Photometric Redshift Surveys Research Articles

Reconstructing galaxy fundamental distributions and scaling relations from photometric redshift surveys. Applications to the SDSS early-type sample

Noisy distance estimates associated with photometric rather than spectroscopic redshifts lead to a mis-estimate of the luminosities, and produce a correlated mis-estimate of the sizes. We consider a sample of early-type galaxies from the SDSS DR6 for which both spectroscopic and photometric information is available, and apply the generalization of the V_max method to correct for these biases. We show that our technique recovers the true redshift, magnitude and size distributions, as well as the true size-luminosity relation. We find that using only 10% of the spectroscopic information randomly spaced in our catalog is sufficient for the reconstructions to be accurate within about 3%, when the photometric redshift error is dz = 0.038. We then address the problem of extending our method to deep redshift catalogs, where only photometric information is available. In addition to the specific applications outlined here, our technique impacts a broader range of studies, when at least one distance-dependent quantity is involved. It is particularly relevant for the next generation of surveys, some of which will only have photometric information.

Locating the baryon acoustic peak

Forthcoming photometric redshift surveys should provide an accurate probe of the acoustic peak in the two-point galaxy correlation function, in the form of angular clustering of galaxies within a given shell in redshift space. We investigate the form of the anticipated signal, quantifying the distortions that arise due to projection effects, and, in particular, explore the validity of applying the Limber approximation. A single-integral prescription is presented, which provides an alternative to Limber's equation, and produces a significantly improved prediction in the regime of interest. The position of the acoustic peak within the angular correlation function relates to the angular diameter distance to the far side of the redshift bin. Thicker redshift bins therefore shift comoving features toward smaller angular scales. As a result, the value of the photometric redshift error acquires a greater significance, particularly at lower redshifts. In order to recover the dark energy equation of state to a level of 1 %, we find the total redshift dispersion must be determined to within Δ σz ≤ 10 -3 , which may prove challenging to achieve in practice.

Recovering the real-space correlation function from photometric redshift surveys

Measurements of clustering in large-scale imaging surveys that make use of photometric redshifts depend on the uncertainties in the redshift determination. We have used light-cone simulations to show how the deprojection method successfully recovers the real space correlation function when applied to mock photometric redshift surveys. We study how the errors in the redshift determination affect the quality of the recovered two-point correlation function. Considering the expected errors associated to the planned photometric redshift surveys, we conclude that this method provides information on the clustering of matter useful for the estimation of cosmological parameters that depend on the large scale distribution of galaxies.

STAGES: the Space Telescope A901/2 Galaxy Evolution Survey

We present an overview of the Space Telescope A901/2 Galaxy Evolution Survey (STAGES). STAGES is a multiwavelength project designed to probe physical drivers of galaxy evolution across a wide range of environments and luminosity. A complex multicluster system at z similar to 0.165 has been the subject of an 80-orbit F606W Hubble Space Telescope (HST)/Advanced Camera for Surveys (ACS) mosaic covering the full 0 degrees.5 x 0 degrees.5 (similar to 5 x 5 Mpc(2)) span of the supercluster. Extensive multiwavelength observations with XMM-Newton, GALEX, Spitzer, 2dF, Giant Metrewave Radio Telescope and the 17-band COMBO-17 photometric redshift survey complement the HST imaging. Our survey goals include simultaneously linking galaxy morphology with other observables such as age, star formation rate, nuclear activity and stellar mass. In addition, with the multiwavelength data set and new high-resolution mass maps from gravitational lensing, we are able to disentangle the large-scale structure of the system. By examining all aspects of an environment we will be able to evaluate the relative importance of the dark matter haloes, the local galaxy density and the hot X-ray gas in driving galaxy transformation. This paper describes the HST imaging, data reduction and creation of a master catalogue. We perform the Sersic fitting on the HST images and conduct associated simulations to quantify completeness. In addition, we present the COMBO-17 photometric redshift catalogue and estimates of stellar masses and star formation rates for this field. We define galaxy and cluster sample selection criteria, which will be the basis for forthcoming science analyses, and present a compilation of notable objects in the field. Finally, we describe the further multiwavelength observations and announce public access to the data and catalogues.

