derived by Croom et al. (2005) based on measurements of QSO clustering. This enables us to trace the Mbh-Mdh relation over the redshift range z=0.5 to 2.5. We calculate the mean zero-point of the Mbh-Mdh relation to be Mbh=10^(8.4+/-0.2)Msun for an Mdh=10^(12.5)Msun. These data are then compared with several models connecting Mbh and Mdh as well as recent hydrodynamical simulations of galaxy evolution. We note that the flux limited nature of QSO samples can cause a Malmquist-type bias in the measured zero-point of the Mbh-Mdh relation. The magnitude of this bias depends on the scatter in the Mbh-Mdh relation, and we reevaluate the zero-point assuming three published values for this scatter. (abridged)

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arXiv2006

The 2dF-SDSS LRG and QSO survey: Evolution of the Luminosity Function of Luminous Red Galaxies to z=0.6

We present new measurements of the luminosity function (LF) of Luminous Red Galaxies (LRGs) from the Sloan Digital Sky Survey (SDSS) and the 2dF-SDSS LRG and Quasar (2SLAQ) survey. We have carefully quantified, and corrected for, uncertainties in the K and evolutionary corrections, differences in the colour selection methods, and the effects of photometric errors, thus ensuring we are studying the same galaxy population in both surveys. Using a limited subset of 6326 SDSS LRGs (with 0.17<z<0.24) and 1725 2SLAQ LRGs (with 0.5 <z<0.6), for which the matching colour selection is most reliable, we find no evidence for any additional evolution in the LRG LF, over this redshift range, beyond that expected from a simple passive evolution model. This lack of additional evolution is quantified using the comoving luminosity density of SDSS and 2SLAQ LRGs, brighter than M_r - 5logh = -22.5, which are 2.51+/-0.03 x 10^-7 L_sun Mpc^-3 and 2.44+/-0.15 x 10^-7 L_sun Mpc^-3 respectively (<10% uncertainty). We compare our LFs to the COMBO-17 data and find excellent agreement over the same redshift range. Together, these surveys show no evidence for additional evolution (beyond passive) in the LF of LRGs brighter than M_r - 5logh = -21 (or brighter than L*). We test our SDSS and 2SLAQ LFs against a simple ``dry merger'' model for the evolution of massive red galaxies and find that at least half of the LRGs at z=0.2 must already have been well-assembled (with more than half their stellar mass) by z=0.6. This limit is barely consistent with recent results from semi-analytical models of galaxy evolution.

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arXiv2006

The 2dF-SDSS LRG and QSO (2SLAQ) Luminous Red Galaxy Survey

We present a spectroscopic survey of almost 15,000 candidate intermediate-redshift Luminous Red Galaxies (LRGs) brighter than i=19.8, observed with 2dF on the Anglo-Australian Telescope. The targets were selected photometrically from the Sloan Digital Sky Survey (SDSS) and lie along two narrow equatorial strips covering 180 sq deg. Reliable redshifts were obtained for 92% of the targets and the selection is very efficient: over 90% have redshifts between 0.45 and 0.8. More than 80% of the ~11,000 red galaxies have pure absorption-line spectra consistent with a passively-evolving old stellar population. The redshift, photometric and spatial distributions of the LRGs are described. The 2SLAQ data will be released publicly from mid-2006, providing a powerful resource for observational cosmology and the study of galaxy evolution.

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arXiv2005

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<14 counts from 2MASS. First, we examine 2MASS counts extracted for the 4000 sq.deg. APM survey area and find a deficiency of 25% at H=13, in line with previous results. In addition the |b|>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.

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arXiv2005

An H-band survey of the Herschel Deep Field

We present H-band infra-red galaxy data to a 3 sigma limit of H=22.9 and optical-infra-red colours of galaxies on the William Herschel Deep Field. These data were taken from a 7'x 7' area observed for 14 hours with the Omega Prime camera on the 3.5-m Calar Alto telescope. We derive H-band number counts, colour-magnitude diagrams and colour histograms. We review our Pure Luminosity Evolution galaxy count models based on the spectral synthesis models of Bruzual & Charlot. These PLE models give an excellent fit to the our H band count data to H<22.5 and HDF count data to H<28. However, PLE models with a Salpeter IMF for early-type galaxies overestimate the average galaxy redshift in K<20 galaxy redshift surveys. Models that assume a steep x=3 IMF give better agreement data, although they do show an unobserved peak in B-H and I-H colour distributions at faint H magnitudes corresponding to z>1 early-type galaxies. This feature may simply reflect a larger scatter in optical-infra-red colours than in the B-R colour of early-type galaxies at this redshift. This scatter is obvious in optical-IR colour-colour diagrams and may be explained by on-going star-formation in an intermediate sub-population of early-type galaxies. The numbers of EROs detected are a factor of 2-3 lower than predicted by the early-type models that assume the Salpeter IMF and in better agreement with those that assume the x=3 IMF. The tight sequence of early-type galaxies also shows a sub-class which is simultaneously redder in infrared bands and bluer in the bluer bands than the classical, passive early-type galaxy; this sub-class appears at relatively low redshifts and may constitute an intermediate age, early-type population.

