The CosmoDB data have been published in the following papers:
Bayesian group finder based on marked/object point processes. Application to the 2MRS data set
Tempel E., Kruuse M., Kipper R., Tuvikene T., Sorce J. G., Stoica R. S. 2018, in prep
Abstract: Galaxy groups and clusters are formidable cosmological probes. They permit studying the environmental effects on galaxy formation. A reliable detection of galaxy groups is an open problem and is important for ongoing and future cosmological surveys. We propose a new galaxy group and cluster detection algorithm based on a marked/object point processes with interactions. The proposed methodology relies on modelling the underlying cluster pattern and assigns probabilities for marked/object
points in the model using the locations and (in principal) properties of galaxies. Using the Bayesian approach and Monte Carlo simulations, we use our model to generate a probabilistic galaxy group/cluster detection field (called a visit map). Single galaxy systems from the data set are then extracted using the probabilistic output of the marked/object point process simulations. Applying the methodology to the 2MRS data set, we compile a catalogue of galaxy groups that we make publicly available. Compared to previously published Friends-of-Friends (FoF) group finders, the Bayesian group finder gives overall similar results. However for specific applications, like the reconstruction of the local Universe, the details of the grouping algorithms are important. The proposed Bayesian group finder is tested on the 2MRS galaxy redshift survey, but the mathematical framework permits adapting it easily for other data sets (in astronomy and in other fields of sciences). In cosmology, one promising application is the detection of galaxy groups in photometric galaxy redshift surveys, while taking into account the full photometric redshift posteriors.
Catalogues in ascii format: 2MRS_Bayes_groups.zip
Merging groups and clusters of galaxies from the SDSS data. The catalogue of groups and potentially merging systems
Tempel E., Tuvikene T., Kipper R., Libeskind N. I. 2017, A&A
Abstract: Galaxy groups and clusters are the main tools to test cosmological models and to study the environmental effect of galaxy formation. This work aims to provide a catalogue of galaxy groups/clusters and potentially merging systems based on the SDSS main galaxy survey. We identify galaxy groups and clusters using the modified friends-of-friends (FoF) group finder that is designed specifically for flux-limited galaxy surveys. FoF group membership is refined by multimodality analysis to find subgroups and by using the group virial radius and escape velocity to expose unbound galaxies. We look for merging systems by comparing distances between group centres with group radii. The analysis results in a catalogue of 88662 galaxy groups with at least two members. Among them are 6873 systems with at least 6 members which we consider as more reliable groups. We find 498 group mergers with up to six groups. We performed brief comparison with some known clusters in nearby Universe, including Coma cluster and Abell 1750. Coma cluster in our catalogue is a merging system with six distinguishable sub-components. In case of Abell 1750 we found a clear sign of filamentary infall toward this cluster. Our analysis of mass-to-light ratio (M/L) of galaxy groups reveals that M/L slightly increases together with group richness.
Catalogues in ascii format: sdss_dr12_groups.zip
Friends-of-friends galaxy group finder with membership refinement. Application to the local Universe
Tempel E., Kipper R., Tamm A. et al. 2016, A&A 588, A14
Abstract: Groups form the most abundant class of galaxy systems. They act as the principal drivers of galaxy evolution and can be used as tracers of the large-scale structure and the underlying cosmology. However, the detection of galaxy groups from galaxy redshift survey data is hampered by several observational limitations. We improve the widely used friends-of-friends (FoF) group finding algorithm with membership refinement procedures and apply the method to a combined dataset of galaxies in the local Universe. A major aim of the refinement is to detect subgroups within the FoF groups, enabling a more reliable suppression of the Fingers-of-God effect. The FoF algorithm is often suspected of leaving subsystems of groups and clusters undetected. We use a galaxy sample built of the 2MRS, CF2, and 2M++ survey data comprising nearly 80000 galaxies within the local volume of 430 Mpc radius to carry out FoF group detection. We conduct a multimodality check on the detected groups in search for subgroups. We further refine group membership using group virial radius and escape velocity to expose unbound galaxies. We use the virial theorem to estimate group masses. The analysis results in a catalogue of 6282 galaxy groups in the 2MRS sample with two or more members, together with their mass estimates. About a half of the initial FoF groups with ten or more members were split into smaller systems with the multimodality check.
