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Register a new userPredictions for anisotropic X-ray signatures in the circumgalactic medium: imprints of supermassive black hole driven outflows
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The circumgalactic medium (CGM) encodes signatures of the galaxy-formation process, including the interaction of galactic outflows driven by stellar and supermassive black hole (SMBH) feedback with the gaseous halo. Moving beyond spherically symmetric radial profiles, we study the textit{angular} dependence of CGM properties around $z=0$ massive galaxies in the IllustrisTNG simulations. We characterize the angular signal of density, temperature, and metallicity of the CGM as a function of galaxy stellar mass, halo mass, distance, and SMBH mass, via stacking. TNG predicts that the CGM is anisotropic in its thermodynamical properties and chemical content over a large mass range, $M_*sim10^{10-11.5}M_odot$. Along the minor axis directions, gas density is diluted, whereas temperature and metallicity are enhanced. These feedback-induced anisotropies in the CGM have a magnitude of $0.1-0.3$ dex, extend out to the halo virial radius, and peak at Milky Way-like masses, $M_*sim10^{10.8}M_odot$. In TNG, this mass scale corresponds to the onset of efficient SMBH feedback and the production of strong outflows. By comparing the anisotropic signals predicted by TNG versus other simulations -- Illustris and EAGLE -- we find that each simulation produces distinct signatures and mass dependencies, implying that this phenomenon is sensitive to the underlying physical models. Finally, we explore X-ray emission as an observable of this CGM anistropy, finding that future X-ray observations, including the eROSITA all-sky survey, will be able to detect and characterize this signal, particularly in terms of an angular modulation of the X-ray hardness.
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We simulate stacked observations of nearby hot X-ray coronae associated with galaxies in the EAGLE and Illustris-TNG hydrodynamic simulations. A forward modeling pipeline is developed to predict 4-year eROSITA observations and stacked image analysis, including the effects of instrumental and astrophysical backgrounds. We propose an experiment to stack z~0.01 galaxies separated by specific star-formation rate (sSFR) to examine how the hot (T>=10^6 K) circumgalactic medium (CGM) differs for high- and low-sSFR galaxies. The simulations indicate that the hot CGM of low-mass (M_*~10^{10.5} Msol), high-sSFR (defined as the top one-third ranked by sSFR) central galaxies will be detectable to a galactocentric radius r~30-50 kpc. Both simulations predict lower luminosities at fixed stellar mass for the low-sSFR galaxies (the lower third of sSFR) with Illustris-TNG predicting 3x brighter coronae around high-sSFR galaxies than EAGLE. Both simulations predict detectable emission out to r~150-200 kpc for stacks centered on high-mass (M_*~10^{11.0} Msol) galaxies, with EAGLE predicting brighter X-ray halos. The extended soft X-ray luminosity correlates strongly and positively with the mass of circumgalactic gas within the virial radius (f_{CGM}). Prior analyses of both simulations have established that f_{CGM} is reduced by expulsive feedback driven mainly by black hole growth, which quenches galaxy growth by inhibiting replenishment of the ISM. Both simulations predict that eROSITA stacks should not only conclusively detect and resolve the hot CGM around L^* galaxies for the first time, but provide a powerful probe of how the baryon cycle operates, for which there remains an absence of consensus between state-of-the-art simulations.
We carry out a comprehensive Bayesian correlation analysis between hot halos and direct masses of supermassive black holes (SMBHs), by retrieving the X-ray plasma properties (temperature, luminosity, density, pressure, masses) over galactic to cluster scales for 85 diverse systems. We find new key scalings, with the tightest relation being the $M_bullet-T_{rm x}$, followed by $M_bullet-L_{rm x}$. The tighter scatter (down to 0.2 dex) and stronger correlation coefficient of all the X-ray halo scalings compared with the optical counterparts (as the $M_bullet-sigma_{rm e}$) suggest that plasma halos play a more central role than stars in tracing and growing SMBHs (especially those that are ultramassive). Moreover, $M_bullet$ correlates better with the gas mass than dark matter mass. We show the important role of the environment, morphology, and relic galaxies/coronae, as well as the main departures from virialization/self-similarity via the optical/X-ray fundamental planes. We test the three major channels for SMBH growth: hot/Bondi-like models have inconsistent anti-correlation with X-ray halos and too low feeding; cosmological simulations find SMBH mergers as sub-dominant over most of the cosmic time and too rare to induce a central-limit-theorem effect; the scalings are consistent with chaotic cold accretion (CCA), the rain of matter condensing out of the turbulent X-ray halos that sustains a long-term self-regulated feedback loop. The new correlations are major observational constraints for models of SMBH feeding/feedback in galaxies, groups, and clusters (e.g., to test cosmological hydrodynamical simulations), and enable the study of SMBHs not only through X-rays, but also via the Sunyaev-Zeldovich effect (Compton parameter), lensing (total masses), and cosmology (gas fractions).
