Status report to DOE Nuclear Data Committee

This status report from Lawrence Livermore Laboratory covers work in the areas of nuclear data applications - measurements, nuclear data application - calculations, nuclear data for reactor safety, fission physics, and data evaluation and compilation. Separate abstracts were prepared for seven of the contributions to this report. 7 figures, 3 tables. (RWR

Photometric validation of a model independent procedure to extract galaxy clusters

By means of CCD photometry in three bands (Gunn g, r, i) we investigate the existence of 12 candidate clusters extracted via a model independent peak finding algorithm (\cite{memsait}) from DPOSS data. The derived color-magnitude diagrams allow us to confirm the physical nature of 9 of the cluster candidates, and to estimate their photometric redshifts. Of the other candidates, one is a fortuitous detection of a true cluster at z~0.4, one is a false detection and the last is undecidable on the basis of the available data. The accuracy of the photometric redshifts is tested on an additional sample of 8 clusters with known spectroscopic redshifts. Photometric redshifts turn out to be accurate within z~0.01 (interquartile range).Comment: A&A in pres

Radio-optically selected clusters of galaxies. II. The cluster sample

We present a sample of 171 candidate groups and clusters of galaxies at intermediate redshift over an area of ~550 square degrees at the South Galactic Pole selected by using optically identified radio sources from the NRAO VLA Sky Survey as tracers of dense environment. Out of these 171 candidates, 76 have a counterpart in the literature while 95 of them are previously unknown clusters. This paper presents the cluster selection technique, based on the search of excesses in the optical surface density of galaxies near identified radiogalaxies, and the first spectroscopic results aimed to confirm the presence of a cluster. Spectroscopy for 11 candidates led to the detection of 9 clusters at redshift in the range 0.13 - 0.3, with estimated velocity dispersions ranging from values typical of clusters to those of galaxy groups. These results show that this technique represents a powerful tool for the selection of homogeneous samples of intermediate redshift clusters over a wide range of richness.Comment: 13 pages, 3 Postscript and 2 GIF figures. Accepted for publication in A&

Radio spectral study of the cluster of galaxies Abell 2255

Spectral index studies of halos, relics, and radio galaxies provide useful information on their origin and connection with merger processes. We present WSRT multi-wavelength observations of the galaxy cluster Abell 2255 at 25 cm, 85 cm, and 2 m. The spectral index images allowed us to study the integrated spectrum of halo and relic and to investigate the physical properties of the Beaver head-tail radio galaxy belonging to the cluster. In the radio halo, the spectral index is steeper at the center and flatter at the locations of the radio filaments, clearly detected at 25 cm. In the relics, the spectral index flattens, moving away from the cluster center. For the Beaver radio galaxy, the spectrum severely steepens from the head towards the end of the tail, because of the energy losses suffered by the relativistic particles. In the 2 m map, which is the first high-sensitivity image presented in the literature at such a long wavelength, a new Mpc-size emission region is detected between the known radio halo and the NW relic. Not detecting this feature in the more sensitive 85 cm observations implies that it must have a very steep spectrum (alpha <= -2.6). The observational properties of the radio halo suggest that either we are looking at a superposition of different structures (filaments in the foreground plus real halo in the background) seen in projection across the cluster center or that the halo is intrinsically peculiar. The newly detected extended region to the NW of the halo could be considered as an asymmetric extension of the halo itself. However, since radio halos are known in the literature as structures showing a regular morphology, the new feature could represent the first example of steep Mpc-size diffuse structures (MDS), detected around clusters at very low frequencies.Comment: 23 pages, 18 figures. A&A, in pres

The Northern ROSAT All-Sky (NORAS) Galaxy Cluster Survey I: X-ray Properties of Clusters Detected as Extended X-ray Sources

In the construction of an X-ray selected sample of galaxy clusters for cosmological studies, we have assembled a sample of 495 X-ray sources found to show extended X-ray emission in the first processing of the ROSAT All-Sky Survey. The sample covers the celestial region with declination $\delta \ge 0\deg$ and galactic latitude $|b_{II}| \ge 20\deg$ and comprises sources with a count rate $\ge 0.06$ counts s$^{-1}$ and a source extent likelihood of 7. In an optical follow-up identification program we find 378 (76%) of these sources to be clusters of galaxies. ...Comment: 61 pages; ApJS in press; fixed bug in table file; also available at (better image quality) http://www.xray.mpe.mpg.de/theorie/NORAS

