arXiv subjects

Sabrina De Grandi

Publications and source records attributed to Sabrina De Grandi.

At least 19 recordsLinked to original sources

arXiv2026

The Advanced X-ray Imaging Satellite (AXIS) Community Science Book

The AXIS Community Science Book represents the collective effort of 592 scientists worldwide to define the transformative science enabled by the Advanced X-ray Imaging Satellite (AXIS), a next-generation X-ray mission selected by NASA's Astrophysics Probe Program for Phase A study. AXIS will advance the legacy of high-angular-resolution X-ray astronomy with ~1.5'' imaging over a wide 24' field of view and an order of magnitude greater collecting area than Chandra in the 0.3-12 keV band. Combining sharp imaging, high throughput, and rapid response capabilities, AXIS will open new windows on virtually every aspect of modern astrophysics, exploring the birth and growth of supermassive black holes, the feedback processes that shape galaxies, the life cycles of stars and exoplanet environments, and the nature of compact stellar remnants, supernova remnants, and explosive transients. This book compiles 138 community-contributed science cases developed by five Science Working Groups focused on AGN and supermassive black holes, galaxy evolution and feedback, compact objects and supernova remnants, stellar physics and exoplanets, and time-domain and multi-messenger astrophysics. Together, these studies establish the scientific foundation for next-generation X-ray exploration in the 2030s and highlight strong synergies with facilities of the 2030s, such as JWST, Roman, Rubin/LSST, SKA, ALMA, ngVLA, and next-generation gravitational-wave and neutrino networks.

astro-ph.HE↗

arXiv2024

CHEX-MATE: CLUster Multi-Probes in Three Dimensions (CLUMP-3D), I. Gas Analysis Method using X-ray and Sunyaev-Zel'dovich Effect Data

Galaxy clusters are the products of structure formation through myriad physical processes that affect their growth and evolution throughout cosmic history. As a result, the matter distribution within galaxy clusters, or their shape, is influenced by cosmology and astrophysical processes, in particular the accretion of new material due to gravity. We introduce an analysis method to investigate the 3D triaxial shapes of galaxy clusters from the Cluster HEritage project with XMM-Newton -- Mass Assembly and Thermodynamics at the Endpoint of structure formation (CHEX-MATE). In this work, the first paper of a CHEX-MATE triaxial analysis series, we focus on utilizing X-ray data from XMM and Sunyaev-Zel'dovich (SZ) effect maps from Planck and ACT to obtain a three dimensional triaxial description of the intracluster medium (ICM) gas. We present the forward modeling formalism of our technique, which projects a triaxial ellipsoidal model for the gas density and pressure to compare directly with the observed two dimensional distributions in X-rays and the SZ effect. A Markov chain Monte Carlo is used to estimate the posterior distributions of the model parameters. Using mock X-ray and SZ observations of a smooth model, we demonstrate that the method can reliably recover the true parameter values. In addition, we apply the analysis to reconstruct the gas shape from the observed data of one CHEX-MATE galaxy cluster, Abell 1689, to illustrate the technique. The inferred parameters are in agreement with previous analyses for that cluster, and our results indicate that the geometrical properties, including the axial ratios of the ICM distribution, are constrained to within a few percent. With much better precision than previous studies, we thus further establish that Abell 1689 is significantly elongated along the line of sight, resulting in its exceptional gravitational lensing properties.

astro-ph.CO↗

arXiv2020

Iron in X-COP: tracing enrichment in cluster outskirts with high accuracy abundance profiles

We present the first metal abundance profiles for a representative sample of massive clusters. Our measures extend to $R_{500}$ and are corrected for a systematic error plaguing previous outskirt estimates. Our profiles flatten out at large radii, admittedly not a new result, however the radial range and representative nature of our sample extends its import well beyond previous findings. We find no evidence of segregation between cool-core and non-cool-core systems beyond $\sim 0.3 R_{500}$, implying that, as was found for thermodynamic properties (Ghirardini et al, 2019), the physical state of the core does not affect global cluster properties. Our mean abundance within $R_{500}$ shows a very modest scatter, $< $15%, suggesting the enrichment process must be quite similar in all these massive systems. This is a new finding and has significant implications on feedback processes. Together with results from thermodynamic properties presented in a previous X-COP paper, it affords a coherent picture where feedback effects do not vary significantly from one system to another. By combing ICM with stellar measurements we have found the amount of Fe diffused in the ICM to be about ten times higher than that locked in stars. Although our estimates suggest, with some strength, that the measured iron mass in clusters is well in excess of the predicted one, systematic errors prevent us from making a definitive statement. Further advancements will only be possible when systematic uncertainties, principally those associated to stellar masses, both within and beyond $R_{500}$, can be reduced.

