arXiv subjects

Norbert Werner

Publications and source records attributed to Norbert Werner.

89 records · Page 5Linked to original sources

arXiv2017

The Metallicity of the Intracluster Medium Over Cosmic Time: Further Evidence for Early Enrichment

We use Chandra X-ray data to measure the metallicity of the intracluster medium (ICM) in 245 massive galaxy clusters selected from X-ray and Sunyaev-Zel'dovich (SZ) effect surveys, spanning redshifts $0<z<1.2$. Metallicities were measured in three different radial ranges, spanning cluster cores through their outskirts. We explore trends in these measurements as a function of cluster redshift, temperature, and surface brightness "peakiness" (a proxy for gas cooling efficiency in cluster centers). The data at large radii (0.5--1 $r_{500}$) are consistent with a constant metallicity, while at intermediate radii (0.1-0.5 $r_{500}$) we see a late-time increase in enrichment, consistent with the expected production and mixing of metals in cluster cores. In cluster centers, there are strong trends of metallicity with temperature and peakiness, reflecting enhanced metal production in the lowest-entropy gas. Within the cool-core/sharply peaked cluster population, there is a large intrinsic scatter in central metallicity and no overall evolution, indicating significant astrophysical variations in the efficiency of enrichment. The central metallicity in clusters with flat surface brightness profiles is lower, with a smaller intrinsic scatter, but increases towards lower redshifts. Our results are consistent with other recent measurements of ICM metallicity as a function of redshift. They reinforce the picture implied by observations of uniform metal distributions in the outskirts of nearby clusters, in which most of the enrichment of the ICM takes place before cluster formation, with significant later enrichment taking place only in cluster centers, as the stellar populations of the central galaxies evolve.

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arXiv2017

Large Synoptic Survey Telescope Galaxies Science Roadmap

The Large Synoptic Survey Telescope (LSST) will enable revolutionary studies of galaxies, dark matter, and black holes over cosmic time. The LSST Galaxies Science Collaboration has identified a host of preparatory research tasks required to leverage fully the LSST dataset for extragalactic science beyond the study of dark energy. This Galaxies Science Roadmap provides a brief introduction to critical extragalactic science to be conducted ahead of LSST operations, and a detailed list of preparatory science tasks including the motivation, activities, and deliverables associated with each. The Galaxies Science Roadmap will serve as a guiding document for researchers interested in conducting extragalactic science in anticipation of the forthcoming LSST era.

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arXiv2017

Radial metal abundance profiles in the intra-cluster medium of cool-core galaxy clusters, groups, and ellipticals

The hot intra-cluster medium (ICM) permeating galaxy clusters and groups is not pristine, as it is continuously enriched by metals synthesised in Type Ia (SNIa) and core-collapse (SNcc) supernovae since the major epoch of star formation (z ~ 2-3). The cluster/group enrichment history and the mechanisms responsible for releasing and mixing the metals can be probed via the radial distribution of SNIa and SNcc products within the ICM. In this paper, we use deep XMM-Newton/EPIC observations from a sample of 44 nearby cool-core galaxy clusters, groups, and ellipticals (CHEERS) to constrain the average radial O, Mg, Si, S, Ar, Ca, Fe, and Ni abundance profiles. The radial distributions of all these elements, averaged over a large sample for the first time, represent the best constrained profiles available currently. We find an overall decrease of the Fe abundance with radius out to ~$0.9 r_{500}$ and ~$0.6 r_{500}$ for clusters and groups, respectively, in good agreement with predictions from the most recent hydrodynamical simulations. The average radial profiles of all the other elements (X) are also centrally peaked and, when rescaled to their average central X/Fe ratios, follow well the Fe profile out to at least ~0.5$r_{500}$. Using two sets of SNIa and SNcc yield models reproducing well the X/Fe abundance pattern in the core, we find that, as predicted by recent simulations, the relative contribution of SNIa (SNcc) to the total ICM enrichment is consistent with being uniform at all radii, both for clusters and groups. In addition to implying that the central metal peak is balanced between SNIa and SNcc, our results suggest that the enriching SNIa and SNcc products must share the same origin, and that the delay between the bulk of the SNIa and SNcc explosions must be shorter than the timescale necessary to diffuse out the metals.

