Photometric Redshifts Of Galaxies Research Articles

Photometric redshifts for the CFHTLS T0004 deep and wide fields

We compute photometric redshifts based on the template-fitting method in the fourth public release of the Canada-France-Hawaii Telescope Legacy Survey. This unique multi-colour catalogue comprises u*,g',r',i',z' photometry in four deep fields of 1 deg2 each and 35 deg2 distributed over three Wide fields. Our photometric redshifts are calibrated with and compared to 16,983 high-quality spectroscopic redshifts from several surveys. We find a dispersion of 0.028 and an outlier rate of 3.5% in the Deep field at i'AB < 24 and a dispersion of 0.036 and an outlier rate of 2.8% in the Wide field at i'AB < 22.5. Beyond i'AB = 22.5 in the Wide field the number of outliers rises from 5% to 10% at i'AB<23 and i'AB<24 respectively. For the Wide sample, we find the systematic redshift bias keeps below 1% to i'AB < 22.5, whereas we find no significant bias in the Deep field. We investigated the effect of tile-to-tile photometric variations and demonstrate that the accuracy of our photometric redshifts is reduced by at most 21%. We separate stars from galaxies using both the size and colour information, reducing the contamination by stars in our catalogues from 50% to 8% at i'AB < 22.5 in fields with the highest stellar density while keeping a complete galaxy sample. Our CFHTLS T0004 photometric redshifts are distributed to the community. Our release include 592,891 (i'AB < 22.5) and 244,701 (i'AB < 24) reliable galaxy photometric redshifts in the Wide and Deep fields, respectively.

Photometric redshifts of galaxies from SDSS and 2MASS

In order to find the physical parameters which determine the accuracy of photometric redshifts, we compare the spectroscopic and photometric redshifts (photo-z's) for a large sample of ∼ 80000 SDSS–2MASS galaxies. Photo-z's in this paper are estimated by using the artificial neural network photometric redshift method (ANNz). For a subset of ∼40000 randomly selected galaxies, we find that the photometric redshift recovers the spectroscopic redshift distribution very well with rms of 0.016. Our main results are as follows: (1) Using magnitudes directly as input parameters produces more accurate photo-z's than using colors; (2) The inclusion of 2MASS (J, H, Ks) bands does not improve photo-z's significantly, which indicates that near infrared data might not be important for the low-redshift sample; (3) Adding the concentration index (essentially the steepness of the galaxy brightness profile) as an extra input can improve the photo-z's estimation up to ∼ 10 percent; (4) Dividing the sample into early- and late-type galaxies by using the concentration index, normal and abnormal galaxies by using the emission line flux ratios, and red and blue galaxies by using color index (g – r), we can improve the accuracy of photo-z's significantly; (5) Our analysis shows that the outliers (where there is a big difference between the spectroscopic and photometric redshifts) are mainly correlated with galaxy types, e.g., most outliers are late-type (blue) galaxies.

Classical cosmological tests for galaxies of the Hubble Ultra Deep Field

Images of the Hubble Ultra Deep Field are analyzed to obtain a catalog of galaxies for which the angular sizes, surface brightness, photometric redshifts, and absolute magnitudes are found. The catalog contains a total of about 4000 galaxies identified at a high signal-to-noise ratio, which allows the cosmological relations angular size{redshift and surface brightness-redshift to be analyzed. The parameters of the evolution of linear sizes and surface brightness of distant galaxies in the redshift interval 0.5-6.5 are estimated in terms of a grid of cosmological models with different density parameters. The distribution of photometric redshifts of galaxies is analyzed and possible superlarge inhomogeneities in the radial distribution of galaxies are found with scale lengths as large as 2000 Mpc.

A New Galaxy Group Finding Algorithm: Probability Friends‐of‐Friends

A new algorithm is developed, based on the friends-of-friends (FOF) algorithm, to identify galaxy groups in a galaxy catalog in which the redshift errors have large dispersions (e.g., a photometric redshift galaxy catalog in which a portion of the galaxies also have much more precise spectroscopic redshifts). The DEEP2 mock catalogs, with our additionalsimulated photometric redshift errors, areused totest the performance of ouralgorithm. The association of the reconstructed galaxy groups with the dark halos in the mock catalogs gives an idea about the completeness and purity of the derived group catalog. Our results show that in a 0:6 � z � 1:6 galaxy catalog with an R-band limiting magnitude of 24.1 and an average 1 � photometric redshift error of � 0.03, the overallpurity of our new algorithm for richness 4–7 (line-of-sight velocity dispersion � 300 km s � 1 ) groups is higher than 70% (i.e., 70% of the groups reconstructedbyouralgorithmarerelatedtorealgalaxygroups).Theperformanceof thenewalgorithmiscomparedwith the performance of the FOF algorithm, and it is suggested that this new algorithm is better than FOF for a database, given the same redshift uncertainties. Subject headingg catalogs — galaxies: clusters: general — galaxies: halos — galaxies: high-redshift — galaxies: photometry — methods: data analysis

