arXiv subjects

H. Andernach

Publications and source records attributed to H. Andernach.

At least 91 records · Page 5Linked to original sources

arXiv1999

X-ray Spectra of the RIXOS source sample

We present results of an extensive study of the X-ray spectral properties of sources detected in the RIXOS survey, that is nearly complete down to a flux limit of 3e-14 cgs (0.5-2 keV). We show that for X-ray surveys containing sources with low count rate spectral slopes estimated using simple hardness ratios in the ROSAT band can be biased. Instead we analyse three-colour X-ray data using statistical techniques appropriate to the Poisson regime which removes the effects of this bias. We have then applied this technique to the RIXOS survey to study the spectral properties of the sample. For the AGN we find an average energy index of 1.05+-0.05 with no evidence for spectral evolution with redshift. Individual AGN are shown to have a range of properties including soft X-ray excesses and intrinsic absorption. Narrow Emission Line Galaxies also seem to fit to a power-law spectrum, which may indicate a non-thermal origin for their X-ray emission. We infer that most of the clusters in the sample have a bremsstrahlung temperature >3 keV, although some show evidence for a cooling flow. The stars deviate strongly from a power-law model but fit to a thermal model. Finally, we have analysed the whole RIXOS sample containing 1762 sources. We find that the mean spectral slope of the sources hardens at lower fluxes in agreement with results from other samples. However, a study of the individual sources demonstrates that the hardening of the mean is caused by the appearance of a population of very hard sources at the lowest fluxes. This has implications for the nature of the soft X-ray background.

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arXiv1998

Steps toward the power spectrum of matter. I.The mean spectrum of galaxies

We calculate the mean power spectrum of galaxies using published power spectra of galaxies and clusters of galaxies. On small scales we use the power spectrum derived from the 2-dimensional distribution of APM galaxies, on large scales we use power spectra derived from 3-dimensional data for galaxy and cluster samples. Spectra are reduced to real space and to the amplitude of the power spectrum of APM galaxies. Available data indicate the presence of two different populations in the nearby Universe. Clusters of galaxies sample a relatively large region in the Universe where rich, medium and poor superclusters are well represented. Their mean power spectrum has a spike on scale 120 h^{-1}Mpc, followed by an approximate power-law spectrum of index n = -1.9 towards small scales. The power spectrum found from LCRS and IRAS 1.2 Jy surveys is flatter around the maximum, which may represent regions of the Universe with medium-rich and poor superclusters.

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arXiv1998

VLA Observations of the giant Radio Galaxy 3C 449

In this paper we present multifrequency VLA observations of the giant radio galaxy 3C 449, obtained with high sensitivity and resolution in total intensity and polarized flux. These images show the source morphology in great detail, in particular we detect plumes and wiggles in the low brightness lobes. The source is considerably polarized at all frequencies. The spectral index map between 5 GHz and 8.4 GHz shows that the northern region beyond 1' from the core has a much flatter spectrum than the southern one. We analyse the jet dynamics, and conclude that the jets are relativistic at the beginning, and decelerate significantly within 10" (5 kpc) from the core. We compute the rotation measure, and detect significant values within +-50 rad/m^2 of the expected contribution of our Galaxy. The Faraday effect is likely to originate in an external screen, which is most probably the intergalactic medium of the group of galaxies around 3C pap449.

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arXiv1998

The Supercluster-Void Network. IV. The Shape and Orientation of Superclusters

We present a study of the shape, size, and spatial orientation of superclusters of galaxies. Approximating superclusters by triaxial ellipsoids we show that superclusters are flattened, triaxial objects. We find that there are no spherical superclusters. The sizes of superclusters grow with their richness: the median semi-major axis of rich and poor superclusters (having at least 8 and less than 8 member clusters) is 42 and 31 Mpc, respectively. Similarly, the median semi-minor axis is 12 and 5 Mpc for rich and poor superclusters. The spatial orientation of superclusters, as determined from the axes of ellipsoids, is nearly random. We do not detect any preferable orientation of superclusters, neither with respect to the line of sight, nor relative to some other outstanding feature in the large scale structure, nor with respect to the directions of principal axes of adjacent superclusters.