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arXiv2005

High-order 2MASS galaxy correlation functions: Probing the primordial density field and the linearity of galaxy bias

We use the 2MASS extended source catalogue to determine angular correlation functions, w_p, to high orders (p<=9). The main sample contains 650,745 galaxies and represents an order of magnitude increase in solid angle over previous samples used in such analysis. The high-order correlation functions are used to determine the projected and real space hierarchical amplitudes, s_p and S_p. In contrast to recent results, for p<=6 these parameters are found to be quite constant over a wide range of scales to r=40 Mpc, consistent with a Gaussian form to the primordial distribution of density fluctuations which has evolved under the action of gravitational instability. We test the sensitivity of our results to the presence of rare fluctuations in the local galaxy distribution by cutting various regions of over-density from the main sample; unlike previous analyses, we find that our results are relatively robust to the removal of the largest superclusters. We use our constraints on the K-band S_p parameters in two ways. First, we examine their consistency with non-Gaussian initial conditions; we are able to rule out strong non-Gaussianity in the primordial density field, as might be seeded by topological defects such as cosmic strings or global textures at the 2.5 sigma confidence level. Second, we investigate the way in which galaxies trace the underlying mass distribution. We find evidence for a non-zero quadratic contribution to the galaxy bias, parameterised by c_2=0.57+/-0.33. This positive result represents a significant difference from the negative values found previously; we examine a possible explanation in the light of recent observations which universally provide negative values for c_2.

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arXiv2005

The 2MASS galaxy angular power spectrum: Probing the galaxy distribution to Gigaparsec scales

We present an angular power spectrum analysis of the 2MASS full release extended source catalogue. The main sample used includes 518,576 galaxies below an extinction-corrected magnitude of K=13.5 and limited to |b|>20. The power spectrum results provide an estimate of the galaxy density fluctuations at extremely large scales, r<1000 Mpc. We compare this with mock predictions constructed from the LCDM Hubble Volume mock catalogue. We find that over the range 1 50 Mpc). We obtain constraints on the galaxy power spectrum shape of Gamma=0.14+/-0.02, in good agreement with previous estimates inferred at smaller scales. We also constrain the galaxy power spectrum normalisation to (sigma_8 b_K)^2=1.36+/-0.10; in combination with previous constraints on sigma_8 we infer a K-band bias of b_K=1.39+/-0.12. We are also able to provide weak constraints on Omega_m h and Omega_b/Omega_m. These results are based on the usual assumption that the errors derived from the Hubble Volume mocks are applicable to all other models. If we instead assume that the error is proportional to the C_l amplitude then the constraints weaken; for example it becomes more difficult to reject cosmologies with lower Gamma.

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arXiv2005

Constraining beta(z) and Omega_m from redshift-space distortions in z~3 galaxy surveys

We use sample of 813 Lyman-break galaxies (LBGs) with 2.6<z<3.4 to perform a detailed analysis of the redshift-space (z-space) distortions in their clustering pattern and from them derive confidence levels in the [Omega_m,beta(z=3)] plane. We model the z-space distortions in the shape of the correlation function measured in orthogonal directions, xi(sigma,pi). This modeling requires an accurate description of the real-space correlation function to be given as an input. From the projection of xi(sigma,pi) in the angular direction, w_p(sigma), we derive the best fitting amplitude and slope for the LBG real-space correlation function: r_0=4.48(+0.17)(-0.18) h(-1) Mpc and gamma=1.76(+0.08)(-0.09) (xi(r)= (r/r_0)^-gamma). A comparison between the shape of xi(s) and w_p(sigma) suggests that xi(r) deviates from a simple power-law model, with a break at ~9 h(-1) Mpc. This model is consistent with the observed projected correlation function. However, due to the limited size of the fields used, the w_p(sigma) results are limited to sigma < 10 h(-1) Mpc. Assuming this double power-law model, and by analysing the shape distortions in xi(sigma,pi), we find the following constraints: beta(z=3) = 0.15 (+0.20)(-0.15), Omega_m = 0.35 (+0.65)(-0.22). Combining these results with orthogonal constraints from linear evolution of density perturbations, we find that beta(z=3) = 0.25 (+0.05)(-0.06), Omega_m = 0.55 (+0.45)(-0.16).

