Cavagnolo, Kenneth - The Entropy-Feedback Connection and Quantifying Cluster Virialization
Dupke, Renato - Constraining the Age of Fossil Groups with Chandra
Fuse, Chris - Dynamical Evolution Diagnostics of Compact Galaxy Groups & Isolated Systems
Miller, Eric - Intermediate-Redshift Groups in the XBootes Survey
Plucinsky, Paul - Chandra ACIS Survey of M33 (ChASeM33): The First Look Source Catalog
Kenneth Cavagnolo (Michigan State University) , Megan Donahue (Mich. St. Univ.), Mark Voit (Mich. St. Univ.), Ming Sun (Mich. St. Univ.)
Understanding the entropy of intracluster gas is the key to understanding 1) the feedback mechanisms active within clusters and 2) the role of the cluster environment on galaxy formation. Our presented work focuses on examining feedback mechanisms together with the breaking of self-similar relations expected in cluster and galaxy formation models with star formation and AGN. In this poster, we present and describe radial profiles of the entropy distribution in cluster gas. We also examine a metric proposed to quantify the degree of cluster virialization which may in turn reduce scatter in scaling relations, thus increasing clusters utility in cosmological studies. We have assembled a library of entropy profiles for a sample of 100 clusters in the Chandra Data Archive (CDA) covering broad mass and morphological ranges, together with the radio and optical properties of the central galaxy. We will discuss the interconnection of central entropy with radio luminosity and H emission. We will describe the distribution of central entropy levels in our sample and briefly discuss what can be learned about the range of central heating mechanisms and the timescale of feedback mechanisms from this distribution. We will also present recently completed work for which we explore the band-dependence of the inferred X-ray temperature of the ICM for 179 clusters selected from the Chandra archive. We compare the X-ray temperatures inferred for single-temperature fits of global spectra (with the central R=70 kpc excluded and an outer radius of R2500) when the energy range of the fit is 0.7-7.0 keV (full) and when the energy range is 2.0/(1+z)-7.0 keV (hard). We find, on average, the hard-band temperature is significantly higher than the full-band temperature. Upon further exploration, we find the ratio THFR = T2.0-7.0/T0.7-7.0 is enhanced preferentially for clusters which are known merger systems and for clusters which do not have detectable cool cores. Annular regions surrounding cool core clusters tend to have best-fit hard-band temperatures that are statistically consistent with their best-fit full-band temperatures.
Edmund Douglass (Boston University) , E.L. Blanton (Boston University), T. E. Clarke (NRL, Interferometrics, Inc.), Craig L. Sarazin (University of Virginia)
Named for their characteristic C-shape, wide angle tail (WAT) radio sources are assumed to be formed by the interaction between the radio jets and the intracluster medium in which they are embedded. We present Chandra observations of two clusters that host WAT radio sources, Abell 562 and Abell 1446. While both clusters display isothermal radial temperature profiles and a typically smooth decline in pressure and density with radius, both exhibit evidence for some degree of merger activity and WAT/ICM interaction. We find that the clusters have an excess of emission offset from the cluster core and WAT hosting galaxy. There is significant two-dimensional temperature substructure within the central regions of the clusters as is consistent with infalling clumps or galaxy groups, while the surface brightness distribution of the inner regions of the clusters reflects that of unrelaxed systems. It is possible that this merger activity may be leading to the shaping of the bent radio sources within each cluster. In addition there is evidence that the lobes of both WAT sources have carved out cavities within the intracluster gas.
Renato Dupke (University of Michigan) , Claudia Mendes de Oliveira (University of Sao Paulo, Brazil)
Indications that fossil groups are formed at early epochs come not just from the expected high time scale for dynamical friction to merge the core galaxies, but also from recent X-ray observations, including high concentration parameters and featureless X-ray morphologies. However, the lack of cooling cores in fossil groups with short cooling times and the sensitiveness of the dynamical friction time scale on the satellite galaxies’ impact parameter are also consistent with a more recent formation time. Here, we discuss new constraints on the formation time of fossil groups based on the residual chemical profiles of the intra-group gas as measured by X-ray elemental abundance ratios.
