arXiv subjects

H. Andernach

Publications and source records attributed to H. Andernach.

At least 73 records · Page 4Linked to original sources

arXiv2007

Current status of the CATS database

We describe the current status of CATS, a publicly accessible database (web-server http://cats.sao.ru) allowing one to search in hundreds of catalogs of astronomical objects discovered all along the electromagnetic spectrum. Our emphasis is mainly laid on catalogs of radio continuum sources observed from 30 to 15000 MHz, secondly on catalogs of objects such as radio and active stars, planetary nebulae, HII regions, supernova remnants (SNR), pulsars, nearby galaxies, AGN and quasars. CATS also includes the catalogs from the largest extragalactic surveys, like NVSS, FIRST, WENSS, VLSS, TXS, GB6, SUMSS, IRAS, 2MASS, SDSS, ROSAT, PGC, MCG, etc. In 2004 CATS comprised a total of $\sim10^9$ records from over 400 catalogs in the radio, IR, optical and X-ray windows, including most of RATAN--600 catalogs. CATS is being expanded and updated, both with newly published catalogs as well as older ones which we have created in electronic form for the first time. We describe the principles of organization of the database of astrophysical catalogs and the main functions of CATS.

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arXiv2006

The Association of Compact Groups of Galaxies with Large-scale Structures

We use various samples of compact groups (CGs) to examine the types of association CGs have with rich and poor clusters of galaxies at low (z~0.04) and intermediate (z~0.1) redshifts. We find that ~10-20 % of CGs are associated with rich clusters and a much larger fraction with poorer clusters or loose groups. Considering the incompleteness of catalogs of poorer systems at intermediate redshift, our result is consistent with all CGs at intermediate redshift being associated with larger-scale systems. The richness of the clusters associated with CGs significantly increases from z~0.04 to z~0.1, while their Bautz-Morgan type changes from early to late type for the same range in z. Neither trend is compatible with a selection effect in the cluster catalogs used. We find earlier morphological types of galaxies to be more frequent in CGs associated with larger-scale structures, compared to those in CGs not associated to such structures. We consider this as new evidence that CGs are part of the large-scale structure formation process and that they may play an important role in the evolution of galaxies in these structures.

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arXiv2006

Dynamics and Shape of Brightest Cluster Galaxies

We identified Brightest Cluster Members (BCM) on DSS images of 1083 Abell clusters, derived their individual and host cluster redshifts from literature and determined the BCM ellipticity. Half the BCMs move at a speed higher than 37 % of the cluster velocity dispersion sigma_{cl}, suggesting that most BCMs are part of substructures falling into the main cluster. Both, the BCM's velocity offset in units of sigma_{cl}, and BCM ellipticity, weakly decrease with cluster richness.

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arXiv2006

Diffuse radio sources in the cluster of galaxies Abell 548b

We report extensive VLA and ATCA observations of the two diffuse radio sources in the cluster of galaxies Abell 548b, which confirm their classification as relics. The two relics (named A and B) show similar flux density, extent, shape, polarization and spectral index and are located at projected distances of about 430 and 500 kpc from the cluster center, on the same side of the cluster's X-ray peak. On the basis of spectral indices of discrete radio sources embedded within the diffuse features, we have attempted to distinguish emission peaks of the diffuse sources from unrelated sources. We have found that both relics, in particular the B-relic, show possible fine structure, when observed at high resolution. Another diffuse source (named C) is detected close in projection to the cluster center. High-resolution images show that it contains two discrete radio sources and a diffuse component, which might be a candidate for a small relic source. The nature and properties of the diffuse radio sources are discussed. We conclude that they are likely related to the merger activity in the cluster.

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arXiv2004

Morphological and Luminosity Content of Poor Galaxy Groups

We find that the fraction of early-type galaxies in poor groups (containing from 4 to 10 members) is a weakly increasing function of the number of the group members and is about two times higher than in a sample of isolated galaxies. We also find that the group velocity dispersion increases weakly with the fraction of early-type galaxies. Early-type galaxies in poor groups are brighter in the near-infrared with respect to isolated ones by 0.75 mags (in K) and to a lesser degree (by 0.5 mags) also in the blue. We also find early-type galaxies in groups to be redder than those in the field. These findings suggest that the formation history for early-type galaxies in overdense regions is different from that of in underdense regions, and that their formation in groups is triggered by merging processes.

