arXiv subjects

Vittorio Ghirardini

Publications and source records attributed to Vittorio Ghirardini.

24 records · Page 2Linked to original sources

arXiv2020

Characterisation of the Particle-Induced Background of XMM-Newton EPIC-pn: Short and Long Term Variability

The particle-induced background of X-ray observatories is produced by Galactic Cosmic Ray (GCR) primary protons, electrons, and He ions. Events due to direct interaction with the detector are usually removed by on board processing. The interactions of these primary particles with the detector environment produce secondary particles that mimic X-ray events from celestial sources and are much more difficult to identify. The filter wheel closed data from the XMM-Newton EPIC-pn camera in small window mode (SWM) contains both the X-ray-like background events and the events due to direct interactions with the primary particles. From this data we demonstrate that X-ray-like background events are spatially correlated with the primary particle interaction. This result can be used to further characterise and reduce the non-X-ray background in silicon-based X-ray detectors in current and future missions. We also show that spectrum and pattern fractions of secondary particle events are different from those produced by cosmic X-rays.

astro-ph.HE↗

arXiv2019

Toward the low-scatter selection of X-ray clusters: Galaxy cluster detection with eROSITA through cluster outskirts

One key ingredient in using galaxy clusters (GCs) as a precision cosmological probe in large X-ray surveys is to understand selection effects. The dependence of the X-ray emission on the square of the gas density leads to a predominant role of cool cores in the detection of GCs. The contribution of cool cores to the X-ray luminosity does not scale with GC mass and cosmology and therefore affects the use of X-ray GCs in producing cosmological constraints. One of the main science goals of the eROSITA mission is to constrain cosmology with a wide X-ray survey. We propose an eROSITA GC detection scheme that avoids the use of X-ray GC centers in detection. We calculate theoretical expectations and characterize the performance of this scheme by simulations. Performing realistic simulations of point sources (PSs) in survey mode we search for spatial scales where the extended signal is uncontaminated by the PS flux. We derive a combination of scales and thresholds, which result in a clean extended source catalog. We design the output of the GC detection which enables calibrating the core-excised luminosity using external mass measurements. We provide a way to incorporate the results of this calibration in the production of final core-excised luminosity. Similarly to other GC detection pipelines, we sample the flux - core radius detection space of our method and find many similarities with the pipeline used in the 400d survey. Both detection methods require large statistics on compact GCs, in order to reduce the contamination from PSs. The benefit of our pipeline consists in the sensitivity to the outer GC shapes, which are characterized by large core sizes with little GC to GC variation at a fixed total mass. GC detection through cluster outskirts improves the GC characterization using eROSITA survey data and is expected to yield well characterized GC catalogs having simple selection functions.

astro-ph.CO↗

arXiv2019

Pressure profiles and mass estimates using high-resolution Sunyaev-Zel'dovich effect observations of Zwicky 3146 with MUSTANG-2

The galaxy cluster Zwicky 3146 is a sloshing cool core cluster at $z=0.291$ that in X-ray imaging does not appear to exhibit significant pressure substructure in the intracluster medium (ICM). The published $M_{500}$ values range between $3.88^{+0.62}_{-0.58}$ to $22.50 \pm 7.58 \times 10^{14}$ M$_{\odot}$, where ICM-based estimates with reported errors $<20$\% suggest that we should expect to find a mass between $6.53^{+0.44}_{-0.44} \times 10^{14}$ M$_{\odot}$ (from Planck, with an $8.4σ$ detection) and $8.52^{+1.77}_{-1.47} \times 10^{14}$ M$_{\odot}$ (from ACT, with a $14σ$ detection). This broad range of masses is suggestive that there is ample room for improvement for all methods. Here, we investigate the ability to estimate the mass of Zwicky 3146 via the Sunyaev-Zel'dovich (SZ) effect with data taken at 90 GHz by MUSTANG-2 to a noise level better than $15\ μ$K at the center, and a cluster detection of $104σ$. We derive a pressure profile from our SZ data which is in excellent agreement with that derived from X-ray data. From our SZ-derived pressure profiles, we infer $M_{500}$ and $M_{2500}$ via three methods -- $Y$-$M$ scaling relations, the virial theorem, and hydrostatic equilibrium -- where we employ X-ray constraints from \emph{XMM-Newton} on the electron density profile when assuming hydrostatic equilibrium. Depending on the model and estimation method, our $M_{500}$ estimates range from $6.23 \pm 0.59$ to $10.6 \pm 0.95 \times 10^{14}$ M$_{\odot}$, where our estimate from hydrostatic equilibrium, is $8.29^{+1.93}_{-1.24}$ ($\pm 19.1$\% stat) ${}^{+0.74}_{-0.68}$ ($\pm 8.6$\% sys, calibration) $\times 10^{14}$ M$_{\odot}$. Our fiducial mass, derived from a $Y$-$M$ relation is $8.16^{+0.44}_{-0.54}$ ($\pm 5.5$\% stat) ${}^{+0.46}_{-0.43}$ ($\pm 5.5$\% sys, $Y$-$M$) ${}^{+0.59}_{-0.55}$ ($\pm 7.0$\% sys, cal.) $\times 10^{14}$ M$_{\odot}$.

