427 research outputs found
Non-thermal pressure in the outskirts of Abell 2142
No full textClumping and turbulence are expected to affect the matter accreted on to the outskirts of galaxy clusters. To determine their impact on the thermodynamic properties of Abell 2142, we perform an analysis of the X-ray temperature data from XMM-Newton via our SuperModel, a state-of-the-art tool for investigating the astrophysics of the intracluster medium already tested on many individual clusters (since Cavaliere, Lapi & Fusco-Femiano 2009). Using the gas density profile corrected for clumpiness derived by Tchernin et al. (2016), we find evidence for the presence of a non-thermal pressure component required to sustain gravity in the cluster outskirts of Abell 2142, that amounts to about 30 per cent of the total pressure at the virial radius. The presence of the non-thermal component implies the gas fraction to be consistent with the universal value at the virial radius and the electron thermal pressure profile to be in good agreement with that inferred from the SZ data. Our results indicate that the presence of gas clumping and of a non-thermal pressure component are both necessary to recover the observed physical properties in the cluster outskirts. Moreover, we stress that an alternative method often exploited in the literature (included Abell 2142) to determine the temperature profile kBT = Pe/nebasing on a combination of the Sunyaev-Zel'dovich (SZ) pressure Peand of the X-ray electron density nedoes not allow us to highlight the presence of non-thermal pressure support in the cluster outskirts
SuperModel Analysis of A1246 and J255: On the Evolution of Galaxy Clusters from High to Low Entropy States
No full textWe present an analysis of high-quality X-ray data out to the virial radius for the two galaxy clusters A1246 and GMBCG J255.34805+64.23661 (J255) by means of our entropy-based SuperModel. For A1246 we find that the spherically averaged entropy profile of the intracluster medium (ICM) progressively flattens outward, and that a nonthermal pressure component amounting to ≈20% of the total is required to support hydrostatic equilibrium in the outskirts; there we also estimate a modest value C ≈ 1.6 of the ICM clumping factor. These findings agree with previous analyses on other cool-core, relaxed clusters, and lend further support to the picture by Lapi et al. that relates the entropy flattening, the development of the nonthermal pressure component, and the azimuthal variation of ICM properties to weakening boundary shocks. In this scenario clusters are born in a high-entropy state throughout, and are expected to develop on similar timescales a low-entropy state both at the center due to cooling, and in the outskirts due to weakening shocks. However, the analysis of J255 testifies how such a typical evolutionary course can be interrupted or even reversed by merging especially at intermediate redshift, as predicted by Cavaliere et al. In fact, a merger has rejuvenated the ICM of this cluster at z ≈ 0.45 by reestablishing a high-entropy state in the outskirts, while leaving intact or erasing only partially the low-entropy, cool core at the center
Massive Black Hole Mergers
No full textAt low redshift, massive black holes are found in the centers of almost all
large elliptical galaxies, and also in many lower-mass systems. Their evolution
is believed to be inextricably entangled with that of their host galaxies. On
the one hand, the galactic environment provides gas for the black holes to grow
via accretion and shine as active galactic nuclei. On the other hand, massive
black holes are expected to backreact on the galactic dynamics, by injecting
energy in their surroundings via jets or radiative feedback. Moreover, if
galaxies and dark-matter halos form hierarchically, from small systems at high
redshift coalescing into larger ones at more recent epochs, massive black holes
may also merge, potentially generating gravitational-wave signals detectable by
present and future experiments. In this Chapter, we discuss the predictions of
current astrophysical models for the mergers of massive black holes in the mHz
frequency band of the Laser Interferometer Space Antenna (LISA) and in the nHz
frequency band of pulsar-timing array experiments. We focus in particular on
the astrophysical uncertainties affecting these predictions, including the
poorly known dynamical evolution of massive black hole pairs at separations of
hundreds of parsecs; the possible formation of 'stalled' binaries at parsec
separations ('final-parsec problem'); and the effect of baryonic physics (e.g.
SN feedback) on the growth of massive black holes. We show that nHz-band
predictions are much more robust than in the mHz band, and comment on the
implications of this fact for LISA and pulsar-timing arrays.Comment: Invited review to be published in "Handbook of Gravitational Wave
Astronomy" (Eds. C. Bambi, S. Katsanevas and K. Kokkotas; Springer Singapore,
2021); 36 pages and 12 figures; minor changes from v1 (references added,
sections re-organized
Oxidation of N-Methyl-9-t-butylacridane by Iodosylbenzene Catalyzed by Tetrakis(pentafluorophenyl) Porphyrin Iron(III). A Tool to Investigate the Mechanism of the Biomimetic N-Demethylation of Aromatic Tertiary Amines.
