Monthly Notices of the Royal Astronomical Society, 2000
We present a counts-in-cells analysis of clustering in the optically selected Durham/UKST and Str... more We present a counts-in-cells analysis of clustering in the optically selected Durham/UKST and Stromlo-APM Galaxy Redshift Surveys. Minimum variance estimates of the second moment, skewness (S 3 ) and kurtosis (S 4 ) of the count probability distribution are extracted from a series of volume limited samples of varying radial depth. The corresponding theoretical error calculation takes into account all sources of statistical error on the measurement of the moments, and is in good agreement with the dispersion over mock redshift catalogues. The errors that we find on S 3 and S 4 are larger than those quoted in previous studies, in spite of the fact that the surveys we consider cover larger volumes. S 3 varies little with cell size, with values in the range 1.8 − 2.2 and errors ∼ < 20%, for cubical cells of side 3 − 20h −1 Mpc. Direct measurements of S 3 are possible out to ∼ 35h −1 Mpc, though with larger errors. A significant determination of S 4 is only possible for one scale, l ∼ 6h −1 Mpc, with S 4 ≈ 5. We compare our results with theoretical predictions from N-body simulations of cold dark matter universes. Qualitatively, the skewness of the dark matter has the same form as that of the galaxies. However, the amplitude of the galaxy S 3 is lower than that predicted for the dark matter. Our measurements of S 3 are consistent with the predictions of a simple model in which initially Gaussian fluctuations in the dark matter evolve gravitationally, if a second order bias term is specified, in addition to the traditional linear bias, in order to describe the relation between the distribution of galaxies and dark matter.
The 2dFGRS (), now completed, is selected in the photometric bJ band from the Automated Plate Mea... more The 2dFGRS (), now completed, is selected in the photometric bJ band from the Automated Plate Measuring (APM, ) galaxy survey and its subsequent extensions. We use the data obtained prior to 2002 May, when the survey was nearly complete. This includes 221283 unique, reliable galaxy redshifts. (6 data files).
Recent measurements of the cosmic microwave background radiation (CMB), particularly when combine... more Recent measurements of the cosmic microwave background radiation (CMB), particularly when combined with other datasets, have revolutionised our knowledge of the values of the basic cosmological parameters. Here we summarize the state of play at the end of 2006, focusing on the combination of CMB measurements with the power spectrum of galaxy clustering. We compare the constraints derived from the extant CMB data circa 2005 and the final 2dFGRS galaxy power spectrum, with the results obtained when the WMAP 1-year data is replaced by the 3-year measurements (hereafter WMAP1 and WMAP3). Remarkably, the picture has changed relatively little with the arrival of WMAP3, though some aspects have been brought into much sharper focus. One notable example of this is the index of primordial scalar fluctuations, n s . Prior to WMAP3, Sánchez et al. (2006) found that the scale invariant value of n s = 1 was excluded at the 95% level. With WMAP3, this becomes a 3 σ result, with implications for models of inflation. We find some disagreement between the constraints on certain parameters when the 2dFGRS P(k) is replaced by the SDSS measurement. This suggests that more work is needed to understand the relation between the clustering of different types of galaxies and the linear perturbation theory prediction for the power spectrum of matter fluctuations.
Monthly Notices of the Royal Astronomical Society, 1999
We analyse parallel N-body simulations of three Cold Dark Matter (CDM) universes to study the abu... more We analyse parallel N-body simulations of three Cold Dark Matter (CDM) universes to study the abundance and clustering of galaxy clusters. The simulation boxes are 500h −1 Mpc on a side and cover a volume comparable to that of the forthcoming Sloan Digital Sky Survey. The use of a treecode algorithm and 47 million particles allows us at the same time to achieve high mass and force resolution. We are thus able to make robust measurements of cluster properties with good number statistics up to a redshift larger than unity. We extract halos using two independent, public domain group finders designed to identify virialised objects -'Friends-of-Friends' and 'HOP' (Eisenstein & Hut 1998) -and find consistent results. The correlation function of clusters as a function of mass in the simulations is in very good agreement with a simple analytic prescription based upon a Lagrangian biasing scheme developed by and the Press-Schechter (PS) formalism for the mass function. The correlation length of clusters as a function of their number density, the R 0 -D c relation, is in good agreement with the APM Cluster Survey in our open CDM model. The critical density CDM model (SCDM) shows much smaller correlation lengths than are observed. We also find that the correlation length does not grow as rapidly with cluster separation in any of the simulations as suggested by the analysis of very rich Abell clusters. Our SCDM simulation shows a robust deviation in the shape and evolution of the mass function when compared with that predicted by the PS formalism. Critical models with a low σ 8 normalization or small shape parameter Γ have an excess of massive clusters compared with the PS prediction. When cluster normalized, the SCDM universe at z = 1 contains 10 times more clusters with temperatures greater than 7keV, compared with the Press & Schechter prediction. The agreement between the analytic and N-body mass functions can be improved, for clusters hotter than 3 keV in the critical density SCDM model, if the value of δ c (the extrapolated linear theory threshold for collapse) is revised to be δ c (z) = 1.685 [(0.7/σ 8 )(1 + z)] −0.125 (σ 8 is the rms density fluctuation in spheres of radius 8h −1 Mpc). Our best estimate for the amplitude of fluctuations inferred from the local cluster abundance for the SCDM model is σ 8 = 0.5 ± 0.04. However, the discrepancy between the temperature function predicted in a critical density universe and that observed at z = 0.33 ) is reduced by a modest amount using the modified Press-Schechter scheme. The discrepancy is still large enough to rule out Ω 0 = 1, unless there are significant differences in the relation between mass and temperature for clusters at high and low redshift.