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arXiv2005

The 2dF QSO Redshift Survey - XV. Correlation analysis of redshift-Space distortions

We analyse the redshift-space (z-space) distortions of QSO clustering in the 2dF QSO Redshift Survey (2QZ). To interpret the z-space correlation function, xi(sigma,pi), we require an accurate model for the QSO real-space correlation function, xi(r). Although a single power-law xi(r) model fits the projected correlation function (wp(sigma)) at small scales, it implies somewhat too shallow a slope for both wp(sigma) and the z-space correlation function, xi(s), at larger scales > 20 h^(-1) Mpc. Motivated by the form for xi(r) seen in the 2dF Galaxy Redshift Survey (2dFGRS) and in standard LCDM predictions, we use a double power-law model for xi(r) which gives a good fit to xi(s) and wp(sigma). The model is parametrized by a slope of gamma=1.45 for 1<r<10 h^(-1) Mpc and gamma=2.30 for 10<r<40 h^(-1) Mpc. As found for 2dFGRS, the value of beta determined from the ratio of xi(s)/xi(r) depends sensitively on the form of xi(r) assumed. With our double power-law form for xi(r), we measure beta(z=1.4)=0.32(+0.09)(-0.11). Assuming the same model for xi(r) we then analyse the z-space distortions in the 2QZ xi(sigma,pi) and put constraints on the values of Omega m and beta(z=1.4), using an improved version of the method of Hoyle et al. The constraints we derive are Omega m=0.35(+0.19)(-0.13), beta(z=1.4)=0.50(+0.13)(-0.15), in agreement with our xi(s)/ξ(r) results at the ~1 sigma level.

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arXiv2005

200 Mpc Sized Structure in the 2dF QSO Redshift Survey

The completed 2dF QSO Redshift (2QZ) Survey has been used to search for extreme large-scale cosmological structure (around 200 Mpc) over the redshift range 0 100Mpc are in the linear or only weakly non-linear regime and do not represent collapsed non-linear structures. We compare the measurements with the expectation of a standard LCDM model by measuring the variance of counts in cells and find that, provided the distribution of QSOs on large scales exhibits a mild bias with respect to the distribution of dark matter, the observed fluctuations are found to be in good agreement with the model. There is no evidence on such scales for any extreme structures that might require, for example, departures from the assumption of Gaussian initial perturbations. Thus the power-spectrum derived from the 2QZ Survey appears to provide a complete description of the distribution of QSOs. The amount of bias and its redshift dependence that is required is consistent with that found from studying the clustering of 2QZ QSOs on 10 Mpc scales, and may be adequately described by an approximately redshift-invariant power spectrum with normalisation sigma_8=1.0 corresponding to a bias at z=0 of b=1.1 rising to b=2 at the survey's mean redshift z=1.5.

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arXiv2005

On Statistical Lensing and the Anti-Correlation Between 2dF QSOs and Foreground Galaxies

We cross-correlate APM and SDSS galaxies with background QSOs from the 2dF QSO Redshift Survey, and detect a significant (2.8sigma) anti-correlation. The lack of a signal between 2dF stars and our galaxy samples suggests the anti-correlation is not due to a systematic error. The possibility that dust in the foreground galaxies could produce the anti-correlation is marginally rejected, at the 2sigma level through consideration of QSO colours. It is possible that dust that obscures QSOs without reddening them, or preferentially discards reddened QSOs from the 2QZ sample, could produce such an anti-correlation, however, such models are at odds with the positive QSO-galaxy correlations found at bright magnitudes by other authors. Our detection of a galaxy-QSO anti-correlation is consistent with statistical lensing theory. When combined with earlier results that have reported a positive galaxy-QSO correlation, a consistent, compelling picture emerges that spans faint and bright QSO samples showing positive or negative correlations according to the QSO N(m) slope. We find that galaxies are highly anti-biased on small scales. We consider two models that use different descriptions of the lensing matter and find they yield consistent predictions for the strength of galaxy bias on 0.1Mpc/h scales of b~0.1 (for LCDM). Whilst the slope of our power-law fit to the QSO-galaxy cross-correlation does not rule out linear bias, when we compare our measurement of b on 100 kpc/h scales to independent methods that determine b~1 on Mpc/h scales, we conclude that bias, on these small scales, is scale-dependent. These results indicate more mass, at least on the 100 kpc/h scales probed, than predicted by simple LCDM biasing prescriptions, and can thus constrain halo occupation models of the galaxy distribution.

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