Aims.
We studied the star formation rate (SFR) in cosmological hydrodynamical simulations of galaxy (proto-)clusters in the redshift range 0 <
z
< 4, comparing them to recent observational ...studies; we also investigated the effect of varying the parameters of the star formation model on galaxy properties such as SFR, star-formation efficiency, and gas fraction.
Methods.
We analyse a set of zoom-in cosmological hydrodynamical simulations centred on 12 clusters. The simulations are carried out with the GADGET-3 Tree-PM smoothed-particle hydro-dynamics code which includes various subgrid models to treat unresolved baryonic physics, including AGN feedback.
Results.
Simulations do not reproduce the high values of SFR observed within protocluster cores, where the values of SFR are underpredicted by a factor ≳4 both at
z
∼ 2 and
z
∼ 4. The difference arises as simulations are unable to reproduce the observed starburst population and is greater at
z
∼ 2 because simulations underpredict the normalisation of the main sequence (MS) of star forming galaxies (i.e. the correlation between stellar mass and SFR) by a factor of ∼3. As the low normalisation of the MS seems to be driven by an underestimated gas fraction, it remains unclear whether numerical simulations miss starburst galaxies due to overly underpredicted gas fractions or overly low star formation efficiencies. Our results are stable against varying several parameters of the star formation subgrid model and do not depend on the details of AGN feedback.
Conclusions.
The subgrid model for star formation, introduced to reproduce the self-regulated evolution of quiescent galaxies, is not suitable to describe violent events like high-redshift starbursts. We find that this conclusion holds, independently of the parameter choice for the star formation and AGN models. The increasing number of multi-wavelength high-redshift observations will help to improve the current star formation model, which is needed to fully recover the observed star formation history of galaxy clusters.
Chemical enrichment of the Universe at all scales is related to stellar winds and explosive supernovae phenomena. Metals produced by stars and later spread throughout the intracluster medium (ICM) at ...the megaparsec scale become a fossil record of the chemical enrichment of the Universe and of the dynamical and feedback mechanisms determining their circulation. As demonstrated by the results of the soft X-ray spectrometer onboard Hitomi, high-resolution X-ray spectroscopy is the path to differentiating among the models that consider different metal-production mechanisms, predict the outcoming yields, and are a function of the nature, mass, and/or initial metallicity of their stellar progenitor. Transformational results shall be achieved through improvements in the energy resolution and effective area of X-ray observatories, allowing them to detect rarer metals (e.g. Na, Al) and constrain yet-uncertain abundances (e.g. C, Ne, Ca, Ni). The X-ray Integral Field Unit (X-IFU) instrument onboard the next-generation European X-ray observatory
Athena
is expected to deliver such breakthroughs. Starting from 100 ks of synthetic observations of 12 abundance ratios in the ICM of four simulated clusters, we demonstrate that the X-IFU will be capable of recovering the input chemical enrichment models at both low (
z
= 0.1) and high (
z
= 1) redshifts, while statistically excluding more than 99.5% of all the other tested combinations of models. By fixing the enrichment models which provide the best fit to the simulated data, we also show that the X-IFU will constrain the slope of the stellar initial mass function within ∼12%. These constraints will be key ingredients in our understanding of the chemical enrichment of the Universe and its evolution.
We present the X-ray properties and scaling relations of a large sample of clusters extracted from the Marenostrum MUltidark SImulations of galaxy Clusters (MUSIC) data set. We focus on a sub-sample ...of 179 clusters at redshift z ∼ 0.11, with 3.2 × 1014 h
−1 M < M
vir < 2 × 1015 h
−1 M, complete in mass. We employed the X-ray photon simulator phox to obtain synthetic Chandra
observations and derive observable-like global properties of the intracluster medium (ICM), as X-ray temperature (T
X) and luminosity (L
X). T
X is found to slightly underestimate the true mass-weighted temperature, although tracing fairly well the cluster total mass. We also study the effects of T
X on scaling relations with cluster intrinsic properties: total (M
500 and gas M
g,500 mass; integrated Compton parameter (Y
SZ) of the Sunyaev-Zel'dovich (SZ) thermal effect; Y
X = M
g,500 T
X. We confirm that Y
X is a very good mass proxy, with a scatter on M
500-Y
X and Y
SZ-Y
X lower than 5 per cent. The study of scaling relations among X-ray, intrinsic and SZ properties indicates that simulated MUSIC clusters reasonably resemble the self-similar prediction, especially for correlations involving T
X. The observational approach also allows for a more direct comparison with real clusters, from which we find deviations mainly due to the physical description of the ICM, affecting T
X and, particularly, L
X.
