Sylvain Veilleux, Roberto Maiolino, Alberto D. Bolatto, Susanne Aalto
备注：
Review accepted for publication in Astronomy & Astrophysics Reviews, 168 pages, 34 figures; slightly revised version with updated text and figure captions. Now electronically published as https://doi.org/10.1007/s00159-019-0121-9
Neutral-atomic and molecular outflows are a common occurrence in galaxies, near and far. They operate over the full extent of their galaxy hosts, from the innermost regions of galactic nuclei to the outermost reaches of galaxy halos. They carry a substantial amount of material that would otherwise have been used to form new stars. These cool outflows may have a profound impact on the evolution of their host galaxies and environments. This article provides an overview of the basic physics of cool outflows, a comprehensive assessment of the observational techniques and diagnostic tools used to characterize them, a detailed description of the best-studied cases, and a more general discussion of the statistical properties of these outflows in the local and distant universe. The remaining outstanding issues that have not yet been resolved are summarized at the end of the review to inspire new research directions.
Galactic outflows commonly contain multiphase gas, and its physical origin requires explanation. Using the CGOLS (Cholla Galactic OutfLow Simulations) suite of high-resolution isolated galaxy models, we demonstrate the viability of rapid radiative cooling as a source of fast-moving ($v \sim 1000$ km/s), cool ($10^4$ K) gas observed in absorption line studies of outflows around some star-forming galaxies. By varying the mass-loading and geometry of the simulated winds, we identify a region of parameter space that leads to cool gas in outflows. In particular, when using an analytically-motivated…
We study how outflows of gas launched from a central galaxy undergoing repeated starbursts propagate through the circumgalactic medium (CGM), using the simulation code RAMSES. We assume that the outflow from the disk can be modelled as a rapidly moving bubble of hot gas at $\mathrm{\sim1\;kpc}$ above disk, then ask what happens as it moves out further into the halo around the galaxy on $\mathrm{\sim 100\;kpc}$ scales. To do this we run 60 two-dimensional simulations scanning over parameters of the outflow. Each of these is repeated with and without radiative cooling, assuming a primordial gas …
Tracing AGN Feedback Power with Cool/Warm Outflow Densities: Predictions and Observational Implications
Max Planck Institute for Astronomy（马克斯·普朗克天文学研究所）；Newcastle University（纽卡斯尔大学）；Center for Computational Astrophysics, Flatiron Institute（平顿研究所计算天体物理中心）
I present a suite of three-dimensional simulations of the evolution of initially-hot material ejected by starburst-driven galaxy outflows. The simulations are conducted in a comoving frame that moves with the material, tracking atomic/ionic cooling, Compton cooling, and dust cooling and destruction. Compton cooling is most efficient of these processes, while the main role of atomic/ionic cooling is to enhance density inhomogeneities. Dust, on the other hand, has little effect on the outflow evolution, and is rapidly destroyed in all the simulations except the case with the smallest mass flux. …
We present the fourth of the Cholla Galactic OutfLow Simulations suite (CGOLS). Using a physically-motivated prescription for clustered supernova feedback, we successfully drive a multiphase outflow from a disk galaxy. The high resolution ($< 5\,\mathrm{pc}$) across a relatively large domain ($20\,\mathrm{kpc}$) allows us to capture the hydrodynamic mixing and dynamical interactions between the hot and cool ($T \sim 10^4\,\mathrm{K}$) phases in the outflow, which in turn leads to direct evidence of a qualitatively new mechanism for cool gas acceleration in galactic winds. We show that mixing o…
Energy injection by supernovae may drive hot supersonic galactic winds in rapidly star-forming galaxies, driving metal-enriched gas into the circumgalactic medium and potentially accelerating cool gas. If sufficiently mass-loaded, such flows become radiative within the wind-driving region, reducing the overall mass outflow rate from the host galaxy. We show that this sets a maximum on the total outflow momentum for hot energy-driven winds. For a spherical wind of Solar metallicity driven by continuous star formation, $\dot p_\rm{max} \simeq 1.9\times10^4\ M_\odot/\rm{yr\ km/s}\ (α/0.9)^{0.86}(…
SQuIGG$\vec{L}$E: Ubiquitous Cool Gas Outflows with Large Mass-Loading Factors in $z\sim0.7$ Post-starburst Galaxies
Texas A&M University（德克萨斯农工大学）；Princeton University（普林斯顿大学）；Johns Hopkins University（约翰斯·霍普金斯大学）；Arizona State University（亚利桑那州立大学）；University of Pittsburgh（匹兹堡大学）
Cool outflows are now commonly observed in galaxies, but their physical origin and driving mechanism remain unclear. Active galactic nucleus (AGN) feedback can potentially accelerate cool galactic outflows via cosmic rays (CR) and radiation pressure on dust. Here we investigate the relative importance of CR and radiation feedback in AGNs, and we analyse the physical conditions for outflow launching as a function of the black hole accretion flow mode. We assume CRs from AGN jet origin and consider the analogy with Galactic X-ray binaries, whereby the jet is prominent at low accretion rates (har…
