arXiv subjects

Renato A. Dupke

Publications and source records attributed to Renato A. Dupke.

At least 37 records · Page 2Linked to original sources

arXiv2009

An optical and X-ray study of the fossil group RX J1340.6+4018

Fossil groups are systems with one single central elliptical galaxy and an unusual lack of luminous galaxies in the inner regions. The standard explanation for the formation of these systems suggests that the lack of bright galaxies is due to galactic cannibalism. In this study we show the results of an optical and X-ray analysis of RX J1340.6+4018, the prototype fossil group. The data indicates that RX J1340.6+4018 is similar to clusters in almost every sense, dynamical mass, X-ray luminosity, M/L and luminosity function, except for the lack of L* galaxies. There are claims in the literature that fossil systems have a lack of small mass haloes, compared to predictions based on the LCDM scenario. The observational data gathered on this and other fossil groups so far offer no support to this idea. Analysis of the SN Ia/SN II ejecta ratio in the inner and outer regions shows a marginally significant central dominance of SN Ia material. This suggests that either the merger which originated the central galaxy was dry or the group has been formed at early epochs, although better data are needed to confirm this result.

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arXiv2007

Different Methods of Forming Cold Fronts in Non-Merging Clusters

Sharp edges in X-ray surface brightness with continuous gas pressure called cold fronts have been often found in relaxed galaxy clusters such as Abell 496. Models that explain cold fronts as surviving cores of head-on subcluster mergers do not work well for these clusters and competing models involving gas sloshing have been recently proposed. Here, we test some concrete predictions of these models in a combined analysis of density, temperature, metal abundances and abundance ratios in a deep Chandra exposure of Abell 496. We confirm that the chemical discontinuities found in this cluster are not consistent with a core merger remnant scenario. However, we find chemical gradients across a spiral "arm" discovered at 73 kpc north of the cluster center and coincident with the sharp edge of the main cold front in the cluster. Despite the overall SN Ia iron mass fraction dominance found within the cooling radius of this cluster, the metal enrichment along the arm, determined from silicon and iron abundances, is consistent with a lower SN Ia iron mass fraction (51% +- 14%) than that measured in the surrounding regions (85% +- 14%). The "arm" is also significantly colder than the surroundings by 0.5-1.6 keV. The arm extends from a boxy colder region surrounding the center of the cluster, where two other cold fronts are found. This cold arm is a prediction of current high resolution numerical simulations as a result of an off-center encounter with a less massive pure dark matter halo and we suggest that the cold fronts in A496 provide the first clear corroboration of such model, where the closest encounter happened ~ 0.5 Gyr ago. We also argue for a possible candidate dark matter halo responsible for the cold fronts in the outskirts of A496.

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arXiv2007

The Merger in Abell 576: A Line of Sight Bullet Cluster?

Using a combination of Chandra and XMM observations, we confirmed the presence of a significant velocity gradient along the NE/E-W/SW direction in the intracluster gas of the cluster Abell 576. The results are consistent with a previous ASCA SIS analysis of this cluster. The error weighted average over ACIS-S3, EPIC MOS 1 & 2 spectrometers for the maximum velocity difference is >3.3E03 km/s at the 90% confidence level, similar to the velocity limits estimated indirectly for the "bullet" cluster (1E0657-56). The probability that the velocity gradient is generated by standard random gain fluctuations with Chandra and XMM is <0.1%. The regions of maximum velocity gradient are in CCD zones that have the lowest temporal gain variations. It is unlikely that the velocity gradient is due to Hubble distance differences between projected clusters (probability<~0.01%). We mapped the distribution of elemental abundance ratios across the cluster and detected a strong chemical discontinuity using the abundance ratio of silicon to iron, equivalent to a variation from 100% SN Ia iron mass fraction in the West-Northwest regions to 32% in the Eastern region. The "center" of the cluster is located at the chemical discontinuity boundary, which is inconsistent with the radially symmetric chemical gradient found in some regular clusters, but consistent with a cluster merging scenario. We predict that the velocity gradient as measured will produce a variation of the CMB temperature towards the East of the core of the cluster that will be detectable by current and near-future bolometers. The measured velocity gradient opens for the possibility that this cluster is passing through a near line-of-sight merger stage where the cores have recently crossed.

