Environmental Effects in Clusters: Modified Far-Infrared--Radio Relations within Virgo Cluster Galaxies

(abridged) We present a study on the effects of the intracluster medium (ICM) on the interstellar medium (ISM) of 10 Virgo cluster spiral galaxies using {\it Spitzer} far-infrared (FIR) and VLA radio continuum imaging. Relying on the FIR-radio correlation within normal galaxies, we use our infrared data to create model radio maps which we compare to the observed radio images. For 6 of our sample galaxies we find regions along their outer edges that are highly deficient in the radio compared with our models. We believe these observations are the signatures of ICM ram pressure. For NGC 4522 we find the radio deficit region to lie just exterior to a region of high radio polarization and flat radio spectral index, although the total 20 cm radio continuum in this region does not appear strongly enhanced. These characteristics seem consistent for other galaxies with radio polarization data in the literature. The strength of the radio deficit is inversely correlated with the time since peak pressure as inferred from stellar population studies and gas stripping simulations, suggesting the strength of the radio deficit is good indicator of the strength of the current ram pressure. We also find that galaxies having {\it local} radio {\it deficits} appear to have {\it enhanced global} radio fluxes. Our preferred physical picture is that the observed radio deficit regions arise from the ICM wind sweeping away cosmic-ray (CR) electrons and the associated magnetic field, thereby creating synchrotron tails as observed for some of our galaxies. We propose that CR particles are also re-accelerated by ICM-driven shocklets behind the observed radio deficit regions which in turn enhances the remaining radio disk brightness.Comment: 19 pages, 10 figures; Astrophysical Journa

The cool wake around 4C 34.16 as seen by XMM-Newton

We present XMM-Newton observations of the wake-radiogalaxy system 4C34.16, which shows a cool and dense wake trailing behind 4C34.16's host galaxy. A comparison with numerical simulations is enlightening, as they demonstrate that the wake is produced mainly by ram pressure stripping during the galactic motion though the surrounding cluster. The mass of the wake is a substantial fraction of the mass of an elliptical galaxy's X-ray halo. This observational fact supports a wake formation scenario similar to the one demonstrated numerically by Acreman et al (2003): the host galaxy of 4C34.16 has fallen into its cluster, and is currently crossing its central regions. A substantial fraction of its X-ray halo has been stripped by ram pressure, and remains behind to form the galaxy wake.Comment: 9 pages, 6 figures, accepted for publication in MNRA

The Infrared Luminosity of Galaxy Clusters

The aim of this study is to quantify the infrared luminosity of clusters as a function of redshift and compare this with the X-ray luminosity. This can potentially constrain the origin of the infrared emission to be intracluster dust and/or dust heated by star formation in the cluster galaxies. We perform a statistical analysis of a large sample of galaxy clusters selected from existing databases and catalogues.We coadd the infrared IRAS and X-ray RASS images in the direction of the selected clusters within successive redshift intervals up to z = 1. We find that the total infrared luminosity is very high and on average 20 times higher than the X-ray luminosity. If all the infrared luminosity is to be attributed to emission from diffuse intracluster dust, then the IR to X-ray ratio implies a dust-to-gas mass abundance of 5e-4. However, the infrared luminosity shows a strong enhancement for 0.1 < z < 1, which cannot be attributed to cluster selection effects. We show that this enhancement is compatible with a star formation rate in the member galaxies that is typical of the central Mpc of the Coma cluster at z = 0 and evolves with the redshift as (1+z)^5. It is likely that most of the infrared luminosity that we measure is generated by the ongoing star formation in the member galaxies. From theoretical predictions calibrated on extinction measurements (dust mass abundance equal to 1e-5), we expect only a minor contribution, of a few percent, from intracluster dust.Comment: 9 pages, 7 figures, accepted july 31st 2008 for publication in Astronomy and Astrophysics, language improved for this versio

Two-Phased Intra-Cluster Medium in the Centaurus Cluster of Galaxies

ASCA and ROSAT data of the Centaurus cluster were analyzed. A central excess in the radial brightness profile is found in the hard energy band up to 10keV. This requires a deeper central potential than a King-type one. A double-beta brightness distribution gives a good account of the data. A deprojected energy spectrum within a spherical region of radius 30 kpc at the cluster center indicates that the ICM cannot be isothermal there. Simultaneous fitting of the three (PSPC, GIS, and SIS) energy spectra extracted from the central 3' region showed that a two-temperature model that has temperatures of 1.4keV and 4.4keV and a common metallicity of 1.0 solar with the Galactic absorption gives the best description to the spectra. A cooling-flow spectral model did not give satisfactory fit. A 3-dimensional cluster model incorporating the two-phase picture, the double-beta brightness distribution, and the central metallicity increase reproduced the overall ASCA and ROSAT data successfully. The derived spatial distribution of the dark matter deviates from a King-type profile exhibiting a central excess, which is consistent with the Navvaro-Frenk-White model. The iron is revealed to be more widely spread than stars, which may have been caused by energetic supernovae and the motion of the cD galaxy. Since the derived characteristics of the cool phase including the temperature, angular extent, gas mass, and metallicity, are on a smooth extension of those of inter-stellar medium (ISM) of elliptical galaxies, the cool phase can be regarded as the ISM associated with the cD galaxy. The cool-phase X-ray emission is presumably sustained by energies dissipated by infalling mass to the cD galaxy in the course of cluster evolution.Comment: accepted for publication in Ap