We investigate the impact of cosmic rays (CRs) on the circumgalactic medium (CGM) in FIRE-2 simulations, for ultra-faint dwarf through Milky Way (MW)-mass halos hosting star-forming (SF) galaxies. Our CR treatment includes injection by supernovae, anisotropic streaming and diffusion along magnetic field lines, collisional and streaming losses, with constant parallel diffusivity $kappasim3times10^{29},mathrm{cm^2 s^{-1}}$ chosen to match $gamma$-ray observations. With this, CRs become more important at larger halo masses and lower redshifts, and dominate the pressure in the CGM in MW-mass halos at $zlesssim 1-2$. The gas in these CR-dominated halos differs significantly from runs without CRs: the gas is primarily cool (a few $sim10^{4},$K), and the cool phase is volume-filling and has a thermal pressure below that needed for virial or local thermal pressure balance. Ionization of the low and mid ions in this diffuse cool gas is dominated by photo-ionization, with O VI columns $gtrsim 10^{14.5},mathrm{cm^{-2}}$ at distances $gtrsim 150,mathrm{kpc}$. CR and thermal gas pressure are locally anti-correlated, maintaining total pressure balance, and the CGM gas density profile is determined by the balance of CR pressure gradients and gravity. Neglecting CRs, the same halos are primarily warm/hot ($Tgtrsim 10^{5},$K) with thermal pressure balancing gravity, collisional ionization dominates, O VI columns are lower and Ne VIII higher, and the cool phase is confined to dense filaments in local thermal pressure equilibrium with the hot phase.
We present the new TNG50 cosmological, magnetohydrodynamical simulation -- the third and final volume of the IllustrisTNG project. This simulation occupies a unique combination of large volume and high resolution, with a 50 Mpc box sampled by 2160^3 gas cells (baryon mass of 8x10^4 Msun). The median spatial resolution of star-forming ISM gas is ~100-140 parsecs. This resolution approaches or exceeds that of modern zoom simulations of individual massive galaxies, while the volume contains ~20,000 resolved galaxies with M*>10^7 Msun. Herein we show first results from TNG50, focusing on galactic outflows driven by supernovae as well as supermassive black hole feedback. We find that the outflow mass loading is a non-monotonic function of galaxy stellar mass, turning over and rising rapidly above 10^10.5 Msun due to the action of the central black hole. Outflow velocity increases with stellar mass, and at fixed mass is faster at higher redshift. The TNG model can produce high velocity, multi-phase outflows which include cool, dense components. These outflows reach speeds in excess of 3000 km/s out to 20 kpc with an ejective, BH-driven origin. Critically, we show how the relative simplicity of model inputs (and scalings) at the injection scale produces complex behavior at galactic and halo scales. For example, despite isotropic wind launching, outflows exhibit natural collimation and an emergent bipolarity. Furthermore, galaxies above the star-forming main sequence drive faster outflows, although this correlation inverts at high mass with the onset of quenching, whereby low luminosity, slowly accreting, massive black holes drive the strongest outflows.
Hot gaseous atmospheres that permeate galaxies and extend far beyond their stellar distribution, where they are commonly referred to as the circumgalactic medium (CGM), imprint important information about feedback processes powered by the stellar populations of galaxies and their central supermassive black holes (SMBH). In this work we study the properties of this hot X-ray emitting medium using the IllustrisTNG cosmological simulations. We analyse their mock X-ray spectra, obtained from the diffuse and metal-enriched gas in TNG100 and TNG50, and compare the results with X-ray observations of nearby early-type galaxies. The simulations reproduce the observed X-ray luminosities ($L_{rm X}$) and temperature ($T_{rm X})$ at small ($<R_{rm e}$) and intermediate ($<5R_{rm e}$) radii reasonably well. We find that the X-ray properties of lower mass galaxies depend on their star formation rates. In particular, in the magnitude range where the star-forming and quenched populations overlap, $M_{rm K}sim-24$ $ (M_*sim10^{10.7}M_odot)$, we find that the X-ray luminosities of star-forming galaxies are on average about an order of magnitude higher than those of their quenched counterparts. We show that this diversity in $L_{rm X}$ is a direct manifestation of the quenching mechanism in the simulations, where the galaxies are quenched due to gas expulsion driven by SMBH kinetic feedback. The observed dichotomy in $L_{rm X}$ is thus an important observable prediction for the SMBH feedback-based quenching mechanisms implemented in state-of-the-art cosmological simulations. While the current X-ray observations of star forming galaxies are broadly consistent with the predictions of the simulations, the observed samples are small and more decisive tests are expected from the sensitive all-sky X-ray survey with eROSITA.
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