Abstract: A large sub-mm survey with Herschel will enable many exciting science opportunities, es... more Abstract: A large sub-mm survey with Herschel will enable many exciting science opportunities, especially in an era of wide-field optical and radio surveys and high resolution cosmic microwave background experiments. The Herschel-SPIRE Legacy Survey (HSLS), will lead to imaging data over 4000 sq. degrees at 250, 350, and 500 micron. Major Goals of HSLS are:(a) produce a catalog of 2.5 to 3 million galaxies down to 26, 27 and 33 mJy (50% completeness; 5 sigma confusion noise) at 250, 350 and 500 micron, respectively, in the ...
Monthly Notices of the Royal Astronomical Society, 2008
We present an analysis of the small-to-intermediate scale clustering of samples of Luminous Red G... more We present an analysis of the small-to-intermediate scale clustering of samples of Luminous Red Galaxies (LRGs) from the Sloan Digital Sky Survey (SDSS) and the 2dF-SDSS LRG and QSO (2SLAQ) survey carefully matched to have the same restframe colours and luminosity. We study the spatial two-point auto-correlation function in both redshift-space (ξ(s)) and real-space (ξ(r)) of a combined sample of over 10,000 LRGs, which represent the most massive galaxies in the universe with stellar masses > 10 11 h −1 M ⊙ and space densities ≃ 10 −4 h 3 Mpc −3 . We find no significant evolution in the amplitude (r 0 ) of the correlation function with redshift, but do see a slight decrease in the slope (γ) with increasing redshift over 0.19 < z < 0.55 and scales of 0.32 < r < 32h −1 Mpc. We compare our measurements with the predicted evolution of dark matter clustering and use the halo model to interpret our results. We find that our clustering measurements are inconsistent (> 99.9% significance) with a passive model whereby the LRGs do not merge with one another; a model with a merger rate of 7.5±2.3% from z = 0.55 to z = 0.19 (i.e. an average rate of 2.4% Gyr −1 ) provides a better fit to our observations. Our clustering and number density measurements are consistent with the hypothesis that the merged LRGs were originally central galaxies in different haloes which, following the merger of these haloes, merged to create a single Brightest Cluster Galaxy (BCG). In addition, we show that the small scale clustering signal constrains the scatter in halo merger histories. When combined with measurements of the luminosity function, our results suggest that this scatter is sub-Poisson. While this is a generic prediction of hierarchical models, it has not been tested before.
We measure the projected cross-correlation between low redshift (z < 0.5) far-IR selected gala... more We measure the projected cross-correlation between low redshift (z < 0.5) far-IR selected galaxies in the SDP field of the Herschel-ATLAS (H-ATLAS) survey and optically selected galaxies from the Galaxy and Mass Assembly (GAMA) redshift survey. In order to obtain robust correlation functions, we restrict the analysis to a subset of 969 out of 6900 H-ATLAS galaxies, which have reliable optical counterparts with r<19.4 mag and well-determined spectroscopic redshifts. The overlap region between the two surveys is 12.6 sq. deg; the matched sample has a median redshift of z ~ 0.2. The cross-correlation of GAMA and H-ATLAS galaxies within this region can be fitted by a power law, with correlation length r_0 ~ 4.63 +/- 0.51 Mpc. Comparing with the corresponding auto-correlation function of GAMA galaxies within the SDP field yields a relative bias (averaged over 2-8 Mpc) of H-ATLAS and GAMA galaxies of b_H/b_G ~ 0.6. Combined with clustering measurements from previous optical studies,...
Monthly Notices of the Royal Astronomical Society, 2002
We compare the amplitudes of fluctuations probed by the 2dF Galaxy Redshift Survey (2dFGRS) and b... more We compare the amplitudes of fluctuations probed by the 2dF Galaxy Redshift Survey (2dFGRS) and by the latest measurements of the cosmic microwave background (CMB) anisotropies. By combining the 2dFGRS and CMB data, we find the linear-theory rms mass fluctuations in 8 h 21 Mpc spheres to be s 8m ¼ 0:73^0:05 (after marginalization over the matter density parameter V m and three other free parameters). This normalization is lower than the COBE normalization and previous estimates from cluster abundance, but it is in agreement with some revised cluster abundance determinations. We also estimate the scaleindependent bias parameter of present-epoch L s ¼ 1:9L * APM-selected galaxies to be bðL s ; z ¼ 0Þ ¼ 1:10^0:08 on comoving scales of 0:02 , k , 0:15 h Mpc 21 . If luminosity segregation operates on these scales, L * galaxies would be almost unbiased, bðL * ; z ¼ 0Þ < 0:96. These results are derived by assuming a flat LCDM Universe, and by marginalizing over other free parameters and fixing the spectral index n ¼ 1 and the optical depth due to reionization t ¼ 0. We also study the best-fitting pair (V m , b), and the robustness of the results to varying n and t. Various modelling corrections can each change the resulting b by 5 -15 per cent. The results are compared with other independent measurements from the 2dFGRS itself, and from the Sloan Digital Sky Survey (SDSS), cluster abundance and cosmic shear.
Monthly Notices of the Royal Astronomical Society, 2002
We investigate the dependence of galaxy clustering on luminosity and spectral type using the 2dF ... more We investigate the dependence of galaxy clustering on luminosity and spectral type using the 2dF Galaxy Redshift Survey (2dFGRS). Spectral types are assigned using the principal component analysis of Madgwick et al. We divide the sample into two broad spectral classes: galaxies with strong emission lines ('late-types'), and more quiescent galaxies ('early-types'). We measure the clustering in real space, free from any distortion of the clustering pattern due to peculiar velocities, for a series of volumelimited samples. The projected correlation functions of both spectral types are well described by a power law for transverse separations in the range 2<(σ/h −1 Mpc)<15, with a marginally steeper slope for early-types than late-types. Both early and late types have approximately the same dependence of clustering strength on luminosity, with the clustering amplitude increasing by a factor of ∼2.5 between L * and 4L * . At all luminosities, however, the correlation function amplitude for the early-types is ∼50% higher than that of the late-types. These results support the view that luminosity, and not type, is the dominant factor in determining how the clustering strength of the whole galaxy population varies with luminosity.
