Redshift Catalog Research Articles

X-Ray Redshifts of Obscured Chandra Source Catalog Active Galactic Nuclei

We have computed obscured active galactic nuclei (AGN) redshifts using the XZ method, adopting a broad treatment in which we employed a wide-ranging data set and worked primarily at the XZ counts sensitivity threshold, culminating with a redshift catalog containing 121 sources that lack documented redshifts. We considered 363 obscured AGN from the Chandra Source Catalog Release 2.0, 59 of which were selected using multiwavelength criteria while 304 were X-ray selected. One third of the data set had crossmatched spectroscopic or photometric redshifts. These sources, dominated by low-z and low-N H AGN, were supplemented by 1000 simulations to form a data set for testing the XZ method. We used a multilayer perceptron neural network to examine and predict cases in which XZ fails to reproduce the known redshift, yielding a classifier that can identify and discard poor redshift estimates. This classifier demonstrated a statistically significant ∼3σ improvement over the existing XZ redshift information gain filter. We applied the machine-learning model to sources with no documented redshifts, resulting in the 121 source new redshift catalog, all of which were X-ray selected. Our neural network’s performance suggests that nearly 90% of these redshift estimates are consistent with hypothetical spectroscopic or photometric measurements, strengthening the notion that redshifts can be reliably estimated using only X-rays, which is valuable to current and future missions such as Athena. We have also identified a possible Compton-thick candidate that warrants further investigation.

Simulated catalogs and maps of radio galaxies at millimeter wavelengths in Websky

We present simulated millimeter-wavelength maps and catalogs of radio galaxies across the full sky that trace the nonlinear clustering and evolution of dark matter halos from the Websky simulation at z < 4.6 and M halo > 1012 m ⊙/h, and the accompanying framework for generating a new sample of radio galaxies from any halo catalog of positions, redshifts, and masses. Object fluxes are generated using a hybrid approach that combines (1) existing astrophysical halo models of radio galaxies from the literature to determine the positions and rank-ordering of the observed fluxes with (2) empirical models from the literature based on fits to the observed distribution of flux densities and (3) spectral indices drawn from an empirically-calibrated frequency-dependent distribution. The resulting population of radio galaxies is in excellent agreement with the number counts, polarization fractions, and distribution of spectral slopes from the data from observations at millimeter wavelengths from 20-200 GHz, including Planck, ALMA, SPT, and ACT. Since the radio galaxies are correlated with the existing cosmic infrared background (CIB), Compton-y (tSZ), and CMB lensing maps from Websky, our model makes new predictions for the cross-correlation power spectra and stacked profiles of radio galaxies and these other components. These simulations will be important for unbiased analysis of a wide variety of observables that are correlated with large-scale structure, such as gravitational lensing and SZ clusters.

Giant radio galaxies in the LOw-Frequency ARray Two-metre Sky Survey Boötes deep field

ABSTRACT Giant radio galaxies (GRGs) are radio galaxies that have projected linear extents of more than 700 kpc or 1 Mpc, depending on definition. We have carried out a careful visual inspection in search of GRGs of the Boötes LOw-Frequency ARray Deep Field image at 150 MHz. We identified 74 GRGs with a projected size larger than 0.7 Mpc of which 38 are larger than 1 Mpc. The resulting GRG sky density is about 2.8 (1.43) GRGs per square degree for GRGs with linear size larger than 0.7 (1) Mpc. We studied their radio properties and the accretion state of the host galaxies using deep optical and infrared survey data and determined flux densities for these GRGs from available survey images at both 54 MHz and 1.4 GHz to obtain integrated radio spectral indices. We show the location of the GRGs in the P–D diagram. The accretion mode on to the central black holes of the GRG hosts is radiatively inefficient suggesting that the central engines are not undergoing massive accretion at the time of the emission. Interestingly, 14 out of 35 GRGs for which optical spectra are available show a moderate star-formation rate (10–100 $\rm M_{\odot }\,yr^{-1}$). Based on the number density of optical galaxies taken from the Dark Energy Spectroscopic Instrument survey DR9 photometric redshift catalogue, we found no significant differences between the environments of GRGs and other radio galaxies, at least for redshift up to z = 0.7.