Unbiased estimates of galaxy scaling relations from photometric redshift surveys

Many physical properties of galaxies correlate with one another, and these correlations are often used to constrain galaxy formation models. Such correlations include the colour–magnitude relation, the luminosity–size relation, the fundamental plane, etc. However, the transformation from observable (e.g. angular size, apparent brightness) to physical quantity (physical size, luminosity) is often distance dependent. Noise in the distance estimate will lead to biased estimates of these correlations, thus compromising the ability of photometric redshift surveys to constrain galaxy formation models. We describe two methods which can remove this bias. One is a generalization of the Vmax method, and the other is a maximum-likelihood approach. We illustrate their effectiveness by studying the size–luminosity relation in a mock catalogue, although both methods can be applied to other scaling relations as well. We show that if one simply uses photometric redshifts one obtains a biased relation; our methods correct for this bias and recover the true relation.

Cosmological baryonic and matter densities from 600 000 SDSS luminous red galaxies with photometric redshifts

We analyse MegaZ-LRG, a photometric-redshift catalogue of luminous red galaxies (LRGs) based on the imaging data of the Sloan Digital Sky Survey (SDSS) 4th Data Release. MegaZ-LRG, presented in a companion paper, contains >106 photometric redshifts derived with annz, an artificial neural network method, constrained by a spectroscopic subsample of ≈13 000 galaxies obtained by the 2dF-SDSS LRG and Quasar (2SLAQ) survey. The catalogue spans the redshift range 0.4 < z < 0.7 with an rms redshift error σz≈ 0.03(1 +z), covering 5914 deg2 to map out a total cosmic volume 2.5 h−3 Gpc3. In this study we use the most reliable 600 000 photometric redshifts to measure the large-scale structure using two methods: (1) a spherical harmonic analysis in redshift slices, and (2) a direct re-construction of the spatial clustering pattern using Fourier techniques. We present the first cosmological parameter fits to galaxy angular power spectra from a photometric-redshift survey. Combining the redshift slices with appropriate covariances, we determine best-fitting values for the matter density Ωm and baryon density Ωb of Ωmh= 0.195 ± 0.023 and Ωb/Ωm= 0.16 ± 0.036 (with the Hubble parameter h= 0.75 and scalar index of primordial fluctuations nscalar= 1 held fixed). These results are in agreement with and independent of the latest studies of the cosmic microwave background radiation, and their precision is comparable to analyses of contemporary spectroscopic-redshift surveys. We perform an extensive series of tests which conclude that our power spectrum measurements are robust against potential systematic photometric errors in the catalogue. We conclude that photometric-redshift surveys are competitive with spectroscopic surveys for measuring cosmological parameters in the simplest ‘vanilla’ models. Future deep imaging surveys have great potential for further improvement, provided that systematic errors can be controlled.

Probing dark energy with the shear-ratio geometric test

We adapt the Jain-Taylor (2003) shear-ratio geometric lensing method to measure the dark energy equation of state, w = pv /ρv and its time derivative from dark matter haloes in cosmologies with arbitrary spatial curvature. The full shear-ratio covariance matrix is calculated for lensed sources, including the intervening large-scale structure and photometric redshift errors as additional sources of noise, and a maximum likelihood method for applying the test is presented. Decomposing the lensing matter distribution into dark matter haloes we calculate the parameter covariance matrix for an arbitrary experiment. Combining with the expected results from the cosmic microwave background (CMB) we design an optimal survey for probing dark energy. This shows that a targeted survey imaging 60 of the largest clusters in a hemisphere with five-band optical photometric redshifts to a median galaxy depth of Z m = 0.9 could measure ω 0 = ω(z = 0) to a marginal 1σ error of Δω 0 = 0.5. We marginalize over all other parameters including ω a , where the equation of state is parametrized in terms of scalefactor a as w(a) = ω 0 + ω a (1- a). For higher accuracy a large-scale photometric redshift survey is required, where the largest gain in signal arises from the numerous ≈0 14 M ⊙ haloes corresponding to medium-sized galaxy clusters. Combined with the expected Planck Surveyor results, such a near-future five-band survey covering 10000 deg 2 to Z m = 0.7 could measure ω 0 to Δω 0 = 0.075 and Δωa = 0.33. A stronger combined constraint is put on w measured at the pivot redshift z p = 0.27 of Aw(zp) = 0.0298. We compare and combine the geometric test with the cosmological and dark energy parameters measured from planned baryon acoustic oscillation (BAO) and supernova Type Ia experiments, and find that the geometric test results combine with a significant reduction in errors due to different degeneracies. A combination of geometric lensing, CMB and BAO experiments could achieve Δω 0 = 0.047 and Δωa = 0.111 with a pivot redshift constraint of Δω(Z p ) = 0.020 at z p = 0.62. Simple relations are presented that show how our lensing results can be scaled to other telescope classes and survey parameters.