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arXiv2016

Origin of central abundances in the hot intra-cluster medium - I. Individual and average abundance ratios from XMM-Newton EPIC

The hot intra-cluster medium (ICM) is rich in metals, which are synthesized by supernovae (SNe) explosions and accumulate over time into the deep gravitational potential well of clusters of galaxies. Since most of the elements visible in X-rays are formed by type Ia (SNIa) and/or core-collapse (SNcc) supernovae, measuring their abundances gives us direct information on the nucleosynthesis products of billions of SNe since the epoch of the star formation peak (z ~ 2-3). In this study, we use the EPIC and RGS instruments onboard XMM-Newton to measure the abundances of 9 elements (O, Ne, Mg, Si, S, Ar, Ca, Fe and Ni) from a sample of 44 nearby cool-core galaxy clusters, groups, and elliptical galaxies. We find that the Fe abundance shows a large scatter (~20-40%) over the sample, within 0.2$r_{500}$ and, especially, 0.05$r_{500}$. Unlike the absolute Fe abundance, the abundance ratios (X/Fe) are quite uniform over the considered temperature range (~0.6-8 keV), and with a limited scatter. In addition to a unprecedented treatment of systematic uncertainties, we provide the most accurate abundance ratios measured so far in the ICM, including Cr/Fe and Mn/Fe that we firmly detect (>4σ with MOS and pn independently). We find that Cr/Fe, Mn/Fe and Ni/Fe, differ significantly from the proto-solar values. However, the large uncertainties in the proto-solar abundances prevent us from making a robust comparison between the local and the intra-cluster chemical enrichments. We also note that, interestingly, and despite the large net exposure time (~4.5 Ms) of our dataset, no line emission feature is seen around ~3.5 keV.

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arXiv2016

Origin of central abundances in the hot intra-cluster medium - II. Chemical enrichment and supernova yield models

The hot intra-cluster medium (ICM) is rich in metals, which are synthesised by supernovae (SNe) and accumulate over time into the deep gravitational potential well of clusters of galaxies. Since most of the elements visible in X-rays are formed by type Ia (SNIa) and/or core-collapse (SNcc) supernovae, measuring their abundances gives us direct information on the nucleosynthesis products of billions of SNe since the epoch of the star formation peak (z~2-3). In this study, we compare the most accurate average X/Fe abundance ratios (compiled in a previous work from XMM-Newton EPIC and RGS observations of 44 galaxy clusters, groups, and ellipticals), representative of the chemical enrichment in the nearby ICM, to various SNIa and SNcc nucleosynthesis models found in the literature. The use of a SNcc model combined to any favoured standard SNIa model (deflagration or delayed-detonation) fails to reproduce our abundance pattern. In particular, the Ca/Fe and Ni/Fe ratios are significantly underestimated by the models. We show that the Ca/Fe ratio can be reproduced better, either by taking a SNIa delayed-detonation model that matches the observations of the Tycho supernova remnant, or by adding a contribution from the Ca-rich gap transient SNe, whose material should easily mix into the hot ICM. On the other hand, the Ni/Fe ratio can be reproduced better by assuming that both deflagration and delayed-detonation SNIa contribute in similar proportions to the ICM enrichment. In either case, the fraction of SNIa over the total number of SNe (SNIa+SNcc) contributing to the ICM enrichment ranges within 29-45%. This fraction is found to be systematically higher than the corresponding SNIa/SNe fraction contributing to the enrichment of the proto-solar environnement (15-25%). We also discuss and quantify two useful constraints on both SNIa and SNcc that can be inferred from the ICM abundance ratios.