The Dwarf Galaxy Population at z ∼ 0.7: A Catalog of Emission Lines and Redshifts from Deep Keck Observations

We present a catalog of spectroscopically measured redshifts over 0 < z < 2 and emission-line fluxes for 1440 galaxies. The majority (∼65%) of the galaxies come from the HALO7D survey, with the remainder from the DEEPwinds program. This catalog includes redshifts for 646 dwarf galaxies with . Eight-hundred and ten catalog galaxies did not have previously published spectroscopic redshifts, including 454 dwarf galaxies. HALO7D used the DEIMOS spectrograph on the Keck II telescope to take very deep (up to 32 hr exposure, with a median of ∼7 hr) optical spectroscopy in the COSMOS, EGS, GOODS-North, and GOODS-South CANDELS fields, and in some areas outside CANDELS. We compare our redshift results to existing spectroscopic and photometric redshifts in these fields, finding only a 1% rate of discrepancy with other spectroscopic redshifts. We measure a small increase in median photometric redshift error (from 1.0% to 1.3%) and catastrophic outlier rate (from 3.5% to 8%) with decreasing stellar mass. We obtained successful redshift fits for 75% of massive galaxies, and demonstrate a similar 70%–75% successful redshift measurement rate in galaxies, suggesting similar survey sensitivity in this low-mass range. We describe the redshift, mass, and color–magnitude distributions of the catalog galaxies, finding HALO7D galaxies representative of CANDELS galaxies up to i-band magnitudes of 25. The catalogs presented will enable studies of star formation, the mass–metallicity relation, star formation–morphology relations, and other properties of the z ∼ 0.7 dwarf galaxy population.

Ram pressure stripping in the z ∼ 0.5 galaxy cluster MS 0451.6-0305

Context. The pressure exerted by the ambient hot X-ray gas on cluster galaxies can lead to the presence of ram pressure stripped (RPS) galaxies, characterized by asymmetric shapes, and, in some cases, tails of blue stars and/or X-ray gas, with increased star formation. Aims. With the aim of increasing the known sample of RPS galaxies at redshift z ∼ 0.5, notably higher than most RPS samples presently known, we extended our searches for such galaxies to the cluster MS 0451.6-0305. Methods. Our study is based on Hubble Space Telescope (HST) imaging in the F814W band (corresponding to a restframe wavelength of 529 nm), covering a region of about 6 × 6 Mpc2, an eight magnitude ground-based catalogue with photometric redshifts, and a spectroscopic redshift catalogue. We defined as cluster members a spectroscopic redshift sample of 359 galaxies within ±4σv of the mean cluster velocity, and a photometric redshift sample covering the [0.48, 0.61] range. We searched for RPS galaxies in the HST images and tested the error on their classification with a Zooniverse collaboration. We also computed the phase space diagram of RPS candidates in the spectroscopic sample. Finally, we ran the LePhare stellar population synthesis code through the GAZPAR interface to analyze and compare the properties of RPS and non-RPS galaxies. Results. We find 56 and 273 RPS candidates in the spectroscopic and photometric redshift samples, respectively. They are distributed throughout the cluster and tend to avoid high density regions. The phase space diagram gives the percentages of virialized, backsplash, and infall galaxies. RPS galaxy candidates typically show rather high star formation rates, young ages, and relatively low masses. We compare all our results to those previously obtained for the massive merging cluster MACS J0717+3745, at a similar redshift. Conclusions. This study increases by at least 56 objects if we only consider galaxies with spectroscopic redshifts, and probably much more if galaxies with photometric redshifts are taken into account. This study increases the number of RPS candidates at redshift z &gt; 0.5, and confirms that they host, on average, younger stellar populations and strongly form stars when compared with non-RPS counterparts. The fact that RPS candidates with spectroscopic and with photometric redshifts have comparable properties shows that large samples of such objects could be gathered based on multi-band photometry only, a promising result in view of the very large imaging surveys planned in the coming years (DES, Euclid, LSST, etc.).

