A Differential X-Ray Gunn-Peterson Test Using a Giant Cluster Filament

Using CCD detectors onboard the forthcoming X-ray observatories Chandra and XMM, it is possible to devise a measurement of the absolute density of heavy elements in the hypothetical warm gas filling intercluster space. This gas may be the largest reservoir of baryonic matter in the Universe, but even its existence has not been proven observationally at low redshifts. The proposed measurement would make use of a unique filament of galaxy clusters spanning over 700 Mpc (0.1<z<0.2) along the line of sight in a small area of the sky in Aquarius. The surface density of Abell clusters there is more than 6 times the sky average. It is likely that the intercluster matter column density is enhanced by a similar factor, making its detection feasible under certain optimistic assumptions about its density and elemental abundances. One can compare photoabsorption depth, mostly in the partially ionized oxygen edges, in the spectra of clusters at different distances along the filament, looking for a systematic increase of depth with the distance. The absorption can be measured by the same detector and through the same Galactic column, hence the differential test. A CCD moderate energy resolution (about 100 eV) is adequate for detecting an absorption edge at a known redshift.Comment: Latex, 4 pages, 3 figures, uses emulateapj.sty. ApJ Letters in pres

Majorana fermions emerging from magnetic nanoparticles on a superconductor without spin-orbit coupling

There exists a variety of proposals to transform a conventional s-wave superconductor into a topological superconductor, supporting Majorana fermion mid-gap states. A necessary ingredient of these proposals is strong spin-orbit coupling. Here we propose an alternative system consisting of a one-dimensional chain of magnetic nanoparticles on a superconducting substrate. No spin-orbit coupling in the superconductor is needed. We calculate the topological quantum number of a chain of finite length, including the competing effects of disorder in the orientation of the magnetic moments and in the hopping energies, to identify the transition into the topologically nontrivial state (with Majorana fermions at the end points of the chain).Comment: 7 pages, 5 figure

X-ray Properties of the Abell 644 Cluster of Galaxies

We use new ASCA observations and archival ROSAT Position Sensitive Proportional Counter (PSPC) data to determine the X-ray spectral properties of the intracluster gas in Abell 644. From the overall spectrum, we determine the average gas temperature to be 8.64 (+0.67,-0.56) keV, and an abundance of 0.32 (+/-0.04) $Z_{\odot}$. The global ASCA and ROSAT spectra imply a cooling rate of 214 (+100,-91) $M_{\odot}$ yr$^{-1}$. The PSPC X-ray surface brightness profile and the ASCA data suggest a somewhat higher cooling rate. We determine the gravitational mass and gas mass as a function of radius. The total gravitating mass within 1.2 Mpc is $6.2\times10^{14}$ $M_{\odot}$, of which 20% is in the form of hot gas. There is a region of elevated temperature 1.5-5 arcmin to the west of the cluster center. The south-southwest region of the cluster also shows excess emission in the ROSAT PSPC X-ray image, aligned with the major axis of the optical cD galaxy in the center of the cluster. We argue that the cluster is undergoing or has recently undergone a minor merger. The combination of a fairly strong cooling flow and evidence for a merger make this cluster an interesting case to test the disruption of cooling flow in mergers.Comment: 26 pages LaTeX including 9 eps figures + 4 pages LaTeX tables (landscape); accepted to ApJ, uses aaspp

An infrared survey of brightest cluster galaxies: Paper I

We report on an imaging survey with the Spitzer Space Telescope of 62 brightest cluster galaxies with optical line emission. These galaxies are located in the cores of X-ray luminous clusters selected from the ROSAT All-Sky Survey. We find that about half of these sources have a sign of excess infrared emission; 22 objects out of 62 are detected at 70 microns, 18 have 8 to 5.8 micron flux ratios above 1.0 and 28 have 24 to 8 micron flux ratios above 1.0. Altogether 35 of 62 objects in our survey exhibit at least one of these signs of infrared excess. Four galaxies with infrared excesses have a 4.5/3.6 micron flux ratio indicating the presence of hot dust, and/or an unresolved nucleus at 8 microns. Three of these have high measured [OIII](5007A)/Hbeta flux ratios suggesting that these four, Abell 1068, Abell 2146, and Zwicky 2089, and R0821+07, host dusty active galactic nuclei (AGNs). 9 objects (including the four hosting dusty AGNs) have infrared luminosities greater than 10^11 L_sol and so can be classified as luminous infrared galaxies (LIRGs). Excluding the four systems hosting dusty AGNs, the excess mid-infrared emission in the remaining brightest cluster galaxies is likely related to star formation.Comment: accepted for publication in ApJ

Proceedings of a Symposium on Sustaining Rangeland Ecosystems : Eastern Oregon State College, La Grande, Oregon, 29-31 August 1994

Published February 1996. Facts and recommendations in this publication may no longer be valid. Please look for up-to-date information in the OSU Extension Catalog: http://extension.oregonstate.edu/catalo