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arXiv2006

Chemical Gradients in Galaxy Clusters and the Multiple Ways of Making a Cold Front

Cold fronts were originally interpreted as being the result of subsonic/transonic motions of head-on merging substructures. This merger core remnant model is theoretically justified and hold relatively well for clusters that have clear signs of merging, such as 1E0657-56, but they do not work well for the increasing number of cold fronts found in clusters that do not show clear merging signs, such as A496. Here we report the results of a deeper observation of that cluster that allowed us to produce high quality maps of the gas parameters and to compare more closely the observations with the predictions given by different models for cold front formation. We found for the first time a ``cold arm'' characteristic of a flyby of a massive DM halo near the core of the cluster. The cold arm is accompanied by an enhanced SN II Fe mass fraction, inconsistent with the merger core remnant scenario.

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arXiv2005

Direct Measurements of Gas Bulk Flows in the ICM of the Centaurus Cluster with the Chandra Satellite

We present the analysis of the velocity structure of the intracluster gas near the core of Abell 3526 obtained with two off-center Chandra observations, specifically designed to eliminate errors due to spatial variations of the instrumental gain. We detected a significant velocity gradient along the direction NE-SW direction, roughly perpendicular to the direction of the incoming sub-group Cen45, in agreement with previous ASCA SIS measurements. The presence of gas bulk velocities is observed both with and without the inclusion of the FeK line complex in the spectral fittings. The configuration and magnitude of the velocity gradient is consistent with near transonic circulatory motion, either bulk or eddy-like. The velocity difference obtained using the best calibrated central regions of ACIS-S3 is found to be (2.4+-1.0)E03 km/s for rectangular regions 2'.4 x 3' roughly diametrically opposed around the cluster's core. There are also indications of a high velocity zone towards the Southern region with similar magnitudes. The detection of velocity gradients is significant at the >99.4% confidence and simulations show that intrachip gain fluctuations > 1800 km/s are required to explain the velocity gradient by chance. The measurements suggest that >1% of the total merger energy can still be bulk kinetic 0.4 Gyr after the merging event. This is the first direct confirmation of velocity gradients in the intracluster gas with independent instruments and indicates that strong departure from hydrostatic equilibrium is possible even for cool clusters that do not show obvious signs of merging.

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arXiv2005

Constraints on Intracluster Gas Bulk Motions in Clusters of Galaxies with ASCA

The recent detection of Doppler shifts of X-ray spectral lines in the intracluster gas of the Centaurus and Perseus clusters of galaxies with ASCA has raised the question of the frequency of such velocity gradients and their relation to other cluster properties. To address this and improve the sample of ICM velocity gradient candidates we carried out a systematic search of the ASCA archive for clusters with suitable observing conditions that allow full azimuthal mapping of gas velocities near the central regions. Here we present the results of the azimuthal velocity distribution of a sample consisting of the best" observed clusters for velocity analysis. Our sample encompasses clusters with different physical and morphological characteristics, including both well behaved "cooling flow" and dynamically active clusters. The gas temperatures of the clusters in our sample range from 1.4 keV to 6.3 keV. We find velocity substructures in ~ 15% of the clusters in our sample on the order of a few x 1E3 km/s. The significance of the velocity gradients' is greater than 99% in Abell 576 and RXJ0419.6+0225, the clusters where velocity gradients are most significant. The velocity gradients are consistent with transitory and/or rotational bulk motion. The velocity gradients in these clusters are unlikely to be due to projected temperature anisotropies, ASCA PSF, intrachip gain variations, and flux contamination from other sources. Chandra images of these clusters do not show obvious cluster alignments within the field of view covered by ASCA. We also noticed a high frequency (~50%) of anisotropic temperature gradients in the core of "cooling flow" clusters, suggesting the presence of frequent dynamical activity in the core of galaxy clusters.