astro-ph.CO↗

arXiv2020

The Chemical Evolution of Galaxy Clusters: Dissecting the Iron Mass Budget of the Intracluster Medium

We study the chemical evolution of galaxy clusters by measuring the iron mass in the ICM after dissecting the abundance profiles into different components. We use Chandra archival observations of 186 morphologically regular clusters in the redshift range [0.04, 1.07]. For each cluster we compute the iron abundance and gas density profiles. We aim at identifying in the iron distribution a central peak associated with the BCG, and an approximately constant plateau associated with early enrichment. We are able to firmly identify the two components in a significant fraction of the sample, simply relying on the fit of the abundance profile. We compute the iron mass included in the iron peak and plateau, and the gas mass-weighted iron abundance out to $r_{500}$. While the iron plateau shows no evolution, we find marginal decrease with redshift in the iron peak. We measure that the fraction of iron peak mass is typically a few percent (~1%) of the total iron mass within $r_{500}$. Therefore, since the total iron mass budget is dominated by the plateau, we find consistently that the global gas mass-weighted iron abundance does not evolve significantly. We are also able to reproduce past claims of evolution in the global iron abundance, which turn out to be due to the use of cluster samples with different selection methods combined to the use of emission-weighted instead of gas mass-weighted abundance values. Finally, while the intrinsic scatter in the iron plateau mass is consistent with zero, the iron peak mass exhibits a large scatter, in line with the fact that the peak is produced after the virialization of the halo and depends on the formation of the hosting cool core and the associated feedback processes. We conclude that only a spatially-resolved approach can resolve the issue of the ICM iron evolution, reconciling the contradictory results obtained in the last ten years.

astro-ph.GA↗

arXiv2018

Spatial Distribution of Metals in the ICM: Evolution of the Iron Excess in Relaxed Galaxy Clusters

We investigate the spatial distribution of iron in the intra-cluster medium in a selected sample of 41 relaxed clusters in the redshift range $0.05 < z < 1.03$ using {\sl Chandra} archival data. We compute the azimuthally-averaged, deprojected $Z_{\rm Fe}$ profile of each cluster out to $\sim 0.4r_{500}$, and identify a peak in the distribution of iron followed by a flatter distribution at larger radii. Due to the steep gradient both in gas density and abundance, we find that the emission-weighted iron abundance within $0.2r_{500}$, which entirely includes the iron peak in most of the cases, is on average $\sim$25\% higher than the mass-weighted value, showing that spatially resolved analysis and accurate deprojection are key to study the evolution of iron enrichment in the very central regions of cool core clusters. We quantify the extent of the iron distribution in each cluster with a normalized scale parameter $r_{\rm Fe}$, defined as the radius where the iron abundance excess is half of its peak value. We find that $r_{\rm Fe}$ increases by a factor of $\sim 3$ from $z\sim 1$ to $z\sim 0.1$, suggesting that the spatial distribution of iron in the ICM extends with time, possibly due to the mixing with the mechanical-mode feedback from the central galaxy. We also find that the iron mass excess within $0.3r_{500}$, when normalized to the total baryonic mass within the same region, does not evolve significantly, showing that this iron mass component is already established at $z\sim 1$.

astro-ph.CO↗

arXiv2014

Metal distribution in sloshing galaxy clusters: the case of A496

We report results from a detailed study of the sloshing gas in the core of A496. We detect the low temperature/entropy spiral feature found in several cores, we also find that conduction between the gas in the spiral and the ambient medium must be suppressed by more than one order of magnitude with respect to Spitzer conductivity. Intriguingly, while the gas in the spiral features a higher metal abundance than the surrounding medium, it follows the entropy vs metal abundance relation defined by gas lying outside the spiral. The most plausible explanation for this behavior is that the low entropy metal rich plasma uplifted through the cluster atmosphere by sloshing, suffers little heating or mixing with the ambient medium. While sloshing appears to be capable of uplifting significant amounts of gas, the limited heat exchange and mixing between gas in and outside the spiral implies that this mechanism is not at all effective in: 1) permanently redistributing metals within the core region and 2) heating up the coolest and densest gas, thereby providing little or no contribution to staving of catastrophic cooling in cool cores.

