Engineering topics

Henry, J. Patrick

Publications and source records attributed to Henry, J. Patrick.

17 records

NASA NTRS2012

The Outer Limits of Galaxy Clusters: Observations to the Virial Radius with Suzaku, XMM,and Chandra

The outskirts of galaxy clusters, near the virial radius, remain relatively unexplored territory and yet are vital to our understanding of cluster growth, structure, and mass. In this presentation, we show the first results from a program to constrain the sate of the outer intra-cluster medium (ICM) in a large sample of galaxy clusters, exploiting the strengths of three complementary X-ray observatories: Suzaku (low, stable background), XMM-Newton (high sensitivity),and Chandra (good spatial resolution). By carefully combining observations from the cluster core to beyond r200, we are able to identify and reduce systematic uncertainties that would impede our spatial and spectral analysis using a single telescope. Our sample comprises nine clusters at z is approximately 0.1-0.2 fully covered in azimuth to beyond r200, and our analysis indicates that the ICM is not in hydrostatic equilibrium in the cluster outskirts, where we see clear azimuthal variations in temperature and surface brightness. In one of the clusters, we are able to measure the diffuse X-ray emission well beyond r200, and we find that the entropy profile and the gas fraction are consistent with expectations from theory and numerical simulations. These results stand in contrast to recent studies which point to gas clumping in the outskirts; the extent to which differences of cluster environment or instrumental effects factor in this difference remains unclear. From a broader perspective, this project will produce a sizeable fiducial data set for detailed comparison with high-resolution numerical simulations.

Miller, Eric D.↗

NASA NTRS2012

Search for X-Ray Emission Associated with the Shapley Supercluster with Suzaku

Suzaku performed observations of 3 regions in and around the Shapley supercluster: a region located between A3558 and A3556, at approx 0.9 times the virial radii of both clusters, and two other regions at 1 deg and 4 away from the first pointing. The 4 deg -otfset observation was used to evaluate the Galactic foreground emission. We did not detect significant redshifted Oxygen emission lines (O VII and O VIII) in the spectra of all three pointings, after subtracting the contribution of foreground and background emission. An upper limit for the redshifted O VIII Ka line intensity of the warm-hot intergalactic medium (WHIM) is 1.5 x 10(exp -7) photons / s / sq cm / sq arcmin, which corresponds to an overdensity of approx 380 (Z/0.1 Solar Z)(exp -1/2)(L/3 Mpc)(exp -1/2), assuming T = 3 x 10(exp 6) K. We found excess continuum emission in the 1 deg-offset and on-filament regions, represented by thermal models with kT approximates 1 keV and approximates 2 keV, respectively. The redshifts of both 0 and that of the supercluster (0.048) are consistent with the observed spectra. The approx 1 keV emission can be also fitted with Ne-rich Galactic (zero redshift) thin thermal emission. Radial intensity profile of 2 keV component suggests contribution from A3558 and A3556, but with significant steepening of the intensity slope in the outer region of A3558. Finally, we summarized the previous Suzaku search for the WHIM and discussed the feasibility of constraining the WHIM. An overdensity of <400 can be detectable using O VII and O VIII emission lines in a range of 1.4 x 10(exp 6) K < T < 5 x 10(exp 6) K or a continuum emission in a relatively high temperature range T > 5 x 10 (exp 6) K with the Suzaku XIS. The non detection with Suzaku suggests that typical line-of-sight average overdensity is < 400.

Mitsuishi, Ikuyuki↗

NASA NTRS1995

An X-ray temperature map of Abell 754: A major merger

We present the first two-dimensional X-ray temperature map of the rich cluster of galaxies Abell 754. We also present an X-ray surface brightness map with improved spatial resolution and sensitivity compared with previous maps. Both the temperature map and the surface brightness map show that A754 is in the throes of a violent merger; it is probably far from hydrostatic equilibrium.