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arXiv2016

Insights into the location and dynamics of the coolest X-ray emitting gas in clusters of galaxies

We extend our previous study of the cool gas responsible for the emission of OVII X-ray lines in the cores of clusters and groups of galaxies. This is the coolest X-ray emitting phase and connects the 10,000 K H α emitting gas to the million degree phase, providing a useful tool to understand cooling in these objects. We study the location of the O VII gas and its connection to the intermediate Fe XVII and hotter O VIII phases. We use high-resolution X-ray grating spectra of elliptical galaxies with strong Fe XVII line emission and detect O VII in 11 of 24 objects. Comparing the O VII detection level and resonant scattering, which is sensitive to turbulence and temperature, suggests that OVII is preferably found in cooler objects, where the FeXVII resonant line is suppressed due to resonant scattering, indicating subsonic turbulence. Although a larger sample of sources and further observations is needed to distinguish between effects from temperature and turbulence, our results are consistent with cooling being suppressed at high turbulence as predicted by models of AGN feedback, gas sloshing and galactic mergers. In some objects the OVII resonant-to-forbidden line ratio is decreased by either resonant scattering or charge-exchange boosting the forbidden line, as we show for NGC 4636. Charge-exchange indicates interaction between neutral and ionized gas phases. The Perseus cluster also shows a high Fe XVII forbidden-to- resonance line ratio, which can be explained with resonant scattering by low-turbulence cool gas in the line-of-sight.

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arXiv2015

Abundance and temperature distributions in the hot intra-cluster gas of Abell 4059

Using the EPIC and RGS data from a deep (~200 ks) XMM-Newton observation, we investigate the temperature structure (kT and sigma_T ) and the abundances of 9 elements (O, Ne, Mg, Si, S, Ar, Ca, Fe and Ni) of the intra-cluster medium (ICM) in the nearby (z=0.046) cool-core galaxy cluster Abell 4059. Next to a deep analysis of the cluster core, a careful modelling of the EPIC background allows us to build radial profiles up to 12' (~650 kpc) from the core. Probably because of projection effects, the temperature ICM is found not to be in single phase, even in the outer parts of the cluster. The abundances of Ne, Si, S, Ar, Ca and Fe, but also O are peaked towards the core. Fe and O are still significantly detected in the outermost annuli; suggesting that the enrichment by both type Ia and core-collapse SNe started in the early stages of the cluster formation. However, the particularly high Ca/Fe ratio that we find in the core is not well reproduced by the standard SNe yield models. Finally, 2-D maps of temperature and Fe abundance are presented and confirm the existence of a denser, colder, and Fe-rich ridge southwest of the core, previously observed by Chandra. The origin of this asymmetry in the hot gas of the cluster core is still unclear, but might be explained by a past intense ram-pressure stripping event near the central cD galaxy.

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arXiv2015

Chemical Enrichment RGS cluster sample (CHEERS): Constraints on turbulence

Feedback from AGN, galactic mergers, and sloshing are thought to give rise to turbulence, which may prevent cooling in clusters. We aim to measure the turbulence in clusters of galaxies and compare the measurements to some of their structural and evolutionary properties. It is possible to measure the turbulence of the hot gas in clusters by estimating the velocity widths of their X-ray emission lines. The RGS Spectrometers aboard XMM-Newton are currently the only instruments provided with sufficient effective area and spectral resolution in this energy domain. We benefited from excellent 1.6Ms new data provided by the CHEERS project. The new observations improve the quality of the archival data and allow us to place constraints for some clusters, which were not accessible in previous work. One-half of the sample shows upper limits on turbulence less than 500km/s. For several sources, our data are consistent with relatively strong turbulence with upper limits on the velocity widths that are larger than 1000km/s. The NGC507 group of galaxies shows transonic velocities, which are most likely associated with the merging phenomena and bulk motions occurring in this object. Where both low- and high-ionization emission lines have good enough statistics, we find larger upper limits for the hot gas, which is partly due to the different spatial extents of the hot and cool gas phases. Our upper limits are larger than the Mach numbers required to balance cooling, suggesting that dissipation of turbulence may prevent cooling, although other heating processes could be dominant. The systematics associated with the spatial profile of the source continuum make this technique very challenging, though still powerful, for current instruments. The ASTRO-H and Athena missions will revolutionize the velocity estimates and discriminate between different spatial regions and temperature phases.

