Browsing by Author "Sorini, Daniele"

Now showing 1 - 5 of 5
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    Jet feedback and the photon underproduction crisis in SIMBA
    (Oxford University Press, 2020-10-01) Dave, Romeel; Christiansen, Jacob; Sorini, Daniele; Angles-Alc ´ azar, Daniel
    We examine the impact of black hole jet feedback on the properties of the low-redshift intergalactic medium (IGM) in the SIMBA simulation, with a focus on the Lyα forest mean flux decrement DA. Without jet feedback, we confirm the photon underproduction crisis (PUC) in which H I at z = 0 must be increased by 6 times over the Haardt & Madau value in order to match the observed DA. Turning on jet feedback lowers this discrepancy to ∼2.5 times, and additionally using the recent Faucher–Giguere background ` mostly resolves the PUC, along with producing a flux probability distribution function in accord with observations. The PUC becomes apparent at late epochs (z 1) where the jet and no-jet simulations diverge; at higher redshifts SIMBA reproduces the observed DA with no adjustment, with or without jets. The main impact of jet feedback is to lower the cosmic baryon fraction in the diffuse IGM from 39 per cent to 16 per cent at z = 0, while increasing the warm-hot intergalactic medium (WHIM) baryon fraction from 30 per cent to 70 per cent; the lowering of the diffuse IGM content directly translates into a lowering of DA by a similar factor. Comparing to the older MUFASA simulation that employs different quenching feedback but is otherwise similar to SIMBA, MUFASA matches DA less well than SIMBA, suggesting that low-redshift measurements of DA and H I could provide constraints on feedback mechanisms. Our results suggest that widespread IGM heating at late times is a plausible solution to the PUC, and that SIMBA’s jet active galactic nucleus feedback model, included to quench massive galaxies, approximately yields this required heating.
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    The low-redshift circumgalactic medium in SIMBA
    (Oxford University Press, 2021-08) Appleby, Sarah; Dave´, Romeel; Sorini, Daniele; Storey-Fisher, Kate; Smith, Britton
    We examine the properties of the low-redshift circumgalactic medium (CGM) around star-forming and quenched galaxies in the SIMBA cosmological hydrodynamic simulations, focusing on comparing H I and metal line absorption to observations from the Cosmic Origins Spectrograph (COS)-Halos and COS-Dwarfs surveys. Halo baryon fractions are generally 50 per cent of the cosmic fraction due to stellar feedback at low masses, and jet-mode AGN feedback at high masses. Baryons and metals in the CGM of quenched galaxies are 90 per cent hot gas, while the CGM of star-forming galaxies is more multiphase. Hot CGM gas has low metallicity, while warm and cool CGM gas have metallicity close to that of galactic gas. Equivalent widths, covering fractions and total path absorption of H I and selected metal lines (Mg II, Si III, C IV, and O VI) around a matched sample of SIMBA star-forming galaxies are mostly consistent with COS-Halos and COS-Dwarfs observations to 0.4 dex, depending on ion and assumed ionizing background. Around matched quenched galaxies, absorption in all ions is lower, with H I absorption significantly underpredicted. Metal-line absorption is sensitive to choice of photoionizing background; assuming recent backgrounds, SIMBA matches O VI but underpredicts low ions, while an older background matches low ions but underpredicts O VI. SIMBA reproduces the observed dichotomy of O VI absorption around star-forming and quenched galaxies. CGM metals primarily come from stellar feedback, while jet-mode AGN feedback reduces absorption particularly for lower ions.