The Merger Rate of Massive Galaxies

We calculate the projected two point correlation function for samples of luminous and massive galaxies in the COMBO-17 photometric redshift survey, focusing particularly on the amplitude of the correlation function at small projected radii and exploring the constraints such measurements can place on the galaxy merger rate. For nearly volume-limited samples with 0.4<z<0.8, we find that 4+/-1% of luminous M_B<-20 galaxies are in close physical pairs (with real space separation of <30 proper kpc). The corresponding fraction for massive galaxies with M_*>2.5e10 M_sun is 5+/-1%. Incorporating close pair fractions from the literature, the 2dFGRS and the SDSS, we find a fairly rapid evolution of the merger fraction of massive galaxies between z=0.8 and the present day. Assuming that the major merger timescale is of order the dynamical timescale for close massive galaxy pairs, we tentatively infer that ~50% (70%) of all galaxies with present-day masses M_*>5e10 M_sun (remnants of mergers between galaxies with M_*>2.5e10 M_sun) have undergone a major merger since z=0.8(1): major mergers between massive galaxies are a significant driver of galaxy evolution over the last eight billion years.

Weighing the Universe with Photometric Redshift Surveys and the Impact on Dark Energy Forecasts

With a wariness of Occam's razor awakened by the discovery of cosmic acceleration, we abandon the usual assumption of zero mean curvature and ask how well it can be determined by planned surveys. We also explore the impact of uncertain mean curvature on forecasts for the performance of planned dark energy probes. We find that weak lensing and photometric baryon acoustic oscillation data, in combination with cosmic microwave background (CMB) data, can determine the mean curvature well enough that the residual uncertainty does not degrade constraints on dark energy. We also find that determinations of curvature are highly tolerant of photometric redshift errors.

Dry Mergers in GEMS: The Dynamical Evolution of Massive Early‐Type Galaxies

We have used the 28' × 28' Hubble Space Telescope image mosaic from the GEMS (Galaxy Evolution from Morphology and SEDs) survey in conjunction with the COMBO-17 photometric redshift survey to constrain the incidence of major mergers between spheroid-dominated galaxies with little cold gas (dry mergers) since z = 0.7. A set of N-body merger simulations was used to explore the morphological signatures of such interactions: they are recognizable either as <5 kpc separation close pairs or because of broad, low surface brightness tidal features and asymmetries. Data with the depth and resolution of GEMS are sensitive to dry mergers between galaxies with MV -20.5 for z 0.7; dry mergers at higher redshifts are not easily recovered in single-orbit HST imaging. Six dry mergers (12 galaxies) with luminosity ratios between 1 : 1 and 4 : 1 were found from a sample of 379 red early-type galaxies with MV < -20.5 and 0.1 < z < 0.7. The simulations suggest that the morphological signatures of dry merging are visible for ~150 Myr, and we use this timescale to convert the observed merger incidence into a rate. On this basis we find that present-day spheroidal galaxies with MV < -20.5 on average have undergone between 0.5 and 2 major dry mergers since z ~ 0.7. We have compared this result with the predictions of a cold dark matter-based semianalytic galaxy formation model. The model reproduces the observed declining major merger fraction of bright galaxies and the space density of luminous early-type galaxies reasonably well. The predicted dry merger fraction is consistent with our observational result. Hence, hierarchical models predict and observations now show that major dry mergers are an important driver of the evolution of massive early-type galaxies in recent epochs.