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arXiv2014

Discovery of O VII line emitting gas in elliptical galaxies

In the cores of ellipticals, clusters, and groups of galaxies, the gas has a cooling time shorter than 1 Gyr. It is possible to probe cooling flows through the detection of Fe XVII and O VII emission lines, but so far O VII has not been detected in any individual object. The Reflection Grating Spectrometers (RGS) aboard XMM-Newton are currently the only instruments able to detect O VII in extended objects such as elliptical galaxies and galaxy clusters. We searched for evidence of O VII through all the archival RGS observations of galaxy clusters, groups of galaxies, and elliptical galaxies focusing on those with core temperatures below 1 keV. We have discovered O VII resonance (21.6A) and forbidden (22.1A) lines for the first time in the spectra of individual objects. O VII was detected at a level higher than three sigma in six elliptical galaxies: M 84, M 86, M 89, NGC 1316, NGC 4636, and NGC 5846. M 84, M 86 and M 89 are members of the Virgo Cluster, the others are central dominant galaxies of groups, and most them show evidence of O VI in UV spectra. We detect no significant trend between the Fe XVII and O VII resonance-to-forbidden line ratios, possibly because of the limited statistics. The observed line ratios = (0.52+/-0.02, 0.9+/-0.2) indicate that the spectra of all these ellipticals are affected by resonance scattering, suggesting low turbulence. Deeper exposures will help to understand whether the Fe XVII and O VII lines are both produced by the same cooling gas or by multiphase gas. Our O VII luminosities correspond to 0.2-2 Msun/yr, which agree with the predictions for ellipticals. Such weak cooling rates would not be detected in clusters because their spectra are dominated by the emission of hotter gas, and owing to their greater distance, the expected O VII line flux would be undetectable.

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arXiv2013

A uniform metal distribution in the intergalactic medium of the Perseus cluster of galaxies

Most of the metals (elements heavier than helium) ever produced by stars in the member galaxies of galaxy clusters currently reside within the hot, X-ray emitting intra-cluster gas. Observations of X-ray line emission from this intergalactic medium have suggested a relatively small cluster-to-cluster scatter outside of the cluster centers and enrichment with iron out to large radii, leading to the idea that the metal enrichment occurred early in the history of the Universe. Models with early enrichment predict a uniform metal distribution at large radii in clusters, while late-time enrichment, favored by some previous studies, is expected to introduce significant spatial variations of the metallicity. To discriminate clearly between these competing models, it is essential to test for potential inhomogeneities by measuring the abundances out to large radii along multiple directions in clusters, which has not hitherto been done. Here we report a remarkably uniform measured iron abundance, as a function of radius and azimuth, that is statistically consistent with a constant value of 0.306+/-0.012 Solar out to the edge of the nearby Perseus Cluster. This homogeneous distribution requires that most of the metal enrichment of the intergalactic medium occurred before the cluster formed, likely over 10 billion years ago, during the period of maximal star formation and black hole activity.

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arXiv2012

A filament of dark matter between two clusters of galaxies

It is a firm prediction of the concordance Cold Dark Matter (CDM) cosmological model that galaxy clusters live at the intersection of large-scale structure filaments. The thread-like structure of this "cosmic web" has been traced by galaxy redshift surveys for decades. More recently the Warm-Hot Intergalactic Medium (WHIM) residing in low redshift filaments has been observed in emission and absorption. However, a reliable direct detection of the underlying Dark Matter skeleton, which should contain more than half of all matter, remained elusive, as earlier candidates for such detections were either falsified or suffered from low signal-to-noise ratios and unphysical misalignements of dark and luminous matter. Here we report the detection of a dark matter filament connecting the two main components of the Abell 222/223 supercluster system from its weak gravitational lensing signal, both in a non-parametric mass reconstruction and in parametric model fits. This filament is coincident with an overdensity of galaxies and diffuse, soft X-ray emission and contributes mass comparable to that of an additional galaxy cluster to the total mass of the supercluster. Combined with X-ray observations, we place an upper limit of 0.09 on the hot gas fraction, the mass of X-ray emitting gas divided by the total mass, in the filament.

