We study the behaviour of the three-point correlation function ζ of dark matter and mock galaxies, concentrating on the effects of redshift-space distortions and the determination of galaxy bias ...parameters in current redshift galaxy surveys. On large scales, redshift-space distortions tend to wash out slightly the configuration dependence of the reduced three-point function Q3∼ζ/ξ2. On smaller scales (=10 h−1 Mpc), Q3 develops a characteristic U-shape anisotropy between elongated and open triangles due to the effects of velocity dispersion. We show that this shape is quite universal, very weakly dependent on scale, initial spectral index or cosmological parameters and should be detectable in current galaxy surveys even if affected by shot noise or galaxy bias. We present a detailed method for obtaining constraints on galaxy bias parameters from measurements of Q3 in current galaxy redshift surveys, based on the eigenmode analysis similar to that developed for the bispectrum. We show that our method recovers the bias parameters introduced into mock galaxies by a halo occupation distribution prescription and is also able to handle potential systematics in the case when a smaller number than is ideal for mock catalogues is used to estimate the covariance matrix. We find that current redshift surveys (e.g. SDSS or 2dFGRS) are just about large enough to obtain interesting new constraints on bias.
We propose a new method for the extraction cosmological parameters using the baryon acoustic oscillation (BAO) scale as a standard ruler in deep galaxy surveys with photometric determination of ...redshifts. The method consists in a simple empirical parametric fit to the angular two-point correlation function ω(θ). It is parametrized as a power law to describe the continuum and as a Gaussian to describe the BAO bump. The location of the Gaussian is used as the basis for the measurement of the sound horizon scale. This method, although simple, actually provides a robust estimation, since the inclusion of the power law and the use of the Gaussian remove the shifts which affect the local maximum. We discuss the effects of projection bias, non-linearities, redshift space distortions and photo-z precision and apply our method to a mock catalogue of the Dark Energy Survey, built upon a large N-body simulation provided by the MICE collaboration. We discuss the main systematic errors associated with our method and show that they are dominated by the photo-z uncertainty.
We apply a new model for the spherically averaged correlation function at large pair separations to the measurement of the clustering of luminous red galaxies (LRGs) made from the Sloan Digital Sky ...Survey by Cabre & Gaztañaga. Our model takes into account the form of the baryonic acoustic oscillation peak and the large-scale shape of the correlation function. We perform a Monte Carlo Markov chain analysis for different combinations of data sets and for different parameter sets. When used in combination with a compilation of the latest cosmic microwave background (CMB) measurements, the LRG clustering and the latest supernovae results give constraints on cosmological parameters which are comparable and in remarkably good agreement, resolving the tension reported in some studies. The best-fitting model in the context of a flat, Λ cold dark matter cosmology is specified by Ωm= 0.261 ± 0.013, Ωb= 0.044 ± 0.001, ns= 0.96 ± 0.01, H0= 71.6 ± 1.2 km s−1 Mpc−1 and σ8= 0.80 ± 0.02. If we allow the time-independent dark energy equation of state parameter to vary, we find results consistent with a cosmological constant at the 5 per cent level using all data sets: wDE=−0.97 ± 0.05. The large-scale structure measurements by themselves can constrain the dark energy equation-of-state parameter to wDE=−1.05+0.16−0.15, independently of CMB or supernovae data. We do not find convincing evidence for an evolving equation of state. We provide a set of ‘extended distance priors’ that contain the most relevant information from the CMB power spectrum and the shape of the LRG correlation function which can be used to constrain dark energy models and spatial curvature. Our model should provide an accurate description of the clustering even in much larger, forthcoming surveys, such as those planned with NASA's JDEM or ESA's Euclid mission.