The Canada‐France Deep Fields Survey. III. Photometric Redshift Distribution to I AB = 24

We compute accurate redshift distributions to IAB=24 and RAB=24.5 using photometric redshifts estimated from six-band UBVRIZ photometry in the Canada-France Deep Fields Photometric Redshift Survey (CFDF-PRS). Our photometric redshift algorithm is calibrated using hundreds of CFRS spectroscopic redshifts in the same fields. The dispersion in redshift is sigma/(1+z)<~0.04 to the CFRS depth of IAB=22.5, rising to sigma/(1+z)<~0.06 at our nominal magnitude and redshift limits of IAB=24 and z<=1.3, respectively. We describe a new method to compute N(z) that incorporates the full redshift likelihood functions in a Bayesian iterative analysis, and we demonstrate in extensive Monte Carlo simulations that it is superior to distributions calculated using simple maximum likelihood redshifts. The field-to-field differences in the redshift distributions, while not unexpected theoretically, are substantial even on 30' scales. We provide IAB and RAB redshift distributions, median redshifts, and parameterized fits of our results in various magnitude ranges, accounting for both random and systematic errors in the analysis.

Measuring Galaxy Environments with Deep Redshift Surveys

We study the applicability of several galaxy environment measures (nth-nearest neighbor distance, counts in an aperture, and Voronoi volume) within deep redshift surveys. Mock galaxy catalogs are employed to mimic representative photometric and spectroscopic surveys at high redshift (z ~ 1). We investigate the effects of survey edges, redshift precision, redshift-space distortions, and target selection on each environment measure. We find that even optimistic photometric redshift errors (σz = 0.02) smear out the line-of-sight galaxy distribution irretrievably on small scales; this significantly limits the application of photometric redshift surveys to environment studies. Edges and holes in a survey field dramatically affect the estimation of environment, with the impact of edge effects depending on the adopted environment measure. These edge effects considerably limit the usefulness of smaller survey fields (e.g., the GOODS fields) for studies of galaxy environment. In even the poorest groups and clusters, redshift-space distortions limit the effectiveness of each environment statistic; measuring density in projection (e.g., using counts in a cylindrical aperture or a projected nth-nearest neighbor distance measure) significantly improves the accuracy of measures in such overdense environments. For the DEEP2 Galaxy Redshift Survey, we conclude that among the environment estimators tested the projected nth-nearest neighbor distance measure provides the most accurate estimate of local galaxy density over a continuous and broad range of scales.

Universal fitting formulae for baryon oscillation surveys

The next generation of galaxy surveys will attempt to measure the baryon oscillations in the clustering power spectrum with high accuracy. These oscillations encode a preferred scale which may be used as a standard ruler to constrain cosmological parameters and dark energy models. In this paper we present simple analytical fitting formulae for the accuracy with which the preferred scale may be determined in the tangential and radial directions by future spectroscopic and photometric galaxy redshift surveys. We express these accuracies as a function of survey parameters such as the central redshift, volume, galaxy number density and (where applicable) photometric redshift error. These fitting formulae should greatly increase the efficiency of optimizing future surveys, which requires analysis of a potentially vast number of survey configurations and cosmological models. The formulae are calibrated using a grid of Monte Carlo simulations, which are analysed by dividing out the overall shape of the power spectrum before fitting a simple decaying sinusoid to the oscillations. The fitting formulae reproduce the simulation results with a fractional scatter of 7 per cent (10 per cent) in the tangential (radial) directions over a wide range of input parameters. We also indicate how sparse-sampling strategies may enhance the effective survey area if the sampling scale is much smaller than the projected baryon oscillation scale.

Cosmology with photometric redshift surveys

We explore the utility of future photometric redshift imaging surveys for delineating the large-scale structure of the Universe, and assess the resulting constraints on the cosmological model. We perform two complementary types of analysis: (1) We quantify the statistical confidence and the accuracy with which such surveys will be able to detect and measure characteristic features in the clustering power spectrum such as the acoustic oscillations and the turnover, in a 'model-independent' fashion. We show for example that a 10,000 deg^2 imaging survey with depth r = 22.5 and photometric redshift accuracy dz/(1+z) = 0.03 will detect the acoustic oscillations with 99.9% confidence, measuring the associated preferred cosmological scale with 2% precision. Such a survey will also detect the turnover with 95% confidence, determining the corresponding scale with 20% accuracy. (2) By assuming a Lambda-CDM model power spectrum we calculate the confidence with which a non-zero baryon fraction can be deduced from such future galaxy surveys. We quantify 'wiggle detection' by calculating the number of standard deviations by which the baryon fraction is measured, after marginalizing over the shape parameter. This is typically a factor of four more significant (in terms of number of standard deviations) than the 'model-independent' result. We conclude that the precision with which the clustering pattern may be inferred from future photometric redshift surveys will be competitive with contemporaneous spectroscopic redshift surveys, assuming that systematic effects can be controlled. We also note that an analysis of Luminous Red Galaxies in the Sloan Digital Sky Survey may yield a marginal detection of acoustic oscillations in the imaging survey, in addition to that recently reported for the spectroscopic component.