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arXiv2011

Discovery of the first giant double radio relic in a galaxy cluster found in the PLANCK Sunyaev-Zel'dovich cluster survey: PLCK G287.0+32.9

We report the discovery of large scale diffuse non-thermal radio emission in PLCK G287.0+32.9, an exceptionally hot (T ~ 13 keV), massive and luminous galaxy cluster, strongly detected by the PLANCK satellite in a recent, all-sky blind search for new clusters through Sunyaev-Zel'dovich effect. Giant Metrewave Radio telescope 150 MHz and Very Large Array 1.4 GHz radio data reveal a pair of giant (>1 Mpc) "arc" shaped peripheral radio-relics (signatures of shock waves) of unprecedented scale (linear separation ~4.4 Mpc at redshift 0.39), located at distances from the cluster center which are about 0.7 and 1.3 of the cluster's virial radius. Another possible giant relic and a radio-halo is detected closer to the cluster center. These relic sources are unique "signposts" of extremely energetic mergers and shocks (both ongoing and past), that are assembling and heating up this very massive galaxy cluster. They are also a probe of the filamentary cosmic-web structure beyond the cluster virial radius. Optical imaging with the IUCAA 2 meter telescope and XMM-Newton X-ray data confirm a very rich galaxy cluster with a morphologically disturbed core region, suggesting a dynamically perturbed merging system.

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arXiv2011

Baryons at the Edge of the X-ray Brightest Galaxy Cluster

Studies of the diffuse X-ray emitting gas in galaxy clusters have provided powerful constraints on cosmological parameters and insights into plasma astrophysics. However, measurements of the faint cluster outskirts have become possible only recently. Using data from the Suzaku X-ray telescope, we determined an accurate, spatially resolved census of the gas, metals, and dark matter out to the edge of the Perseus Cluster. Contrary to previous results, our measurements of the cluster baryon fraction are consistent with the expected universal value at half of the virial radius. The apparent baryon fraction exceeds the cosmic mean at larger radii, suggesting a clumpy distribution of the gas, which is important for understanding the ongoing growth of clusters from the surrounding cosmic web.

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arXiv2010

Extreme AGN Feedback and Cool Core Destruction in the X-ray Luminous Galaxy Cluster MACS J1931.8-2634

We report on a deep, multiwavelength study of the galaxy cluster MACS J1931.8-2634 using Chandra X-ray, Subaru optical, and VLA 1.4 GHz radio data. This cluster (z=0.352) harbors one of the most X-ray luminous cool cores yet discovered, with an equivalent mass cooling rate within the central 50 kpc is approximately 700 solar masses/yr. Unique features observed in the central core of MACSJ1931.8-2634 hint to a wealth of past activity that has greatly disrupted the original cool core. We observe a spiral of relatively cool, dense, X-ray emitting gas connected to the cool core, as well as highly elongated intracluster light (ICL) surrounding the cD galaxy. Extended radio emission is observed surrounding the central AGN, elongated in the east-west direction, spatially coincident with X-ray cavities. The power input required to inflate these `bubbles' is estimated from both the X-ray and radio emission to reside between 4 and 14e45 erg/s, putting it among the most powerful jets ever observed. This combination of a powerful AGN outburst and bulk motion of the cool core have resulted in two X-ray bright ridges to form to the north and south of the central AGN at a distance of approximately 25 kpc. The northern ridge has spectral characteristics typical of cool cores and is consistent with being a remnant of the cool core after it was disrupted by the AGN and bulk motions. It is also the site of H-alpha filaments and young stars. The X-ray spectroscopic cooling rate associated with this ridge is approximately 165 solar masses/yr, which agrees with the estimate of the star formation rate from broad-band optical imaging (170 solar masses/yr). MACS J1931.8-2634 appears to harbor one of most profoundly disrupted low entropy cores observed in a cluster, and offers new insights into the survivability of cool cores in the context of hierarchical structure formation.