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arXiv2005

Detecting Intracluster Gas Motion in Galaxy Clusters: Mock Astro-E2 Observations

We explore the detectability of bulk motions in the X-ray emitting intracluster medium (ICM) using a catalog of 1,836 mock Astro-E2 observations of simulated clusters of galaxies. We generate high resolution mock spectra for two observing strategies: a four-pointing mosaic and a single central pointing. Normalizing to 200 (400) photons in the iron K-alpha region for the mosaic (central) study, we fit Poisson realizations of each simulated spectrum to a velocity broadened isothermal plasma emission model. We confirm that the velocity characteristics (mean and dispersion) returned by the spectral fittings are unbiased measures of the emission-weighted values within the observed region, with scatter 55 km/s. The maximum velocity difference between mosaic element pairs $Δv_{\rm max}$ has ~ 6% likelihood of being transonic ($Δv_{\rm max} \ge 0.5 c_s$), and the likelihood falls steeply, $p \spropto (Δv_{\rm max}/c_s)^{-4}$, at high Mach number. The velocity broadening parameter $σ_v$ from the central pointing fit exceeds the thermal value in 49% of the cases, with again a $σ_v^{-4}$ tail at large dispersion. We present as case studies the clusters that yield the strongest signal for each observing strategy.

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arXiv2004

Hot Baryons in Supercluster Filaments

Most of the baryons in the local universe are ``missing'' in that they are not in galaxies or in the previously detected gaseous phases. These missing baryons are predicted to be in a moderately hot phase, 10^5-10^7 K, largely in the form of giant cosmic filaments that connect the denser virialized clusters and groups of galaxies. Models show that the highest covering fraction of such filaments occurs in superclusters. To determine whether such filaments exist, we have begun a project to search for UV absorption against AGNs projected behind possible supercluster filaments. Using data from the HST and FUSE archives along with new observations, we have detected UV absorption within about 1300 km/s of seven supercluster sightlines out of a sample of eight. The likelihood of such detections being generated by chance is less than 10^-4.

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arXiv2004

Cosmic Filaments in Superclusters

Large-scale structure calculations show that modest overdensity filaments will connect clusters of galaxies and these filaments are reservoirs of baryons, mainly in gaseous form. To determine whether such filaments exist, we have examined the UV absorption line properties of three AGNs projected behind possible filaments in superclusters of galaxies; the AGNs lie within 3 Mpc of the centerlines of loci connecting clusters. All three lines of sight show absorption in Lyα, Lyβ, or/and OVI at redshifts within about 1300 km/s of the nearby galaxy clusters that would define the closest filaments. For one AGN, the absorption line redshifts are close to the emission line redshift of the AGN, so we cannot rule out self-absorption for this object. These absorption line associations with superclusters are unlikely to have occurred by chance, a result consistent with the presence of cosmic filaments within superclusters.

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arXiv2002

Chandra Analysis of Abell 496 - No Chemical Gradients Across Cold Fronts

We present the results of a spatially-resolved spectroscopic analysis of the galaxy cluster Abell 496 with the S3 chip on-board the Chandra satellite. We confirm the presence of a central positive temperature gradient consistent with a cooling flow, but with a minimum gas temperature of ~0.5-0.9 keV. The cluster also exhibits sharp edges in gas density and temperature which are consistent with "cold front" substructures. The iron abundance profile is not radially symmetric relative to the cluster center. Towards the direction of the most prominent (northerly) cold front, the iron abundance is roughly flat, with nearly solar values. In the opposite (southerly) direction from the center, the iron abundance distribution shows an "off-center" peak. Various abundance ratios suggest that the heavy elements in the central regions of the cluster are dominated by SN Ia ejecta. However, for radii greater than 100 kpc, the abundance ratios vary in such a way that different abundance ratios provide very different estimates of the proportion of SN Ia/II ejecta. Nonetheless, observed abundances and abundance ratios are continuous across the cold fronts, which suggests that the cold fronts are not likely to be the result of a subcluster merger. We suggest instead that the cold fronts in A496 are caused by "sloshing" of the central cooling flow gas, induced by the motion of the cD about the cluster center.