We present a novel, virtual X-ray observatory designed to obtain synthetic observations from hydro-numerical simulations, named phox. In particular, we provide a description of the code constituting ...the photon simulator and of the new approach implemented. We apply phox to simulated galaxy clusters in order to demonstrate its capabilities. In fact, X-ray observations of clusters of galaxies continue to provide us with an increasingly detailed picture of their structure and of the underlying physical phenomena governing the gaseous component, which dominates their baryonic content. Therefore, it is fundamental to find the most direct and faithful way to compare such observational data with hydrodynamical simulations of cluster-like objects, which can currently include various complex physical processes. Here, we present and analyse synthetic Suzaku observations of two cluster-size haloes obtained by processing with phox the hydrodynamical simulation of the large-scale, filament-like region in which they reside. Taking advantage of the simulated data, we test the results inferred from the X-ray analysis of the mock observations against the underlying, known solution. Remarkably, we are able to recover the theoretical temperature distribution of the two haloes by means of the multi-temperature fitting of the synthetic spectra. Moreover, the shapes of the reconstructed distributions allow us to trace the different thermal structure that distinguishes the dynamical state of the two haloes.
ABSTRACT
Cosmological shock waves are ubiquitous to cosmic structure formation and evolution. As a consequence, they play a major role in the energy distribution and thermalization of the ...intergalactic medium (IGM). We analyze the Mach number distribution in the Dianoga simulations of galaxy clusters performed with the SPH code gadget-3. The simulations include the effects of radiative cooling, star formation, metal enrichment, supernova, and active galactic nuclei feedback. A grid-based shock-finding algorithm is applied in post-processing to the outputs of the simulations. This procedure allows us to explore in detail the distribution of shocked cells and their strengths as a function of cluster mass, redshift, and baryonic physics. We also pay special attention to the connection between shock waves and the cool-core/non-cool-core (CC/NCC) state and the global dynamical status of the simulated clusters. In terms of general shock statistics, we obtain a broad agreement with previous works, with weak (low-Mach number) shocks filling most of the volume and processing most of the total thermal energy flux. As a function of cluster mass, we find that massive clusters seem more efficient in thermalizing the IGM and tend to show larger external accretion shocks than less massive systems. We do not find any relevant difference between CC and NCC clusters. However, we find a mild dependence of the radial distribution of the shock Mach number on the cluster dynamical state, with disturbed systems showing stronger shocks than regular ones throughout the cluster volume.
We present a novel approach, based on robust principal components analysis (RPCA) and maximal information coefficient (MIC), to study the redshift dependence of halo baryonic properties. Our data are ...composed of a set of different physical quantities for primordial minihaloes: dark matter mass (M
dm), gas mass (M
gas), stellar mass (M
star), molecular fraction (x
mol), metallicity (Z), star formation rate (SFR) and temperature. We find that M
dm and M
gas are dominant factors for variance, particularly at high redshift. Nonetheless, with the emergence of the first stars and subsequent feedback mechanisms, x
mol, SFR and Z start to have a more dominant role. Standard PCA gives three principal components (PCs) capable to explain more than 97 per cent of the data variance at any redshift (two PCs usually accounting for no less than 92 per cent), whilst the first PC from the RPCA analysis explains no less than 84 per cent of the total variance in the entire redshift range (with two PCs explaining 95 per cent anytime). Our analysis also suggests that all the gaseous properties have a stronger correlation with M
gas than with M
dm, while M
gas has a deeper correlation with x
mol than with Z or SFR. This indicates the crucial role of gas molecular content to initiate star formation and consequent metal pollution from Population III and Population II/I regimes in primordial galaxies. Finally, a comparison between MIC and Spearman correlation coefficient shows that the former is a more reliable indicator when halo properties are weakly correlated.
Gas motions in the hot intracluster medium (ICM) of galaxy clusters have an important effect on the mass determination of the clusters through X-ray observations. The corresponding dynamical pressure ...has to be accounted for in addition to the hydrostatic pressure support to achieve a precise mass measurement. An analysis of the velocity structure of the ICM for simulated cluster-size haloes, especially focusing on rotational patterns, has been performed, demonstrating them to be an intermittent phenomenon, strongly related to the internal dynamics of substructures. We find that the expected build-up of rotation due to mass assembly gets easily destroyed by passages of gas-rich substructures close to the central region. Though, if a typical rotation pattern is established, then the corresponding mass contribution is estimated to be up to ∼17 per cent of the total mass in the innermost region and one has to account for it. Extending the analysis to a larger sample of simulated haloes, we statistically observe that (i) the distribution of the rotational component of the gas velocity in the innermost region has typical values of ∼200-300 km s−1; and (ii) except for few outliers, there is no monotonic increase in the rotational velocity with decreasing redshift, as we would expect from approaching a relaxed configuration. Therefore, the hypothesis that the build-up of rotation is strongly influenced by internal dynamics is confirmed and minor events like gas-rich substructures passing close to the equatorial plane can easily destroy any ordered rotational pattern.