A systematic search for galaxy protocluster cores at the transition epoch of their star formation activity

ABSTRACT The redshift of z ∼ 1.5 is the transition epoch of protoclusters (PCs) from the star-forming phase into the quenching phase, and hence an appropriate era to investigate the build up of the quenched population. We define a ‘core’ as the most massive halo in a given PC, where environmental effects are likely to work most effectively, and search for cores at 1 &amp;lt; z &amp;lt; 1.5. We use a photometric redshift catalogue of a wide (effective area of ${\sim}22.2\, \mathrm{deg}^{2}$) and deep ($i\sim 26.8\, \mathrm{mag}$) optical survey with Subaru Hyper-Suprime Cam. Regarding galaxies with log (M*/M⊙) &amp;gt; 11.3 as the central galaxies of PC cores, we estimate their average halo mass by clustering analysis and find it to be log (Mh/M⊙) ∼ 13.7. An expected mass growth by the IllustrisTNG simulation and the observed overdensities around them suggest that the PC cores we find are progenitors of present-day clusters. Classifying our galaxy sample into red and blue galaxies, we calculate the stellar mass function (SMF) and the red galaxy fraction. The SMFs in the PC cores are more-top heavy than field, implying early high-mass galaxy formation and disruption of low-mass galaxies. We also find that the red fraction increases with stellar mass, consistent with stellar mass dependent environmental quenching recently found at z &amp;gt; 1. Interestingly, although the cores with red and blue centrals have similar halo masses, only those with red centrals show a significant red fraction excess compared to the field, suggesting a conformity effect. Some observational features of PC cores may imply that the conformity is caused by assembly bias.

Extending the SAGA Survey (xSAGA). I. Satellite Radial Profiles as a Function of Host-galaxy Properties

Abstract We present “Extending the Satellites Around Galactic Analogs Survey” (xSAGA), a method for identifying low-z galaxies on the basis of optical imaging and results on the spatial distributions of xSAGA satellites around host galaxies. Using spectroscopic redshift catalogs from the SAGA Survey as a training data set, we have optimized a convolutional neural network (CNN) to identify z &lt; 0.03 galaxies from more-distant objects using image cutouts from the DESI Legacy Imaging Surveys. From the sample of &gt;100,000 CNN-selected low-z galaxies, we identify &gt;20,000 probable satellites located between 36–300 projected kpc from NASA-Sloan Atlas central galaxies in the stellar-mass range 9.5 &lt; log ( M ⋆ / M ⊙ ) &lt; 11 . We characterize the incompleteness and contamination for CNN-selected samples and apply corrections in order to estimate the true number of satellites as a function of projected radial distance from their hosts. Satellite richness depends strongly on host stellar mass, such that more-massive host galaxies have more satellites, and on host morphology, such that elliptical hosts have more satellites than disky hosts with comparable stellar masses. We also find a strong inverse correlation between satellite richness and the magnitude gap between a host and its brightest satellite. The normalized satellite radial distribution between 36–300 kpc does not depend on host stellar mass, morphology, or magnitude gap. The satellite abundances and radial distributions we measure are in reasonable agreement with predictions from hydrodynamic simulations. Our results deliver unprecedented statistical power for studying satellite galaxy populations and highlight the promise of using machine-learning for extending galaxy samples of wide-area surveys.

Probing cosmology and gastrophysics with fast radio bursts: cross-correlations of dark matter haloes and cosmic dispersion measures

ABSTRACT For future surveys of fast radio bursts (FRBs), we clarify information available from cosmic dispersion measures (DMs) through cross-correlation analyses of foreground dark matter haloes (hosting galaxies and galaxy clusters) with their known redshifts. With a halo-model approach, we predict that the cross-correlation with cluster-sized haloes is less affected by the details of gastrophysics, providing robust cosmological information. For less massive haloes, the cross-correlation at angular scales of ${\lt} 10\, \mathrm{arcmin}$ is sensitive to gas expelled from the halo centre due to galactic feedback. Assuming 20 000 FRBs over $20\,000 \, {\rm deg}^2$ with a localization error being 3 arcmin, we expect that the cross-correlation signal at halo masses of 1012–$10^{14}\, {\rm M}_\odot$ can be measured with a level of ${\sim} 1{{\ \rm per\ cent}}$ precision in a redshift range of 0 &amp;lt; z &amp;lt; 1. Such precise measurements enable one to put a 1.5 per cent level constraint on $\sigma _8\, (\Omega _\mathrm{M}/0.3)^{0.5}$ and a 3 per cent level constraint on (Ωb/0.049)(h/0.67)(fe/0.95) (σ8, ΩM, Ωb, h, and fe are the linear mass variance smoothed at $8\, h^{-1}\mathrm{\,Mpc}$, mean mass density, mean baryon density, the present-day Hubble parameter, and fraction of free electrons in cosmic baryons today, respectively), whereas the gas-to-halo mass relation in galaxies and clusters can be constrained with a level of $10$–$20{{\ \rm per\ cent}}$. Furthermore the cross-correlation analyses can break the degeneracy among Ωb, h, and fe, inherent in the DM–redshift relation. Our proposal opens new possibilities for FRB cosmology, while it requires extensive galaxy redshift catalogues and further improvement of the halo model.