TYPE Ia SUPERNOVAE RATES AND GALAXY CLUSTERING FROM THE CFHT SUPERNOVA LEGACY SURVEY

The Canada-France-Hawaii Telescope Supernova Legacy Survey (SNLS) has created a large homogeneous database of intermediate redshift (0.2 < z < 1.0) type Ia supernovae (SNe Ia). The SNLS team has shown that correlations exist between SN Ia rates, properties, and host galaxy star formation rates. The SNLS SN Ia database has now been combined with a photometric redshift galaxy catalog and an optical galaxy cluster catalog to investigate the possible influence of galaxy clustering on the SN Ia rate, over and above the expected effect due to the dependence of SFR on clustering through the morphology-density relation. We identify three cluster SNe Ia, plus three additional possible cluster SNe Ia, and find the SN Ia rate per unit mass in clusters at intermediate redshifts is consistent with the rate per unit mass in field early-type galaxies and the SN Ia cluster rate from low redshift cluster targeted surveys. We also find the number of SNe Ia in cluster environments to be within a factor of two of expectations from the two component SNIa rate model.

The Fifth Data Release of the Sloan Digital Sky Survey

This paper describes the Fifth Data Release (DR5) of the Sloan Digital Sky Survey (SDSS). DR5 includes all survey quality data taken through June 2005 and represents the completion of the SDSS-I project (whose successor, SDSS-II will continue through mid-2008). It includes five-band photometric data for 217 million objects selected over 8000 square degrees, and 1,048,960 spectra of galaxies, quasars, and stars selected from 5713 square degrees of that imaging data. These numbers represent a roughly 20% increment over those of the Fourth Data Release; all the data from previous data releases are included in the present release. In addition to "standard" SDSS observations, DR5 includes repeat scans of the southern equatorial stripe, imaging scans across M31 and the core of the Perseus cluster of galaxies, and the first spectroscopic data from SEGUE, a survey to explore the kinematics and chemical evolution of the Galaxy. The catalog database incorporates several new features, including photometric redshifts of galaxies, tables of matched objects in overlap regions of the imaging survey, and tools that allow precise computations of survey geometry for statistical investigations.

Empirical photometric redshifts of luminous red galaxies and clusters in the Sloan Digital Sky Survey

Abstract In this work I discuss the necessary steps for deriving photometric redshifts for luminous red galaxies (LRGs) and galaxy clusters through simple empirical methods. The data used are from the Sloan Digital Sky Survey (SDSS). I show that with three bands only (gri) it is possible to achieve results as accurate as the ones obtained by other techniques, generally based on more filters. In particular, the use of the (g−i) colour helps improving the final redshifts (especially for clusters), as this colour monotonically increases up to z∼ 0.8. For the LRGs I generate a catalogue of ∼1.5 million objects at z &amp;lt; 0.70. The accuracy of this catalogue is σ= 0.027 for z≤ 0.55 and σ= 0.049 for 0.55 &amp;lt; z≤ 0.70. The photometric redshift technique employed for clusters is independent of a cluster selection algorithm. Thus, it can be applied to systems selected by any method or wavelength, as long as the proper optical photometry is available. When comparing the redshift listed in literature to the photometric estimate, the accuracy achieved for clusters is σ= 0.024 for z≤ 0.30 and σ= 0.037 for 030 &amp;lt; z≤ 0.55. However, when considering the spectroscopic redshift as the mean value of SDSS galaxies on each cluster region, the accuracy is at the same level as found by other authors: σ= 0.011 for z≤ 0.30 and σ= 0.016 for 030 &amp;lt; z≤ 0.55. The photometric redshift relation derived here is applied to thousands of cluster candidates selected elsewhere. I have also used galaxy photometric redshifts available in SDSS to identify groups in redshift space and then compare the redshift peak of the nearest group to each cluster redshift. This procedure provides an alternative approach for cluster selection, especially at high redshifts, as the cluster red sequence may be poorly defined.

