P. Nurmi

Twenty years monitoring of extragalactic sources at 22, 37 and 87 GHz

Long term monitoring results from mid 1995 to the end of 2000 of quasar observations at 22, 37 and 87 GHz done at the Metsahovi radio observatory are presented. Approximately 15 700 observations are published here.

Groups of galaxies in the SDSS Data Release 7: Flux- and volume-limited samples

Aims. We extract groups of galaxies as flux-limited and volume-limited samples from the SDSS Data Release 7 (DR7) to study the supercluster-void network and environmental properties of groups therein. Volume-limited catalogues are particularly useful for a comparison of numerical simulations of dark matter halos and the large-scale structure with observations. Methods. The extraction of a volume-limited sample of galaxies and groups requires special care to avoid excluding too much observational data. We use a modified friends-of-friends (FoF) method with a slightly variable linking length to obtain a preliminary flux-limited sample. We take the flux-limited groups as the basic sample to include as many galaxies as possible in the volume-limited samples. To determine the scaling of the linking length we calibrated group sizes and mean galaxy number densities within groups by magnitude dilution of a nearby group sub-sample to follow the properties of groups with higher luminosity limits. Results. Our final flux-limited sample contains 78800 groups and volume-limited subsamples with absolute magnitude limits M r = -18, -19, -20, and -21 contain 5463, 12590, 18 973, and 9139 groups, respectively, in the DR7 main galaxy main area survey. The group catalogue is available at the CDS. Conclusions. The spatial number densities of our groups within the subsamples, as well as the mean sizes and rms velocities of our groups practically do not change from sub-sample to sub-sample. This means that the catalogues are homogeneous and well suited for a comparison with simulations.

Multimodality in galaxy clusters from SDSS DR8: substructure and velocity distribution

Context. The study of the signatures of multimodality in groups and clusters of galaxies, an environment for most of the galaxies in the Universe, gives us information about the dynamical state of clusters and about merging processes, which affect the formation and evolution of galaxies, groups and clusters, and larger structures – superclusters of galaxies and the whole cosmic web. Aims. We search for the presence of substructure, a non-Gaussian, asymmetrical velocity distribution of galaxies, and large peculiar velocities of the main galaxies in clusters with at least 50 member galaxies, drawn from the SDSS DR8. Methods. We employ a number of 3D, 2D, and 1D tests to analyse the distribution of galaxies in clusters: 3D normal mixture modelling, the Dressler-Shectman test, the Anderson-Darling and Shapiro-Wilk tests, as well as the Anscombe-Glynn and the D’Agostino tests. We find the peculiar velocities of the main galaxies, and use principal component analysis to characterise our results. Results. More than 80% of the clusters in our sample have substructure according to 3D normal mixture modelling, and the DresslerShectman (DS) test shows substructure in about 70% of the clusters. The median value of the peculiar velocities of the main galaxies in clusters is 206 km s −1 (41% of the rms velocity). The velocities of galaxies in more than 20% of the clusters show significant non-Gaussianity. While multidimensional normal mixture modelling is more sensitive than the DS test in resolving substructure in the sky distribution of cluster galaxies, the DS test determines better substructure expressed as tails in the velocity distribution of galaxies (possible line-of-sight mergers). Richer, larger, and more luminous clusters have larger amount of substructure and larger (compared to the rms velocity) peculiar velocities of the main galaxies. Principal component analysis of both the substructure indicators and the physical parametres of clusters shows that galaxy clusters are complicated objects, the properties of which cannot be explained with a small number of parametres or delimited by one single test. Conclusions. The presence of substructure, the non-Gaussian velocity distributions, as well as the large peculiar velocities of the main galaxies, shows that most of the clusters in our sample are dynamically young.

Multimodality of rich clusters from the SDSS DR8 within the supercluster-void network

Context. The study of the properties of galaxy clusters and their environment gives us information about the formation and evolution of galaxies, groups and clusters, and larger structures – superclusters of galaxies and the whole cosmic web. Aims. We study the relations between the multimodality of galaxy clusters drawn from the SDSS DR8 and the environment where they reside. As cluster environment we consider the global luminosity density field, supercluster membership, and supercluster morphology. Methods. We use 3D normal mixture modelling, the Dressler-Shectman test, and the peculiar velocity of cluster main galaxies as signatures of multimodality of clusters. We calculate the luminosity density field to study the environmental densities around clusters, and to find superclusters where clusters reside. We determine the morphology of superclusters with the Minkowski functionals and compare the properties of clusters in superclusters of different morphology. We apply principal component analysis to study the relations between the multimodality parameters of clusters and their environment simultaneously. Results. Multimodal clusters reside in higher density environment than unimodal clusters. Clusters in superclusters have higher probability to have substructure than isolated clusters. The superclusters can be divided into two main morphological types, spiders and filaments. Clusters in superclusters of spider morphology have higher probabilities to have substructure and larger peculiar velocities of their main galaxies than clusters in superclusters of filament morphology. The most luminous clusters are located in the high-density cores of rich superclusters. Five of seven most luminous clusters, and five of seven most multimodal clusters reside in spider-type superclusters; four of seven most unimodal clusters reside in filament-type superclusters. Conclusions. Our study shows the importance of the role of superclusters as high density environment, which affects the properties of galaxy systems in them.