Chris Fuse (TCU) , Pamela Marcum (NASA HQ,TCU), Michael Fanelli (TCU)
Compact groups contain galaxies within dense galactic environments, typically with separations less than a few diameters. Due to their short dynamical timescales, these systems are excellent probes of merging and interaction phenomena. Compact groups are the likely precursors to “fossil groups” and highly isolated elliptical galaxies. The morphology of hot gas is uniquely suited for distinguishing isolated ellipticals with a merged group origin from systems which evolved along alternative paths. As part of a larger study to understand the origin and evolution of isolated early-type galaxies identified in the Sloan Digital Sky Survey, we have analyzed the diffuse x-ray emission of 11 Hickson Compact Groups (HCG) and several isolated early-type systems, using archival data from NASA’s Chandra X-ray Observatory. We use the morphology and physical extent of the soft (0.3-2.5 keV) emission, x-ray luminosity, and gas temperature as diagnostics of the dynamical state of these systems. Correlations of x-ray measurements with other group properties provide a tool for assessing dynamical evolution, which can be used to infer the properties of the precursors of isolated ellipticals. A hot intergroup medium is not detected in 5 groups. Most of the members of these spiral-dominated groups exhibit axisymmetric x-ray emission, suggesting that this gas has experienced few external perturbations. The remaining 6 contain an intergroup medium, which extends beyond the optical extent of individual galaxies and shows significant structure. The x-ray luminosity of these groups ranges from 6.8 x 10^39 to 8 x 10^41 ergs/sec, with gas temperatures ranging from 0.62 keV kT 1.1 keV. The HCGs are observed to have sub-solar abundance values. This project is supported by NASA’s Astrophysical Data Program, grant # NNG05C53G, and a Texas Space Grant Consortium fellowship.
Eric Miller (MIT) , Mark Bautz, Catherine Grant (MIT), William Forman, Christine Jones, Stephen Murray, Alexey Vikhlinin (SAO)
Galaxy groups are key tracers of galaxy evolution, cluster evolution, and structure formation, yet they are difficult to study at even moderate redshift. We have undertaken a project to observe a flux-limited sample of intermediate-redshift (0.15 < z < 0.35) group candidates identified by the XBootes Chandra survey. By exploiting the unique multiwavelength coverage of the XBootes/NOAO Deep Wide Field Survey (NDWFS) field, we aim to (1) understand the connection between the X-ray and optical properties of groups, and (2) constrain non-gravitational processes that affect the energetics of the intragroup medium. Here we present deep Chandra/ACIS and Suzaku/XIS follow-up observations of the first four targets in this project. All four are confirmed sources of diffuse, thermal emission with derived temperatures between 1 and 5 keV and bolometric X-ray luminosities between 10^43 and 10^44 erg/s. We discuss these early results in the context of group and cluster evolution.
Tony Mroczkowski (Columbia University) , Daisuke Nagai (Caltech), Amber Miller (Columbia), Max Bonamente (MSFC), John E. Carlstrom (U. Chicago), Christopher Greer (U. Chicago), David Hawkins (Caltech-OVRO), Ryan Hennessy (U.Chicago), Marshall Joy (MSFC), James W. Lamb (Caltech-OVRO), Erik M. Leitch (Caltech/JPL), Michael Loh (U.Chicago), Ben Maughan (Bristol, SAO, Chandra Fellow), Stephen Muchovej (Columbia University), Clem Pryke (U.Chicago), Ben Reddall (Caltech-OVRO), Matthew Sharp (U.Chicago), and David Woody (Caltech-OVRO)
We demonstrate the utility of a new model, recently shown to be a robust, self-similar pressure profile, for fitting the current and future generations of Sunyaev-Zel'dovich effect (SZE) observations of galaxy clusters. It has been shown that traditional isothermal -model cannot describe the cluster gas out to the virial, even when the cluster core is excluded. The gas density profile begins to steepen and isothermality is a poor assumption at large radii. When jointly fitting Chandra X-ray and SZ cluster data, the higher signal-to-noise X-ray data drive model shape parameters. For SZE observations of cluster pressure profiles, which are steeper than cluster density profiles due to the decrease in temperature with radius, departures from the isothermal -model are compounded. The isothermal -profile systematically overpredicts the integrated SZ decrement, Yint, which scales as SZ flux and is sensitive to the integrated gas pressure, by
. The need for a model that can describe a cluster's pressure profile at all observable radii has become crucial to the study of the SZE from clusters. Therefore, a new pressure profile, which is not constrained by the X-ray derived density model shape parameters, has been tested. We find this model provides an unbiased estimate of Yint, and, when combined with X-ray image data through the ideal gas law, yields a reasonably-accurate electron temperature profile without relying on X-ray spectroscopic information. In addition to yielding more accurate relationships between cluster observables and physical cluster properties, this model could prove to be a useful tool in helping to constrain the temperatures of high redshift clusters.