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arXiv1998

Extragalactic database. VII Reduction of astrophysical parameters

The Lyon-Meudon Extragalactic database (LEDA) gives a free access to the main astrophysical parameters for more than 100,000 galaxies. The most common names are compiled allowing users to recover quickly any galaxy. All these measured astrophysical parameters are first reduced to a common system according to well defined reduction formulae leading to mean homogeneized parameters. Further, these parameters are also transformed into corrected parameters from widely accepted models. For instance, raw 21-cm line widths are transformed into mean standard widths after correction for instrumental effect and then into maximum velocity rotation properly corrected for inclination and non-circular velocity. This paper presents the reduction formulae for each parameter: coordinates, morphological type and luminosity class, diameter and axis ratio, apparent magnitude (UBV, IR, HI) and colors, maximum velocity rotation and central velocity dispersion, radial velocity, mean surface brightness, distance modulus and absolute magnitude, and group membership. For each of these parameters intermediate quantities are given: galactic extinction, inclination, K-correction etc.. All these parameters are available from direct connexion to LEDA (telnet lmc.univ-lyon1.fr, login: leda, no passwd OR http://www-obs.univ-lyon1.fr/leda ) and distributed on a standard CD-ROM (PGC-ROM 1996) by the Observatoire de Lyon via the CNRS (mail to petit@obs.univ-lyon1.fr).

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arXiv1997

Current Status of the ACO Cluster Redshift Compilation

We present an update of our compilation of measured redshifts of galaxy clusters in the all-sky Abell catalog. In the last 7 years the number of ACO clusters with measured z has doubled to now ~2100, but still ~56% of these are based on only 1 or 2 measured member galaxies. Our October 1997 version gives 2247 redshifts (including components or line-of-sight superpositions) for 2114 distinct A- and S-clusters. Velocity dispersions are listed for 536 different ACO clusters (613 subclusters) and the median is 695 km/s. We mention some applications of our compilation for determining the large-scale structure of the nearby Universe.

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arXiv1997

Searching (the) FIRST radio arcs near ACO clusters

Gravitational lensing (GL) of distant radio sources by galaxy clusters should produce radio arc(let)s. We extracted radio sources from the FIRST survey near Abell cluster cores and found their radio position angles to be uniformly distributed with respect to the cluster centres. This result holds even when we restrict the sample to the richest or most centrally condensed clusters, and to sources with high S/N and large axial ratio. Our failure to detect GL with statistical methods may be due to poor cluster centre positions. We did not find convincing candidates for arcs either. Our result agrees with theoretical estimates predicting that surveys much deeper than FIRST are required to detect the effect. This is in apparent conflict with the detection of such an effect claimed by Bagchi & Kapahi (1995).

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arXiv1997

The supercluster--void network II. An oscillating cluster correlation function

We use rich clusters of galaxies in the Northern and Southern Galactic hemispheres up to a redshift z=0.12 to determine the cluster correlation function. We show that superclusters of galaxies and voids between them form a moderately regular network. As a result the correlation function determined for clusters located in rich superclusters oscillates: it has a series of regularly spaced secondary maxima and minima. The scale of the supercluster-void network, determined from the period of oscillations, is P=115 Mpc. The amplitude of oscillations is about 3 times larger than the estimated error. We compare the observed cluster correlation function with similar functions derived for popular models of structure formation. We find that the production of the observed cluster correlation function in any model with a smooth transition of the power spectrum from a Harrison-Zeldovich regime with positive spectral index on long wavelengths to a negative spectral index on short wavelengths is highly unlikely. The power spectrum must have an extra peak located at the wavelength equal to the period of oscillations of the correlation function.

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arXiv1997

Current Status of Radio Source Databases

We review the history and present status of radio-source catalogue archiving and on-line retrieval of radio source data. Large efforts were spent by the first author in collecting and restoring electronic versions of new and old source catalogues. Some 67 catalogues with ~520,000 entries were searchable via the "Einstein On-line Service" (EOLS). When EOLS lost maintenance support in 1994 a group at SAO (Russia) started building software tools to search and cross-identify objects between the major radio catalogues, maintained as the "CATalog supporting System" (CATS) at the Special Astrophysical Observatory (SAO, Russia). The independent efforts in east and west have recently been joined. Almost 400 different source lists with ~2,000,000 entries have been archived (and partly prepared) by us. All 5C and Penticton "P"-surveys and many of the published WSRT survey lists are now available. CATS has been developed by O. Verkhodanov, S. Trushkin, V. Chernenkov at SAO primarily to support RATAN-600 radio observations. CATS runs under LINUX and can process requests on the basis of various net protocols and via email. Almost 70 well-known radio source catalogues and tables with about 1.3 Mrecords are now available via ftp from CATS, as well as their documentation files. Twenty of the larger tables may be searched simultaneously for objects in rectangular boxes of coordinates. New routines for cross-matching are in progress. More and more catalogues are being folded into CATS. CATS is supported by RFBR grant 96-07-89075.

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arXiv1997

Radio Spectra and NVSS Maps of Decametric Sources

We constructed radio spectra for ~1400 UTR-2 sources and find that 46% of them have concave curvature. Inspection of NVSS maps of 700 UTR sources suggests that half of all UTR sources are either blends of two or more sources or have an ultra-steep spectrum (USS). The fraction of compact USS sources in UTR may be near 10%. Using NVSS and the Digitized Sky Survey(s) we expect to double the UTR optical identification rate from currently ~19%.