The cooling flow problem is one of the central problems in galaxy clusters, and active galactic nucleus (AGN) feedback is considered to play a key role in offsetting cooling. However, how AGN jets heat and suppress cooling flows remains highly debated. Using an idealized simulation of a cool-core cluster, we study the development of central cooling catastrophe and how a subsequent powerful AGN jet event averts cooling flows, with a focus on complex gasdynamical processes involved. We find that the jet drives a bow shock, which reverses cooling inflows and overheats inner cool core regions. The…
The MUSE Ultra Deep Field (MUDF) VIII. The cool gas distribution surrounding galaxies at redshifts z ~ 0.5-2
Università degli Studi di Milano-Bicocca（米兰比可卡大学）；INAF – Osservatorio Astronomico di Trieste（意大利国家天体物理研究所的里雅斯特天文台）；Max-Planck-Institut für Astrophysik（马克斯·普朗克天体物理学研究所）；IUCAA（印度联合大学宇宙学及应用天文学中心）；INAF – Osservatorio Astronomico di Brera（意大利国家天体物理研究所布雷拉天文台）；Space Telescope Science Institute（太空望远镜科学研究所）；Johns Hopkins University（约翰斯·霍普金斯大学）
利用MUDF调查的深MUSE数据，研究红移0.5 < z < 2星系周围低温气体分布，通过径向和横向分析探讨气体出流与星系际介质特性。
Superwinds and superbubbles driven by mechanical feedback from super star clusters (SSCs) are common features in many star-forming galaxies. While the adiabatic fluid model can well describe the dynamics of superwinds, several observations of starburst galaxies revealed the presence of compact regions with suppressed superwinds and strongly radiative cooling, i.e., catastrophic cooling. In the present study, we employ the non-equilibrium atomic chemistry and cooling package MAIHEM, built on the FLASH hydrodynamics code, to generate a grid of models investigating the dependence of cooling modes…
This paper investigates the neutral gas phase of galactic winds via the Na I D$λλ5890,5895$Å feature within $z \sim 0.04$ MaNGA galaxies, and directly compares their incidence and strength to the ionized winds detected within the same parent sample. We find evidence for neutral outflows in 127 galaxies ($\sim 5$ per cent of the analysed line-emitting sample). Na I D winds are preferentially seen in galaxies with dustier central regions and both wind phases are more often found in systems with elevated SFR surface densities, especially when there has been a recent upturn in the star formation a…
Resolving the Unresolved Galactic Winds in Multi-phase Models. I. Methodology and Application
Northwestern University（西北大学）；Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA)（天体物理学跨学科探索与研究中心）；Cornell University（康奈尔大学）；New York University（纽约大学）；Johns Hopkins University（约翰斯·霍普金斯大学）；Arizona State University（亚利桑那州立大学）；Columbia University（哥伦比亚大学）；Flatiron Institute（平顶山研究所）；Space Telescope Science Institute（太空望远镜科学研究所）；University of Edinburgh（爱丁堡大学）；Zhejiang University（浙江大学）
We recently used hydro-chemical simulations to demonstrate that molecular outflows observed in luminous quasars can be explained by molecule formation within the AGN wind. However, these simulations cover a limited parameter space, due to their computational cost. We have therefore developed an analytic model to follow cooling in the shocked ISM layer of an AGN wind. We explore different ambient densities ($1-10^{4} \, \rm{cm}^{-3}$), density profile slopes ($0-1.5$), AGN luminosities ($10^{44}-10^{47} \, \rm{erg} \, \rm{s}^{-1}$), and metallicities ($0.1-3 \rm{Z}_{\odot}$). The swept up gas m…
The characterization of the large amount of gas residing in the galaxy halos, the so called circumgalactic medium (CGM), is crucial to understand galaxy evolution across cosmic time. We focus here on the the cool ($T\sim10^4$ K) phase of this medium around star-forming galaxies in the local universe, whose properties and dynamics are poorly understood. We developed semi-analytical parametric models to describe the cool CGM as an outflow of gas clouds from the central galaxy, as a result of supernova explosions in the disc (galactic wind). The cloud motion is driven by the galaxy gravitational …
Galactic outflows play a major role in the evolution of galaxies, but the underlying physical processes are poorly understood. This is mainly because we have little information about the outflow structure, especially on large scales. In this paper, we probe the structure of galactic outflows in low-$z$ starburst by using a combination of ultra-violet spectroscopy and imaging of the fluorescence emission lines (associated with transitions to excited fine-structure levels) and spectroscopy of the corresponding strongly blue-shifted resonance absorption lines. We find that in the majority of case…
