We study the impact of cosmic rays (CRs) on the structure of virial shocks, using a large suite of high-resolution cosmological FIRE-2 simulations accounting for CR injection by supernovae. In massive ($M_{\rm halo} \gtrsim 10^{11}\,M_{\odot}$), low-redshift ($z\lesssim 1-2$) halos, which are expected to form "hot halos" with slowly-cooling gas in quasi-hydrostatic equilibrium (with a stable virial shock), our simulations without CRs do exhibit clear virial shocks. The cooler phase condensing out from inflows becomes pressure-confined to over-dense clumps, embedded in low-density, volume-filling hot gas whose cooling time is much longer than inflow time. The gas thus transitions sharply from cool free-falling inflow, to hot and thermal-pressure supported at approximately the virial radius ($\approx R_{\rm vir}$), and the shock is quasi-spherical. With CRs, we previously argued that halos in this particular mass and redshift range build up CR-pressure-dominated gaseous halos. Here, we show that when CR pressure dominates over thermal pressure, there is no significant virial shock. Instead, inflowing gas is gradually decelerated by the CR pressure gradient and the gas is relatively subsonic out to and even beyond $R_\mathrm{vir}$. Rapid cooling also maintains sub-virial temperatures in the inflowing gas within $\sim R_\mathrm{vir}$.
Previous X-ray studies of the Perseus Cluster, consisting of 85 Suzaku pointings along eight azimuthal directions, revealed a particularly steep decrease in the projected temperature profile near the virial radius (~r200) towards the northwest (NW). To further explore this shock candidate, another 4 Suzaku observations on the NW edge of the Perseus Cluster have been obtained. These deeper data were designed to provide the best possible control of systematic uncertainties in the spectral analysis. Using the combined Suzaku observations, we have carefully investigated this interesting region by …
Virial shocks at edges of cosmic-web structures are a clear prediction of standard structure formation theories. We derive a criterion for the stability of the post-shock gas and of the virial shock itself in spherical, filamentary and planar infall geometries. When gas cooling is important, we find that shocks become unstable, and gas flows uninterrupted towards the center of the respective halo, filament or sheet. For filaments, we impose this criterion on self-similar infall solutions. We find that instability is expected for filament masses between $10^{11}-10^{13}M_\odot Mpc^{-1}.$ Using …
The limits of feedback from active galactic nuclei
Institute for Computational Cosmology, Department of Physics, Durham University（达勒姆大学物理学院计算宇宙学研究所）；Institute of Astronomy and Kavli Institute for Cosmology, University of Cambridge（剑桥大学天体物理与卡弗里宇宙学研究所）；Cavendish Laboratory, Department of Physics, University of Cambridge（剑桥大学物理学院卡文迪许实验室）；The Oskar Klein Centre, Department of Physics, Stockholm University（斯德哥尔摩大学物理学院奥斯卡·克莱因中心）；Leiden Observatory, Leiden University（莱顿大学莱顿天文台）；Lorentz Institute for Theoretical Physics, Leiden University（莱顿大学洛伦兹理论物理研究所）
Galaxy clusters are known to be reservoirs of Cosmic Rays (CRs), as inferred from theoretical calculations or detection of CR-derived observables. CR acceleration in clusters is mostly attributed to the dynamical activity that produces shocks. Shocks in clusters emerge out of merger or accretion, but which one is more effective in producing CRs? at which dynamical phase? and why? To this aim, we study the production or injection of CRs through shocks and its evolution in the galaxy clusters using cosmological simulations with the {\sc enzo} code. Particle acceleration model considered here is …
We perform adaptive mesh refinement (AMR) and smoothed particle hydrodynamics (SPH) cosmological zoom simulations of a region around a forming galaxy cluster, comparing the ability of the methods to handle successively more complex baryonic physics. In the simplest, non-radiative case, the two methods are in good agreement with each other, but the SPH simulations generate central cores with slightly lower entropies and virial shocks at slightly larger radii, consistent with what has been seen in previous studies. The inclusion of radiative cooling, star formation, and stellar feedback leads to…