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arXiv2004

XMM-Newton Observations of A133: A Weak Shock Passing through the Cool Core

We use XMM-Newton observations of the cluster of galaxies A133 to study the X-ray spectrum of the intracluster medium (ICM). We find a cold front to the southeast of the cluster core. From the pressure profile near the cold front, we derive an upper limit to the velocity of the core relative to the rest of the cluster of <230 km s^-1. Our previous Chandra image of A133 showed a complex, bird-like morphology in the cluster core. Based on the XMM-Newton spectra and hardness ratio maps, we argue that the wings of this structure are a weak shock front. The shock was probably formed outside the core of the cluster, and may be heating the cluster core. Our Chandra image also showed a ``tongue'' of relatively cool gas extending from the center of the cD to the center of the radio relic. The XMM-Newton results are consistent with the idea that the tongue is the gas which has been uplifted by a buoyant radio bubble including the radio relic to the northwest of the core. Alternatively, the tongue might result from a cluster merger. The small velocity of the core suggests that the bubble including the relic has moved by buoyancy, rather than by motions of the core or the ICM. We do not find clear evidence for nonthermal X-ray emission from the radio relic. Based on the upper limit on the inverse Compton emission, we derive a lower limit on the magnetic field in the relic of B>~1.5μG.

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arXiv2004

Redshifts and Distribution of ACO Clusters of Galaxies

The June 2004 version of our compilation of measured redshifts for clusters in the Abell-ACO catalogue lists redshifts for 3715 clusters/subclusters in 3033 distinct (2396 A- and 637 S-) clusters, 67% of these with N_z>=3 galaxies measured. We provide velocity dispersions (sigma_V) for 1875 (sub)clusters towards 1353 unique ACO clusters. The median sigma_V is 650 km/s for A-(sub)clusters and 575 km/s for S-(sub)clusters, and sigma_V clearly increases with both, N_z and richness, and also, somewhat surprising, with later Bautz-Morgan type of the clusters. We show examples of supercluster properties based on these data.

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arXiv2004

The Cluster M/L and the Value of Omega_m

From an up-to-date compilation of ACO cluster redshifts and velocity dispersions we extract a homogeneous sample of 459 clusters with robust velocity dispersion. Using the virial theorem to estimate cluster masses, and a correlation between Abell galaxy counts and R-band luminosity, we find a median M/L_R of 174 h_50 M_sun/L_sun. However, if we correct the virial masses according to the X-ray vs. virial mass correlation, as derived from our analysis, we obtain M/L_R ~100 h_50 M_sun/L_sun. These two values of M/L imply a mass content of the Universe of Omega_m ~0.26 and 0.15, respectively.

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arXiv2002

Chandra Observations of the Disruption of the Cool Core in Abell 133

We present the analysis of a Chandra observation of the galaxy cluster Abell 133, which has a cooling flow core, a central radio source, and a diffuse, filamentary radio source which has been classified as a radio relic. The X-ray image shows that the core has a complex structure. The most prominent feature is a "tongue" of emission which extends from the central cD galaxy to the northwest and partly overlaps the radio relic. One possibility is that this tongue is produced by Kelvin-Helmholtz (KH) instabilities through the interaction between the cold gas around the cD galaxy and hot intracluster medium. We estimate the critical velocity and time scale for the KH instability to be effective for the cold core around the cD galaxy. We find that the KH instability can disrupt the cold core if the relative velocity is >~400 km s^-1. We compare the results with those of clusters in which sharp, undisrupted cold fronts have been observed; in these clusters, the low temperature gas in their central regions has a more regular distribution. In contrast to Abell 133, these cluster cores have longer timescales for the disruption of the core by the KH instability when they are normalized to the timescale of the cD galaxy motion. Thus, the other cores are less vulnerable to KH instability. Another possible origin of the tongue is that it is gas which has been uplifted by a buoyant bubble of nonthermal plasma that we identify with the observed radio relic. From the position of the bubble and the radio estimate of the age of the relic source, we estimate avelocity of ~700 km s^-1 for the bubble. The structure of the bubble and this velocity are consistent with numerical models for such buoyant bubbles. (abridged)