Henry, J. Patrick↗

NASA NTRS1994

Groups of galaxies in the ROSAT north ecliptic pole survey

The X-ray properties of groups of galaxies are presented. Their distribution of luminosity and temperature appears to be associated with the extrapolation of these distributions from rich clusters of galaxies. The properties of the ensemble of groups of galaxies are almost totally unknown. Only a few X-ray observations of groups that were selected by optical methods were published so far. A sample of eight groups with 'z' inferior to 0.04, of which three have 'z' inferior to 0.03 was investigated. The temperature and the luminosity functions at one point were determined.

Henry, J. Patrick↗

NASA NTRS1993

X-ray emission from a complete sample of Abell clusters of galaxies

The ROSAT All-Sky Survey (RASS) is used to investigate the X-ray properties of a complete sample of Abell clusters with measured redshifts and accurate positions. The sample comprises the 145 clusters within a 561 square degree region at high galactic latitude. The mean redshift is 0.17. This sample is especially well suited to be studied within the RASS since the mean exposure time is higher than average and the mean galactic column density is very low. These together produce a flux limit of about 4.2 x 10(exp -13) erg/sq cm/s in the 0.5 to 2.5 keV energy band. Sixty-six (46%) individual clusters are detected at a significance level higher than 99.7% of which 7 could be chance coincidences of background or foreground sources. At redshifts greater than 0.3 six clusters out of seven (86%) are detected at the same significance level. The detected objects show a clear X-ray luminosity -- galaxy count relation with a dispersion consistent with other external estimates of the error in the counts. By analyzing the excess of positive fluctuations of the X-ray flux at the cluster positions, compared with the fluctuations of randomly drawn background fields, it is possible to extend these results below the nominal flux limit. We find 80% of richness R greater than or = 0 and 86% of R greater than or = 1 clusters are X-ray emitters with fluxes above 1 x 10(exp -13) erg/sq cm/s. Nearly 90% of the clusters meeting the requirements to be in Abell's statistical sample emit above the same level. We therefore conclude that almost all Abell clusters are real clusters and the Abell catalog is not strongly contaminated by projection effects. We use the Kaplan-Meier product limit estimator to calculate the cumulative X-ray luminosity function. We show that the shape of the luminosity functions are similiar for different richness classes, but the characteristic luminosities of richness 2 clusters are about twice those of richness 1 clusters which are in turn about twice those of richness 0 clusters. This result is another manifestation of the luminosity -- richness elation for Abell clusters.

Briel, Ulrich G.↗

NASA NTRS1993

X-ray emission from a complete sample of Abell clusters of galaxies

The Rosat all sky survey is used to investigate the X-ray properties of a sample of Abell clusters with measured redshifts and accurate positions. The sample comprises the 145 clusters within a 561 square degree region at high galactic latitude. The mean redshift is 0.17. The sample mean exposure time is higher than average and its mean galactic column density is very low. These together produce a flux limit of about 4.2 x 10(exp -13) erg/sq cm/s in the 0.5 to 2.5 keV energy band. By analyzing the excess of positive fluctuations of the X-ray flux at the cluster positions, compared with the fluctuations of randomly drawn background fields, it is possible to extend these results below the nominal flux limit. It is found that 80 of richness R equal to or greater than 0 and 86 of R equal to or greater than 1 clusters are X-ray emitters with fluxes above 1.10 to the power of minus 13 erg/sq cm/s. Nearly 90 of the clusters meeting the requirements to be in Abell's statistical sample emit above the same level. It is concluded that almost all Abell clusters are real clusters and the Abell catalogue is not strongly contaminated by projection effects. The Kaplan-Meier product limit estimator is used to calculate the cumulative X-ray luminosity function. It is shown that the shape of the luminosity functions are similar for different richness classes, but the characteristic luminosities of richness 2 clusters are about twice of those of richness 1 clusters which are in turn about twice of those of richness zero clusters. This result is another manifestation of the luminosity richness relation for Abell cluster.