Large OVI columns are observed around star-forming, low-redshift ~L* galaxies, with a dependence on impact parameter indicating that most O^5+ particles reside beyond half the halo virial radius (>~100 kpc). In order to constrain the nature of the gas traced by OVI, we analyze additional observables of the outer halo, namely HI to OVI column ratios of 1-10, an absence of low-ion absorption, a mean differential extinction of E(B-V)~10^-3, and a linear relation between OVI column and velocity width. We contrast these observations with two physical scenarios: (1) OVI traces high-pressure (~30 cm^…
Several types/classes of shocks naturally arise during formation and evolution of galaxy clusters. One such class is represented by accretion shocks, associated with deceleration of infalling baryons. Such shocks, characterized by a very high Mach number, are present even in 1D models of cluster evolution. Another class is composed of "runaway merger shocks", which appear when a merger shock, driven by a sufficiently massive infalling subcluster, propagates away from the main-cluster center. We argue that, when the merger shock overtakes the accretion shock, a new long-living shock is formed t…
We study the dependence of quasar clustering on quasar luminosity and black hole mass by measuring the angular overdensity of photometrically selected galaxies imaged by WISE about z $\sim$ 0.8 quasars from SDSS. By measuring the quasar-galaxy cross-correlation function and using photometrically selected galaxies, we achieve a higher density of tracer objects and a more sensitive detection of clustering than measurements of the quasar autocorrelation function. We test models of quasar formation and evolution by measuring the luminosity dependence of clustering amplitude. We find a significant …
Cosmological Zoom-In Simulation of Odd Radio Circles as Merger-Driven Shocks in Galaxy Groups
Ludwig-Maximilians-Universität München（慕尼黑大学）；The University of Chicago（芝加哥大学）；Max-Planck-Institut für Astrophysik（马克斯·普朗克天体物理学研究所）；Australia Telescope National Facility, CSIRO（澳大利亚望远镜国家设施，CSIRO）；Western Sydney University（西悉尼大学）
We use the FIRE-2 cosmological simulations to study the formation of a quasi-static, virial-temperature gas phase in the circumgalactic medium (CGM) at redshifts 0<z<5, and how the formation of this virialized phase affects the evolution of galactic discs. We demonstrate that when the halo mass crosses ~10^12 M_sun, the cooling time of shocked gas in the inner CGM (~0.1 R_vir, where R_vir is the virial radius) exceeds the local free-fall time. The inner CGM then experiences a transition from on average sub-virial temperatures (T<<T_vir), large pressure fluctuations and supersonic inflow/outflo…
Early onset of the hot circumgalactic medium around Milky Way galaxies
Lund University（隆德大学）；University of Bath（巴斯大学）；University of Sydney（悉尼大学）；University of Surrey（萨里大学）；Sorbonne Université（索邦大学）；University of Oxford（牛津大学）
We analyze the impact of thermal conduction on the appearance of a shock-heated gas shell which is produced when a spherically symmetric outburst of a supermassive black hole inflates bubbles of relativistic plasma at the center of a galaxy cluster. The presence of the hot and low-density shell can be used as an ancillary indicator for a high rate of energy release during the outburst, which is required to drive strong shocks into the gas. Here we show that conduction can effectively erase such shell, unless the diffusion of electrons is heavily suppressed. We conclude that a more robust proxy…
CMZoom survey observations with the Submillimeter Array are analyzed to describe the virial equilibrium (VE) and star-forming potential of 755 clumps in 22 clouds in the Central Molecular Zone (CMZ) of the Milky Way. In each cloud, nearly all clumps follow the column-density-mass trend N~M^s, where s = 0.38 +- 0.03 is near the pressure-bounded limit s=1/3. This trend is expected when gravitationally unbound clumps in VE have similar velocity dispersion and external pressure. Nine of these clouds also harbor one or two distinctly more massive clumps. These properties allow a VE model of bound a…