Paul Plucinsky (SAO) , Benjamin Williams (UW), Knox S. Long (STScI), Terrance J. Gaetz (SAO), Manami Sasaki (SAO), Wolfgang Pietsch (MPE), Ralph Tuellmann (SAO), Randall K. Smith (JHU/GSFC), and the ChASeM33 team
We present a source catalog from the Chandra ACIS Survey of M33 (ChASeM33): A Deep Survey of the Nearest Face-on Spiral Galaxy. The 1.4 Ms survey covers the galaxy out to R 18 arcmin ( 4 kpc). These data provide the most intensive, high spatial resolution assessment of the X-ray source populations available for the confused inner regions of M33. Mosaic images of the ChASeM33 observations show several hundred individual X-ray sources as well as soft diffuse emission from the hot interstellar medium. Bright, extended emission surrounds the nucleus and is also seen from the giant HII regions NGC604 and IC131. Fainter extended emission and numerous individual sources appear to trace the inner spiral structure. The initial source catalog, arising from 2/3 of the expected survey data, includes 394 sources significant at the 3 sigma confidence level or greater, down to a limiting luminosity (absorbed) of 1.6e35 ergs (0.35 - 8.0 keV). The hardness ratios of the sources separate those with soft, thermal spectra such as supernova remnants from those with hard, non-thermal spectra such as X-ray binaries and background active galactic nuclei. Emission extended beyond the Chandra point spread function is evident in 23 of the 394 sources. Cross-correlation of the ChASeM33 sources against previous catalogs of X-ray sources in M33 results in matches for the vast majority of the brighter sources and shows 28 ChASeM33 sources within 10 arcsec of supernova remnants identified by prior optical and radio searches. Support for this work was provided by NASA through Chandra Award Number G06-7073A and contract NAS8-03060
Shanil Virani (Yale University) , Jeff Kenney (Yale), Christine Jones (CfA), and Bill Forman (CfA)
We present results from a 30 ks Chandra-S observation of NGC 4569, a large spiral galaxy in the Virgo cluster core currently undergoing ram-pressure stripping. We detect X-ray emission on three scales: emission from a central compact core likely from a low luminosity AGN, soft diffuse emission just outside of the core which has a ``horseshoe''-like morphology, and emission on 4' scales that is associated with the star-forming disk. The soft diffuse X-ray gas just outside of the core closely traces H-filaments and is likely associated with a nuclear outflow from either an AGN or a starburst. Spectral fits performed on data extracted from the central 2" are best-fit using a power law model with a photon slope of 1.8 ±0.2, consistent with the typical indices found for AGNs detected with Chandra and XMM-Newton. Spectral fits performed on data extracted from the central 35" and excluding the central 2", are best-fit using a collionsionally ionized plasma model (MEKAL) with a temperature of 0.63 ±0.04 keV. The detection of an AGN in NGC 4569 resolves a long-standing controversy in the literature on whether the X-ray emission from the core is from an AGN or from a compact starburst.
Raymond White (University of Alabama) , Renato Dupke (University of Michigan), Joel Bregman (University of Michigan)
Cold fronts, discontinuities in X-ray surface brightness accompanied by continuous gas pressure distributions, are often found in relaxed galaxy clusters. Explaining cold fronts as remnant cores of head-on subcluster mergers does not generally work for such clusters, which has led to competing models invoking gas sloshing. We use a deep Chandra exposure of Abell 496 to test predictions of these sloshing models by analyzing the spatial distributions of density, temperature, metal abundances and abundance ratios. We confirm that the temperature and chemical discontinuities in this cluster are not consistent with being directly identified with a core merger remnant. Nonetheless, we find that these structures could have been caused by sloshing induced by an off-center collision with a dark matter halo. We find a relatively cool "arm" of gas, with different abundance ratios than its surroundings, stretching from the central regions. The spiral shape of this arm emanating from the center is reminiscent of structures induced by off-center encounters with less massive dark matter halos, as found in recent numerical simulations of Ascasibar and Markevitch (2006).
Mihoko Yukita (UAH) , D. Swartz (NASA/MSFC), R. Soria (MSSL)
We present a multi-wavelength analysis of the central 6 kpc region of NGC 2403, where most of the star formation is located in the nearby, face-on, spiral galaxy. From a distance of only 3.2 Mpc, we are able to resolve an individual HII region from most observatories. This allows us to investigate the correlations between soft X-ray diffuse emission and other star-formation tracers, such as H-alpha, GALEX UV, and Spitzer Mid-IR, focusing not only on the galactic scale but also on individual HII regions. The soft X-ray emission in the central region shows internal contributions from young HII regions (< 30 Myrs) and also from extra-diffuse coronal gas, which may be accounted for by older, star-forming activities.