The Cosmic Evolution Survey (COSMOS): A Large‐Scale Structure at z = 0.73 and the Relation of Galaxy Morphologies to Local Environment

We have identified a large-scale structure at z ≃ 0.73 in the COSMOS field, coherently described by the distribution of galaxy photometric redshifts, an ACS weak-lensing convergence map, and the distribution of extended X-ray sources in a mosaic of XMM-Newton observations. The main peak seen in these maps corresponds to a rich cluster with TX = 3.51 keV and LX = (1.56 ± 0.04) × 1044 ergs s-1 (0.1-2.4 keV band). We estimate an X-ray mass within r500 corresponding to M500 ≃ 1.6 × 1014 M☉ and a total lensing mass (extrapolated by fitting a NFW profile) MNFW = (6 ± 3) × 1015 M☉. We use an automated morphological classification of all galaxies brighter than IAB = 24 over the structure area to measure the fraction of early-type objects as a function of local projected density Σ10, based on photometric redshifts derived from ground-based deep multiband photometry. We recover a robust morphology-density relation at this redshift, indicating, for comparable local densities, a smaller fraction of early-type galaxies than today. Interestingly, this difference is less strong at the highest densities and becomes more severe in intermediate environments. We also find, however, local "inversions" of the observed global relation, possibly driven by the large-scale environment. In particular, we find direct correspondence of a large concentration of disk galaxies to (the colder side of) a possible shock region detected in the X-ray temperature map and surface brightness distribution of the dominant cluster. We interpret this as potential evidence of shock-induced star formation in existing galaxy disks, during the ongoing merger between two subclusters. Our analysis reveals the value of combining various measures of the projected mass density to locate distant structures and their potential for elucidating the physical processes at work in the transformation of galaxy morphologies.

μ-PhotoZ: Photometric Redshifts by Inverting the Tolman Surface Brightness Test

Surface brightness is a fundamental observational parameter of galaxies. We show, for the first time in detail, how it can be used to obtain photometric redshifts for galaxies, the μ-PhotoZ method. We demonstrate that the Tolman surface brightness relation, μ ∝ (1 + z)-4, is a powerful tool for determining galaxy redshifts from photometric data. We develop a model using μ and a color percentile (ranking) measure to demonstrate the μ-PhotoZ method. We apply our method to a set of galaxies from the SHELS survey, and demonstrate that the photometric redshift accuracy achieved using the surface brightness method alone is comparable with the best color-based methods. We show that the μ-PhotoZ method is very effective in determining the redshift for red galaxies using only two photometric bands. We discuss the properties of the small, skewed, non-Gaussian component of the error distribution. We calibrate μr, (r - i) from the SDSS to redshift and tabulate the result, providing a simple but accurate look-up table to estimate the redshift of distant red galaxies.

A Galaxy Photometric Redshift Catalog for the Sloan Digital Sky Survey Data Release 6

We present and describe a catalog of galaxy photometric redshifts (photo-z's) for the Sloan Digital Sky Survey (SDSS) Data Release 6 (DR6). We use the Artificial Neural Network (ANN) technique to calculate photo-z's and the Nearest Neighbor Error (NNE) method to estimate photo-z errors for ~ 77 million objects classified as galaxies in DR6 with r < 22. The photo-z and photo-z error estimators are trained and validated on a sample of ~ 640,000 galaxies that have SDSS photometry and spectroscopic redshifts measured by SDSS, 2SLAQ, CFRS, CNOC2, TKRS, DEEP, and DEEP2. For the two best ANN methods we have tried, we find that 68% of the galaxies in the validation set have a photo-z error smaller than sigma_{68} =0.021 or $0.024. After presenting our results and quality tests, we provide a short guide for users accessing the public data.