Interstellar ultraviolet absorption-lines provide crucial information about the properties of galactic outflows. In this paper, we augment our previous analysis of the systematic properties of starburst-driven galactic outflows by expanding our sample to include a rare population of starbursts with exceptionally high outflow velocities. In principle, these could be a qualitatively different phenomenon from more typical outflows. However, we find that instead these starbursts lie on, or along the extrapolation of, the trends defined by the more typical systems studied previously by us. We explo…
Motivated by observations of outflowing galaxies, we investigate the combined impact of magnetic fields and radiative cooling on the evolution of cold clouds embedded in a hot wind. We perform a collection of three-dimensional adaptive mesh refinement, magnetohydrodynamical simulations that span two resolutions, and include fields that are aligned and transverse to the oncoming, super-Alfvénic material. Aligned fields have little impact on the overall lifetime of the clouds over the non-magnetized case, although they do increase the mixing between the wind and cloud material by a factor of $\a…
We develop a semi-analytic model to explore the physical properties of cool pressure-confined circumgalactic clouds with mass ranging from $10$ to $10^{8} \, \rm M_{\odot}$ in a hot diffuse halo. We consider physical effects that control the motion and mass loss of the clouds, and estimate the lifetime and the observed properties of individual cool gas clouds inferred from the CLOUDY simulation. Our results show that the cool pressure-confined gas clouds have physical properties consistent with absorption line systems with neutral hydrogen column densities $N_{\rm HI}\geq10^{18.5} \rm cm^{-2}$…
We present spatially-resolved morphological properties of [CII] 158 $μ$m, [OIII] 88 $μ$m, dust, and rest-frame ultraviolet (UV) continuum emission for A1689-zD1, a strongly lensed, sub-L* galaxy at $z=7.13$, by utilizing deep Atacama Large Millimeter/submillimeter Array (ALMA) and Hubble Space Telescope (HST) observations. While the [OIII] line and UV continuum are compact, the [CII] line is extended up to a radius of $r \sim 12$ kpc. Using multi-band rest-frame far-infrared (FIR) continuum data ranging from 52-400 $μ$m, we find an average dust temperature and emissivity index of $T_{\rm dust}…
Dynamics of stellar wind in a Roche potential: implications for (i) outflows & periodicities relevant to astronomical masers, and (ii) generation of baroclinicity
Implication of a galaxy-scale negative feedback by one of the most powerful multi-phase outflows in a hyper-luminous infrared galaxy at the intermediate redshift
本文通过 Gemini 和 ALMA 观测发现中等红移超亮红外星系 J1126 中存在快速电离与高质量损失率分子外流并存的多相外流，揭示其由 AGN 热风或辐射压力驱动，能引发电离激波并增强气体解离，产生星系尺度负反馈，具长期调节宿主增长潜力。
The link between hot and cool stellar outflows is shown to be critical for correctly predicting the masses of the most massive black holes (BHs) below the so-called pair-instability supernova (PISN) mass gap. Gravitational Wave (GW) event 190521 allegedly hosted an "impossibly" heavy BH of 85 Solar Masses. Here we show how our increased knowledge of both metallicity Z and temperature dependent mass loss is critical for our evolutionary scenario of a low-Z blue supergiant (BSG) progenitor of an initially approx 100 Solar Masses star to work. We show using MESA stellar evolution modelling experi…
We carry out a suite of simulations of the evolution of cosmic-ray (CR) driven, radiatively-cooled cold clouds embedded in hot material, as found in galactic outflows. In such interactions, CRs stream towards the cloud at the Alfvén speed, which decreases dramatically at the cloud boundary, leading to a bottleneck in which pressure builds up in front of the cloud. At the same time, CRs stream along the sides of the cloud, forming a boundary layer where large filaments develop. Shear in this boundary layer is the primary mode of cloud destruction, which is relatively slow in all cases, but slow…
We report on the first ALMA observation of the CO(3$-$2) and rest-frame ~340 GHz continuum emission in PDS 456, which is the most luminous, radio-quiet QSO in the local Universe ($z$~0.18), with a bolometric luminosity $L_{\rm Bol}\sim10^{47}$ erg s$^{-1}$. ALMA angular resolution allowed us to map scales as small as ~700 pc. The molecular gas reservoir, traced by the core of the very bright CO(3$-$2) emission line, is distributed in a compact rotating disk, with size of ~1.3 kpc, seen close to face-on ($i$~25 deg). Fast CO(3$-$2) emission in the velocity range $v\in[-1000,+500]$ km s$^{-1}$ i…
The shape of emission lines in the optical spectra of star-forming galaxies reveals the kinematics of the diffuse gaseous component. We analyse the shape of prominent emission lines in a sample of ~53,000 star-forming galaxies from the Sloan Digital Sky Survey, focusing on departures from gaussianity. Departures from a single gaussian profile allow us to probe the motion of gas and to assess the role of outflows. The sample is divided into groups according to their stellar velocity dispersion and star formation rate. The spectra within each group are stacked to improve the signal-to-noise rati…