Monthly Notices of the Royal Astronomical Society, 2011
We measure the projected cross-correlation between low redshift (z < 0.5) far-IR selected galaxie... more We measure the projected cross-correlation between low redshift (z < 0.5) far-IR selected galaxies in the SDP field of the Herschel-ATLAS (H-ATLAS) survey and optically selected galaxies from the Galaxy and Mass Assembly (GAMA) redshift survey. In order to obtain robust correlation functions, we restrict the analysis to a subset of 969 out of 6900 H-ATLAS galaxies, which have reliable optical counterparts with r < 19.4 mag and well-determined spectroscopic redshifts. The overlap region between the two surveys is 12.6 deg 2 ; the matched sample has a median redshift of z ≈ 0.2. The cross-correlation of GAMA and H-ATLAS galaxies within this region can be fitted by a power law, with correlation length r 0 ≈ 4.63 ± 0.51 Mpc. Comparing with the corresponding auto-correlation function of GAMA galaxies within the SDP field yields a relative bias (averaged over 2-8 Mpc) of H-ATLAS and GAMA galaxies of b H /b G ≈ 0.6. Combined with clustering measurements from previous optical studies, this indicates that most of the low redshift H-ATLAS sources are hosted by halos with masses comparable to that of the Milky Way. The correlation function appears to depend on the 250 µm luminosity, L 250 , with bright (median luminosity νL 250 ∼ 1.6 × 10 10 L ⊙ ) objects being somewhat more strongly clustered than faint (νL 250 ∼ 4.0 × 10 9 L ⊙ ) objects. This implies that galaxies with higher dust-obscured star formation rates are hosted by more massive halos.
We measure the projected cross-correlation between low redshift (z < 0.5) far-IR selected gala... more We measure the projected cross-correlation between low redshift (z < 0.5) far-IR selected galaxies in the SDP field of the Herschel-ATLAS (H-ATLAS) survey and optically selected galaxies from the Galaxy and Mass Assembly (GAMA) redshift survey. In order to obtain robust correlation functions, we restrict the analysis to a subset of 969 out of 6900 H-ATLAS galaxies, which have reliable optical counterparts with r<19.4 mag and well-determined spectroscopic redshifts. The overlap region between the two surveys is 12.6 sq. deg; the matched sample has a median redshift of z ~ 0.2. The cross-correlation of GAMA and H-ATLAS galaxies within this region can be fitted by a power law, with correlation length r_0 ~ 4.63 +/- 0.51 Mpc. Comparing with the corresponding auto-correlation function of GAMA galaxies within the SDP field yields a relative bias (averaged over 2-8 Mpc) of H-ATLAS and GAMA galaxies of b_H/b_G ~ 0.6. Combined with clustering measurements from previous optical studies,...
Monthly Notices of the Royal Astronomical Society: Letters, 2005
We present predictions for the abundance of Ly-α emitters in hierarchical structure formation mod... more We present predictions for the abundance of Ly-α emitters in hierarchical structure formation models. We use the GALFORM semi-analytical model of galaxy formation to explore the impact on the predicted counts of varying assumptions about the escape fraction of Ly-α photons, the redshift at which the universe reionized and the cosmological density parameter. A model with a fixed escape fraction gives a remarkably good match to the observed counts over a wide redshift interval. The counts at bright fluxes are dominated by ongoing starbursts. We present predictions for the expected counts in a typical observation with the Multi-Unit Spectroscopic Explorer (MUSE) instrument proposed for the Very Large Telescope.
Interactions between dark matter (DM) and radiation (photons or neutrinos) in the early Universe ... more Interactions between dark matter (DM) and radiation (photons or neutrinos) in the early Universe suppress density fluctuations on small mass scales. Here we perform a thorough analysis of structure formation in the fully non-linear regime using N-body simulations for models with DM-radiation interactions and compare the results to a traditional calculation in which DM only interacts gravitationally. Significant differences arise due to the presence of interactions, in terms of the number of low-mass DM haloes and their properties, such as their spin and density profile. These differences are clearly seen even for haloes more massive than the scale on which density fluctuations are suppressed. We also show that semi-analytical descriptions of the matter distribution in the non-linear regime fail to reproduce our numerical results, emphasizing the challenge of predicting structure formation in models with physics beyond collisionless DM.
The cold dark matter (CDM) model faces persistent challenges on small scales. In particular, take... more The cold dark matter (CDM) model faces persistent challenges on small scales. In particular, taken at face value, the model significantly overestimates the number of satellite galaxies around the Milky Way. Attempts to solve this problem remain open to debate and have even led some to abandon CDM altogether. However, current simulations are limited by the assumption that dark matter feels only gravity. Here, we show that including interactions between CDM and radiation (photons or neutrinos) leads to a dramatic reduction in the number of satellite galaxies, alleviating the Milky Way satellite problem and indicating that physics beyond gravity may be essential to make accurate predictions of structure formation on small scales. The methodology introduced here gives constraints on dark matter interactions that are significantly improved over those from the cosmic microwave background.