Catalogues in ascii format: 2MRS_FoF_groups.tar.gz
Flux- and volume-limited groups/clusters for the SDSS galaxies: catalogues and mass estimation
Tempel E., Tamm A., Gramann M. et al. 2014, A&A 566, A1
Abstract: We provide flux-limited and volume-limited galaxy group and cluster catalogues, based on the spectroscopic sample of the SDSS data release 10 galaxies. We used a modified friends-of-friends (FoF) method with a variable linking length in the transverse and radial directions to identify as many realistic groups as possible. The flux-limited catalogue incorporates galaxies down to m_r = 17.77 mag. It includes 588193 galaxies and 82458 groups. The volume-limited catalogues are complete for absolute magnitudes down to M_r = -18.0, -18.5, -19.0, -19.5, -20.0, -20.5, and -21.0; the completeness is achieved within different spatial volumes, respectively. Our analysis shows that flux-limited and volume-limited group samples are well compatible to each other, especially for the larger groups/clusters. Dynamical mass estimates, based on radial velocity dispersions and group extent in the sky, are added to the extracted groups.
Detecting filamentary pattern in the cosmic web: a catalogue of filaments for the SDSS
Tempel E., Stoica R. S., Martínez V. J. et al. 2014, MNRAS 438, 3465
Abstract: The main feature of the spatial large-scale galaxy distribution is its intricate network of galaxy filaments. This network is spanned by the galaxy locations that can be interpreted as a three-dimensional point distribution. The global properties of the point process can be measured by different statistical methods, which, however, do not describe directly the structure elements. The morphology of the large-scale structure, on the other hand, is an important property of the galaxy distribution. Here, we apply an object point process with interactions (the Bisous model) to trace and extract the filamentary network in the presently largest galaxy redshift survey, the Sloan Digital Sky Survey (SDSS). We search for filaments in the galaxy distribution that have a radius of about 0.5 h-1 Mpc. We divide the detected network into single filaments and present a public catalogue of filaments. We study the filament length distribution and show that the longest filaments reach the length of 60 h-1Mpc. The filaments contain 35-40 per cent of the total galaxy luminosity and they cover roughly 5-8 per cent of the total volume, in good agreement with N-body simulations and previous observational results.
Groups and clusters of galaxies in the SDSS DR8. Value-added catalogues
Tempel E., Tago E., Liivamägi L. J. 2012, A&A 540, A106
Abstract: Aims: We intend to compile a new galaxy group and cluster sample of the latest available SDSS data, adding several parameter for the purpose of studying the supercluster network, galaxy and group evolution, and their connection to the surrounding environment.
Methods: We used a modified friends-of-friends (FoF) method with a variable linking length in the transverse and radial directions to eliminate selection effects and to find reliably as many groups as possible. Using the galaxies as a basis, we calculated the luminosity density field.
Results: We create a new catalogue of groups and clusters for the SDSS data release 8 sample. We find and add environmental parameters to our catalogue, together with other galaxy parameters (e.g., morphology), missing from our previous catalogues. We take into account various selection effects caused by a magnitude limited galaxy sample. Our final sample contains 576 493 galaxies and 77 858 groups.
SDSS DR7 superclusters. The catalogues
Liivamägi L. J., Tempel E., Saar E. 2012, A&A 539, A80
Abstract: We have constructed a set of supercluster catalogues for the galaxies from the SDSS survey main and luminous red galaxy (LRG) flux-limited samples. To delineate superclusters, we calculated luminosity density fields using the B3-spline kernel of the radius of 8 h-1 Mpc for the main sample and 16 h-1 Mpc for the LRG sample and define regions with densities over a selected threshold as superclusters, while utilising almost the whole volume of both samples. We created two types of catalogues, one with an adaptive local threshold and a set of catalogues with different global thresholds. We describe the supercluster catalogues and their general properties. Using smoothed bootstrap, we find uncertainty estimates for the density field and use these to attribute confidence levels to the catalogue objects. We have also created a test catalogue for the galaxies from the Millennium simulation to compare the simulated and observed superclusters and to clarify the methods we use. We find that the superclusters are well-defined systems, and the properties of the superclusters of the main and LRG samples are similar. We also show that with adaptive local thresholds we get a sample of superclusters, the properties of which do not depend on their distance from the observer. The Millennium galaxy catalogue superclusters are similar to those observed.