astro-ph.CO↗

arXiv2014

On the Fe abundance peak formation in cool-core clusters of galaxies: hints from cluster WARPJ1415.1+3612 at z=1.03

We present a detailed study of the iron content of the core of the high-redshift cluster WARPJ1415.1+3612 (z=1.03). By comparing the central Fe mass excess observed in this system, M_Fe^exc = (1.67 +/- 0.40) x 10^9 M_sun, with those measured in local cool-core systems, we infer that the bulk of the mass excess was already in place at z=1, when the age of the Universe was about half of what it is today. Our measures point to an early and intense period of star formation most likely associated with the formation of the BCG. Indeed, in the case of the power-law delay time distribution with slope -1, which reproduces the data of WARPJ1415.1+3612 best, half of the supernovae explode within 0.4 Gyr of the formation of the BCG. Finally, while for local cool-core clusters the Fe distribution is broader than the near infrared light distribution of the BCG, in WARPJ1415.1+3612 the two distributions are consistent, indicating that the process responsible for broadening the Fe distribution in local systems has not yet started in this distant cluster.

astro-ph.GA↗

arXiv2013

Metal jumps across sloshing cold fronts: the case of A496

Cold-fronts in cool-core clusters are thought to be induced by minor mergers and to develop through a sloshing mechanism. While temperature and surface-brightness jumps have been detected and measured in many systems, a detailed characterization of the metal abundance across the discontinuity is only available for a handful of objects. Within the sloshing scenario, we expect the central cool and metal rich gas to be displaced outwards into lower abundance regions, thus generating a metal discontinuity across the front. We analyzed a long (120 ksec) XMM-Newton observation of A496 to study the metal distribution and its correlation with the cold-fronts. We find Fe discontinuities across the two main cold-fronts located ~60 kpc NNW and ~160 kpc South of the peak and a metal excess in the South direction.

astro-ph.CO↗

arXiv2010

A decline and fall in the future of Italian Astronomy?

On May 27th 2010, the Italian astronomical community learned with concern that the National Institute for Astrophysics (INAF) was going to be suppressed, and that its employees were going to be transferred to the National Research Council (CNR). It was not clear if this applied to all employees (i.e. also to researchers hired on short-term contracts), and how this was going to happen in practice. In this letter, we give a brief historical overview of INAF and present a short chronicle of the few eventful days that followed. Starting from this example, we then comment on the current situation and prospects of astronomical research in Italy.

astro-ph.IM↗

arXiv2009

The inverse iron-bias in action in Abell 2028

Recent work based on a global measurement of the ICM properties find evidence for an increase of the iron abundance in galaxy clusters with temperature around 2-4 keV. We have undertaken a study of the metal distribution in nearby clusters in this temperature range, aiming at resolving spatially the metal content of the ICM. The XMM observation of the first object of the sample, the cluster Abell 2028, reveals a complex structure of the cluster over scale of ~ 300 kpc, showing an interaction between two sub-clusters in a ``cometary'' configuration. We show that a naive one-component fit for the core of Abell 2028 returns a biased high metallicity. This is due to the inverse iron-bias, which is not related to the presence in the spectrum of both Fe-L and Fe-K emission lines but to the behavior of the fitting code in shaping the Fe-L complex of a one temperature component to adjust to the multi-temperature structure of the projected spectrum.

astro-ph.CO↗

arXiv2004

A note on Temperature Profiles of rich Clusters of Galaxies

We derive here the mean temperature profile for a sample of hot, medium distant clusters recently observed with XMM-Newton, whose profiles are available from the literature, and compare it with the mean temperature profile found from BeppoSAX data. The XMM-Newton and BeppoSAX profiles are in good agreement between 0.05 and 0.25 r_180. From 0.25 to about 0.5 r_180 both profiles decline, however the BeppoSAX profile does so much more rapidly than the XMM-Newton profile.