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arXiv2002

Prospects for Detection of Intracluster Gas Bulk Velocities Through the Sunyaev-Zel'dovich Effect

Intracluster gas velocity gradients have been recently detected by the authors in the Centaurus cluster (Abell 3526) using the Doppler shift of X-ray spectral lines with ASCA Solid-state Imaging Spectrometers. The velocity gradient was found to be maximum along a line roughly perpendicular to the direction of the incoming subgroup Cen 45 and has a correspondent velocity difference of ~ (3.4+-1.1) x 1000 km/s within a ~10'-diameter region centered on the cD galaxy NGC 4696. Such bulk velocities should Comptonize the Cosmic Microwave Background Radiation producing variations of intensity and temperature that can be detectable in the near future with bolometers such as BOLOCAM . In this paper we realistically estimate the expected CMBR Comptonization for the central region of Abell 3526, using ASCA and ROSAT data to constrain the S-Z parameter expectations.

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arXiv2001

Chandra Analysis of Abell 496

We present preliminary results of imaging and spectral analysis of the cluster A496 with the S3 chip on-board the Chandra satellite. We confirm the presence of a cooling flow and radial gradients in elemental abundances. The cluster's core has clear signs of substructures (sharp edges, cavities), similar to those recently found in other cooling flow clusters. The O/Fe ratio distribution indicates that the gas in the core of the cluster is significantly enriched by SN Ia ejecta.

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arXiv2001

Detection of Bulk Motions in the ICM of the Centaurus Cluster

Several recent numerical simulations of off-center cluster mergers predict that significant angular momentum with associated velocities of a few x 10^{3} km/s can be imparted to the resulting cluster. Such gas bulk velocities can be detected by the Doppler shift of X-ray spectral lines with ASCA spectrometers. Using two ASCA observations of the Centaurus cluster, we produced a velocity map for the gas in the cluster's central regions. We also detected radial and azimuthal gradients in temperature and metal abundance distributions, which seem to be associated with the infalling sub-group centered at NGC 4709 (Cen 45). More importantly, we found a significant (>99.8% confidence level) velocity gradient along a line near-perpendicular to the direction of the incoming sub-group and with a maximum velocity difference of ~3.4+-1.1 x 10^{3} km/s. It is unlikely (P < 0.002) that the observed velocity gradient is generated by gain fluctuations across the detectors. While the observed azimuthal temperature and abundance variations can be attributed to the interaction with Cen 45, we argue that the intracluster gas velocity gradient is more likely due to a previous off-center merging event in the main body of the Centaurus cluster.

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arXiv2000

Detection of Intracluster Gas Bulk Velocities in the Perseus and Centaurus Clusters

We report the results of spatially resolved X-ray spectroscopy of 8 different ASCA pointings distributed symmetrically around the center of the Perseus cluster. The outer region of the intracluster gas is roughly isothermal, with temperature ~6-7 keV, and metal abundance ~ 0.3 Solar. Spectral analysis of the central pointing is consistent with the presence of a cooling flow and a central metal abundance gradient. A significant velocity gradient is found along an axis highly discrepant with the major axis of the X-ray elongation. The radial velocity difference is found to be greater than 1000 km/sMpc at the 90% confidence level. Simultaneous fittings of GIS 2 & 3 indicate that two symmetrically opposed regions have different radial velocities at the 95% confidence level and the F-test rules out constant velocities for these regions at the 99% level. Intrinsic short and long term variations of gain are unlikely (P < 0.03) to explain the velocity discrepancies. We also report the preliminary results of a similar analysis carried out for the Centaurus cluster, where long-exposure SIS data is available. We also find a significant velocity gradient near the central regions (3'-8') of Centaurus. If attributed to bulk rotation the correspondent circular velocity is ~1500+-150km/s (at 90% confidence). The line of maximum velocity gradient in Centaurus is near-perpendicular to the infalling galaxy group associated with NGC 4709.