Context. Galaxy clusters are continuously growing through the accretion of matter in their outskirts. This process induces inhomogeneities in the gas density distribution (clumping) which need to be taken into account to recover the physical properties of the intracluster medium (ICM) at large radii. Aims. We studied the thermodynamic properties in the outskirts (R > R500) of the massive galaxy cluster Abell 2142 by combining the Sunyaev Zel'dovich (SZ) effect with the X-ray signal. Methods. We combined the SZ pressure profile measured by Planck with the XMM-Newton gas density profile to recov…
Observations reveal massive amounts of OVI around star-forming $L_*$ galaxies, with covering fractions of near unity extending to the host halo's virial radius. This OVI absorption is typically kinematically centered upon photoionized gas, with line widths that are suprathermal and kinematically offset from the galaxy. We discuss various scenarios and whether they could result in the observed phenomenology (cooling gas flows, boundary layers, shocks, virialized gas, photoionized clouds in thermal equilibrium). If predominantly collisionally ionized, as we argue is most probable, the OVI observ…
A self-similar spherical collapse model predicts a dark matter (DM) splashback and accretion shock in the outskirts of galaxy clusters while misses a key ingredient of structure formation - processes associated with mergers. To fill this gap, we perform simulations of merging self-similar clusters and investigate their DM and gas evolution in an idealized cosmological context. Our simulations show that the cluster rapidly contracts during the major merger and the splashback radius $r_{\rm sp}$ decreases, approaching the virial radius $r_{\rm vir}$. While $r_{\rm sp}$ correlates with a smooth m…
We propose a new model for the ignition of star formation in low-mass halos by a self-sustaining shock front in cosmic filaments at high redshifts. The gaseous fuel for star formation resides in low mass halos which can not cool on their own due to their primordial composition and low virial temperatures. We show that star formation can be triggered in these filaments by a passing shock wave. The shells swept-up by the shock cool and fragment into cold clumps that form massive stars via thermal instability on a timescale shorter than the front's dynamical timescale. The shock, in turn, is self…
We use high-resolution three-dimensional adaptive mesh refinement simulations to investigate the interaction of high-redshift galaxy outflows with low-mass virialized clouds of primordial composition. While atomic cooling allows star formation in objects with virial temperatures above $10^4$ K, "minihaloes" below this threshold are generally unable to form stars by themselves. However, these objects are highly susceptible to triggered star formation, induced by outflows from neighboring high-redshift starburst galaxies. Here we conduct a study of these interactions, focusing on cooling through…
Highly Ionized Oxygen in the Circumgalactic Medium of TNG100 Galaxies: Distributions, Thermal States, and Ionization Mechanisms
School of Physics and Astronomy, Tel Aviv University（特拉维夫大学物理与天文学学院）；Center for Computational Astrophysics, Flatiron Institute（平顿研究所计算天体物理学中心）；Max-Planck-Institut für extraterrestrische Physik (MPE)（马克斯·普朗克地外物理学研究所）；Department of Physics, University of California, Berkeley（加州大学伯克利分校物理系）；Department of Astronomy, University of California, Berkeley（加州大学伯克利分校天文学系）
We investigate the formation of molecular clouds from atomic gas by using three-dimensional magnetohydrodynamical simulations,including non-equilibrium chemical reactions, heating/cooling processes, and self-gravity by changing the collision speed $V_0$ and the angle $θ$ between the magnetic field and colliding flow. We found that the efficiency of the dense gas formation depends on $θ$. For small $θ$, anisotropic super-Alfvénic turbulence delays the formation of gravitationally unstable clumps. An increase in $θ$ develops shock-amplified magnetic fields along which the gas is accumulated, mak…