Bandpass Dependence of X-ray Temperatures in Galaxy Clusters

We explore the band dependence of the inferred X-ray temperature of the intracluster medium (ICM) for 192 well-observed galaxy clusters selected from the Chandra Data Archive. If the hot ICM is nearly isothermal in the projected region of interest, the X-ray temperature inferred from a broad-band (0.7-7.0 keV) spectrum should be identical to the X-ray temperature inferred from a hard-band (2.0-7.0 keV) spectrum. However, if unresolved cool lumps of gas are contributing soft X-ray emission, the temperature of a best-fit single-component thermal model will be cooler for the broad-band spectrum than for the hard-band spectrum. Using this difference as a diagnostic, the ratio of best-fitting hard-band and broad-band temperatures may indicate the presence of cooler gas even when the X-ray spectrum itself may not have sufficient signal-to-noise to resolve multiple temperature components. To test this possible diagnostic, we extract X-ray spectra from core-excised annular regions for each cluster in our archival sample. We compare the X-ray temperatures inferred from single-temperature fits when the energy range of the fit is 0.7-7.0 keV (broad) and when the energy range is 2.0/(1+z)-7.0 keV (hard). We find that the hard-band temperature is significantly higher, on average, than the broad-band temperature. Upon further exploration, we find this temperature ratio is enhanced preferentially for clusters which are known merging systems. In addition, cool-core clusters tend to have best-fit hard-band temperatures that are in closer agreement with their best-fit broad-band temperatures. We show, using simulated spectra, that this diagnostic is sensitive to secondary cool components (TX = 0.5-3.0 keV) with emission measures >10-30% of the primary hot component.Comment: Accepted for publication in Ap

The binary period and outburst behaviour of the SMC X-ray binary pulsar system SXP504

A probable binary period has been detected in the optical counterpart to the X-ray source CXOU J005455.6-724510 = RX J0054.9-7245 = AXJ0054.8-7244 = SXP504 in the Small Magellanic Cloud. This source was detected by Chandra on 04 Jul 2002 and subsequently observed by XMM-Newton on 18 Dec 2003. The source is coincident with an Optical Gravitational Lensing (OGLE) object in the lightcurves of which several optical outburst peaks are visible at ~ 268 day intervals. Timing analysis shows a period of 268.6 +/- 0.1 days at > 99% significance. Archival Rossi X-ray Timing Explorer (RXTE) data for the 504s pulse-period has revealed detections which correspond closely with predicted or actual peaks in the optical data. The relationship between this orbital period and the pulse period of 504s is within the normal variance found in the Corbet diagram.Comment: Accepted by MNRAS. 1 LATEX page. 4 figure

Cluster Evolution in the ROSAT North Ecliptic Pole Survey

The deepest region of the ROSAT All-Sky Survey, at the North Ecliptic Pole, has been studied to produce a complete and unbiased X-ray selected sample of clusters of galaxies. This sample is used to investigate the nature of cluster evolution and explore potential implications for large-scale structure models. The survey is 99.6% optically identified. Spectroscopic redshifts have been measured for all the extragalactic identifications. In this Letter, first results on cluster evolution are presented based on a comparison between the number of the observed clusters in the North Ecliptic Pole survey and the number of expected clusters assuming no-evolution models. At z>0.3 there is a deficit of clusters with respect to the local universe which is significant at > 4.7sigma. The evolution appears to commence at L_{0.5-2.0} > 1.8x10^{44} erg s^{-1} in our data. The negative evolution goes in the same direction as the original EMSS result, the results from the 160 deg^{2} survey by Vikhlinin et al. (1998) and the recent results from the RDCS (Rosati et al. 2000). At lower redshifts there is no evidence for evolution, a result in agreement with these and other cluster surveys.Comment: 17 pages, 3 figures. Accepted for publication in ApJ Letter

Cosmic Ray Protons and Magnetic Fields in Clusters of Galaxies and their Cosmological Consequences

The masses of clusters of galaxies estimated by gravitational lensing exceed in many cases the mass estimates based on hydrostatic equilibrium. This may suggest the existence of nonthermal pressure. We ask if radio galaxies can heat and support the cluster gas with injected cosmic ray protons and magnetic field densities, which are permitted by Faraday rotation and gamma ray observations of clusters of galaxies. We conclude that they are powerful enough to do this within a cluster radius of roughly 1 Mpc. If present, nonthermal pressures could lead to a revised estimate of the ratio of baryonic mass to total mass, and the apparent baryonic overdensity in clusters would disappear. In consequence, $\Omega_{\rm cold}$, the clumping part of the cosmological density $\Omega_{o}$, would be larger than $0.4\,h_{50}^{-1/2}$.Comment: Accepted by ApJ, 16 pages, LaTeX, 2 figures, epsfig.sty, aaspp4.st

Constraints on UV Absorption in the Intracluster Medium of Abell 1030

We present results from an extensive HST spectroscopic search for UV absorption lines in the spectrum of the quasar B2~1028+313, which is associated with the central dominant galaxy in the cluster Abell~1030 ($z=0.178$). This is one of the brightest known UV continuum sources located in a cluster, and therefore provides an ideal opportunity to obtain stringent constraints on the column densities of any cool absorbing gas that may be associated with the intracluster medium (ICM). Our HST spectra were obtained with the FOS and GHRS, and provide continuous coverage at rest-frame wavelengths from $\sim 975$ to 4060~\AA, thereby allowing the investigation of many different elements and ionization levels. We utilize a new technique that involves simultaneous fitting of large numbers of different transitions for each species, thereby yielding more robust constraints on column densities than can be obtained from a single transition. This method yields upper limits of $\lesssim 10^{11} - 10^{13}$ cm$^{-2}$ on the column densities of a wide range of molecular, atomic and ionized species that may be associated with the ICM. We also discuss a possible \Lya and C IV absorption system associated with the quasar. We discuss the implications of the upper limits on cool intracluster gas in the context of the physical properties of the ICM and its relationship to the quasar.Comment: Astrophysical Journal, in press, 19 pages, includes 5 PostScript figures. Latex format, uses aas2pp4.sty and epsfig.sty file