Calibrating Photometric Redshift Measurements with the Multi-channel Imager (MCI) of the China Space Station Telescope (CSST)

The China Space Station Telescope (CSST) photometric survey aims to perform a high spatial resolution (∼0.″15) photometric imaging for the targets that cover a large sky area (∼17,500 deg2) and wide wavelength range (from NUV to NIR). It expects to explore the properties of dark matter, dark energy, and other important cosmological and astronomical areas. In this work, we evaluate whether the filter design of the Multi-channel Imager (MCI), one of the five instruments of the CSST, can provide accurate photometric redshift (photoz) measurements with its nine medium-band filters to meet the relevant scientific objectives. We generate the mock data based on the COSMOS photometric redshift catalog with astrophysical and instrumental effects. The application of upper limit information of low signal-to-noise ratio data is adopted in the estimation of photoz. We investigate the dependency of photoz accuracy on the filter parameters, such as band position and width. We find that the current MCI filter design can achieve good photoz measurements with accuracy σ z ≃ 0.017 and outlier fraction f c ≃ 2.2%. It can effectively improve the photoz measurements of the main CSST survey using the Survey Camera to an accuracy σ z ≃ 0.015 and outlier fraction f c ≃ 1.5%. This indicates that the original MCI filters are proper for the photoz calibration.

Accretion processes in the galaxy cluster Hydra A/Abell 780

Context. Clusters of galaxies evolve and accrete mass, mostly from small galaxy systems. Aims. Our aim is to study the velocity field of the galaxy cluster Abell 780, which is known for the powerful radio source Hydra A at its center and where a spectacular X-ray tail associated with the galaxy LEDA 87445 has been discovered. Methods. Our analysis is based on the new spectroscopic data for hundreds of galaxies obtained with the Italian Telescopio Nazionale Galileo and the Very Large Telescope. We have constructed a redshift catalog of 623 galaxies and selected a sample of 126 cluster members. We analyzed the internal structure of the cluster using a number of techniques. Results. We estimate the mean redshift z = 0.0545, the line-of-sight velocity dispersion σV ∼ 800 km s−1, and the dynamical mass M200 ∼ 5.4 × 1014 M⊙. The global properties of Abell 780 are typical of relaxed clusters. On a smaller scale, we can detect the presence of a galaxy group associated with LEDA 87445 in projected phase space. The mean velocity and position of the center of the group agree well with the velocity and position of LEDA 87445. We estimate the following parameters of the collision. The group is characterized by a higher velocity relative to the main system. It is infalling at a rest frame velocity of Vrf ∼ +870 km s−1 and lies at a projected distance of D ∼ 1.1 Mpc to the south, slightly southeast of the cluster center. The mass ratio of the group to the cluster is ∼1:5. We also find evidence of an asymmetry in the velocity distribution of galaxies in the inner cluster region, which might be related to a small low-velocity group detected as a substructure at Vrf ∼ −750 km s−1. Conclusions. We conclude that A780, although dynamically relaxed at first sight, contains small substructures that may have some impact on the energetics of the core region.

Compact groups from semi-analytical models of galaxy formation – III. Purity and completeness of Hickson-like catalogues

ABSTRACT Many catalogues of isolated compact groups of galaxies (CGs) have been extracted using Hickson’s criteria to identify isolated, dense systems of galaxies, with at least three or four galaxies concordant in magnitude and redshift. But is not clear to what extent the catalogues of CGs are complete and reliable, relative to 3D truly isolated, dense groups. Using five different semi-analytical models of galaxy formation (SAMs), we identify isolated dense groups in 3D real space, containing at least three galaxies. We then build mock redshift space galaxy catalogues and run a Hickson-like CG finder. We find that the Hickson-like algorithm in redshift space is poor at recovering 3D CGs of at least three galaxies, with a purity of $\sim 10{{\ \rm per \, cent}}$ and a completeness of $\sim 22{{\ \rm per \, cent}}$. Among the $\sim 90{{\ \rm per \, cent}}$ of spurious systems, typically $60{{\ \rm per\ cent}}$ are dense structures that failed the 3D isolation criteria, while the remaining $40{{\ \rm per \, cent}}$ are chance alignments of galaxies along the line of sight, nearly all of which are within regular groups, with some variation with the SAM used for the analysis. In other words, while only 10 per cent of CGs are isolated dense groups, as intended, half are dense structures embedded within larger groups, and one-third are chance alignments within larger groups. The low completeness of the extracted CG sample is mainly due to the flux limits of the selection criteria. Our results suggest that a new observational algorithm to identify compact groups in redshift space is required to obtain dense isolated galaxy systems.