The Multiwavelength Survey by Yale-Chile (MUSYC): Deep Near-Infrared Imaging and the Selection of Distant Galaxies

We present deep near-infrared JHK imaging of four 10' × 10' fields. The observations were carried out as part of the Multiwavelength Survey by Yale-Chile (MUSYC) with ISPI on the CTIO 4 m telescope. The typical point-source limiting depths are J ~ 22.5, H ~ 21.5, and K ~ 21 (5 σ; Vega). The effective seeing in the final images is ~1.0''. We combine these data with MUSYC UBVRIz imaging to create K-selected catalogs that are unique for their uniform size, depth, filter coverage, and image quality. We investigate the rest-frame optical colors and photometric redshifts of galaxies that are selected using common color selection techniques, including distant red galaxies (DRGs), star-forming and passive BzKs, and the rest-frame UV-selected BM, BX, and Lyman break galaxies (LBGs). These techniques are effective at isolating large samples of high-redshift galaxies, but none provide complete or uniform samples across the targeted redshift ranges. The DRG and BM/BX/LBG criteria identify populations of red and blue galaxies, respectively, as they were designed to do. The star-forming BzKs have a very wide redshift distribution, extending down to z ~ 1, a wide range of colors, and may include galaxies with very low specific star formation rates. In comparison, the passive BzKs are fewer in number, have a different distribution of K magnitudes, and have a somewhat different redshift distribution. By combining either the DRG and BM/BX/LBG criteria, or the star-forming and passive BzK criteria, it appears possible to define a reasonably complete sample of galaxies to our flux limit over specific redshift ranges. However, the redshift dependence of both the completeness and sampled range of rest-frame colors poses an ultimate limit to the usefulness of these techniques.

Statistical Cluster-QSO Weak Lensing in the Sloan Digital Sky Survey

We investigate the cross-correlation between galaxy clusters and QSOs using Sloan Digital Sky Survey (SDSS) DR4 ~5000 deg2 data. With photometric redshifts of galaxies, we select galaxy clusters based on the local projected densities of LRGs brighter than Mr' = −22. The QSOs are from the main sample of SDSS QSO spectroscopic survey to i' = 19. A significant positive correlation is found between the clusters and QSOs. Under the assumption that the signal is caused by gravitational lensing, we fit the signal with singular isothermal sphere (SIS) model and NFW profile halo model. The velocity dispersion σv = 766 km s−1 is derived for the best-fit of SIS model. Best-fit for the NFW model requires the dark matter halo mass within 1.5 h−1 Mpc to be 4.6×1014 h−1 M⊙. The mass parameter Ωcl of the cluster sample is deduced as 0.077 with the SIS model and 0.083 with the NFW model. Our results of Ωcl are smaller than those given by Croom & Shanks and by Myers et al.

Alignment between luminous red galaxies and surrounding structures at z∼ 0.5

We analyse a high-redshift sample (0.4 < z < 0.5) of luminous red galaxies (LRGs) extracted from the Sloan Digital Sky Survey data release 4 and their surrounding structures to explore the presence of alignment effects of these bright galaxies with neighbour objects. In order to avoid projection effects, we compute photometric redshifts for galaxies within 3 h -1 Mpc in projection of LRGs and calculate the relative angle between the LRG major axis and the direction to neighbours within 1000 km s -1 . We find a clear signal of alignment between LRG orientations and the distribution of galaxies within 1.5 h -1 Mpc. The alignment effects are present only for the red population of tracers; LRG orientation is uncorrelated to the blue population of neighbour galaxies. These results add evidence to the alignment effects between primaries and satellites detected at low redshifts. We conclude that such alignments were already present at z ∼ 0.5.

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.

An 850 Micron SCUBA Survey of the Hubble Deep Field–North GOODS Region

The Hubble Deep Field-North (HDF-N) is one of the best-studied extragalactic fields, and ultradeep optical, radio, X-ray, and mid-infrared wide-field images are available for this area. Here we present an 850 μm survey around the HDF-N, covering most of the area imaged by the Advanced Camera for Surveys as a part of the Great Observatories Origins Deep Survey. Our map has 0.4-4 mJy sensitivities (1 σ) over an area of ~110 arcmin2, and there are 45 sources detected at greater than 3 σ. After correcting for the effects of noise, confusion, incompleteness, and the Eddington bias using Monte Carlo simulations, we find that the detected 850 μm sources with fluxes greater than 2 mJy have a surface density of 3200 deg-2 and account for about 24%-34% of the far-infrared extragalactic background light. Using the deep radio interferometric image and the deep X-ray image, we are able to accurately locate ~60% of the bright submillimeter sources. In addition, by assuming the Arp 220 spectral energy distribution in the submillimeter and radio, we estimate millimetric redshifts for the radio-detected submillimeter sources and redshift lower limits for the ones not detected in the radio. Using the millimetric redshifts of the radio-identified sources and spectroscopic and optical photometric redshifts for galaxies around the submillimeter positions, we find a median redshift of 2.0 for 11 possibly identified sources, or a lower limit of 2.4 for the median redshift of our 4 σ sample.