Calibrating photometric redshifts of luminous red galaxies

We discuss the construction of a photometric redshift catalogue of luminous red galaxies (LRGs) from the Sloan Digital Sky Survey (SDSS), emphasizing the principal steps necessary for constructing such a catalogue: (i) photometrically selecting the sample, (ii) measuring photometric redshifts and their error distributions, and (iii) estimating the true redshift distribution. We compare two photometric redshift algorithms for these data and find that they give comparable results. Calibrating against the SDSS and SDSS–2dF (Two Degree Field) spectroscopic surveys, we find that the photometric redshift accuracy is σ∼ 0.03 for redshifts less than 0.55 and worsens at higher redshift (∼ 0.06 for z < 0.7). These errors are caused by photometric scatter, as well as systematic errors in the templates, filter curves and photometric zero-points. We also parametrize the photometric redshift error distribution with a sum of Gaussians and use this model to deconvolve the errors from the measured photometric redshift distribution to estimate the true redshift distribution. We pay special attention to the stability of this deconvolution, regularizing the method with a prior on the smoothness of the true redshift distribution. The methods that we develop are applicable to general photometric redshift surveys.

A Photometric Redshift Galaxy Catalog from the Red‐Sequence Cluster Survey

The Red-Sequence Cluster Survey (RCS) provides a large and deep photometric catalog of galaxies in the z' and Rc bands for 90 deg2 of sky, and supplemental V and B data have been obtained for 33.6 deg2. We compile a photometric redshift catalog from these four-band data by utilizing the empirical quadratic polynomial photometric redshift fitting technique in combination with CNOC2 and GOODS/HDF-N redshift data. The training set includes 4924 spectral redshifts. The resulting catalog contains more than one million galaxies with photometric redshifts <1.5 and Rc < 24, giving an rms scatter σ(Δz) < 0.06 within the redshift range 0.2 < z < 0.5 and σ(Δz) < 0.11 for galaxies at 0.0 < z < 1.5. We describe the empirical quadratic polynomial photometric redshift fitting technique that we use to determine the relation between redshift and photometry. A kd-tree algorithm is used to divide up our sample to improve the accuracy of our catalog. We also present a method for estimating the photometric redshift error for individual galaxies. We show that the redshift distribution of our sample is in excellent agreement with smaller and much deeper photometric and spectroscopic redshift surveys.

Constraints on perfect fluid and scalar field dark energy models from future redshift surveys

We discuss the constraints that future photometric and spectroscopic redshift surveys can put on dark energy through the baryon oscillations of the power spectrum. We model the dark energy either with a perfect fluid or a scalar field and take into account the information contained in the linear growth function. We show that the growth function helps to break the degeneracy in the dark energy parameters and reduce the errors on w 0 , w 1 roughly by 30 per cent, making more appealing multicolour surveys based on photometric redshifts. We find that a 200-deg 2 spectroscopic survey reaching z 3 can constrain w 0 , w 1 to within Δw 0 = 0.21, Δw 1 = 0.26, to Δw 0 = 0.39, Δw 1 = 0.54 using photometric redshifts with an absolute uncertainty of 0.02, and to Δw 0 = 0.43, Δw 1 = 0.66 with an uncertainty of 0.04. In the scalar field case, we show that the slope n of the inverse power-law potential for dark energy can be constrained to An = 0.26 (spectroscopic redshifts) or Δn = 0.40 (photometric redshifts), i.e. better than with future ground-based supernovae surveys or cosmic microwave background data.

GEMS Imaging of Red-Sequence Galaxies at [FORMULA][F]z~0.7[/F][/FORMULA]: Dusty or Old?