We describe the scientific motivations, the mission concept and the instrumentation of SPACE, a c... more We describe the scientific motivations, the mission concept and the instrumentation of SPACE, a class-M mission proposed for concept study at the first call of the ESA Cosmic-Vision 2015-2025 planning cycle. SPACE aims to produce the largest three-dimensional evolutionary map of the Universe over the past 10 billion years by taking near-IR spectra and measuring redshifts for more than half a billion galaxies at 0 < z < 2 down to AB ∼ 23 over 3π sr of the sky. In addition, SPACE will also target a smaller sky field, performing a deep spectroscopic survey of millions of galaxies to AB ∼ 26 and at 2 < z < 10+. These goals are unreachable with ground-based observations due to the ≈500 times higher sky background (see e.g. [2]). To achieve the main science objectives, SPACE will use a 1.5m diameter Ritchey-Chretien telescope equipped with a set of arrays of Digital Micro-mirror Devices (DMDs) covering a total field of view of 0.4 deg 2 , and will perform large-multiplexing
The large-scale structure in the distribution of galaxies is thought to arise from the gravitatio... more The large-scale structure in the distribution of galaxies is thought to arise from the gravitational instability of small fluctuations in the initial density field of the Universe. A key test of this hypothesis is that forming superclusters of galaxies should generate a systematic infall of other galaxies. This would be evident in the pattern of recessional velocities, causing an anisotropy in the inferred spatial clustering of galaxies. Here we report a precise measurement of this clustering, using the redshifts of more than 141,000 galaxies from the two-degree-field (2dF) galaxy redshift survey. We determine the parameter  ¼ ⍀ 0:6 =b ¼ 0:43 Ϯ 0:07, where ⍀ is the total mass-density parameter of the Universe and b is a measure of the 'bias' of the luminous galaxies in the survey. (Bias is the difference between the clustering of visible galaxies and of the total mass, most of which is dark.) Combined with the anisotropy of the cosmic microwave background, our results favour a low-density Universe with ⍀ Ϸ 0:3.
Monthly Notices of the Royal Astronomical Society, 2010
A space-based galaxy redshift survey would have enormous power in constraining dark energy and te... more A space-based galaxy redshift survey would have enormous power in constraining dark energy and testing general relativity, provided that its parameters are suitably optimized. We study viable space-based galaxy redshift surveys, exploring the dependence of the Dark Energy Task Force (DETF) figure-of-merit (FoM) on redshift accuracy, redshift range, survey area, target selection, and forecast method. Fitting formulae are provided for convenience. We also consider the dependence on the information used: the full galaxy power spectrum P (k), P (k) marginalized over its shape, or just the Baryon Acoustic Oscillations (BAO). We find that the inclusion of growth rate information (extracted using redshift space distortion and galaxy clustering amplitude measurements) leads to a factor of ∼ 3 improvement in the FoM, assuming general relativity is not modified. This inclusion partially compensates for the loss of information when only the BAO are used to give geometrical constraints, rather than using the full P (k) as a standard ruler. We find that a space-based galaxy redshift survey covering ∼20,000 deg 2 over 0.5 < ∼ z < ∼ 2 with σ z /(1 + z) 0.001 exploits a redshift range that is only easily accessible from space, extends to sufficiently low redshifts to allow both a vast 3-D map of the universe using a single tracer population, and overlaps with ground-based surveys to enable robust modeling of systematic effects. We argue that these parameters are close to their optimal values given current instrumental and practical constraints.
Monthly Notices of the Royal Astronomical Society, 2002
We compare the amplitudes of fluctuations probed by the 2dF Galaxy Redshift Survey (2dFGRS) and b... more We compare the amplitudes of fluctuations probed by the 2dF Galaxy Redshift Survey (2dFGRS) and by the latest measurements of the cosmic microwave background (CMB) anisotropies. By combining the 2dFGRS and CMB data, we find the linear-theory rms mass fluctuations in 8 h 21 Mpc spheres to be s 8m ¼ 0:73^0:05 (after marginalization over the matter density parameter V m and three other free parameters). This normalization is lower than the COBE normalization and previous estimates from cluster abundance, but it is in agreement with some revised cluster abundance determinations. We also estimate the scaleindependent bias parameter of present-epoch L s ¼ 1:9L * APM-selected galaxies to be bðL s ; z ¼ 0Þ ¼ 1:10^0:08 on comoving scales of 0:02 , k , 0:15 h Mpc 21 . If luminosity segregation operates on these scales, L * galaxies would be almost unbiased, bðL * ; z ¼ 0Þ < 0:96. These results are derived by assuming a flat LCDM Universe, and by marginalizing over other free parameters and fixing the spectral index n ¼ 1 and the optical depth due to reionization t ¼ 0. We also study the best-fitting pair (V m , b), and the robustness of the results to varying n and t. Various modelling corrections can each change the resulting b by 5 -15 per cent. The results are compared with other independent measurements from the 2dFGRS itself, and from the Sloan Digital Sky Survey (SDSS), cluster abundance and cosmic shear.
Monthly Notices of the Royal Astronomical Society, 2004
We derive the fraction of blue galaxies in a sample of clusters at z < 0.11 and the general field... more We derive the fraction of blue galaxies in a sample of clusters at z < 0.11 and the general field at the same redshift. The value of the blue fraction is observed to depend on the luminosity limit adopted, cluster-centric radius and, more generally, local galaxy density, but it does not depend on cluster properties. Changes in the blue fraction are due to variations in the relative proportions of red and blue galaxies but the star formation rate for these two galaxy groups remains unchanged. Our results are most consistent with a model where the star formation rate declines rapidly and the blue galaxies tend to be dwarfs and do not favour mechanisms where the Butcher-Oemler effect is caused by processes specific to the cluster environment.