Briel, Ulrich G.↗

NASA NTRS1993

X ray archeology in the Coma cluster

Images of X-ray emission from hot gas within the Coma cluster of galaxies are presented. These maps, made with the Rosat satellite, have high signal to noise ratio and allow cluster structure to be analyzed in unprecedented detail. They show greater structural irregularity than could be anticipated from earlier observations of Coma. Emission is detected from a number of bright cluster galaxies in addition to the two known previously. In four cases there is evidence that these galaxies lie at the center of an extended subconcentration within the cluster, possibly the remnant of their associated groups. For at least two galaxies the images show direct evidence for ongoing disruption of their gaseous atmosphere. The luminosity associated with these galaxies is comparable to that detected around similar ellipticals in much poorer environments. Emission is easily detected and appears to become more regular at large radii. The data show that this archetype of a rich and regular galaxy cluster was formed by the merging of several distinct subunits which are not yet fully destroyed.

White, Simon D. M.↗

NASA NTRS1993

The distribution of dark matter in the A2256 cluster

Using spatially resolved X-ray spectroscopy, it was determined that the X-ray emitting gas in the rich cluster A2256 is nearly isothermal to a radius of at least 0.76/h Mpc, or about three core radii. These data can be used to measure the distribution of the dark matter in the cluster. It was found that the total mass interior to 0.76/h Mpc and 1.5/h Mpc is (0.5 +/- 0.1 and 1.0 +/- 0.5) x 10(exp 15)/h of the solar mass respectively where the errors encompass the full range allowed by all models used. Thus, the mass appropriate to the region where spectral information was obtained is well determined, but the uncertainties become large upon extrapolating beyond that region. It is shown that the galaxy orbits are midly anisotropic which may cause the beta discrepancy in this cluster.

Henry, J. Patrick↗

NASA NTRS1992

Participation in the north ecliptic pole sky survey

This grant supported research into the nature of the faintest x-ray sources found in the ROSAT All Sky Survey, with particular emphasis on distant clusters of galaxies. The project was broadened to include sources found in the ROSAT deep pointing at the North Ecliptic Pole. Progress on the research is briefly summarized.

Henry, J. Patrick↗

NASA NTRS1991

A measurement of the mass fluctuation spectrum from the cluster X-ray temperature function

A statistically complete sample of galaxy clusters is presented which also has complete X-ray temperature information. Using this sample, the cluster bolometric luminosity and temperature functions are derived. The temperature function constrains the shape and amplitude of the mass fluctuation power spectrum. For a power law, i.e., with the fluctuation power spectrum proportional to k exp n, n = -(1.7 + 0.65, - 0.35), and an amplitude is obtained which implies that the rms value of delta-M/M is 0.59 + or - 0.02 on a scale of 8/h Mpc at the present epoch.

Henry, J. Patrick↗

NASA NTRS1991

The x ray morphology of the relaxed cluster of galaxies A2256. 1: Evidence for a merger event

The rich cluster of galaxies A2256 was studied utilizing the imaging proportional counter (PSPC (Position Sensitive Proportional Counters)) on board the x-ray observatory ROSAT. A2256 is considered to be a relaxed, Comalike cluster which is dynamically well evolved. However, clear evidence for substructure in A2256 was found. The x-ray surface brightness distribution reveals two separate maxima in the center, one of which is coincident with the central cD galaxy while the morphology of the other shows indications that it is merging with the main cluster body. The x-ray temperatures of the two maxima are different; the probable merging object being about a factor of five cooler than the cluster. The previously measured broad velocity distribution supports the idea that a merger in this cluster is being observed.