ABSTRACT
Galaxy pairs constitute the initial building blocks of galaxy evolution, which is driven through merger events and interactions. Thus, the analysis of these systems can be valuable in ...understanding galaxy evolution and studying structure formation. In this work, we present a new publicly available catalogue of close galaxy pairs identified using photometric redshifts provided by the Physics of the Accelerating Universe Survey (PAUS). To efficiently detect them, we take advantage of the high-precision photo−z (σ68 < 0.02) and apply an identification algorithm previously tested using simulated data. This algorithm considers the projected distance between the galaxies (rp < 50 kpc), the projected velocity difference (ΔV < 3500 km s−1) and an isolation criterion to obtain the pair sample. We applied this technique to the total sample of galaxies provided by PAUS and to a subset with high-quality redshift estimates. Finally, the most relevant result we achieved was determining the mean mass for several subsets of galaxy pairs selected according to their total luminosity, colour, and redshift, using galaxy–galaxy lensing estimates. For pairs selected from the total sample of PAUS with a mean r-band luminosity 1010.6 h−2 L⊙, we obtain a mean mass of M200 = 1012.2 h−1 M⊙, compatible with the mass–luminosity ratio derived for elliptical galaxies. We also study the mass-to-light ratio M/L as a function of the luminosity L and find a lower M/L (or steeper slope with L) for pairs than the one extrapolated from the measurements in groups and galaxy clusters.
ABSTRACT
We present an application of unsupervised Machine Learning clustering to the PAU survey of galaxy spectral energy distribution (SED) within the COSMOS field. The clustering algorithm is ...implemented and optimized to get the relevant groups in the data SEDs. We find 12 groups from a total number of 5234 targets in the survey at 0.01 < z < 0.28. Among the groups, 3545 galaxies (68 per cent) show emission lines in the SEDs. These groups also include 1689 old galaxies with no active star formation. We have fitted the SED to every single galaxy in each group with CIGALE. The mass, age, and specific star formation rates (sSFR) of the galaxies range from 0.15 < age/Gyr <11; 6 < log (M⋆/M⊙) <11.26, and −14.67 < log (sSFR/yr−1) <−8. The groups are well-defined in their properties with galaxies having clear emission lines also having lower mass, are younger and have higher sSFR than those with elliptical like patterns. The characteristic values of galaxies showing clear emission lines are in agreement with the literature for starburst galaxies in COSMOS and GOODS-N fields at low redshift. The star-forming main sequence, sSFR versus stellar mass and UVJ diagram show clearly that different groups fall into different regions with some overlap among groups. Our main result is that the joint of low- resolution (R ∼ 50) photometric spectra provided by the PAU survey together with the unsupervised classification provides an excellent way to classify galaxies. Moreover, it helps to find and extend the analysis of extreme ELGs to lower masses and lower SFRs in the local Universe.
The possibility of measuring redshift-space distortions (RSDs) using photometric data has been recently highlighted. This effect complements and significantly alters the detectability of baryon ...acoustic oscillations (BAO) in photometric surveys. In this paper we present measurements of the angular correlation function of luminous red galaxies (LRGs) in the photometric catalogue of the final data release data release 7 (DR7) of the Sloan Digital Sky Survey II (SDSS-II). The sample compromises ∼1.5 × 106 LRGs distributed in 0.45 < z < 0.65, with a characteristic photometric error of ∼0.05. Our measured correlation centred at z= 0.55 is in very good agreement with predictions from standard Λcold dark matter (ΛCDM) in a broad range of angular scales, 0°.5 < θ < 6°. We find that the growth of structure can indeed be robustly measured, with errors matching expectations. The velocity growth rate is recovered as fσ8= 0.53 ± 0.42 when no prior is imposed on the growth factor and the background geometry follows a ΛCDM model with 7-year Wilkinson Microwave Anisotropy Probe (WMAP7)+SNIa priors. This is compatible with the corresponding General Relativity (GR) prediction fσ8= 0.45 for our fiducial cosmology. If we adopt a parametrization such that f=Ωγ
m(z), with γ≈ 0.55 in GR, and combine our fσ8 measurement with the corresponding ones from spectroscopic LRGs at lower redshifts, we obtain γ= 0.54 ± 0.17. In addition we find evidence for the presence of the baryon acoustic feature matching the amplitude, location and shape of ΛCDM predictions. The photometric BAO feature is detected with 98 per cent confidence level at z= 0.55.