Monthly Notices of the Royal Astronomical Society, 2000
We present a counts-in-cells analysis of clustering in the optically selected Durham/UKST and Str... more We present a counts-in-cells analysis of clustering in the optically selected Durham/UKST and Stromlo-APM Galaxy Redshift Surveys. Minimum variance estimates of the second moment, skewness (S 3 ) and kurtosis (S 4 ) of the count probability distribution are extracted from a series of volume limited samples of varying radial depth. The corresponding theoretical error calculation takes into account all sources of statistical error on the measurement of the moments, and is in good agreement with the dispersion over mock redshift catalogues. The errors that we find on S 3 and S 4 are larger than those quoted in previous studies, in spite of the fact that the surveys we consider cover larger volumes. S 3 varies little with cell size, with values in the range 1.8 − 2.2 and errors ∼ < 20%, for cubical cells of side 3 − 20h −1 Mpc. Direct measurements of S 3 are possible out to ∼ 35h −1 Mpc, though with larger errors. A significant determination of S 4 is only possible for one scale, l ∼ 6h −1 Mpc, with S 4 ≈ 5. We compare our results with theoretical predictions from N-body simulations of cold dark matter universes. Qualitatively, the skewness of the dark matter has the same form as that of the galaxies. However, the amplitude of the galaxy S 3 is lower than that predicted for the dark matter. Our measurements of S 3 are consistent with the predictions of a simple model in which initially Gaussian fluctuations in the dark matter evolve gravitationally, if a second order bias term is specified, in addition to the traditional linear bias, in order to describe the relation between the distribution of galaxies and dark matter.
The 2dFGRS (), now completed, is selected in the photometric bJ band from the Automated Plate Mea... more The 2dFGRS (), now completed, is selected in the photometric bJ band from the Automated Plate Measuring (APM, ) galaxy survey and its subsequent extensions. We use the data obtained prior to 2002 May, when the survey was nearly complete. This includes 221283 unique, reliable galaxy redshifts. (6 data files).
Recent measurements of the cosmic microwave background radiation (CMB), particularly when combine... more Recent measurements of the cosmic microwave background radiation (CMB), particularly when combined with other datasets, have revolutionised our knowledge of the values of the basic cosmological parameters. Here we summarize the state of play at the end of 2006, focusing on the combination of CMB measurements with the power spectrum of galaxy clustering. We compare the constraints derived from the extant CMB data circa 2005 and the final 2dFGRS galaxy power spectrum, with the results obtained when the WMAP 1-year data is replaced by the 3-year measurements (hereafter WMAP1 and WMAP3). Remarkably, the picture has changed relatively little with the arrival of WMAP3, though some aspects have been brought into much sharper focus. One notable example of this is the index of primordial scalar fluctuations, n s . Prior to WMAP3, Sánchez et al. (2006) found that the scale invariant value of n s = 1 was excluded at the 95% level. With WMAP3, this becomes a 3 σ result, with implications for models of inflation. We find some disagreement between the constraints on certain parameters when the 2dFGRS P(k) is replaced by the SDSS measurement. This suggests that more work is needed to understand the relation between the clustering of different types of galaxies and the linear perturbation theory prediction for the power spectrum of matter fluctuations.
Monthly Notices of the Royal Astronomical Society, 1999
We analyse parallel N-body simulations of three Cold Dark Matter (CDM) universes to study the abu... more We analyse parallel N-body simulations of three Cold Dark Matter (CDM) universes to study the abundance and clustering of galaxy clusters. The simulation boxes are 500h −1 Mpc on a side and cover a volume comparable to that of the forthcoming Sloan Digital Sky Survey. The use of a treecode algorithm and 47 million particles allows us at the same time to achieve high mass and force resolution. We are thus able to make robust measurements of cluster properties with good number statistics up to a redshift larger than unity. We extract halos using two independent, public domain group finders designed to identify virialised objects -'Friends-of-Friends' and 'HOP' (Eisenstein & Hut 1998) -and find consistent results. The correlation function of clusters as a function of mass in the simulations is in very good agreement with a simple analytic prescription based upon a Lagrangian biasing scheme developed by and the Press-Schechter (PS) formalism for the mass function. The correlation length of clusters as a function of their number density, the R 0 -D c relation, is in good agreement with the APM Cluster Survey in our open CDM model. The critical density CDM model (SCDM) shows much smaller correlation lengths than are observed. We also find that the correlation length does not grow as rapidly with cluster separation in any of the simulations as suggested by the analysis of very rich Abell clusters. Our SCDM simulation shows a robust deviation in the shape and evolution of the mass function when compared with that predicted by the PS formalism. Critical models with a low σ 8 normalization or small shape parameter Γ have an excess of massive clusters compared with the PS prediction. When cluster normalized, the SCDM universe at z = 1 contains 10 times more clusters with temperatures greater than 7keV, compared with the Press & Schechter prediction. The agreement between the analytic and N-body mass functions can be improved, for clusters hotter than 3 keV in the critical density SCDM model, if the value of δ c (the extrapolated linear theory threshold for collapse) is revised to be δ c (z) = 1.685 [(0.7/σ 8 )(1 + z)] −0.125 (σ 8 is the rms density fluctuation in spheres of radius 8h −1 Mpc). Our best estimate for the amplitude of fluctuations inferred from the local cluster abundance for the SCDM model is σ 8 = 0.5 ± 0.04. However, the discrepancy between the temperature function predicted in a critical density universe and that observed at z = 0.33 ) is reduced by a modest amount using the modified Press-Schechter scheme. The discrepancy is still large enough to rule out Ω 0 = 1, unless there are significant differences in the relation between mass and temperature for clusters at high and low redshift.
