Simulation view of galaxy clusters with low X-ray surface brightness
Abstract: Context. X-ray selected samples are known to miss galaxy clusters that are gas poor and have a low surface brightness. This is different for the optically selected samples such as the X-ray Unbiased Selected Sample (XUCS). Aims. We characterise the origin of galaxy clusters that are gas poor and have a low surface-brightness by studying covariances between various cluster properties at fixed mass using hydrodynamic cosmological simulations. Methods. We extracted ≈1800 galaxy clusters from a high-resolution Mag… Show more
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Cited by 5 publications
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We study the redshift evolution of the baryon budget in a large set of galaxy clusters from the Magneticum suite of smoothed particle hydrodynamical cosmological simulations. At high redshifts (z ≳ 1), we obtain ‘closed-box’ (i.e. baryon mass fraction fbar = Ωbar/Ωtot) systems independently of the mass of the systems on radii greater than 3R500, c, whereas at lower redshifts, only the most massive halos can be considered closed box. Furthermore, in the innermost regions (r < R500, c), the baryon fraction shows a general decrease with redshift, and for less massive objects we observe a much more prominent decrease than for massive halos (fbar × Ωtot/Ωbar = Ybar decreases by ∼4% from z ∼ 2.8 to z ∼ 0.2 for massive systems and by ∼15% for less massive objects in the same redshift range). The gas depletion parameter Ygas = fgas/(Ωbar/Ωtot) shows a steeper and highly scattered radial distribution in the central regions (0.5R500, c ≤ r ≤ 2R500, c) of less massive halos with respect to massive objects at all redshifts, while on larger radii (r ≥ 2R500, c) the gas fraction distributions are independent of the masses or the redshifts. We divide the gas content of halos into the hot and cold phases. The hot, X-ray-observable component of the gas accurately traces the total amount of gas at low redshifts (e.g., for z ∼ 0.2 at R500, c, in the most massive subsample, that is, 4.6 × 1014 ≤ M500, c/M⊙ ≤ 7.5 × 1014 and least massive subsample, that is, 6.0 × 1013 ≤ M500, c/M⊙ ≤ 1.9 × 1014, we obtain Ygas ∼ 0.75 and 0.67, Yhot ∼ 0.73 and 0.64, and Ycold ∼ 0.02 and 0.02, respectively). On the other hand, at higher redshifts, the cold component provides a non-negligible contribution to the total amount of baryons in our simulated systems, especially in less massive objects (e.g., for z ∼ 2.8 at R500, c, in the most massive subsample, that is, 2.5 × 1013 ≤ M500, c/M⊙ ≤ 5.0 × 1013 and least massive subsample, that is, 5.8 × 1012 ≤ M500, c/M⊙ ≤ 9.7 × 1012, we obtain Ygas ∼ 0.63 and 0.64, Yhot ∼ 0.50 and 0.45, and Ycold ∼ 0.13 and 0.18, respectively). Moreover, the behaviour of the baryonic, entire-gas, and hot-gas-phase depletion parameters as functions of radius, mass, and redshift are described by some functional forms for which we provide the best-fit parametrization. The evolution of metallicity and stellar mass in halos suggests that the early (z > 2) enrichment process is dominant, while more recent star-formation processes make negligible contributions to the enrichment of the gas metallicity. In addition, active galactic nuclei (AGN) play an important role in the evolution of the baryon content of galaxy clusters. Therefore, we investigate possible correlations between the time evolution of AGN feedback and the depletion parameters in our numerical simulations. Interestingly, we demonstrate that the energy injected by the AGN activity shows a particularly strong positive correlation with Ybar, Ycold, and Ystar and a negative correlation with Yhot and ZTot. On the other hand, Ygas shows a less prominent level of negative correlation, a result which is highly dependent on the mass of the halos. These trends are consistent with previous theoretical and numerical works, meaning that our results, combined with findings derived from current and future X-ray observations, represent possible proxies with which to test the AGN feedback models used in different suites of numerical simulations.