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arXiv2001

Four Extreme Relic Radio Sources in Clusters of Galaxies

(Abridged) We describe the results of the highest-resolution radio observations yet made of four relic radio sources in the Abell clusters A13, A85, A133 and A4038. Our VLA images at 1.4 GHz with 4" resolution show a remarkable variety of fine structure in the form of spectacular arcs, wisps, plumes and loops. Their integrated radio flux densities fall very rapidly with frequency, with power-law slopes between 2.1 and 4.4 near 1.4 GHz The relics possess linear polarization levels ranging between 2.3 % (A133) and 35 % (A85); the higher polarization fractions imply a highly ordered magnetic field in the fine structure and low differential Faraday rotation in the intervening cluster gas. The optical identification of host galaxies remains problematic. In A85, A133 and A4038 the travel times for the brightest cluster galaxies are significantly longer than the modeled ages of the relics and nearby bright ellipticals provide a better match. Excess X-ray emission in the 0.5 keV-to-2 keV band was found near the relics in A85 and A133. The surface brightness was too high to be attributed to the inverse-Compton mechanism alone. We found excellent fits to the broad-band radio spectra using the anisotropic (KGKP) model of spectral ageing, and we have extended the model to include diffusion of particles between regions of different field strength (the Murgia-JP, or MJP, model). The steep radio spectra imply ages for the relics of ~ 10^8 yr, at the start of which period their radio luminosities would have been ~ 10^25 W/Hz at 1.4 GHz.

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arXiv2000

Optical and X-ray clusters as tracers of the supercluster-void network. I Superclusters of Abell and X-ray clusters

We study the distribution of X-ray selected clusters of galaxies with respect to superclusters determined by Abell clusters of galaxies and show that the distribution of X-ray clusters follows the supercluster-void network determined by Abell clusters. We find that in this network X-ray clusters are more strongly clustered than other clusters. Poor, non-Abell X-ray clusters follow the supercluster-void network as well: these clusters are embedded in superclusters determined by rich clusters and populate filaments between them. We present a new catalog of superclusters of Abell clusters out to a redshift of z_{lim}=0.13, a catalog of X-ray clusters located in superclusters determined by Abell clusters, and a list of additional superclusters of X-ray clusters.

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arXiv2000

Optical and X-ray clusters as tracers of the supercluster-void network. III Distribution of Abell and APM clusters

We present a comparison of Abell and APM clusters of galaxies as tracers of the large scale structure of the Universe. We investigate selection functions of both cluster catalogs. We show that the supercluster-void network can be traced with both cluster samples; the network has a well-defined period of ~120 h^{-1} Mpc. We calculate the correlation function and the power spectrum for Abell and APM cluster samples. The APM cluster sample with measured redshifts covers a small volume which contains only a few very rich superclusters that surround one void and have exceptionally large mutual separations. Due to this property the maximum of the power spectrum of APM clusters with measured velocities is shifted to larger scales than the corresponding feature in the power spectrum of Abell clusters. We conclude that the APM sample is not representative for the large-scale structure as a whole due to the small space coverage. We present a catalog of superclusters of galaxies, based on APM clusters up to a redshift z_{lim}=0.13.

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arXiv2000

Optical and X-ray clusters as tracers of the supercluster-void network. II The spatial correlation function

We study the space distribution of Abell and X-ray selected clusters of galaxies from the ROSAT Bright Source Catalog, and determine correlation functions for both cluster samples. On small scales the correlation functions depend on the cluster environment: clusters in rich superclusters have a larger correlation length and amplitude than all clusters. On large scales correlation functions depend on the distribution of superclusters. On these scales correlation functions for both X-ray and Abell clusters are oscillating with a period of ~115 h^{-1} Mpc. This property shows the presence of a dominating scale in the distribution of rich superclusters.