Briel, U. G.↗

NASA NTRS1991

The x ray morphology of the relaxed cluster of galaxies A2256. 2: Sources around the extended cluster emission

X-ray emission from cluster galaxies as well as from 'dark objects' (i.e. not visible on the Palomar Observatory Sky Survey (POSS)) seen in the x-ray observation of A2256 with the imaging proportional counter on board ROSAT (x-ray astronomy satellite), is reported. This observation revealed significantly more sources in the field around the extended cluster emission than one would expect by chance. In a preliminary investigation, 14 sources were discovered at the limiting flux for this exposure, whereas about 7 sources would have been expected by chance. At least two of those sources are coincident with cluster member galaxies, having x-ray luminosities of approximately 10(exp +42) erg/s in the ROSAT energy band from 0.1 to 2.4 keV, but at least four more are from 'dark' objects. The similarity of these objects to those in A1367 suggests the existence of a new class of x-ray sources in clusters.

Henry, J. Patrick↗

NASA NTRS1990

A deep Abell cluster redshift survey

Redshifts have been measured for a complete sample of 145 Abell clusters of galaxies of median redshift 0.16 covering a 561 sq deg region at high Galactic latitude. Clustering on scales greater than about 70/h Mpc cannot be detected. A large void of diameter about 20,000 km/s seen in maps of the cluster distribution is consistent with smaller scale behavior of the correlation function of the survey. Large-scale peculiar motions are about 1000 km/s or less, a limit inconsistent with the claimed detection by Bahcall et al. (1986) of peculiar motions of about 2000 km/s.

Huchra, John P.↗

NASA NTRS1990

MS 0129.2 - 2237 - Interacting galaxies at z = 0.11

The X-ray source MS 0129.2 - 2237 is positionally coincident with an interacting system of galaxies. This paper presents the results of a spectroscopic and photometric investigation of the system, which show that a Seyfert 1.5, a Seyfert 2 nucleus or H II region, or a starburst galaxy, a normal galaxy plus possibly another galaxy where star-forming activity is taking place are strongly interacting. The redshift of the system is z = 0.11. The maximum projected diameter of the envelope common to the four spectroscopically distinct objects is about 98 kpc (H0 = 50 km/s M/pc and q0 = 0.5). The isolated environment in which the system lies suggests that these results present evidence of the final stage of the life of a compact group of galaxies where members are merging into an elliptical galaxy.

Maccagni, Dario↗

NASA NTRS1990

Studies of the evolution of the x ray emission of clusters of galaxies

The x ray luminosity function of clusters of galaxies was determined at different cosmic epoches using data from the Einstein Observatory Extended Medium Survey. The sample consisted of 67 x ray selected clusters that were grouped into three redshift shells. Evolution was detected in the x ray properties of clusters. The present volume density of high luminosity clusters was found to be greater than it was in the past. This result is the first convincing evidence for evolution in the x ray properties of clusters. Investigations into the constraints provided by these data on various Cold Dark Matter models are underway.

Henry, J. Patrick↗

NASA NTRS1987

Narrowband imaging and spectroscopy close to the nucleus of the Seyfert galaxy NGC 7682

Keel's (1985) report of a jet-like optical feature emanating from the nucleus of NGC 7682 is investigated. Deep CCD images of NGC 7682 were taken with narrowband filters centered on the redshifted wavelength of H-alpha + forbidden N II and on a nearby continuum region. The continuum-subtracted line images show no evidence of the jet feature, although numerous H II regions appear clearly, both close to the nucleus and in the extended spiral arm structure. Spectra were taken at various dispersions and position angles, including the supposed position angle of the jet. These data were used to obtain background-subtracted spectra at the precise location of the jet. No excess emission was detected above the background-galaxy contribution. The highest-resolution spectra were used to determine the redshift of the galaxy to high precision.

Brodie, Jean↗

NASA NTRS1986

X-ray observations of distant blue clusters of galaxies

X-ray observations are reported for a sample of distant clusters for which the percentage of apparent cluster members that are blue has been determined optically. The X-ray properties of the clusters are not simply related to the optical properties. The X-ray observations do not support models in which blue galaxies change color as a result of ram-pressure stripping, or in which star formation is triggered by interaction with an intracluster medium. The data lend some support to the idea that blue galaxies in distant clusters are being observed immediately after the removal of galactic halos, and before the interstellar medium is depleted (Larson et al., 1980).

Lea, Susan M.↗