We study the redshift evolution of the baryon budget in a large set of galaxy clusters from the Magneticum suite of smoothed particle hydrodynamical cosmological simulations. At high redshifts (z ≳ 1), we obtain ‘closed-box’ (i.e. baryon mass fraction fbar = Ωbar/Ωtot) systems independently of the mass of the systems on radii greater than 3R500, c, whereas at lower redshifts, only the most massive halos can be considered closed box. Furthermore, in the innermost regions (r < R500, c), the baryon fraction shows a general decrease with redshift, and for less massive objects we observe a much more prominent decrease than for massive halos (fbar × Ωtot/Ωbar = Ybar decreases by ∼4% from z ∼ 2.8 to z ∼ 0.2 for massive systems and by ∼15% for less massive objects in the same redshift range). The gas depletion parameter Ygas = fgas/(Ωbar/Ωtot) shows a steeper and highly scattered radial distribution in the central regions (0.5R500, c ≤ r ≤ 2R500, c) of less massive halos with respect to massive objects at all redshifts, while on larger radii (r ≥ 2R500, c) the gas fraction distributions are independent of the masses or the redshifts. We divide the gas content of halos into the hot and cold phases. The hot, X-ray-observable component of the gas accurately traces the total amount of gas at low redshifts (e.g., for z ∼ 0.2 at R500, c, in the most massive subsample, that is, 4.6 × 1014 ≤ M500, c/M⊙ ≤ 7.5 × 1014 and least massive subsample, that is, 6.0 × 1013 ≤ M500, c/M⊙ ≤ 1.9 × 1014, we obtain Ygas ∼ 0.75 and 0.67, Yhot ∼ 0.73 and 0.64, and Ycold ∼ 0.02 and 0.02, respectively). On the other hand, at higher redshifts, the cold component provides a non-negligible contribution to the total amount of baryons in our simulated systems, especially in less massive objects (e.g., for z ∼ 2.8 at R500, c, in the most massive subsample, that is, 2.5 × 1013 ≤ M500, c/M⊙ ≤ 5.0 × 1013 and least massive subsample, that is, 5.8 × 1012 ≤ M500, c/M⊙ ≤ 9.7 × 1012, we obtain Ygas ∼ 0.63 and 0.64, Yhot ∼ 0.50 and 0.45, and Ycold ∼ 0.13 and 0.18, respectively). Moreover, the behaviour of the baryonic, entire-gas, and hot-gas-phase depletion parameters as functions of radius, mass, and redshift are described by some functional forms for which we provide the best-fit parametrization. The evolution of metallicity and stellar mass in halos suggests that the early (z > 2) enrichment process is dominant, while more recent star-formation processes make negligible contributions to the enrichment of the gas metallicity. In addition, active galactic nuclei (AGN) play an important role in the evolution of the baryon content of galaxy clusters. Therefore, we investigate possible correlations between the time evolution of AGN feedback and the depletion parameters in our numerical simulations. Interestingly, we demonstrate that the energy injected by the AGN activity shows a particularly strong positive correlation with Ybar, Ycold, and Ystar and a negative correlation with Yhot and ZTot. On the other hand, Ygas shows a less prominent level of negative correlation, a result which is highly dependent on the mass of the halos. These trends are consistent with previous theoretical and numerical works, meaning that our results, combined with findings derived from current and future X-ray observations, represent possible proxies with which to test the AGN feedback models used in different suites of numerical simulations.
Detecting galaxy groups populating the local Universe in the eROSITA era
eROSITA will deliver an unprecedented volume of X-ray survey observations, $20-30$ times more sensitive than ROSAT in the soft band ($0.5-2.0$ keV) and for the first time imaging in the hard band ($2-10$ keV). The final observed catalogue of sources will include galaxy clusters and groups along with obscured and unobscured ( active galactic nuclei ) AGNs. This calls for a powerful theoretical effort to mitigate potential systematics and biases that may influence the data analysis. We investigate the detection technique and selection biases in the galaxy group and AGN populations within a simulated X-ray observation conducted at the depth equivalent to a four-year eROSITA survey (eRASS:4). We generate a mock observation spanning $30 30$ deg2 based on the cosmological hydrodynamical simulation Magneticum Pathfinder from $z=0$ up to redshift $z=0.2$, mirroring the depth of eRASS:4 (with an average exposure of$ 600$ s). We combined a physical background from the real eFEDS background analysis with realistic simulations of X-ray emission for the hot gas, AGNs, and XRB. Using a detection method similar to that utilised for eRASS data, we assessed completeness and contamination levels to reconstruct the luminosity functions for both extended and point sources within the catalogue. We define the completeness of extended detections as a function of the input X-ray flux $S_ $ and halo mass $M_ $ at the depth of eRASS:4. Notably, we fully recovered the brightest (most massive) galaxy clusters and AGNs. However, a significant fraction of galaxy groups ($M_ M_ odot $) remain undetected. Examining gas properties between the detected and undetected galaxy groups at a fixed halo mass, we observe that the detected population typically displays higher X-ray brightness compared to the undetected counterpart. Furthermore, we establish that X-ray luminosity primarily correlates with the hot gas fraction, rather than temperature or metallicity. Our simulation suggests a systematic selection bias in current surveys, leading to X-ray catalogues predominantly composed of the lowest-entropy, gas-richest, and highest surface brightness halos on galaxy group scales.
The Three Hundred Project: the evolution of physical baryon profiles
The distribution of baryons provides a significant way to understand the formation of galaxy clusters by revealing the details of its internal structure and changes over time. In this paper, we present theoretical studies on the scaled profiles of physical properties associated with the baryonic components, including gas density, temperature, metallicity, pressure and entropy as well as stellar mass, metallicity and satellite galaxy number density in galaxy clusters from z = 4 to z = 0 by tracking their progenitors. These mass-complete simulated galaxy clusters are coming from The Three Hundred with two runs: Gizmo-SIMBA and Gadget-X. Through comparisons between the two simulations, and with observed profiles which are generally available at low redshift, we find that (1) the agreements between the two runs and observations are mostly at outer radii r ≳ 0.3r500, in line with the self-similarity assumption. While Gadget-X shows better agreements with the observed gas profiles in the central regions compared to Gizmo-SIMBA; (2) the evolution trends are generally consistent between the two simulations with slightly better consistency at outer radii. In detail, the gas density profile shows less discrepancy than the temperature and entropy profiles at high redshift. The differences in the cluster centre and gas properties imply different behaviours of the AGN models between Gadget-X and Gizmo-SIMBA, with the latter, maybe too strong for this cluster simulation. The high-redshift difference may be caused by the star formation and feedback models or hydrodynamics treatment, which requires observation constraints and understanding.
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