Abstract: A large sub-mm survey with Herschel will enable many exciting science opportunities, es... more Abstract: A large sub-mm survey with Herschel will enable many exciting science opportunities, especially in an era of wide-field optical and radio surveys and high resolution cosmic microwave background experiments. The Herschel-SPIRE Legacy Survey (HSLS), will lead to imaging data over 4000 sq. degrees at 250, 350, and 500 micron. Major Goals of HSLS are:(a) produce a catalog of 2.5 to 3 million galaxies down to 26, 27 and 33 mJy (50% completeness; 5 sigma confusion noise) at 250, 350 and 500 micron, respectively, in the ...
Monthly Notices of the Royal Astronomical Society, 2008
We present an analysis of the small-to-intermediate scale clustering of samples of Luminous Red G... more We present an analysis of the small-to-intermediate scale clustering of samples of Luminous Red Galaxies (LRGs) from the Sloan Digital Sky Survey (SDSS) and the 2dF-SDSS LRG and QSO (2SLAQ) survey carefully matched to have the same restframe colours and luminosity. We study the spatial two-point auto-correlation function in both redshift-space (ξ(s)) and real-space (ξ(r)) of a combined sample of over 10,000 LRGs, which represent the most massive galaxies in the universe with stellar masses > 10 11 h −1 M ⊙ and space densities ≃ 10 −4 h 3 Mpc −3 . We find no significant evolution in the amplitude (r 0 ) of the correlation function with redshift, but do see a slight decrease in the slope (γ) with increasing redshift over 0.19 < z < 0.55 and scales of 0.32 < r < 32h −1 Mpc. We compare our measurements with the predicted evolution of dark matter clustering and use the halo model to interpret our results. We find that our clustering measurements are inconsistent (> 99.9% significance) with a passive model whereby the LRGs do not merge with one another; a model with a merger rate of 7.5±2.3% from z = 0.55 to z = 0.19 (i.e. an average rate of 2.4% Gyr −1 ) provides a better fit to our observations. Our clustering and number density measurements are consistent with the hypothesis that the merged LRGs were originally central galaxies in different haloes which, following the merger of these haloes, merged to create a single Brightest Cluster Galaxy (BCG). In addition, we show that the small scale clustering signal constrains the scatter in halo merger histories. When combined with measurements of the luminosity function, our results suggest that this scatter is sub-Poisson. While this is a generic prediction of hierarchical models, it has not been tested before.
We measure the projected cross-correlation between low redshift (z < 0.5) far-IR selected gala... more We measure the projected cross-correlation between low redshift (z < 0.5) far-IR selected galaxies in the SDP field of the Herschel-ATLAS (H-ATLAS) survey and optically selected galaxies from the Galaxy and Mass Assembly (GAMA) redshift survey. In order to obtain robust correlation functions, we restrict the analysis to a subset of 969 out of 6900 H-ATLAS galaxies, which have reliable optical counterparts with r<19.4 mag and well-determined spectroscopic redshifts. The overlap region between the two surveys is 12.6 sq. deg; the matched sample has a median redshift of z ~ 0.2. The cross-correlation of GAMA and H-ATLAS galaxies within this region can be fitted by a power law, with correlation length r_0 ~ 4.63 +/- 0.51 Mpc. Comparing with the corresponding auto-correlation function of GAMA galaxies within the SDP field yields a relative bias (averaged over 2-8 Mpc) of H-ATLAS and GAMA galaxies of b_H/b_G ~ 0.6. Combined with clustering measurements from previous optical studies,...
Monthly Notices of the Royal Astronomical Society, 2002
We compare the amplitudes of fluctuations probed by the 2dF Galaxy Redshift Survey (2dFGRS) and b... more We compare the amplitudes of fluctuations probed by the 2dF Galaxy Redshift Survey (2dFGRS) and by the latest measurements of the cosmic microwave background (CMB) anisotropies. By combining the 2dFGRS and CMB data, we find the linear-theory rms mass fluctuations in 8 h 21 Mpc spheres to be s 8m ¼ 0:73^0:05 (after marginalization over the matter density parameter V m and three other free parameters). This normalization is lower than the COBE normalization and previous estimates from cluster abundance, but it is in agreement with some revised cluster abundance determinations. We also estimate the scaleindependent bias parameter of present-epoch L s ¼ 1:9L * APM-selected galaxies to be bðL s ; z ¼ 0Þ ¼ 1:10^0:08 on comoving scales of 0:02 , k , 0:15 h Mpc 21 . If luminosity segregation operates on these scales, L * galaxies would be almost unbiased, bðL * ; z ¼ 0Þ < 0:96. These results are derived by assuming a flat LCDM Universe, and by marginalizing over other free parameters and fixing the spectral index n ¼ 1 and the optical depth due to reionization t ¼ 0. We also study the best-fitting pair (V m , b), and the robustness of the results to varying n and t. Various modelling corrections can each change the resulting b by 5 -15 per cent. The results are compared with other independent measurements from the 2dFGRS itself, and from the Sloan Digital Sky Survey (SDSS), cluster abundance and cosmic shear.
Monthly Notices of the Royal Astronomical Society, 2002
We investigate the dependence of galaxy clustering on luminosity and spectral type using the 2dF ... more We investigate the dependence of galaxy clustering on luminosity and spectral type using the 2dF Galaxy Redshift Survey (2dFGRS). Spectral types are assigned using the principal component analysis of Madgwick et al. We divide the sample into two broad spectral classes: galaxies with strong emission lines ('late-types'), and more quiescent galaxies ('early-types'). We measure the clustering in real space, free from any distortion of the clustering pattern due to peculiar velocities, for a series of volumelimited samples. The projected correlation functions of both spectral types are well described by a power law for transverse separations in the range 2<(σ/h −1 Mpc)<15, with a marginally steeper slope for early-types than late-types. Both early and late types have approximately the same dependence of clustering strength on luminosity, with the clustering amplitude increasing by a factor of ∼2.5 between L * and 4L * . At all luminosities, however, the correlation function amplitude for the early-types is ∼50% higher than that of the late-types. These results support the view that luminosity, and not type, is the dominant factor in determining how the clustering strength of the whole galaxy population varies with luminosity.