COSMOS2020: A Panchromatic View of the Universe to z ∼ 10 from Two Complementary Catalogs

Abstract The Cosmic Evolution Survey (COSMOS) has become a cornerstone of extragalactic astronomy. Since the last public catalog in 2015, a wealth of new imaging and spectroscopic data have been collected in the COSMOS field. This paper describes the collection, processing, and analysis of these new imaging data to produce a new reference photometric redshift catalog. Source detection and multiwavelength photometry are performed for 1.7 million sources across the 2 deg2 of the COSMOS field, ∼966,000 of which are measured with all available broadband data using both traditional aperture photometric methods and a new profile-fitting photometric extraction tool, The Farmer, which we have developed. A detailed comparison of the two resulting photometric catalogs is presented. Photometric redshifts are computed for all sources in each catalog utilizing two independent photometric redshift codes. Finally, a comparison is made between the performance of the photometric methodologies and of the redshift codes to demonstrate an exceptional degree of self-consistency in the resulting photometric redshifts. The i &lt; 21 sources have subpercent photometric redshift accuracy and even the faintest sources at 25 &lt; i &lt; 27 reach a precision of 5%. Finally, these results are discussed in the context of previous, current, and future surveys in the COSMOS field. Compared to COSMOS2015, it reaches the same photometric redshift precision at almost one magnitude deeper. Both photometric catalogs and their photometric redshift solutions and physical parameters will be made available through the usual astronomical archive systems (ESO Phase 3, IPAC-IRSA, and CDS).

Redshift identification of X-ray-selected active galactic nuclei in the J1030 field: searching for large-scale structures and high-redshift sources

We publicly release the spectroscopic and photometric redshift catalog of the sources detected withChandrain the field of thez= 6.3 quasar SDSS J1030+0525. This is currently the fifth-deepest extragalactic X-ray field, and reaches a 0.5–2 keV flux limit off0.5 − 2= 6 × 10−17erg s−1cm−2. Using two independent methods, we measure a photometric redshift for 243 objects, while 123 (51%) sources also have a spectroscopic redshift, 110 of which come from an INAF-Large Binocular Telescope (LBT) Strategic Program. We use the spectroscopic redshifts to determine the quality of the photometric ones, and find it to be in agreement with that of other X-ray surveys which used a similar number of photometric data points. In particular, we measure a sample normalized median absolute deviation ofσNMAD= 1.48 × median(||zphot − zspec||/(1 +zspec)) = 0.065. We use these new spectroscopic and photometric redshifts to study the properties of theChandraJ1030 field. We observe several peaks in our spectroscopic redshift distribution betweenz= 0.15 andz= 1.5, and find that the sources in each peak are often distributed across the wholeChandrafield of view. This confirms that X-ray-selected AGNs can efficiently track large-scale structures over physical scales of several megaparsecs. Finally, we computed theChandraJ1030z&gt; 3 number counts: while the spectroscopic completeness of our sample is limited at high redshift, our results point towards a potential source excess atz ≥ 4, which we plan to either confirm or reject in the near future with dedicated spectroscopic campaigns.

Interrelation of the Environment of Lyα Emitters and Massive Galaxies at 2 &lt; z &lt; 4.5

Abstract We present a comparison of the spatial distributions of Lyα emitters (LAEs) and massive star-forming and quiescent galaxies (SFGs and QGs) at 2 &lt; z &lt; 4.5. We use the photometric redshift catalog to select SFGs and QGs and an LAE catalog from intermediate/narrow bands obtained from the Subaru Telescope and Isaac Newton Telescope in the Cosmic Evolution Survey (COSMOS). We derive the auto-/cross-correlation signals of SFGs, QGs, and LAEs and the galaxy overdensity distributions at the position of them. Whereas the cross-correlation signals of SFGs and QGs are explained solely by their halo mass differences, those of SFGs and LAEs are significantly lower than those expected from their autocorrelation signals, suggesting that some additional physical processes are segregating these two populations. Such segregation of SFGs and LAEs becomes stronger for rest-frame ultraviolet faint LAEs (M UV &gt; −20). From the overdensity distributions, LAEs are located in less dense regions than SFGs and QGs, whereas SFGs and QGs tend to be in the same overdensity distributions. The different spatial distributions of LAEs compared to those of massive galaxies may be attributed to assembly bias or large amounts of neutral hydrogen gas associated with massive halos. These results reinforce the importance of exploring multiple galaxy populations in quantifying the intrinsic galaxy environment of the high-z universe.