astro-ph.CO↗

arXiv2019

The polytropic state of the intracluster medium in the X-COP cluster sample

In this work, we investigate the relation between the radially-resolved thermodynamic quantities of the intracluster medium in the X-COP cluster sample, aiming to assess the stratification properties of the ICM. We model the relations between radius, gas temperature, density and pressure using a combination of power-laws, also evaluating the intrinsic scatter in these relations. We show that the gas pressure is remarkably well correlated to the density, with very small scatter. Also, the temperature correlates with gas density with similar scatter. The slopes of these relations have values that show a clear transition from the inner cluster regions to the outskirts. This transition occurs at the radius $r_t = 0.19(\pm0.04)R_{500}$ and electron density $n_t = (1.91\pm0.21)\cdot10^{-3} cm^{-3} E^2 (z)$. We find that above 0.2 $R_{500}$ the radial thermodynamic profiles are accurately reproduced by a well defined and physically motivated framework, where the dark matter follows the NFW potential and the gas is represented by a polytropic equation of state. By modeling the gas temperature dependence upon both the gas density and radius, we propose a new method to reconstruct the hydrostatic mass profile based only on the quite inexpensive measurement of the gas density profile.

astro-ph.CO↗

arXiv2019

Probing Macro-Scale Gas Motions and Turbulence in Diffuse Cosmic Plasmas

Clusters of galaxies, the largest collapsed structures in the Universe, are located at the intersection of extended filaments of baryons and dark matter. Cosmological accretion onto clusters through large scale filaments adds material at cluster outskirts. Kinetic energy in the form of bulk motions and turbulence due to this accretion provides a form of pressure support against gravity, supplemental to thermal pressure. Significant amount of non-thermal pressure support could bias cluster masses derived assuming hydrostatic equilibrium, the primary proxy for cluster cosmology studies. Sensitive measurements of Doppler broadening and shift of astrophysical lines, and the relative fluctuations in thermodynamical quantities (e.g., density, pressure, and entropy) are primary diagnostic tools. Forthcoming planned and proposed X-ray (with large etendue, throughput, and high spectral resolution) and SZ observatories will provide crucial information on the assembly and virialisation processes of clusters, involving turbulent eddies cascading at various spatial scales and larger gas bulk motions in their external regions to the depth or their potential wells.

astro-ph.CO↗

arXiv2019

The Physics of Galaxy Cluster Outskirts

As the largest virialized structures in the universe, galaxy clusters continue to grow and accrete matter from the cosmic web. Due to the low gas density in the outskirts of clusters, measurements are very challenging, requiring extremely sensitive telescopes across the entire electromagnetic spectrum. Observations using X-rays, the Sunyaev-Zeldovich effect, and weak lensing and galaxy distributions from the optical band, have over the last decade helped to unravel this exciting new frontier of cluster astrophysics, where the infall and virialization of matter takes place. Here, we review the current state of the art in our observational and theoretical understanding of cluster outskirts, and discuss future prospects for exploration using newly planned and proposed observatories.

astro-ph.CO↗