Monthly Notices of the Royal Astronomical Society, 2011
We measure the projected cross-correlation between low redshift (z < 0.5) far-IR selected galaxie... more We measure the projected cross-correlation between low redshift (z < 0.5) far-IR selected galaxies in the SDP field of the Herschel-ATLAS (H-ATLAS) survey and optically selected galaxies from the Galaxy and Mass Assembly (GAMA) redshift survey. In order to obtain robust correlation functions, we restrict the analysis to a subset of 969 out of 6900 H-ATLAS galaxies, which have reliable optical counterparts with r < 19.4 mag and well-determined spectroscopic redshifts. The overlap region between the two surveys is 12.6 deg 2 ; the matched sample has a median redshift of z ≈ 0.2. The cross-correlation of GAMA and H-ATLAS galaxies within this region can be fitted by a power law, with correlation length r 0 ≈ 4.63 ± 0.51 Mpc. Comparing with the corresponding auto-correlation function of GAMA galaxies within the SDP field yields a relative bias (averaged over 2-8 Mpc) of H-ATLAS and GAMA galaxies of b H /b G ≈ 0.6. Combined with clustering measurements from previous optical studies, this indicates that most of the low redshift H-ATLAS sources are hosted by halos with masses comparable to that of the Milky Way. The correlation function appears to depend on the 250 µm luminosity, L 250 , with bright (median luminosity νL 250 ∼ 1.6 × 10 10 L ⊙ ) objects being somewhat more strongly clustered than faint (νL 250 ∼ 4.0 × 10 9 L ⊙ ) objects. This implies that galaxies with higher dust-obscured star formation rates are hosted by more massive halos.
We measure the projected cross-correlation between low redshift (z < 0.5) far-IR selected gala... more We measure the projected cross-correlation between low redshift (z < 0.5) far-IR selected galaxies in the SDP field of the Herschel-ATLAS (H-ATLAS) survey and optically selected galaxies from the Galaxy and Mass Assembly (GAMA) redshift survey. In order to obtain robust correlation functions, we restrict the analysis to a subset of 969 out of 6900 H-ATLAS galaxies, which have reliable optical counterparts with r<19.4 mag and well-determined spectroscopic redshifts. The overlap region between the two surveys is 12.6 sq. deg; the matched sample has a median redshift of z ~ 0.2. The cross-correlation of GAMA and H-ATLAS galaxies within this region can be fitted by a power law, with correlation length r_0 ~ 4.63 +/- 0.51 Mpc. Comparing with the corresponding auto-correlation function of GAMA galaxies within the SDP field yields a relative bias (averaged over 2-8 Mpc) of H-ATLAS and GAMA galaxies of b_H/b_G ~ 0.6. Combined with clustering measurements from previous optical studies,...
Monthly Notices of the Royal Astronomical Society: Letters, 2005
We present predictions for the abundance of Ly-α emitters in hierarchical structure formation mod... more We present predictions for the abundance of Ly-α emitters in hierarchical structure formation models. We use the GALFORM semi-analytical model of galaxy formation to explore the impact on the predicted counts of varying assumptions about the escape fraction of Ly-α photons, the redshift at which the universe reionized and the cosmological density parameter. A model with a fixed escape fraction gives a remarkably good match to the observed counts over a wide redshift interval. The counts at bright fluxes are dominated by ongoing starbursts. We present predictions for the expected counts in a typical observation with the Multi-Unit Spectroscopic Explorer (MUSE) instrument proposed for the Very Large Telescope.
Interactions between dark matter (DM) and radiation (photons or neutrinos) in the early Universe ... more Interactions between dark matter (DM) and radiation (photons or neutrinos) in the early Universe suppress density fluctuations on small mass scales. Here we perform a thorough analysis of structure formation in the fully non-linear regime using N-body simulations for models with DM-radiation interactions and compare the results to a traditional calculation in which DM only interacts gravitationally. Significant differences arise due to the presence of interactions, in terms of the number of low-mass DM haloes and their properties, such as their spin and density profile. These differences are clearly seen even for haloes more massive than the scale on which density fluctuations are suppressed. We also show that semi-analytical descriptions of the matter distribution in the non-linear regime fail to reproduce our numerical results, emphasizing the challenge of predicting structure formation in models with physics beyond collisionless DM.
The cold dark matter (CDM) model faces persistent challenges on small scales. In particular, take... more The cold dark matter (CDM) model faces persistent challenges on small scales. In particular, taken at face value, the model significantly overestimates the number of satellite galaxies around the Milky Way. Attempts to solve this problem remain open to debate and have even led some to abandon CDM altogether. However, current simulations are limited by the assumption that dark matter feels only gravity. Here, we show that including interactions between CDM and radiation (photons or neutrinos) leads to a dramatic reduction in the number of satellite galaxies, alleviating the Milky Way satellite problem and indicating that physics beyond gravity may be essential to make accurate predictions of structure formation on small scales. The methodology introduced here gives constraints on dark matter interactions that are significantly improved over those from the cosmic microwave background.