H I content in Coma cluster substructure

Context. Galaxy clusters are some of largest structures in the universe. These very dense environments tend to be home to higher numbers of evolved galaxies than found in lower-density environments. It is well known that dense environments can influence the evolution of galaxies through the removal of the neutral gas (H I) reservoirs that fuel star formation. It is unclear which environment has a stronger effect: the local environment (i.e., the substructure within the cluster), or the cluster itself. Aims. Using the new H I data from the Westerbork Coma Survey, we explore the average H I content of galaxies across the cluster comparing galaxies that reside in substructure to those that do not. Methods. We applied the Dressler–Shectman test to our newly compiled redshift catalogue of the Coma cluster to search for substructure. With so few of the Coma galaxies directly detected in H I, we used the H I stacking technique to probe the average H I content below what can be directly detected. Results. Using the Dressler–Shectman test, we find 15 substructures within the footprint of the Westerbork Coma Survey. We compare the average H I content for galaxies within substructure to those not in substructure. Using the H I stacking technique, we find that those Coma galaxies not detected in H I are more than 10–50 times more H I deficient than expected, which supports the scenario of an extremely efficient and rapid quenching mechanism. By studying the galaxies that are not directly detected in H I, we also find Coma to be more H I deficient than previously thought.

Galaxy Clusters from the DESI Legacy Imaging Surveys. I. Cluster Detection

Abstract Based on the photometric redshift catalog of Zou et al., we apply a fast clustering algorithm to identify 540,432 galaxy clusters at z ≲ 1 in the DESI legacy imaging surveys, which cover a sky area of about 20,000 deg2. Monte Carlo simulations indicate that the false-detection rate of our detecting method is about 3.1%. The total masses of galaxy clusters are derived using a calibrated richness–mass relation that is based on the observations of X-ray emission and the Sunyaev and Zel’dovich effect. The median redshift and mass of our detected clusters are about 0.53 and 1.23 × 1014 M ⊙, respectively. Comparing with previous clusters identified using the data of the Sloan Digital Sky Survey; we can recognize most of them, especially those with high richness. Our catalog will be used for further statistical studies on galaxy clusters and environmental effects on galaxy evolution, etc.

The VANDELS ESO public spectroscopic survey

VANDELS is an ESO Public Spectroscopic Survey designed to build a sample of high-signal-to-noise ratio, medium-resolution spectra of galaxies at redshifts between 1 and 6.5. Here we present the final Public Data Release of the VANDELS Survey, comprising 2087 redshift measurements. We provide a detailed description of sample selection, observations, and data reduction procedures. The final catalogue reaches a target selection completeness of 40% at iAB = 25. The high signal-to-noise ratio of the spectra (above 7 in 80% of the spectra) and the dispersion of 2.5 Å allowed us to measure redshifts with high precision, the redshift measurement success rate reaching almost 100%. Together with the redshift catalogue and the reduced spectra, we also provide optical mid-infrared photometry and physical parameters derived through fitting the spectral energy distribution. The observed galaxy sample comprises both passive and star forming galaxies covering a stellar mass range of 8.3 &lt; Log(M*/M⊙) &lt; 11.7.

A hierarchical clustering method for quantifying satellite abundance

ABSTRACT We present a new method for quantifying the abundance of satellites around field galaxies and in groups. The method is designed to work with samples such as photometric redshift catalogues, that do not have full spectroscopic coverage, but for which some redshift or distance information is available. It consists of identifying the galaxies most likely to be centrals, and using the clustering signal around them as a template to iteratively decompose the full population into satellite and central populations. Thus, it is similar to performing crowded-field photometry by using isolated stars to determine the point spread function of the image. The method does not identify individual satellites or centrals conclusively, but assigns a probability to each galaxy of being one or the other. Averaged over a large sample, it provides a statistical estimate of satellite abundance, even in crowded fields with large redshift uncertainties. We test the method using data from the COSMOS field, which includes a large set of local objects with accurate photometric redshifts. We measure satellite abundance as a function of central stellar or halo mass, as well as the satellite luminosity function, and find results consistent with previous studies, but extending over a broader range of central masses. We also consider a number of possible systematic uncertainties in the method, and show that they are generally smaller than our random errors. Having presented the method in this paper, we will use it to study the properties of the satellite populations in a forthcoming one.