No full textThe PhIO promoted oxidation of N-methyl-9-t-butylacridane (1) catalyzed by tetrakis(pentafluorophenyl) porphyrin iron(III) leads first to 9-t-butylacridane and then to acridine. It is suggested that 1 can represent a reliable machanistic probe to detect the intervention of radical cations in the oxidation of aromatic amines. (C) 1999 Elsevier Science Ltd. All rights reserved
The astrophysics of the intracluster plasma
No full textSince 1971 observations in X rays of several thousands of galaxy clusters have uncovered huge amounts of hot baryons filling up the deep gravitational potential wells provided by dark matter (DM) halos with masses of some 1015 M&sun; and sizes of millions of light-years. At temperatures T~108 K and with average densities of n~1 particle per liter, such baryons add up to some 1014 M&sun;. With the neutralizing electrons, they constitute the best proton-electron plasma in the Universe (whence the apt name Intra Cluster Plasma, ICP), one where the thermal energy per particle overwhelms the electron-proton Coulomb interaction by extralarge factors of order 1012. The ICP shines in X rays by thermal bremsstrahlung radiation, with powers up to several 1045erg s-1 equivalent to some 1011 solar luminosities. The first observations were soon confirmed in X rays by the detection of high excitation emission lines, and in the radio band by studies of streamlined radiogalaxies moving through the ICP. Later on they were nailed down by the first measurements in microwaves of the Sunyaev-Zel'dovich effect, i.e., the inverse Compton upscattering of cold cosmic background photons at T≈2.73 K off the hot ICP electrons at kBT~5 keV. A key physical feature of the ICP is constituted by its good local thermal equilibrium, and by its overall hydrostatic condition in the DM wells, modulated by entropy. The latter is set up in the cluster center by the initial halo collapse, and is progressively added at the outgrowing cluster boundary by standing shocks in the supersonic flow of intergalactic gas into the DM potential wells. Such physical conditions are amenable to detailed modeling. We review here these entropy-based models and discuss their outcomes and predictions concerning the ICP observables in X rays and in microwaves, as well as the underlying DM parameters. These quantitative outcomes highlight the tight relationship between the detailed ICP profiles and the cosmological evolution of the containing DM potential wells. The results also provide the simplest baseline for disentangling a number of additional and intriguing physical processes superposed to the general equilibrium. The present Report is focused on the ICP physics as driven by the two-stage evolution of the containing DM halos. We extensively discuss the basic entropy pattern established by the cluster formation and development, and cover: the central entropy erosion produced by radiative cooling that competes with the intermittent energy inputs due to active galactic nuclei and mergers; outer turbulent support linked with weakening shocks and decreasing inflow through the virial boundary, causing reduced entropy production during the late stage of DM halo evolution; the development from high to low entropy levels throughout a typical cluster; perturbations of the equilibrium up to outright disruption due to deep impacts of infalling galaxy groups or collisions with comparable companion clusters; relativistic energy distributions of electrons accelerated during such events, producing extended radio emission by synchrotron radiation and contributing non thermal pressure support for the ICP. We conclude with discussing selected contributions from cluster astrophysics to cosmology at large, and by addressing how the ICP features and processes will constitute enticing targets for observations with the ongoing Planck mission, for upcoming instrumentation like ALMA and other ground-based radio observatories, and for the next-generation of X-ray satellites from ASTRO-H to eROSITA
Recent photo- and radiation chemical studies of sulfur radical cations
No full textThis review summarizes most of the recent work on photo- and radiation chemical studies involving sulfur radical cations with the main focus on their fragmentation reactions, the photooxygenation of organic sulfides involving radical cations as reactive intermediates and sulfur radical cations in biochemical oxidation processes of amino acids and peptides. [GRAPHICS]
Cross-correlation between cosmological and astrophysical datasets: the Planck and Herschel case
No full textWe present the first measurement of the correlation between the map of the CMB lensing potential derived from the Planck nominal mission data and z% 1.5 galaxies detected by Herschel-ATLAS (H-ATLAS) survey covering about 550 deg2. We detect the cross-power spectrum with a significance of ∼ 8.5σ, ruling out the absence of correlation at 9σ. We check detection with a number of null tests. The amplitude of cross-correlation and the galaxy bias are estimated using joint analysis of the cross-power spectrum and the galaxy survey auto-spectrum, which allows to break degeneracy between these parameters. The estimated galaxy bias is consistent with previous estimates of the bias for the H-ATLAS data, while the cross-correlation amplitude is higher than expected for a ΛCDM model. The content of this work is to appear in a forthcoming pape
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