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arXiv1997

Radio-optical orientation of E/S0 galaxies: APM versus FIRST

We searched for extended radio sources in isolated E/S0 galaxies comparing the FIRST and APM catalogues for a single POSS plate. The 35 most promising candidates were visually inspected on the Digitized Sky Survey (DSS) and on FIRST images: we find several spirals and interacting galaxies and a few E/S0s with very weak, marginally extended radio cores. The only double-lobed (previously known) radio source is a dumbbell. For the rest of the objects, all hosting small and weak radio sources, the DSS is inadequate to determine morphological types. Thus a significant increase in sample size will be a major effort.

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arXiv1997

A 120-Mpc Periodicity in the Three-Dimensional Distribution of Galaxy Superclusters

Using a new compilation of available data on galaxy clusters and superclusters we present evidence for a quasiregular three-dimensional network of rich superclusters and voids, with the regions of high density separated by about 120 Mpc. We calculate the power spectrum for clusters of galaxies; it has a peak on the wavelength equal to the step of the network; the excess in the amplitude of the spectrum over that of the cold dark matter model is by a factor of 1.4. The probability that the spectrum can be formed within the framework of the standard cosmogony is very small. If the cluster distribution reflects the distribution of all matter (luminous and dark), then there must exists some hithero unknown process that produces regular structure on large scales.

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arXiv1996

Gamma-Ray Bursts from Radio-Quiet Quasars

We study positional coincidences between gamma-ray bursts in the BATSE 3B catalogue and quasars/AGN taken from the Veron-Cetty & Veron compilation. For most classes of AGN, for BL Lac objects and for radio-loud quasars, we find no excess coincidences above random expectation, and we give upper limits for their burst emission rate. However, surprising evidence is found for a positional correlation between gamma-ray bursts and radio-quiet quasars. A total of 134 selected bursts with a position error radius <1.8d and the nearest and intrinsically brightest radio-quiet quasars (M_v<-24.2 and z<1.0) have a probability of >99.7% to be associated with each other. An analysis of a smaller sample of well-localized interplanetary network gamma-ray burst positions supports this result. This correlation strongly favours the cosmological origin of gamma-ray bursts and enables to estimate its distance scale. The average luminosity of those gamma-ray bursts which we associate directly with radio-quiet quasars is of the order of 4*10^52 erg (assuming isotropic emission).

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arXiv1996

Preparing a public database of radio sources

We have collected the largest existing set of radio source lists in machine-readable form: 320 tables with 1.75 million records. Only a minor fraction of these is accessible via public databases. We describe our plans to make this huge amount of heterogeneous data accessible in a homogeneous way via the World Wide Web, with reliable cross-identifications, and searchable by various observables.

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arXiv1996

WWW Access to radio measurements of clusters of galaxies

Radio measurements of rich Abell clusters of galaxies have been collected both from radio source catalogues and dedicated publications. By gathering these data for every cluster, complemented by optical data, an overall picture of each cluster may be obtained and samples may be drawn suitable for statistical studies.

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arXiv1994

Extragalactic Databases: Present and Future

Current extragalactic databases are reviewed, including object-oriented databases, astronomical catalogues and compilations, as well as image archives and object catalogues from large-scale surveys. One challenge of the future will be to maintain the accessibility of all published information on individual objects; the other will be the cross-identification between various ongoing and planned large-scale surveys, some of them resulting in several hundred million objects each. Powerful user interfaces are being developed to tackle these tasks.

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arXiv1994

How Complete is the Electronic Catalogue Archive at CDS in the Extragalactic Domain?

From the literature of 1987 to 1993 a representative sample was prepared of 500 papers with tabular information for >~50 supposedly extragalactic objects each. Regardless of their scientific value, but corrected for redundancy, these papers contain 842,000 entries. For the 374 papers with >100 entries each, the CDS FTP-archive of catalogues contains tables for 21 % of them, increasing from 11 % for 1987 to 29 % for 1993. The coverage in terms of entries is much higher, and half of all papers with >1500 entries are in the archive. Valuable and/or large data sets are identified among the missing ones. Some of these can be found in other archives, and it is argued that tabular material published in future should be preserved more systematically in a collaborative effort between authors, journal editors and data centres.

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arXiv1994

Network Resources for Astronomers

The amount of data produced by large observational facilities and space missions has led to the archiving and on-line accessibility of much of this data, available to the entire astronomical community. This allows a much wider multi-frequency approach to astronomical research than previously possible. Here we provide an overview of these services, and give a basic description of their contents and possibilities for accessing them. Apart from services providing observational data, many of those providing general information, e.g. on addresses, bibliographies, software etc. are also described. The field is rapidly growing with improved network technology, and our attempt to keep the report as complete and up-to-date as possible will inevitably be outdated shortly. We will endeavor to maintain an updated version of this document on-line.

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