We have used the 30′ × 30′ Hubble Space Telescope image mosaic from the Galaxy Evolution from Morphology and Spectral energy distributions (GEMS) project in conjunction with the COMBO-17 deep photometric redshift survey to define a sample of nearly 1500 galaxies with 0.65 ≤ z ≤ 0.75. With this sample, we can study the distribution of rest-frame V-band morphologies more than 6 Gyr ago, without differential bandpass shifting and surface brightness dimming across this narrow redshift slice. Focusing on red-sequence galaxies at z ~ 0.7, we find that 85% of their combined rest-frame V-band luminosity density comes from visually classified E/S0/Sa galaxies down to MV - 5 log h ≲ -19.5. Similar results are obtained if automated classifiers are used. This fraction is identical to that found at the present day and is biased by less than 10% by large-scale structure and the morphology-density relation. Under the assumption that peculiar and edge-on disk galaxies are red by virtue of their dust content, we find that less than 13% of the total rest-frame V-band luminosity of the z ~ 0.7 red galaxy population is from dusty galaxies.

The Nature of Damped Lyα Absorbing Galaxies atz≤ 1: A Photometric Redshift Survey of Damped Lyα Absorbers

We study the nature of damped Lyα absorption (DLA) systems at z ≤ 1 using a sample of 11 DLA galaxies, for which accurate redshift measurements are available. Five of the 11 systems are identified in our ongoing photometric redshift survey of DLA galaxies, while the remaining six systems are identified by previous groups using either spectroscopic or photometric redshift techniques. Absolute B-band magnitudes of the galaxies range from MAB(B) = -15.3 to -20.3. Impact parameter separations of the galaxy and absorber pairs range from ρ = 0.31 to 25.4 h-1 kpc. We first demonstrate that the precision of photometric redshifts is sufficient for identifying DLA galaxies because DLA systems are rare, and their intrinsically high column density implies a small impact parameter of the host galaxy to the QSO line of sight. We then adopt this first large DLA galaxy sample to study the neutral gas cross section of intermediate-redshift galaxies and examine the optical properties of DLA galaxies at z ≤ 1. The results of our study are as follows: (1) the extent of neutral gas around intermediate-redshift galaxies scales with B-band luminosity as R/R* = β with R* = 24-30 h-1 kpc and β = 0.26 at N(H ) = 1020 cm-2; (2) the observed incidence of the DLA systems versus the B-band luminosity of the DLA galaxies is consistent with models derived from adopting a known galaxy B-band luminosity function and the best-fit scaling relation of the neutral gas cross section at MAB(B) - 5 log h ≤ -17; (3) comparison of the observed and predicted number density of DLA systems supports that luminous galaxies can explain most of the DLA systems found in QSO absorption line surveys and a large contribution of dwarfs (MAB(B) - 5 log h ≥ -17) to the total neutral gas cross section is not necessary; (4) of the 11 DLA systems studied, 45% are disk dominated, 22% are bulge dominated, 11% are irregular, and 22% are in galaxy groups, indicating that galaxies that give rise to the DLA systems span a wide range of morphological types and arise in a variety of galaxy environments; and (5) galaxies that contain the bulk of neutral gas in the universe do not appear to exhibit a substantial luminosity evolution between z = 0 and 1.

Measuring Feedback Using the Intergalactic Medium State and Evolution Inferred from the Soft X‐Ray Background

We explore the intergalactic medium (IGM) as a potential source of the unresolved soft X-ray background (XRB) and the feasibility of extracting the IGM state and evolution from XRB observations. We build two analytical models, the continuum field model and the halo model, to calculate the IGM XRB mean flux, angular autocorrelation, and cross-correlation with galaxies. Our results suggest that the IGM may contribute a significant fraction to the unresolved soft XRB flux and correlations. We calibrated non-Gaussian errors estimated against our 5123 moving mesh hydro simulation and estimate that the ROSAT All-Sky Survey plus Sloan Galaxy Photometric Redshift Survey would allow a ~10% accuracy in the IGM XRB-galaxy cross-correlation power spectrum measurement for 800 < l < 5000 and a ~20% accuracy in the redshift-resolved X-ray emissivity-galaxy cross-correlation power spectrum measurement for z 0.5. At small scales, nongravitational heating, i.e., feedback, dominates over gravity and leaves unique signatures in the IGM XRB, which allows a comparable accuracy in the measurement of the amount of nongravitational heating and the length scales where nongravitational energy balances gravity.