astro-ph↗

arXiv2003

On the Iron content in rich nearby Clusters of Galaxies

In this paper we study the iron content of a sample of 22 nearby hot clusters observed with BeppoSAX. We find that the global iron mass of clusters is tightly related to the cluster luminosity and that the relatively loose correlation between the iron mass and the cluster temperature follows from the combination of the iron mass vs. luminosity and luminosity vs. temperature correlations. The iron mass is found to scale linearly with the intracluster gas mass, implying that the global iron abundance in clusters is roughly constant. This result suggests that enrichment mechanisms operate at a similar rate in all clusters. By employing population synthesis and chemical enrichment models, we show that the iron mass associated to the abundance excess which is always found in the centre of cool core clusters can be entirely produced by the brightest cluster galaxy (BCG), which is always found at the centre of cool core clusters. The iron mass associated to the excess, the optical magnitude of the BCG and the temperature of the cluster are found to correlate with one another suggesting a link between the properties of the BCG and the hosting cluster. These observational facts lends strength to current formation theories which envisage a strong connection between the formation of the giant BCG and its hosting cluster.

astro-ph↗

arXiv2001

Temperature Profiles of Nearby Clusters of Galaxies

We report results from the analysis of 21 nearby galaxy clusters, 11 with cooling flow (CF) and 10 without cooling flow, observed with BeppoSAX. The temperature profiles of both CF and non-CF systems are characterized by an isothermal core extending out to 0.2 r_180; beyond this radius both CF and non-CF cluster profiles rapidly decline. Our results differ from those derived by other authors who either found continuously declining profiles or substantially flat profiles. Neither the CF nor the non-CF profiles can be modeled by a polytropic temperature profile, the reason being that the radius at which the profiles break is much larger than the core radius characterizing the gas density profiles. For r > 0.2 r_180, where the gas can be treated as a polytrope, the polytropic indices derived for CF and non-CF systems are respectively 1.20 +/- 0.06 and 1.46 +/- 0.06. The former index is closer to the isothermal value, 1, and the latter to the adiabatic value, 5/3. Published hydrodynamic simulations do not reproduce the peculiar shape of the observed temperature profile, probably suggesting that a fundamental ingredient is missing.

astro-ph↗

arXiv2001

The chemical enrichment of the ICM with BeppoSAX

We review observations on the chemical enrichment of the intracluster medium (ICM) performed using BeppoSAX MECS data. The picture emerging is that non-cooling flow clusters have flat metallicity profiles, whereas a strong enhancement in the abundance is found in the central regions of the cooling flow clusters. All the non-cooling flow clusters present evidence of recent merger activity suggesting that the merger events redistributes efficiently the metal content of the ICM. The observed abundance excess in the central regions of cooling flow clusters is probably due to metals ejected from the cD galaxy located in the cluster core. Cooling flow cluster have also enhanced Nickel abundances in their cores with respect to the non cooling flow clusters.

astro-ph↗

arXiv2000

Metallicity Gradients in X-ray Clusters of Galaxies

We present the projected metallicity profiles for a sample of 17 rich galaxy clusters observed by BeppoSAX. We find that the 8 non-cooling flow clusters have flat metallicity profiles. On the contrary, a strong enhancement in the abundance is found in the central regions of the cooling flow clusters. All the non-cooling flow clusters present evidence of recent merger activity suggesting that the merger events redistributes efficiently the metal content of the intracluster medium. For the cooling flow clusters with better statistics and available optical data (A85, A496, A2029 and Perseus) we have tested whether the observed abundance excess is due to metals ejected from the galaxies located in the cluster core. We find that at a resolution > 100 kpc the observed projected abundance excess profiles are consistent with originating from a deprojected metal excess distribution tracing the optical light distribution. In the one case (i.e. Perseus) with higher resolution (~ 50 kpc), we find that the observed metal abundance excess distribution is broader than the predicted one. Such a difference can be reconciled if we assume that the metals have drifted away from their parent ejecting galaxies by a few tens of kpc, or, alternatively, if we assume that the cluster light profile has become significantly more centrally peaked because of the formation process of the central dominant cluster galaxy since the last major merger occurred.

astro-ph↗

arXiv2000

The ROSAT-ESO Flux-Limited X-Ray (REFLEX) Galaxy Cluster Survey III: The Power Spectrum