Mark correlations: relating physical properties to spatial distributions

Mark correlations provide a systematic approach to look at objects both distributed in space and bearing intrinsic information, for instance on physical properties. The interplay of the objects' properties (marks) with the spatial clustering is of vivid interest for many applications; are, e.g., galaxies with high luminosities more strongly clustered than dim ones? Do neighbored pores in a sandstone have similar sizes? How does the shape of impact craters on a planet depend on the geological surface properties? In this article, we give an introduction into the appropriate mathematical framework to deal with such questions, i.e. the theory of marked point processes. After having clarified the notion of segregation effects, we define universal test quantities applicable to realizations of a marked point processes. We show their power using concrete data sets in analyzing the luminosity-dependence of the galaxy clustering, the alignment of dark matter halos in gravitational $N$-body simulations, the morphology- and diameter-dependence of the Martian crater distribution and the size correlations of pores in sandstone. In order to understand our data in more detail, we discuss the Boolean depletion model, the random field model and the Cox random field model. The first model describes depletion effects in the distribution of Martian craters and pores in sandstone, whereas the last one accounts at least qualitatively for the observed luminosity-dependence of the galaxy clustering.Comment: 35 pages, 12 figures. to be published in Lecture Notes of Physics, second Wuppertal conference "Spatial statistics and statistical physics

Further evidence for large central mass-to-light ratios in early-type galaxies: the case of ellipticals and lenticulars in the Abell~262 cluster

We present radially resolved spectroscopy of 8 early-type galaxies in Abell~262, measuring rotation, velocity dispersion, $H_3$ and $H_4$ coefficients along three axes, and line-strength index profiles of Mg, Fe and H$\beta$. Ionized-gas velocity and velocity dispersion is included for 6 galaxies. We derive dynamical mass-to-light ratios and dark matter densities from orbit-based dynamical models, complemented by the galaxies' ages, metallicities, and $\alpha$-elements abundances. Four galaxies have significant dark matter with halos about 10 times denser than in spirals of the same stellar mass. Using dark matter densities and cosmological simulations, assembly redshifts \zdm\approx 1-3, which we found earlier for Coma. The dynamical mass following the light is larger than expected for a Kroupa stellar IMF, especially in galaxies with high velocity dispersion \sigeff inside the effective radius \reff. This could indicate a `massive' IMF in massive galaxies. Alternatively, some dark matter in massive galaxies could follow the light closely. Combining with our comparison sample of Coma early-types, we now have 5 of 24 galaxies where (1) mass follows light to 1-3\,\reff, (2) the dynamical mass-to-light ratio {of all the mass that follows the light is large ($\approx\,8-10$ in the Kron-Cousins $R$ band), (3) the dark matter fraction is negligible to 1-3\,\reff. Unless the IMF in these galaxies is particularly `massive' and somehow coupled to the dark matter content, there seems a significant degeneracy between luminous and dark matter in some early-type galaxies. The role of violent relaxation is briefly discussed.Comment: 62 pages, 13 figures, 8 tables, accepted for publication in A

The short GRB070707 afterglow and its very faint host galaxy

We present the results from an ESO/VLT campaign aimed at studying the afterglow properties of the short/hard gamma ray burst GRB 070707. Observations were carried out at ten different epochs from ~0.5 to ~80 days after the event. The optical flux decayed steeply with a power-law decay index greater than 3, later levelling off at R~27.3 mag; this is likely the emission level of the host galaxy, the faintest yet detected for a short GRB. Spectroscopic observations did not reveal any line features/edges that could unambiguously pinpoint the GRB redshift, but set a limit z < 3.6. In the range of allowed redshifts, the host has a low luminosity, comparable to that of long-duration GRBs. The existence of such faint host galaxies suggests caution when associating short GRBs with bright, offset galaxies, where the true host might just be too dim for detection. The steepness of the decay of the optical afterglow of GRB 070707 challenges external shock models for the optical afterglow of short/hard GRBs. We argue that this behaviour might results from prolonged activity of the central engine or require alternative scenarios.Comment: 6 pages, 5 figures, accepted by A&

Environmental Dependence of the Structure of Brightest Cluster Galaxies

We measure the Petrosian structural properties of 33 brightest cluster galaxies (BCGs) at redshifts z<0.1 in X-ray selected clusters with a wide range of X-ray luminosities. We find that some BCGs show distinct signatures in their Petrosian profiles, likely to be due to cD haloes. We also find that BCGs in high X-ray luminosity clusters have shallower surface brightness profiles than those in low X-ray luminosity clusters. This suggests that the BCGs in high X-ray luminosity clusters have undergone up to twice as many equal-mass mergers in their past as those in low X-ray luminosity clusters. This is qualitatively consistent with the predictions of hierarchical structure formation.Comment: 11 pages, accepted for publication in MNRA