We describe the scientific motivations, the mission concept and the instrumentation of SPACE, a c... more We describe the scientific motivations, the mission concept and the instrumentation of SPACE, a class-M mission proposed for concept study at the first call of the ESA Cosmic-Vision 2015-2025 planning cycle. SPACE aims to produce the largest three-dimensional evolutionary map of the Universe over the past 10 billion years by taking near-IR spectra and measuring redshifts for more than half a billion galaxies at 0 < z < 2 down to AB ∼ 23 over 3π sr of the sky. In addition, SPACE will also target a smaller sky field, performing a deep spectroscopic survey of millions of galaxies to AB ∼ 26 and at 2 < z < 10+. These goals are unreachable with ground-based observations due to the ≈500 times higher sky background (see e.g. [2]). To achieve the main science objectives, SPACE will use a 1.5m diameter Ritchey-Chretien telescope equipped with a set of arrays of Digital Micro-mirror Devices (DMDs) covering a total field of view of 0.4 deg 2 , and will perform large-multiplexing
The large-scale structure in the distribution of galaxies is thought to arise from the gravitatio... more The large-scale structure in the distribution of galaxies is thought to arise from the gravitational instability of small fluctuations in the initial density field of the Universe. A key test of this hypothesis is that forming superclusters of galaxies should generate a systematic infall of other galaxies. This would be evident in the pattern of recessional velocities, causing an anisotropy in the inferred spatial clustering of galaxies. Here we report a precise measurement of this clustering, using the redshifts of more than 141,000 galaxies from the two-degree-field (2dF) galaxy redshift survey. We determine the parameter  ¼ ⍀ 0:6 =b ¼ 0:43 Ϯ 0:07, where ⍀ is the total mass-density parameter of the Universe and b is a measure of the 'bias' of the luminous galaxies in the survey. (Bias is the difference between the clustering of visible galaxies and of the total mass, most of which is dark.) Combined with the anisotropy of the cosmic microwave background, our results favour a low-density Universe with ⍀ Ϸ 0:3.
Monthly Notices of the Royal Astronomical Society, 2010
A space-based galaxy redshift survey would have enormous power in constraining dark energy and te... more A space-based galaxy redshift survey would have enormous power in constraining dark energy and testing general relativity, provided that its parameters are suitably optimized. We study viable space-based galaxy redshift surveys, exploring the dependence of the Dark Energy Task Force (DETF) figure-of-merit (FoM) on redshift accuracy, redshift range, survey area, target selection, and forecast method. Fitting formulae are provided for convenience. We also consider the dependence on the information used: the full galaxy power spectrum P (k), P (k) marginalized over its shape, or just the Baryon Acoustic Oscillations (BAO). We find that the inclusion of growth rate information (extracted using redshift space distortion and galaxy clustering amplitude measurements) leads to a factor of ∼ 3 improvement in the FoM, assuming general relativity is not modified. This inclusion partially compensates for the loss of information when only the BAO are used to give geometrical constraints, rather than using the full P (k) as a standard ruler. We find that a space-based galaxy redshift survey covering ∼20,000 deg 2 over 0.5 < ∼ z < ∼ 2 with σ z /(1 + z) 0.001 exploits a redshift range that is only easily accessible from space, extends to sufficiently low redshifts to allow both a vast 3-D map of the universe using a single tracer population, and overlaps with ground-based surveys to enable robust modeling of systematic effects. We argue that these parameters are close to their optimal values given current instrumental and practical constraints.
Monthly Notices of the Royal Astronomical Society, 2002
We compare the amplitudes of fluctuations probed by the 2dF Galaxy Redshift Survey (2dFGRS) and b... more We compare the amplitudes of fluctuations probed by the 2dF Galaxy Redshift Survey (2dFGRS) and by the latest measurements of the cosmic microwave background (CMB) anisotropies. By combining the 2dFGRS and CMB data, we find the linear-theory rms mass fluctuations in 8 h 21 Mpc spheres to be s 8m ¼ 0:73^0:05 (after marginalization over the matter density parameter V m and three other free parameters). This normalization is lower than the COBE normalization and previous estimates from cluster abundance, but it is in agreement with some revised cluster abundance determinations. We also estimate the scaleindependent bias parameter of present-epoch L s ¼ 1:9L * APM-selected galaxies to be bðL s ; z ¼ 0Þ ¼ 1:10^0:08 on comoving scales of 0:02 , k , 0:15 h Mpc 21 . If luminosity segregation operates on these scales, L * galaxies would be almost unbiased, bðL * ; z ¼ 0Þ < 0:96. These results are derived by assuming a flat LCDM Universe, and by marginalizing over other free parameters and fixing the spectral index n ¼ 1 and the optical depth due to reionization t ¼ 0. We also study the best-fitting pair (V m , b), and the robustness of the results to varying n and t. Various modelling corrections can each change the resulting b by 5 -15 per cent. The results are compared with other independent measurements from the 2dFGRS itself, and from the Sloan Digital Sky Survey (SDSS), cluster abundance and cosmic shear.
Monthly Notices of the Royal Astronomical Society, 2004
We derive the fraction of blue galaxies in a sample of clusters at z < 0.11 and the general field... more We derive the fraction of blue galaxies in a sample of clusters at z < 0.11 and the general field at the same redshift. The value of the blue fraction is observed to depend on the luminosity limit adopted, cluster-centric radius and, more generally, local galaxy density, but it does not depend on cluster properties. Changes in the blue fraction are due to variations in the relative proportions of red and blue galaxies but the star formation rate for these two galaxy groups remains unchanged. Our results are most consistent with a model where the star formation rate declines rapidly and the blue galaxies tend to be dwarfs and do not favour mechanisms where the Butcher-Oemler effect is caused by processes specific to the cluster environment.
Uploads
Papers by Carlton Baugh