We find, using cosmological simulations of galaxy clusters, that the hot X-ray emitting intra-cluster medium (ICM) enclosed within the outer accretion shock extends out to $R_{\rm shock}\sim(2 - 3) R_{\rm vir}$, where $R_{\rm vir}$ is the standard virial radius of the halo. Using a simple analytic model for satellite galaxies in the cluster, we evaluate the effect of ram pressure stripping on the gas in the inner discs and in the haloes at different distances from the cluster centre. We find that significant removal of star-forming disc gas occurs only at $r \lesssim 0.5 R_{\rm vir}$, while ga…
We present a 70ks Chandra observation of the radio galaxy 3C293. This galaxy belongs to the class of molecular hydrogen emission galaxies (MOHEGs) that have very luminous emission from warm molecular hydrogen. In radio galaxies, the molecular gas appears to be heated by jet-driven shocks, but exactly how this mechanism works is still poorly understood. With Chandra, we observe X-ray emission from the jets within the host galaxy and along the 100 kpc radio jets. We model the X-ray spectra of the nucleus, the inner jets, and the X-ray features along the extended radio jets. Both the nucleus and …
The fraction of star formation that results in bound star clusters is influenced by the density spectrum in which stars are formed and by the response of the stellar structure to gas expulsion. We analyse hydrodynamical simulations of turbulent fragmentation in star-forming regions to assess the dynamical properties of the resulting population of stars and (sub)clusters. Stellar subclusters are identified using a minimum spanning tree algorithm. When considering only the gravitational potential of the stars and ignoring the gas, we find that the identified subclusters are close to virial equil…
Satellite Metallicity Enhancement I: Suppressed Star Formation, Stellar Mass Loss, and Enriched Inflow of DESI and EAGLE Galaxies around Massive Clusters
State Key Laboratory of Dark Matter Physics & Tsung-Dao Lee Institute, Shanghai Jiao Tong University（暗物质物理国家重点实验室暨李政道研究所，上海交通大学）；Department of Astronomy, School of Physics and Astronomy, Shanghai Jiao Tong University（上海交大物理与天文学院天文学系）；Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室）；Department of Physics, Boston University（波士顿大学物理系）；Department of Physics & Astronomy, University College London（伦敦大学学院物理与天文系）；Instituto de Física, Universidad Nacional Autónoma de México（墨西哥国立自治大学物理研究所）
We present a new cosmological zoom-in simulation, where the zoom region consists of two halos with virial mass M_v~5x10^{12}M_{sun} and a ~Mpc long cosmic filament connecting them at z~2. Using this simulation, we study the evolution of the intergalactic medium in between these two halos at unprecedented resolution. At 5>z>3, the two halos are found to lie in a large intergalactic sheet, or "pancake", consisting of multiple co-planar dense filaments along which nearly all halos with M_v>10^9M_{sun} are located. This sheet collapses at z~5 from the merger of two smaller sheets. The strong shock…
We revisit the galaxy cluster RXC J1504-0248, a remarkable example of a structure with a strong cool core in a near redshift ($z = 0.216$). We performed a combined analysis using photometric and spectroscopic data obtained at Gemini South Telescope. We estimated the cluster mass through gravitational lensing, obtaining $M_{200} = 5.3\pm0.4 \times 10^{14}$ $h_{70}^{-1}$ M$_\odot$ within $R_{200} = 1.56 \pm 0.04$ $h^{-1}_{70}$ Mpc, in agreement with a virial mass estimate. This cluster presents a prominent filamentary structure associated to its BCG, located mainly along its major axis and align…
Dust waves are a result of gas-grain decoupling in a stream of dusty plasma that flows past a luminous star. The radiation field is sufficiently strong to overcome the collisional coupling between grains and gas at a "rip-point", where the ratio of radiation pressure to gas pressure exceeds a critical value of roughly 1000. When the rip point occurs outside the hydrodynamic bow shock, a separate dust wave may form, decoupled from the gas shell, which can either be drag-confined or inertia-confined, depending on the stream density and relative velocity. In the drag-confined case, there is a min…