Environments of galaxies in groups within the supercluster-void network

Context. The majority of all galaxies reside in groups of fewer than 50 member galaxies. These groups are distributed in various large-scale environments from voids to superclusters. Aims. The evolution of galaxies is affected by the environment in which they reside. Our aim is to study the effects of the local group scale and the supercluster scale environments on galaxy evolution. Methods. We use a luminosity-density field to determine the density of the large-scale environment of galaxies in groups of various richnesses. We calculate the fractions of different types of galaxies in groups with richnesses of up to 50 member galaxies and in different large-scale environments from voids to superclusters. Results. The fraction of passive elliptical galaxies rises and the fraction of star-forming spiral galaxies declines when the richness of a group of galaxies rises from two to approximately ten galaxies. On large scales, passive elliptical galaxies become more numerous than star-forming spirals when the environmental density grows to values typical of superclusters. The large-scale environment affects the level of these fractions in groups: galaxies in equally rich groups are more likely to be elliptical in supercluster environments than at lower densities. The crossing point, where the number of passive and star-forming galaxies is equal, occurs in superclusters in groups that are of lower richness than in voids. Galaxies in low-density environments need to occupy richer groups to evolve from star-forming to passive than galaxies in high-density environments. Groups in superclusters are on average more luminous than groups in large-scale environments of lower density. These results imply that the large-scale environment affects the properties of galaxies and groups. Conclusions. Our results suggest that the evolution of galaxies is affected by both, the group in which the galaxy resides and its largescale environment. Galaxies in lower-density regions develop later than galaxies in similar mass groups in high-density environments.

NATURAL TRANSFER OF VIABLE MICROBES IN SPACE FROM PLANETS IN EXTRA-SOLAR SYSTEMS TO A PLANET IN OUR SOLAR SYSTEM AND VICE VERSA

We investigate whether it is possible that viable microbes could have been transported to the Earth from planets in extra-solar systems by means of natural vehicles such as ejecta expelled by comets or asteroid impacts on such planets. The probabilities of close encounters with other solar systems are taken into account as well as the limitations of bacterial survival times inside ejecta in space, caused by radiation and DNA decay. The conclusion is that no potentially DNA/RNA life-carrying ejecta from another solar system in the general Galactic star field landed on the Earth before life already existed on the Earth, even if the microbial survival time in space is as long as tens of millions of years. However, if the Sun formed initially as a part of a star cluster, as is commonly assumed, we cannot rule out the possibility of transfer of life from one of the sister systems to us. Likewise, there is a possibility that some extra-solar planets carry life that originated in our solar system. It will be of great interest to identify the members of the Suns birth cluster of stars and study them for evidence of planets and life on the planets. The former step may be accomplished by the GAIA mission, the latter step by the SIM and DARWIN missions. Therefore it may not be too long until we have experimental knowledge to answer the question of whether the natural transfer of life from one solar system to another has actually taken place.

The Sloan great wall. Rich clusters

Aims. We present the results of the study of the substructure and ga laxy content of ten rich clusters of galaxies in three different superclusters of the Sloan Great Wall, the richest nearby sy stem of galaxies (hereafter SGW). Methods. We determine the substructure in clusters using the ’Mclust ’ package from the ’R’ statistical environment and analyse their galaxy content with information about colours and morphological types of galaxies. We analyse the distribution of the peculiar velocities of galaxies in clusters and calculate the peculi ar velocity of the first ranked galaxy. Results. We show that five clusters in our sample have more than one comp onent; in some clusters the different components also have different galaxy content. In other clusters there are distinct c omponents in the distribution of the peculiar velocities of galaxies. We find that in some clusters with substructure the peculiar v elocities of the first ranked galaxies are high. All clusters in our sample host luminous red galaxies; in eight clusters their number e xceeds ten. Luminous red galaxies can be found both in the central areas of clusters and in the outskirts, some of them have high peculiar velocities. About 1/3 of the red galaxies in clusters are spirals. The scatter of colours of red ellipticals is in most clusters lar ger than that of red spirals. The fraction of red galaxies in r ich clusters in the cores of the richest superclusters is larger than the fracti on of red galaxies in other very rich clusters in the SGW. Conclusions. The presence of substructure in rich clusters, signs of poss ible mergers and infall, and the high peculiar velocities of the first ranked galaxies suggest that the clusters in our sam ple are not yet virialized. We present merger trees of dark ma tter haloes in an N-body simulation to demonstrate the formation of present-day dark matter haloes via multiple mergers during their e volution. In simulated dark matter haloes we find a substructure similar t o that in observed clusters.