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arXiv2000

Central Elemental Abundance Ratios in the Perseus Cluster: Resonant Scattering or SN Ia Enrichment?

We have determined elemental abundance ratios in the core of the Perseus cluster for several elements. These ratios indicate a central dominance of SN Ia ejecta similar to that found for A496, A2199 and A3571 (Dupke & White 2000). Simultaneous analysis of ASCA spectra from SIS1, GIS 2&3 shows that the ratio of Ni to Fe abundances is ~ (3.4 +- 1.1) times Solar within the central 4'. This ratio is consistent with (and more precise than) that observed in other clusters whose central regions are dominated by SN Ia ejecta. Such a large Ni over-abundance is predicted by "Convective Deflagration" explosion models for SN Ia such as "W7" but is inconsistent with delayed detonation models. We note that with current instrumentation the NiK(alpha) line is confused with FeK(beta) and that the Ni over-abundance we observe has been interpreted by others as an anomalously large ratio of FeK(beta) to FeK(alpha) caused by resonant scattering in the FeK(alpha) line. We argue that a central enhancement of SN Ia ejecta and hence a high ratio of Ni to Fe is naturally explained by scenarios that include the generation of chemical gradients by suppressed SN Ia winds or ram-pressure stripping of cluster galaxies. It is not necessary to suppose that the intracluster gas is optically thick to resonant scattering of the FeK(alpha) line.

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arXiv2000

Velocity Gradients in the Intracluster Gas of the Perseus Cluster

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arXiv2000

Metallicity Gradients in the Intracluster Gas of Abell 496

Analysis of spatially resolved ASCA spectra of the intracluster gas in Abell 496 confirms there are mild metal abundance enhancements near the center, as previously found by White et al. (1994) in a joint analysis of Ginga LAC and Einstein SSS spectra. Simultaneous analysis of spectra from all ASCA instruments (SIS + GIS) shows that the iron abundance is 0.36 +- 0.03 solar 3-12' from the center of the cluster and rises ~50% to 0.53 +- 0.04 solar within the central 2'. The F-test shows that this abundance gradient is significant at the >99.99% level. Nickel and sulfur abundances are also centrally enhanced. We use a variety of elemental abundance ratios to assess the relative contribution of SN Ia and SN II to the metal enrichment of the intracluster gas. We find spatial gradients in several abundance ratios, indicating that the fraction of iron from SN Ia increases toward the cluster center, with SN Ia accounting for ~50% of the iron mass 3-12' from the center and ~70% within 2'. The increased proportion of SN Ia ejecta at the center is such that the central iron abundance enhancement can be attributed wholly to SN Ia; we find no significant gradient in SN II ejecta. These spatial gradients in the proportion of SN Ia/II ejecta imply that the dominant metal enrichment mechanism near the center is different than in the outer parts of the cluster. We show that the central abundance enhancement is unlikely to be due to ram pressure stripping of gas from cluster galaxies, or to secularly accumulated stellar mass loss within the central cD. We suggest that the additional SN Ia ejecta near the center is the vestige of a secondary SN Ia-driven wind from the cD (following a more energetic protogalactic SN II-driven wind phase), which was partially smothered in the cD due to its location at the cluster center.

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arXiv2000

Constraining SN Ia Models Using X-ray Spectra of Clusters of Galaxies

We present constraints on theoretical models of Type Ia SNe using spatially resolved ASCA X-ray spectroscopy of four galaxy clusters: Abell 496, Abell 2199, Abell 3571 & Perseus. All four clusters have central Fe abundance enhancements and an ensemble of abundance ratios are used to show that most of the Fe in the central regions of the clusters comes from SN Ia. At the center of each cluster, simultaneous analysis of spectra from all ASCA instruments shows that the Ni to Fe abundance ratio (normalized by the solar ratio) is ~ 4. We use the Ni/Fe ratio as a discriminator between SN Ia explosion models: the Ni/Fe ratio of ejecta from the "Convective Deflagration" model W7 is consistent with the observations, while those of "delayed detonation" models are not consistent at the 90% confidence level.

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