4,319 research outputs found
The RASS-SDSS galaxy cluster survey
Solid observational evidences indicate a strong dependence of the galaxy
formation and evolution on the environment. In order to study in particular the
interaction between the intracluster medium and the evolution of cluster
galaxies, we have created a large database of clusters of galaxies based on the
largest available X-ray and optical surveys: the ROSAT All Sky Survey (RASS),
and the Sloan Digital Sky Survey (SDSS). We analyzed the correlation between
the total optical and the X-ray cluster luminosity. The resulting correlation
of L_X and L_{op} shows a logarithmic slope of 0.6, a value close to the
self-similar correlation. We analysed also the cluster mass to light ratio, by
finding a significant dependence of M/L on the cluster mass with a logarithmic
slope ranging from 0.27 in the i and r bands to 0.22 in the z band.Comment: proceedings of 'Multiwavelength mapping of galaxy evolution'
conference held in Venice (Italy), October 2003, A. Renzini and R. Bender
(Eds.), 2 pages, 1 figur
SDSS AGNs with X-ray Emission from ROSAT PSPC Pointed Observations
We present a sample of 1744 type 1 active galactic nuclei (AGNs) from the
Sloan Digital Sky Survey (SDSS DR4) spectroscopic catalog with X-ray
counterparts in the White-Giommi-Angelini Catalog (WGACAT) of ROSAT PSPC
pointed observations. Of 1744 X-ray sources, 1410 (80.9%) are new AGN
identifications. Of 4574 SDSS DR4 AGNs for which we found radio matches in the
catalog of radio sources from the FIRST catalog, 224 turned up in our sample of
SDSS X-ray AGNs. The sample objects are given in a catalog that contains
optical and X-ray parameters along with radio emission parameters where
available. We illustrate the content of our catalog and its potential for AGN
science by providing statistical relationships for the catalog data. The
potential of the morphological information is emphasized by confronting the
statistics of optically resolved and unresolved AGNs. The immediate properties
of the catalog objects include significant correlation of X-ray and optical
fluxes, which is consistent with expectations. Also expected is the decrease of
X-ray flux toward higher redshifts. The X-ray to optical flux ratio for the
unresolved AGNs exhibits a decline toward higher redshifts, in agreement with
previous results. The resolved AGNs, however, display the opposite trend. At a
given optical brightness, X-ray fluxes of radio-quiet AGNs by a factor of 2. We
caution, however, that because of the variety of selection effects present in
both the WGACAT and the SDSS, the interpretation of any relationships based on
our sample of X-ray AGNs requires a careful analysis of these effects.Comment: 34 pages, 18 figure
ROSAT All-Sky Survey observations of IRAS galaxies; I. Soft X-ray and far-infrared properties
The 120,000 X-ray sources detected in the RASS II processing of the ROSAT
All-Sky Survey are correlated with the 14,315 IRAS galaxies selected from the
IRAS Point Source Catalogue: 372 IRAS galaxies show X-ray emission within a
distance of 100 arcsec from the infrared position. By inspecting the structure
of the X-ray emission in overlays on optical images we quantify the likelihood
that the X-rays originate from the IRAS galaxy. For 197 objects the soft X-ray
emission is very likely associated with the IRAS galaxy. Their soft X-ray
properties are determined and compared with their far-infrared emission. X-ray
contour plots overlaid on Palomar Digitized Sky Survey images are given for
each of the 372 potential identifications. All images and tables displayed here
are also available in electronic form.Comment: accepted for publication in A&AS, complete version including all
figures and tables available at
http://www.rosat.mpe-garching.mpg.de/~bol/iras_rassI
Search for GRB afterglows in the ROSAT all-sky survey
We report on the status of our search for X-ray afterglows of gamma-ray
bursts (GRBs) using the ROSAT all-sky survey data. The number of potential
X-ray afterglow candidates with respect to the expected number of beamed GRBs
allows to constrain the relative beaming angles of GRB emission and afterglow
emission at about 1-5 hrs after the GRB.Comment: 3 pages A&A style, 1 color ps-figure; To appear in A&A Suppl. Series,
Proc. of Rome 1998 GRB workshop, also available from
http://www.aip.de/~jcg/publis.htm
FUSE Observations of Galactic and Intrinsic Absorption in the Spectrum of the Seyfert 1 Galaxy 2MASX J21362313-6224008
We present the far-ultraviolet spectrum of the Seyfert 1 galaxy 2MASX
J21362313-6224008 obtained with the Far Ultraviolet Spectroscopic Explorer
(FUSE). The spectrum features absorption from Galactic OVI at two velocities
and redshifted HI Lyman beta and gamma, CII, CIII, and O VI. The redshifted
absorption features represent a single kinematic component blueshifted by ~310
km/s relative to the AGN. We use photoionization models to derive constraints
on the physical parameters of the absorbing gas. An alternative interpretation
for the absorption lines is also proposed, whereby the absorbing gas is
associated with an intervening galaxy cluster.Comment: Astrophysical Journal, in pres
Pornography and erotica: Definitions and Prevalence
In this paper, we offer some observations regarding the sex industry, in particular the pornography and erotica sectors. Marketing literature observing pornography and erotica is scant. We find that following exponential growth of the sex industry (given use of the Internet) an evaluation of consumer behaviour and marketing practices is justified. In order to begin a study of these industry sectors, we find it necessary to define both pornography and erotica. Following the development of definitions, we consider these industries from a marketing perspective in the hope that we may encourage research into these areas
Wie Wissen entsteht und weitergegeben wird : Einblicke vom Mittelalter bis heute – Sammelband zum Abschluss des Forschungskollegs
Rezension zu: Johannes Fried und Michael Stolleis (Hrg.) : Wissenskulturen. Ăśber die Erzeugung und Weitergabe von Wissen. Frankfurt, New York 2009, ISBN 9783593390208, 218 Seiten, 19,90 Euro
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