The elemental abundances in the intracluster medium as observed with XMM-Newton

XMM-Newton observations of 19 galaxy clusters are used to measure the elemental abundances and their spatial distributions in the intracluster medium. The sample mainly consists of X-ray bright and relaxed clusters with a cD galaxy. Along with detailed Si, S and Fe radial abundance distributions within 300-700 kpc in radius, the O abundances are accurately derived in the central region of the clusters. The Fe abundance maxima towards the cluster center, possibly due to the metals from the cD galaxy,are spatially resolved. The Si and S abundances also exhibit central increases in general, resulting in uniform Fe-Si-S ratios within the cluster. In contrast, the O abundances are in general uniform over the cluster. The mean O to Fe ratio within the cluster core is sub-solar, while that of the cluster scale is larger than the solar ratio. These measurements indicate that most of the Fe-Si-S and O in the intracluster medium have different origins, presumably in supernovae Ia and II, respectively. The obtained Fe and O mass are also used to discuss the past star formation history in clusters.Comment: Accepted for publication in Astronomy and Astrophysic

Three-Dimensional Simulations of Bi-Directed Magnetohydrodynamic Jets Interacting with Cluster Environments

We report on a series of three-dimensional magnetohydrodynamic simulations of active galactic nucleus (AGN) jet propagation in realistic models of magnetized galaxy clusters. We are primarily interested in the details of energy transfer between jets and the intracluster medium (ICM) to help clarify what role such flows could have in the reheating of cluster cores. Our simulated jets feature a range of intermittency behaviors, including intermittent jets that periodically switch on and off and one model jet that shuts down completely, naturally creating a relic plume. The ICM into which these jets propagate incorporates tangled magnetic field geometries and density substructure designed to mimic some likely features of real galaxy clusters. We find that our jets are characteristically at least 60% efficient at transferring thermal energy to the ICM. Irreversible heat energy is not uniformly distributed, however, instead residing preferentially in regions very near the jet/cocoon boundaries. While intermittency affects the details of how, when, and where this energy is deposited, all of our models generically fail to heat the cluster cores uniformly. Both the detailed density structure and nominally weak magnetic fields in the ICM play interesting roles in perturbing the flows, particularly when the jets are non-steady. Still, this perturbation is never sufficient to isotropize the jet energy deposition, suggesting that some other ingredient is required for AGN jets to successfully reheat cluster cores.Comment: 19 pages, 18 figures, Accepted for publication in the Astrophysical Journa

Structure and Turbulence in Simulated Galaxy Clusters and the Implications for the Formation of Radio Halos

We track the histories of massive clusters of galaxies formed within a cosmological hydrodynamic simulation. Specifically, we track the time evolution of the energy in random bulk motions of the intracluster medium and X-ray measures of cluster structure and their relationship to cluster mergers. We aim to assess the viability of the turbulent re-acceleration model for the generation of giant radio halos by comparing the level of turbulent kinetic energy in simulated clusters with the observed properties of radio halo clusters, giving particular attention to the association of radio halos to clusters with disturbedX-ray structures. The evolution of X-ray cluster structure and turbulence kinetic energy, k, in simulations can then inform us about the expected lifetime of radio halos and the fraction of clusters as a function of redshift expected to host them. We find strong statistical correlation of disturbed structure measures and the presence of enhancements in k. Specifically, quantitatively "disturbed", radio halo-like X-ray morphology in our sample indicates a 92% chance of the cluster in question having k elevated to more than twice its minimum value over the cluster's life. The typical lifetime of episodes of elevated turbulence is on the order of 1 Gyr, though these periods can last 5 Gyrs or more. This variation reflects the wide range of cluster histories; while some clusters undergo complex and repeated mergers spending a majority of their time in elevated k states, other clusters are relaxed over nearly their entire history. We do not find a bimodal relationship between cluster X-ray luminosity and the total energy in turbulence that might account directly for a bimodal L_X-P_{1.4 GHz} relation. However, our result may be consistent with the observed bimodality, as here we are not including a full treatment of cosmic rays sources and magnetic fields.Comment: 15 pages, 12 figures, MNRAS Submitte

The 3D model control of image processing

Telerobotics studies remote control of distant robots by a human operator using supervisory or direct control. Even if the robot manipulators has vision or other senses, problems arise involving control, communications, and delay. The communication delays that may be expected with telerobots working in space stations while being controlled from an Earth lab have led to a number of experiments attempting to circumvent the problem. This delay in communication is a main motivating factor in moving from well understood instantaneous hands-on manual control to less well understood supervisory control; the ultimate step would be the realization of a fully autonomous robot. The 3-D model control plays a crucial role in resolving many conflicting image processing problems that are inherent in resolving in the bottom-up approach of most current machine vision processes. The 3-D model control approach is also capable of providing the necessary visual feedback information for both the control algorithms and for the human operator