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arXiv2000

Radio identification of decametric sources. I. Catalogue

We describe a method of plotting continuous spectra for radio sources on the basis of entries of various source catalogues in comparatively large error boxes around a given sky position. Sources from the UTR-2 catalogue (Braude et al., 1978, 1979, 1981, 1985, 1994), observed at decametric wavelengths (10--25 MHz) with an antenna beam of about 40', were cross-identified with entries from other radio catalogues at higher frequencies. Using the CATS database we extracted all sources within 40' around UTR positions to find candidate identifications. The spectrum for each source was fitted with a set of curves using the least squares method to find the best fit. We preferentially selected radio counterparts whose radio spectrum extrapolated to low frequencies matched the UTR decametric flux densities, and whose coordinates were close to the gravity centre of UTR positions. Among all 1822 sources in the UTR catalogue we found about 350 sources to be blends of two or more sources. As the most probable true coordinates of the radio counterparts we used positions from the FIRST, NVSS, TXS, GB6, or PMN catalogues. Using low-frequency sources (26, 38, 85 MHz) from CATS we checked the reliability of some of our identifications. We show examples `of the above methods, including raw and ``cleaned'' spectra. Identifications with objects from optical, X-ray and infrared catalogues, as well as a subsample of UTR sources with ultra-steep spectrum are presented.

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arXiv2000

Radio-optical identification of very-steep spectrum radio sources from the UTR-2 catalogue

We used radio source catalogues accessible from the CATS database (http://cats.sao.ru) to establish radio continuum spectra for decametric radio sources in the UTR-2 catalogue (Braude et al., 1978--1994). From these, we select a sample of 23 sources with ultra steep radio spectra (α<=-1.2, S ~ ν^α) and present accurate positions and sizes from FIRST and NVSS. The search for optical counterparts from the APM (object) and DSS (image) databases, as well as infrared and X-ray identifications of these UTR sources are in progress.

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arXiv1999

The problem of identifying decametric sources

We describe a method to construct continuum spectra for radio sources on the basis of entries from various source catalogues in comparatively large error boxes around a given sky position. Sources from the UTR-2 catalogue (Braude et al. 1978--1994), observed at decametric wavelengths (10--25 MHz) with an antenna beam of about 40$'$, were cross-identified with entries from other radio catalogues at higher frequencies. Using the CATS database we extracted all sources within 40$'$ around UTR positions to find candidate identifications. A spectrum for each source was fitted with a set of curves using a least-squares method to find the best fit. We preferentially selected radio counterparts whose radio spectrum extrapolated to low frequencies matched the UTR decametric flux densities, and whose coordinates were close to the gravity center of UTR positions. Among all the 1822 sources in the UTR catalogue we found about 350 sources to be blends of two or more sources. As the most probable true coordinates of the radio counterparts we used positions from the NVSS, TXS, GB6, or PMN catalogues. Using low-frequency sources (26, 38, 85 MHz) from CATS we checked the reliability of some of our IDs. We show examples of the above methods, including raw and ``cleaned'' spectra.

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arXiv1999

Low frequency catalogues of the CATS database

The authors describe the largest existing publicly accessible radio source database CATS (``astrophysical CATalogues Supporting system''; http://cats.sao.ru). CATS contains more than 300 catalogues of objects detected in different (but mostly radio) wavelength ranges. These include catalogues from the largest existing surveys, like NVSS, FIRST, WENSS, TXS, GB6, IRAS, ROSAT, PGC, MCG, etc. Thus CATS allows to draw samples of objects to study a great variety of astrophysical problems. CATS also includes all of the largest low-frequency catalogues published so far : UTR(10--25 MHz), Culgoora (80, 160 MHz), Cambridge (38, 151, 178 MHz), Miyun (232 MHz), WENSS (325 MHz), Texas (365 MHz), Bologna and Molonglo (408 MHz) etc., and allows the user to operate with them.

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arXiv1999

The supercluster-void network V. Alternative evidence for its regularity

The distribution of Abell clusters of galaxies is analysed to study the regularity of the supercluster-void network. A new geometric method sensitive to the regularity of the location of clusters is applied. We find that the supercluster-void network resembles a cubical lattice over the whole space investigated. The distribution of rich superclusters is not isotropic: along the main axis of the network it is periodic with a step of length about 130 Mpc (for Hubble constant h=1), whereas along the diagonal of the network the period is larger. This large-scale inhomogeneity is compatible with recent CMB data.

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