Finding structures in photometric redshift galaxy surveys: an extended friends-of-friends algorithm

We present a modified version of the friends-of-friends (FOF) structure-finding algorithm, designed specifically to locate groups or clusters of galaxies in photometric redshift data sets. The main objective of this paper is to show that this extended friends-of-friends (hereafter EXT-FOF) algorithm yields results almost identical to the original FOF, if applied to a spectroscopic redshift data set, and a rather conservative catalogue of structures, in case of a data set with simulated photometric redshifts. Therefore, we create group catalogues for the first Center for Astrophysics Redshift Survey (CFA1), as well as for the Las Campanas Redshift Survey (LCRS), both of which being spectroscopic surveys, using FOF algorithms. We then apply our new algorithm to said surveys and compare the resulting structure catalogue. Furthermore, we bestow simulated photometric redshifts on the LCRS galaxies, and use the EXT-FOF to detect structures, which we compare in size and composition to the ones found in the original, spectroscopic data set. We will show that the properties of this modified algorithm are well understood and that it is suited for finding structures in photometric data sets. This is the first paper in a series of papers, dealing with the application of our new cluster finding algorithm to various photometric redshift galaxy surveys.

Photometric Redshifts for Galaxies in the GOODS Southern Field

We use extensive multi-wavelength photometric data from the Great Observatories Origins Deep Survey (GOODS) to estimate photometric redshifts for a sample of 434 galaxies with spectroscopic redshifts in the Chandra Deep Field South. Using the Bayesian method, which incorporates redshift/magnitude priors, we estimate photometric redshifts for galaxies in the range 18 < R (AB) < 25.5, giving an rms scatter of 0.11. The outlier fraction is < 10%, with the outlier-clipped rms being 0.047. We examine the accuracy of photometric redshifts for several, special sub--classes of objects. The results for extremely red objects are more accurate than those for the sample as a whole, with rms of 0.051 and very few outliers (3%). Photometric redshifts for active galaxies, identified from their X-ray emission, have a dispersion of 0.104, with 10% outlier fraction, similar to that for normal galaxies. Employing a redshift/magnitude prior in this process seems to be crucial in improving the agreement between photometric and spectroscopic redshifts.

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.

Deprojecting Sunyaev‐Zeldovich Statistics

We apply the hierarchical clustering model and nonlinear perturbation theory to the cosmological density and temperature fields. This allows us to calculate the intergalactic gas-pressure power spectrum, Sunyaev-Zeldovich (SZ) anisotropy power spectrum, skewness, and related statistics. Then we show the effect of the nongravitational heating. Our model confirms recent simulations yielding a mass-weighted gas temperature g ~ 0.35 keV and reproduces the power spectra found in these simulations. While the SZ effect contains only angular information, we show that it is possible to extract the full time-resolved gas-pressure power spectrum when combined with galaxy photometric redshift surveys by using a variation on the cross-correlation. This method further allows the disentanglement of the gravitational and the nongravitational heating.

Photometry and Photometric Redshifts of Faint Galaxies in the Hubble Deep Field South NICMOS Field

We present a catalog of photometry and photometric redshifts of 335 faint objects in the Hubble Deep Field South near-infrared camera and multiobject spectrograph (NICMOS) —eld. The analysis is based on (1) infrared images obtained with the Hubble Space Telescope (HST ) using the NICMOS with the F110W, F160W, and F222M —lters; (2) an optical image obtained with HST using the Space Telescope Imaging Spectrograph with no —lter; and (3) optical images obtained with the European Southern Observatory Very Large Telescope with U, B, V , R, and I —lters. The primary utility of the catalog of photometric redshifts is as a survey of faint galaxies detected in the NICMOS F160W and F222M images. The sensitivity of the survey varies signi—cantly with position, reaching a limiting depth of AB(16000) B 28.7 and covering 1.01 arcmin2 to AB(16000) 27 and 1.05 arcmin2 to AB(16000) 26.5. The catalog of photometric redshifts identi—es 21 galaxies (or 6% of the total) of redshift z ( 5, eight galaxies (or 2% of the total) of redshift z ( 10, and 11 galaxies (or 3% of the total) of best-—t spectral type E/S0, of which —ve galaxies (or 1% of the total) are of redshift z ( 1. Subject headings: cosmology: observationsgalaxies: distances and redshifts ¨ galaxies: photometrygalaxies: statistics