Context. Inferences about dark matter, dark energy, and the missing baryons all depend on the accuracy of our model of large-scale structure evolution. In particular, with cosmological simulations in ...our model of the Universe, we trace the growth of structure, and visualize the build-up of bigger structures from smaller ones and of gaseous filaments connecting galaxy clusters. Aims. Here we aim to reveal the complexity of the large-scale structure assembly process in great detail and on scales from tens of kiloparsecs up to more than 10 Mpc with new sensitive large-scale observations from the latest generation of instruments. We also aim to compare our findings with expectations from our cosmological model. Methods. We used dedicated SRG/eROSITA performance verification (PV) X-ray, ASKAP/EMU Early Science radio, and DECam optical observations of a ~15 deg2 region around the nearby interacting galaxy cluster system A3391/95 to study the warm-hot gas in cluster outskirts and filaments, the surrounding large-scale structure and its formation process, the morphological complexity in the inner parts of the clusters, and the (re-)acceleration of plasma. We also used complementary Sunyaev-Zeldovich (SZ) effect data from the Planck survey and custom-made Galactic total (neutral plus molecular) hydrogen column density maps based on the HI4PI and IRAS surveys. We relate the observations to expectations from cosmological hydrodynamic simulations from the Magneticum suite. Results. We trace the irregular morphology of warm and hot gas of the main clusters from their centers out to well beyond their characteristic radii, r200. Between the two main cluster systems, we observe an emission bridge on large scale and with good spatial resolution. This bridge includes a known galaxy group but this can only partially explain the emission. Most gas in the bridge appears hot, but thanks to eROSITA’s unique soft response and large field of view, we discover some tantalizing hints for warm, truly primordial filamentary gas connecting the clusters. Several matter clumps physically surrounding the system are detected. For the “Northern Clump,” we provide evidence that it is falling towards A3391 from the X-ray hot gas morphology and radio lobe structure of its central AGN. Moreover, the shapes of these X-ray and radio structures appear to be formed by gas well beyond the virial radius, r100, of A3391, thereby providing an indirect way of probing the gas in this elusive environment. Many of the extended sources in the field detected by eROSITA are also known clusters or new clusters in the background, including a known SZ cluster at redshift z = 1. We find roughly an order of magnitude more cluster candidates than the SPT and ACT surveys together in the same area. We discover an emission filament north of the virial radius of A3391 connecting to the Northern Clump. Furthermore, the absorption-corrected eROSITA surface brightness map shows that this emission filament extends south of A3395 and beyond an extended X-ray-emitting object (the “Little Southern Clump”) towards another galaxy cluster, all at the same redshift. The total projected length of this continuous warm-hot emission filament is 15 Mpc, running almost 4 degrees across the entire eROSITA PV observation field. The Northern and Southern Filament are each detected at >4σ. The Planck SZ map additionally appears to support the presence of both new filaments. Furthermore, the DECam galaxy density map shows galaxy overdensities in the same regions. Overall, the new datasets provide impressive confirmation of the theoretically expected structure formation processes on the individual system level, including the surrounding warm-hot intergalactic medium distribution; the similarities of features found in a similar system in the Magneticum simulation are striking. Our spatially resolved findings show that baryons indeed reside in large-scale warm-hot gas filaments with a clumpy structure.
Context.
X-ray observations of galaxies with high spatial resolution instruments such as
Chandra
have revealed that major contributions to their diffuse emission originate from X-ray-bright point ...sources in the galactic stellar field. It has been established that these point sources, called X-ray binaries, are accreting compact objects with stellar donors in a binary configuration. They are classified according to the predominant accretion process: wind-fed in the case of high-mass donors and Roche-lobe mass transfer in the case of low-mass donors. Observationally, it is challenging to reliably disentangle these two populations from each other because of their similar spectra.
Aims.
We provide a numerical framework with which spatially and spectrally accurate representations of X-ray binary populations can be studied from hydrodynamical cosmological simulations. We construct average spectra, accounting for a hot gas component, and verify the emergence of observed scaling relations between galaxy-wide X-ray luminosity (
L
X
) and stellar mass (
M
*
) and between
L
X
and the star-formation rate (SFR).
Methods.
Using simulated galaxy halos extracted from the (48
h
−1
cMpc)
3
volume of the Magneticum Pathfinder cosmological simulations at
z
= 0.07, we generate mock spectra with the X-ray photon-simulator P
HOX
. We extend the P
HOX
code to account for the stellar component in the simulation and study the resulting contribution in composite galactic spectra.
Results.
Well-known X-ray binary scaling relations with galactic SFR and
M
*
emerge self-consistently, verifying our numerical approach. Average X-ray luminosity functions are perfectly reproduced up to the one-photon luminosity limit. Comparing our resulting
L
X
− SFR −
M
*
relation for X-ray binaries with recent observations of field galaxies in the Virgo galaxy cluster, we find significant overlap. Invoking a metallicity-dependent model for high-mass X-ray binaries yields an anticorrelation between mass-weighted stellar metallicity and SFR-normalized luminosity. The spatial distribution of high-mass X-ray binaries coincides with star-formation regions of simulated galaxies, while low-mass X-ray binaries follow the stellar mass surface density. X-ray binary emission is the dominant contribution in the hard X-ray band (2–10 keV) in the absence of an actively accreting central super-massive black hole, and it provides a ∼50% contribution in the soft X-ray band (0.5–2 keV), rivaling the hot gas component.
Conclusions.
We conclude that our modeling remains consistent with observations despite the uncertainties connected to our approach. The predictive power and easily extendable framework hold great value for future investigations of galactic X-ray spectra.
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