ABSTRACT
PAUCam is an innovative optical narrow-band imager mounted at the William Herschel Telescope built for the Physics of the Accelerating Universe Survey (PAUS). Its set of 40 filters results ...in images that are complex to calibrate, with specific instrumental signatures that cannot be processed with traditional data reduction techniques. In this paper, we present two pipelines developed by the PAUS data management team with the objective of producing science-ready catalogues from the uncalibrated raw images. The Nightly pipeline takes care of entire image processing, with bespoke algorithms for photometric calibration and scatter-light correction. The Multi-Epoch and Multi-Band Analysis pipeline performs forced photometry over a reference catalogue to optimize the photometric redshift (photo-z) performance. We verify against spectroscopic observations that the current approach delivers an inter-band photometric calibration of 0.8 per cent across the 40 narrow-band set. The large volume of data produced every night and the rapid survey strategy feedback constraints require operating both pipelines in the Port d’Informació Cientifica data centre with intense parallelization. While alternative algorithms for further improvements in photo-z performance are under investigation, the image calibration and photometry presented in this work already enable state-of-the-art photo-z down to iAB = 23.0.
We present CosmoHub (https://cosmohub.pic.es), a web application based on Hadoop to perform interactive exploration and distribution of massive cosmological datasets. Recent Cosmology seeks to unveil ...the nature of both dark matter and dark energy mapping the large-scale structure of the Universe, through the analysis of massive amounts of astronomical data, progressively increasing during the last (and future) decades with the digitization and automation of the experimental techniques.
CosmoHub, hosted and developed at the Port d’Informació Científica (PIC), provides support to a worldwide community of scientists, without requiring the end user to know any Structured Query Language (SQL). It is serving data of several large international collaborations such as the Euclid space mission, the Dark Energy Survey (DES), the Physics of the Accelerating Universe Survey (PAUS) and the Marenostrum Institut de Ciències de l’Espai (MICE) numerical simulations. While originally developed as a PostgreSQL relational database web frontend, this work describes the current version of CosmoHub, built on top of Apache Hive, which facilitates scalable reading, writing and managing huge datasets. As CosmoHub’s datasets are seldomly modified, Hive it is a better fit.
Over 60 TiB of cataloged information and 50×109 astronomical objects can be interactively explored using an integrated visualization tool which includes 1D histogram and 2D heatmap plots. In our current implementation, online exploration of datasets of 109 objects can be done in a timescale of tens of seconds. Users can also download customized subsets of data in standard formats generated in few minutes.
We study halo clustering bias with second- and third-order statistics of halo and matter density fields in the Marenostrum Institut de Ciències de l'Espai (MICE) Grand Challenge simulation. We verify ...that two-point correlations deliver reliable estimates of the linear bias parameters at large scales, while estimations from the variance can be significantly affected by non-linear and possibly non-local contributions to the bias function. Combining three-point auto- and cross-correlations we find, for the first time in configuration space, evidence for the presence of such non-local contributions. These contributions are consistent with predicted second-order non-local effects on the bias functions originating from the dark matter tidal field. Samples of massive haloes show indications of bias (local or non-local) beyond second order. Ignoring non-local bias causes 20–30 and 5–10 per cent overestimation of the linear bias from three-point auto- and cross-correlations, respectively. We study two third-order bias estimators that are not affected by second-order non-local contributions. One is a combination of three-point auto- and cross-correlations. The other is a combination of third-order one- and two-point cumulants. Both methods deliver accurate estimations of the linear bias. Ignoring non-local bias causes higher values of the second-order bias from three-point correlations. Our results demonstrate that third-order statistics can be employed for breaking the growth-bias degeneracy.
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