An atlas of MUSE observations towards twelve massive lensing clusters

Context. Spectroscopic surveys of massive galaxy clusters reveal the properties of faint background galaxies thanks to the magnification provided by strong gravitational lensing. Aims. We present a systematic analysis of integral-field-spectroscopy observations of 12 massive clusters, conducted with the Multi Unit Spectroscopic Explorer (MUSE). All data were taken under very good seeing conditions (∼0″​​.6) in effective exposure times between two and 15 h per pointing, for a total of 125 h. Our observations cover a total solid angle of ∼23 arcmin2 in the direction of clusters, many of which were previously studied by the MAssive Clusters Survey, Frontier Fields (FFs), Grism Lens-Amplified Survey from Space and Cluster Lensing And Supernova survey with Hubble programmes. The achieved emission line detection limit at 5σ for a point source varies between (0.77–1.5) × 10−18 erg s−1 cm−2 at 7000 Å. Methods. We present our developed strategy to reduce these observational data, detect continuum sources and line emitters in the datacubes, and determine their redshifts. We constructed robust mass models for each cluster to further confirm our redshift measurements using strong-lensing constraints, and identified a total of 312 strongly lensed sources producing 939 multiple images. Results. The final redshift catalogues contain more than 3300 robust redshifts, of which 40% are for cluster members and ∼30% are for lensed Lyman-α emitters. Fourteen percent of all sources are line emitters that are not seen in the available HST images, even at the depth of the FFs (∼29 AB). We find that the magnification distribution of the lensed sources in the high-magnification regime (μ = 2–25) follows the theoretical expectation of N(z) ∝ μ−2. The quality of this dataset, number of lensed sources, and number of strong-lensing constraints enables detailed studies of the physical properties of both the lensing cluster and the background galaxies. The full data products from this work, including the datacubes, catalogues, extracted spectra, ancillary images, and mass models, are made available to the community.

The ALPINE-ALMA [CII] survey

Aims. We present the detailed characterisation of a sample of 56 sources serendipitously detected in ALMA band 7 as part of the ALMA Large Program to INvestigate CII at Early Times (ALPINE). These sources, detected in COSMOS and ECDFS, have been used to derive the total infrared luminosity function (LF) and to estimate the cosmic star formation rate density (SFRD) up to z ≃ 6. Methods. We looked for counterparts of the ALMA sources in all the available multi-wavelength (from HST to VLA) and photometric redshift catalogues. We also made use of deeper UltraVISTA and Spitzer source lists and maps to identify optically dark sources with no matches in the public catalogues. We used the sources with estimated redshifts to derive the 250 μm rest-frame and total infrared (8–1000 μm) LFs from z ≃ 0.5 to 6. Results. Our ALMA blind survey (860 μm flux density range: ∼0.3–12.5 mJy) allows us to further push the study of the nature and evolution of dusty galaxies at high-z, identifying luminous and massive sources to redshifts and faint luminosities never probed before by any far-infrared surveys. The ALPINE data are the first ones to sample the faint end of the infrared LF, showing little evolution from z ≃ 2.5 to z ≃ 6, and a “flat” slope up to the highest redshifts (i.e. 4.5 &lt; z &lt; 6). The SFRD obtained by integrating the luminosity function remains almost constant between z ≃ 2 and z ≃ 6, and significantly higher than the optical or ultra-violet derivations, showing a significant contribution of dusty galaxies and obscured star formation at high-z. About 14% of all the ALPINE serendipitous continuum sources are found to be optically and near-infrared (near-IR) dark (to a depth Ks ∼ 24.9 mag). Six show a counterpart only in the mid-IR and no HST or near-IR identification, while two are detected as [C II] emitters at z ≃ 5. The six HST+near-IR dark galaxies with mid-IR counterparts are found to contribute about 17% of the total SFRD at z ≃ 5 and to dominate the high-mass end of the stellar mass function at z &gt; 3.