Toward Understanding Rich Superclusters

We present a morphological study of the two richest superclusters from the 2dF Galaxy Redshift Survey (SCL126, the Sloan Great Wall, and SCL9, the Sculptor supercluster). We use Minkowski functionals, shapefinders, and galaxy group information to study the substructure of these superclusters as formed by different populations of galaxies. We compare the properties of grouped and isolated galaxies in the core region and in the outskirts of superclusters. The fourth Minkowski functional V3 and the morphological signature K1- K2 show a crossover from low-density morphology (outskirts of supercluster) to high-density morphology (core of supercluster) at mass fraction mf � 0.7. The galaxy content and the morphology of the galaxy populations in supercluster cores and outskirts is different. The core regions contain a larger fraction of early type, red galaxies, and richer groups than the outskirts of superclusters. In the core and outskirt regions the fine structure of the two prominent superclusters as delineated by galaxies from different populations also differs. The values of the fourth Minkowski functional V3 show that in the supercluster SCL126 the population of early type, red galaxies is more clumpy than the population of late type, blue galaxies, especially in the outskirts of the supercluster. In the contrary, in the supercluster SCL9, the clumpiness of the spatial distribution of galaxies of different type and color is quite similar in the outskirts of the supercluster, while in the core region the clumpiness of the late type, blue galaxy population is larger than the clumpiness of the early type, red galaxy population. Our results suggest that both local (group/cluster) and global (supercluster) environments are important in forming galaxy morphologies and colors (and determining the star formation activity). The differences between the superclusters indicate that these superclusters have different evolutional histories. Subject headings: cosmology: large-scale structure of the Universe – clusters of galaxies; cosmology: large-scale structure of the Universe – Galaxies; clusters: general

Formation, evolution and properties of isolated field elliptical galaxies

We study the properties, evolution and formation mechanisms of isolated field elliptical (IfE) galaxies. We create a ‘mock’ catalogue of IfE galaxies from the Millennium Simulation Galaxy Catalogue, and trace their merging histories. The formation, identity and assembly redshifts of simulated isolated and non-isolated elliptical galaxies are studied and compared. Observational and numerical data are used to compare age, mass and the colour–magnitude relation. Our results, based on simulation data, show that almost 7 per cent of all elliptical galaxies brighter than −19 mag in B band can be classified as IfE galaxies. Results also show that isolated elliptical galaxies have a rather flat luminosity function; a number density of ∼3 × 10−6 h3 Mpc−3 mag−1, throughout their B-band magnitudes. IfE galaxies show bluer colours than non-isolated elliptical galaxies and they appear younger, in a statistical sense, according to their mass-weighted age. IfE galaxies also form and assemble at lower redshifts compared to non-isolated elliptical galaxies. About 46 per cent of IfE galaxies have undergone at least one major merging event in their formation history, while the same fraction is only ∼33 per cent for non-isolated ellipticals. Almost all (∼98 per cent) isolated elliptical galaxies show merging activity during their evolution, pointing towards the importance of mergers in the formation of IfE galaxies. The mean time of the last major merging is at z∼ 0.6 or 6 Gyr ago for isolated ellipticals, while non-isolated ellipticals experience their last major merging significantly earlier at z∼ 1.1 or 8 Gyr ago. After inspecting merger trees of simulated IfE galaxies, we conclude that three different, yet typical, formation mechanisms can be identified: solitude, coupling and cannibalism. Our results also predict a previously unobserved population of blue, dim and light galaxies that fulfil observational criteria to be classified as IfE galaxies. This separate population comprises ∼26 per cent of all IfEs.

Large-scale environments of z < 0.4 active galaxies

Context. Properties of galaxies depend on their large-scale environment. As the influence of active galactic nuclei (AGN) in galaxy evolution is becoming more evident, their large-scale environments may help us understand the evolutionary processes leading to activity. The effect of activity can be seen particularly by showing whether different types of active galaxies are formed by similar mechanisms. Aims. Our aim is to study the supercluster-scale environments of active galaxies up to redshift 0.4. Our data include quasars, BL Lac objects, Seyfert, and radio galaxies. Methods. We used a three-dimensional, low-resolution luminosity-density field constructed of a sample of luminous red galaxies in the seventh data release of the Sloan Digital Sky Survey. We calculated the average density of this field in a volume of a 3h −1 Mpc sphere around each AGN for estimating the environmental density levels of different types of AGN. This analysis gives us the distribution of AGN in the global environment of superclusters, filaments, and voids. Results. Our results show that, while radio-quiet quasars and Seyfert galaxies are mostly located in low-density regions, radio galaxies have higher environmental densities. BL Lac objects usually have low-density environments, but some of them are also in very high-density regions. Conclusions. Our results give support to the theory of galaxy evolution where galaxies are affected by two modes of AGN feedback: quasar mode that turns a blue star-forming galaxy into a red and dead one, and radio mode that regulates the growth of massive elliptical galaxies. We conclude that quasars are in lower density environments than radio galaxies, most likely because the galaxies in rich environments have evolved to a state suitable for radio-loud activity earlier. Galaxies in poor environment have evolved more slowly, and are still going through the earlier quasar-mode feedback in galaxy evolution.