We present a measure of the power spectrum on scales from 15 to 800 Mpc/h using the ROSAT-ESO Flux-Limited X-Ray(REFLEX) galaxy cluster catalogue. The REFLEX survey provides a sample of the 452 X-ray brightest southern clusters of galaxies with the nominal flux limit S=3.0 10^{-12}erg/s/cm2 for the ROSAT energy band (0.1-2.4)keV. Several tests are performed showing no significant incompletenesses of the REFLEX clusters with X-ray luminosities brighter than 10^{43}erg/s up to scales of about 800 Mpc/h. They also indicate that cosmic variance might be more important than previous studies suggest. We regard this as a warning not to draw general cosmological conclusions from cluster samples with a size smaller than REFLEX. Power spectra, P(k), of comoving cluster number densities are estimated for flux- and volume-limited subsamples. The most important result is the detection of a broad maximum within the comoving wavenumber range 0.022<k<0.030 h/Mpc. The data suggest an increase of the power spectral amplitude with X-ray luminosity. Compared to optically selected cluster samples the REFLEX P(k)is flatter for wavenumbers k<0.05 h/Mpc thus shifting the maximum of P(k) to larger scales. The smooth maximum is not consistent with the narrow peak detected at k=0.05 h/Mpc using the Abell/ACO richness $\ge 0$ data. In the range 0.02<k<0.4 h/Mpc general agreement is found between the slope of the REFLEX P(k) and those obtained with optically selected galaxies. A semi-analytic description of the biased nonlinear power spectrum in redshift space gives the best agreement for low-density Cold Dark Matter models with or without a cosmological constant.

astro-ph↗

arXiv2000

Interaction in Abell 2256: the BeppoSAX view

We present results from a spatially resolved spectral analysis of the merging cluster Abell 2256. The long integration time (135 ks) and the good spatial resolution of the MECS onboard BeppoSAX allow us to derive a new and substantially improved measurement of the temperature structure. We find that, within a central region of the cluster, where the effects of the merger are visible in the ROSAT surface brightness image, the azimuthally averaged projected temperature is remarkably flat; outside this region the projected temperature rapidly declines. The BeppoSAX data also shows clear evidence of an azimuthal temperature gradient in the 4'-8' (0.4-0.8 Mpc) radial bin, oriented in the same direction as the merger itself. Our metal abundance profile shows, for the first time, firm evidence of an abundance gradient in a rich merging cluster. Intriguingly the abundance map shows, in the SE sector, i.e. the one furthest away from the merger, a sharp factor of two drop in abundance at a radius comparable to the core radius of the cluster. A possible interpretation is that, prior to the merger event, a cooling flow had already developed in the core of the infalling subgroup, as suggested by Fabian and Daines (1991). The interaction between the substructures would have disrupted the cooling flow thereby re-heating and re-mixing the gas. As the merger in A2256 is still in a relatively early stage, the gas located on the side opposite to the merger event would still retain the low abundances associated with the intra-cluster medium (ICM) prior to the cooling flow disruption.

astro-ph↗

arXiv2000

The correlation function of X-ray galaxy clusters in the RASS1 Bright Sample

We analyse the spatial clustering properties of the RASS1 Bright Sample, an X-ray flux-limited catalogue of galaxy clusters selected from the southern part of the $ROSAT$ All-Sky Survey. The two-point correlation function $ξ(r)$ of the whole sample is well fitted (in an Einstein-de Sitter model) by the power-law $ξ=(r/r_0)^{-γ}$, with $r_0= 21.5^{+3.4}_{-4.4} h^{-1}$ Mpc and $γ=2.11^{+0.53}_{-0.56}$ (95.4 per cent confidence level with one fitting parameter). We use the RASS1 Bright Sample as a first application of a theoretical model which aims at predicting the clustering properties of X-ray clusters in flux-limited surveys for different cosmological scenarios. The model uses the theoretical and empirical relations between mass, temperature and X-ray cluster luminosity, and fully accounts for the redshift evolution of the underlying dark matter clustering and cluster bias factor. The comparison between observational results and theoretical predictions shows that the Einstein-de Sitter models display too low a correlation length, while models with a matter density parameter $Ω_{\rm 0m}=0.3$ (with or without a cosmological constant) are successful in reproducing the observed clustering. The dependence of the correlation length $r_0$ on the X-ray limiting flux and luminosity of the sample is generally consistent with the predictions of all our models. Quantitative agreement is however only reached for $Ω_{\rm 0m} = 0.3$ models. The model presented here can be reliably applied to future deeper X-ray cluster surveys: the study of their clustering properties will provide a useful complementary tool to the traditional cluster abundance analyses to constrain the cosmological parameters.

astro-ph↗