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arXiv2009

X-ray Spectroscopy of Galaxy Clusters

Galaxy clusters, the largest clearly defined objects in our Universe, are ideal laboratories to study in detail the cosmic evolution of the intergalactic intracluster medium (ICM) and the cluster galaxy population. For the ICM, which is heated to X-ray radiating temperatures, X-ray spectroscopy is the most important tool to obtain insight into the structure and astrophysics of galaxy clusters. In this review we recall the basic principles of the interpretation of X-ray spectra from a hot, tenuous plasma and we illustrate the wide range of scientific applications of X-ray spectroscopy. The determination of galaxy cluster masses, important for cosmology, rest crucially on a precise spectroscopic ICM temperature determination. The study of the thermal structure of the ICM provides a very interesting fossil record of the energy release during galaxy formation and evolution. The temperature and pressure distribution of the ICM gives us important insight into the process of galaxy cluster merging and the dissipation of the merger energy in form of turbulent motion. Cooling cores in the centers are interesting laboratories to investigate the interplay between gas cooling, star- and black hole formation and energy feedback, which is diagnosed by means of X-ray spectroscopy. The element abundances deduced from X-ray spectra of the ICM provide a cosmic history record of the contribution of different supernovae to the nucleosynthesis of heavy elements and their spatial distribution partly reflects important transport processes in the ICM. Some discussion of plasma diagnostics for conditions out of thermal equilibrium and an outlook on the future prospects of X-ray spectroscopic cluster studies complete our review.

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arXiv2009

A diffuse bubble-like radio-halo source MRC 0116+111: imprint of AGN feedback in a low-mass cluster of galaxies

We present detailed observations of MRC 0116+111, revealing a luminous, mini radio-halo of ~240 kpc diameter located at the centre of a cluster of galaxies at redshift z = 0.131. Our optical and multi-wavelength GMRT and VLA radio observations reveal a highly unusual radio source: showing a pair of giant (~100 kpc diameter) bubble-like diffuse structures, that are about three times larger than the analogous extended radio emission observed in M87 - the dominant central radio galaxy in the Virgo Cluster. However, in MRC 0116+111 we do not detect any ongoing Active Galactic Nucleus (AGN) activity, such as a compact core or active radio jets feeding the plasma bubbles. The radio emitting relativistic particles and magnetic fields were probably seeded in the past by a pair of radio-jets originating in the AGN of the central cD galaxy. The extremely steep high-frequency radio spectrum of the north-western bubble, located ~100 kpc from cluster centre, indicates radiation losses, possibly because having detached, it is rising buoyantly and moving away into the putative hot intra-cluster medium. The other bubble, closer to the cluster centre, shows signs of ongoing particle re-acceleration. We estimate that the radio jets which inflated these two bubbles might have also fed enough energy into the intra-cluster medium to create an enormous system of cavities and shock fronts, and to drive a massive outflow from the AGN, which could counter-balance and even quench a cooling flow. Therefore, this source presents an excellent opportunity to understand the energetics and the dynamical evolution of radio-jet inflated plasma bubbles in the hot cluster atmosphere.

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arXiv2009

Diffuse bubble-like radio-halo emission in MRC 0116+111: Imprint of AGN feedback in a distant cluster of galaxies

We report the discovery of a luminous, mini radio halo of ~240 kpc dimension at the center of a distant cluster of galaxies at redshift z = 0.131. Our optical and multi-wavelength GMRT and VLA observations reveal a highly unusual structure showing a twin bubble-like diffuse radio halo surrounding a cluster of bright elliptical galaxies; very similar to the large-scale radio structure of M87, the dominant galaxy in Virgo cluster. It presents an excellent opportunity to understand the energetics and the dynamical evolution of such radio jet inflated plasma bubbles in the hot cluster atmosphere.

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