We study the distribution and kinematics of the cool circumgalactic medium (CGM) of emission line galaxies (ELGs) traced by metal absorption lines. Using about 200,000 ELGs from SDSS-IV eBOSS and half a million background quasars from SDSS, we measure the median absorption strength of MgII and FeII lines in quasar spectra for impact parameters ranging from 10 kpc to 1 Mpc. For comparison we measure the same quantity around luminous red galaxies (LRGs). On scales greater than 100 kpc both ELGs and LRGs exhibit similar absorption profiles. However, metal absorption is 5-10 times stronger around …
We compare 5 sub-grid models for supernova (SN) feedback in adaptive mesh refinement (AMR) simulations of isolated dwarf and L-star disk galaxies with 20-40 pc resolution. The models are thermal dump, stochastic thermal, 'mechanical' (injecting energy or momentum depending on the resolution), kinetic, and delayed cooling feedback. We focus on the ability of each model to suppress star formation and generate outflows. Our highest-resolution runs marginally resolve the adiabatic phase of the feedback events, which correspond to 40 SN explosions, and the first three models yield nearly identical …
Observations at intermediate redshifts reveal the presence of numerous, compact, weak MgII absorbers with near to super-solar metallicities, often surrounded by more extended regions that produce CIV and/or OVI absorption in the circumgalactic medium at large impact parameters from luminous galaxies. Their origin and nature remains unclear. We hypothesize that undetected, satellite dwarf galaxies are responsible for producing some of these weak MgII absorbers. We test our hypothesis using gas dynamical simulations of galactic outflows from a dwarf satellite galaxy with a halo mass of $5\times1…
We have recently improved our model of active galactic nucleus (AGN) by attaching the supermassive black hole (SMBH) to a massive nuclear star cluster (NSC). Here we study the effects of this new model in massive, gas-rich galaxies with several simulations of different feedback recipes with the hydrodynamics code RAMSES. These simulations are compared to a reference simulation without any feedback, in which the cooling halo gas is quickly consumed in a burst of star formation. In the presence of strong supernovae (SN) feedback, we observe the formation of a galactic fountain that regulates sta…
Witnessing the Earliest Phases of Galactic Wind Formation in Superluminous Supernova Hosts: Implications for Star-formation-driven Outflows in Low- and High-redshift Galaxies
Stockholm University（斯德哥尔摩大学）；University of Michigan（密歇根大学）；University of Minnesota（明尼苏达大学）；Weizmann Institute of Science（魏茨曼科学研究所）
Cool clouds are expected to be destroyed and incorporated into hot supernova-driven galactic winds. The mass-loading of a wind by the cool medium modifies the bulk velocity, temperature, density, entropy, and abundance profiles of the hot phase relative to an un-mass-loaded outflow. We provide general equations and limits for this physics that can be used to infer the rate of cool gas entrainment from X-ray observations, accounting for non-spherical expansion. In general, mass-loading flattens the density and temperature profiles, decreases the velocity and increases the entropy if the Mach nu…
Large scale outflows in star-forming galaxies are observed to be ubiquitous, and are a key aspect of theoretical modeling of galactic evolution in a cosmological context, the focus of the SMAUG (Simulating Multiscale Astrophysics to Understand Galaxies) project. Gas blown out from galactic disks, similar to gas within galaxies, consists of multiple phases with large contrasts of density, temperature, and other properties. To study multiphase outflows as emergent phenomena, we run a suite of ~pc-resolution local galactic disk simulations using the TIGRESS framework. Explicit modeling of the int…
We investigate the interactions of energetic hadronic particles with the media in outflows from star-forming protogalaxies. These particles undergo pion-producing interactions which can drive a heating effect in the outflow, while those advected by the outflow also transport energy beyond the galaxy, heating the circumgalactic medium. We investigate how this process evolves over the length of the outflow and calculate the corresponding heating rates in advection-dominated and diffusion-dominated cosmic ray transport regimes. In a purely diffusive transport scenario, we find the peak heating ra…
Supernovae (SNe) drive multiphase galactic outflows, impacting galaxy formation; however, cosmological simulations mostly use \textit{ad hoc} feedback models for outflows, making outflow-related predictions from first principles problematic. Recent small-box simulations resolve individual SNe remnants in the interstellar medium (ISM), naturally driving outflows and permitting a determination of the wind loading factors of energy $η_E$, mass $η_m$, and metals $η_Z$. In this Letter, we compile small-box results, and find consensus that the hot outflows are much more powerful than the cool outflo…