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    The physical nature of circumgalactic medium absorbers in SIMBA
    (Oxford University Press, 2023) Appleby, Sarah; Dave, Romeel; Sorini, Daniele
    We study the nature of the low-redshift circumgalactic medium (CGM) in the SIMBA cosmological simulations as traced by ultraviolet absorption lines around galaxies in bins of stellar mass (M > 1010M) for star-forming, green valley and quenched galaxies at impact parameters r⊥ ≤ 1.25r200. We generate synthetic spectra for H I , Mg II , C II , Si III , C IV , and O VI , fit Voigt profiles to obtain line properties, and estimate the density, temperature, and metallicity of the absorbing gas. We find that CGM absorbers are most abundant around star-forming galaxies with M < 1011 M, while the abundance of green valley galaxies show similar behaviour to those of quenched galaxies, suggesting that the CGM ‘quenches’ before star formation ceases. H I absorbing gas exists across a broad range of cosmic phases [condensed gas, diffuse gas, hot halo gas, and Warm-Hot Intergalactic Medium (WHIM)], while essentially all low ionization metal absorption arises from condensed gas. O VI absorbers are split between hot halo gas and the WHIM. The fraction of collisionally ionized CGM absorbers is ∼ 25–55 per cent for C IV and ∼ 80–95 per cent for O VI , depending on stellar mass and impact parameter. In general, the highest column density absorption features for each ion arise from dense gas. Satellite gas, defined as that within 10r1/2,, contributes ∼ 3 per cent of overall H I absorption but∼ 30 per cent of Mg II absorption, with the fraction fromsatellites decreasing with increasing ion excitation energy.
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    SIMBA: the average properties of the circumgalactic medium of 2 ≤ z ≤ 3 quasars are determined primarily by stellar feedback
    (Oxford University Press, 2020-10-05) Dave´, Romeel; Sorini, Daniele; Angles-Alc ´ azar, Daniel
    We use the SIMBA cosmological hydrodynamic simulation suite to explore the impact of feedback on the circumgalactic medium (CGM) and intergalactic medium (IGM) around 2 ≤ z ≤ 3 quasars. We identify quasars in SIMBA as the most rapidly accreting black holes, and show that they are well matched in bolometric luminosity and correlation strength to real quasars. We extract Lyα absorption in spectra passing at different transverse distances (10 kpc b 10 Mpc) around those quasars, and compare to observations of the mean Lyα absorption profile. The observations are well reproduced, except within 100 kpc from the foreground quasar, where SIMBA overproduces absorption; this could potentially be mitigated by including ionization from the quasar itself. By comparing runs with different feedback modules activated, we find that (mechanical) AGN feedback has little impact on the surrounding CGM even around these most highly luminous black holes, while stellar feedback has a significant impact. By further investigating thermodynamic and kinematic properties of CGM gas, we find that stellar feedback, and not AGN feedback, is the primary physical driver in determining the average properties of the CGM around z ∼ 2–3 quasars. We also compare our results with previous works, and find that SIMBA predicts much more absorption within 100 kpc than the NYX and ILLUSTRIS simulations, showing that the Lyα absorption profile can be a powerful constraint on simulations. Instruments such as VLT-MUSE and upcoming surveys (e.g. WEAVE and DESI) promise to further improve such constraints.
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    The cosmic baryon partition between the IGM and CGM in the SIMBA simulations
    (Oxford University Press, 2024) Khrykin, Ilya S.; Davé, Romeel; Sorini, Daniele
    We use the SIMBA suite of cosmological hydrodynamical simulations to investigate the importance of various stellar and active galactic nuclei (AGN) feedback mechanisms in partitioning the cosmic baryons between the intergalactic (IGM) and circumgalactic (CGM) media in the z ≤ 1 Universe. We identify the AGN jets as the most prominent mechanism for the redistribution of baryons between the IGM and CGM. In contrast to the full feedback models, deactivating AGN jets results in ≈20 per cent drop in fraction of baryons residing in the IGM and a consequent increase of CGM baryon fraction by ≈50 per cent. We find that stellar feedback modifies the partition of baryons on a 10 per cent level. We further examine the physical properties of simulated haloes in different mass bins, and their response to various feedback models. On average, a sixfold decrease in the CGM mass fraction due to the inclusion of feedback from AGN jets is detected in 1012 M☉ ≤ M200 ≤ 1014 M☉ haloes. Examination of the average radial gas density profiles of M200 > 1012 M☉ haloes reveals up to an order of magnitude decrease in gas densities due to the AGN jet feedback. We compare gas density profiles from SIMBA simulations to the predictions of the modified Navarro-Frenk-White model, and show that the latter provides a reasonable approximation within the virial radii of the full range of halo masses, but only when rescaled by the appropriate mass-dependent CGM fraction of the halo. The relative partitioning of cosmic baryons and, subsequently, the feedback models can be constrained observationally with fast radio bursts in upcoming surveys.