The accretion history of protostars remains widely mysterious even though it represents one of the best ways to understand the protostellar collapse that leads to the formation of stars. Molecular outflows are here used to characterize the protostellar accretion phase in W43-MM1. The W43-MM1 protocluster host a sufficient number of protostars to statistically investigate molecular outflows in a single, homogeneous region. We used the CO(2-1) and SiO(5-4) line datacubes, taken as part of an ALMA mosaic with a 2000 AU resolution, to search for protostellar outflows, evaluate the influence that the environment has on these outflows' characteristics and put constraints on outflow variability in W43-MM1. We discovered a rich cluster of 46 outflow lobes, driven by 27 protostars with masses of 1-100 Msun. The complex environment inside which these outflow lobes develop has a definite influence on their length, limiting the validity of using outflows' dynamical timescales as a proxy of the ejection timescale in clouds with high dynamics and varying conditions. We performed a detailed study of Position-Velocity (PV) diagrams of outflows that revealed clear events of episodic ejection. The time variability of W43-MM1 outflows is a general trend and is more generally observed than in nearby, low- to intermediate-mass star-forming regions. The typical timescale found between two ejecta, about 500 yr, is consistent with that found in nearby protostars. If ejection episodicity reflects variability in the accretion process, either protostellar accretion is more variable or episodicity is easier to detect in high-mass star-forming regions than in nearby clouds. The timescale found between accretion events could be resulting from disk instabilities, associated with bursts of inflowing gas arising from the dynamical environment of high-mass star-forming cores.
The accretion of material onto young protostars is accompanied by the launching of outflows. Observations show that accretion, and therefore also outflows, are episodic. However, the effects of episodic outflow feedback on the core-scale are not well understood. We have performed 88 Smoothed Particle Hydrodynamic simulations of turbulent dense $1 \, \mathrm{M}_{\odot}$ cores, to study the influence of episodic outflow feedback on the stellar multiplicity and the star formation efficiency (SFE). Protostars are represented by sink particles, which use a sub-grid model to capture stellar evolutio…
During star formation, the accretion disk drives fast MHD winds which usually contain two components, a collimated jet and a radially distributed wide-angle wind. These winds entrain the surrounding ambient gas producing molecular outflows. We report recent observation of 12CO (2-1) emission of the HH 46/47 molecular outflow by the Atacama Large Millimeter/sub-millimeter Array, in which we identify multiple wide-angle outflowing shell structures in both the blue and red-shifted outflow lobes. These shells are highly coherent in position-position-velocity space, extending to >40-50 km/s in velo…
Young low-mass protostars undergo short phases of high accretion and outburst activity leading to lumpy outflows. Recent observations have shown that the position-velocity and mass-velocity diagrams of such outflows exhibit individual bullet-like features; some of these bullets subscribe to a `Hubble Law' velocity relation, and others are manifest as `Hubble wedges'. In order to explore the origin of these features, we have developed a new episodic outflow model for the SPH code {\sc gandalf}, which mimics the accretion and ejection behaviour of FU Ori type stars. We apply this model to simula…
We report signatures of episodic accretion in young stellar objects (YSOs) that emerge in protobinary configurations in a gravoturbulent gas collapse. We find in most of these protobinary systems strong accretion bursts between the two companions with a recurrence time-scale of about 1 kyr. The accretion rate onto the secondary star typically exceeds that onto the primary with a peak value of 2 $\times 10^{-2}$ M$_{\odot}$ yr$^{-1}$ for the former and 6 $\times 10^{-3}$ M$_{\odot}$ yr$^{-1}$ for the latter. We propose that the secondary companion which remains more active in its episodes of ac…
Water fountains are evolved stars showing early stages of collimated mass loss during transition from the asymptotic giant branch, providing valuable insight into the formation of asymmetric planetary nebulae. We report the results of multi-epoch VLBI observations, which determine the spatial and three-dimensional kinematic structure of H2O masers associated with the water fountain IRAS 18113-2503. The masers trace three pairs of high-velocity (~150-300 km/s) bipolar bow shocks on a scale of 0.18'' (~2000 au). The expansion velocities of the bow shocks exhibit an exponential decrease as a func…
We develop a semi-analytic formalism for the determination of the evolution of the stellar mass accretion rate for specified density and velocity profiles that emerge from the runaway collapse of a prestellar cloud core. In the early phase, when the infall of matter from the surrounding envelope is substantial, the star accumulates mass primarily because of envelope-induced gravitational instability in a protostellar disc. In this phase, we model the envelope mass accretion rate from the isothermal free-fall collapse of a molecular cloud core. The disc gains mass from the envelope, and transpo…
A star acquires much of its mass by accreting material from a disc. Accretion is probably not continuous but episodic. We have developed a method to include the effects of episodic accretion in simulations of star formation. Episodic accretion results in bursts of radiative feedback, during which a protostar is very luminous, and its surrounding disc is heated and stabilised. These bursts typically last only a few hundred years. In contrast, the lulls between bursts may last a few thousand years; during these lulls the luminosity of the protostar is very low, and its disc cools and fragments. …
It is speculated that the accretion of material onto young protostars is episodic. We present a computational method to include the effects of episodic accretion in radiation hydrodynamic simulations of star formation. We find that during accretion events protostars are "switched on", heating and stabilising the discs around them. However, these events typically last only a few hundred years, whereas the intervals in between them may last for a few thousand years. During these intervals the protostars are effectively "switched off", allowing gravitational instabilities to develop in their disc…
Aims: Our goal is to investigate how the strength of episodic accretion bursts depends on eccentricity. Methods: We investigate the binary trigger hypothesis in longer-period (>20yr) binaries by carrying out three-dimensional magnetohydrodynamical (MHD) simulations of the formation of low-mass binary stars down to final separations of $\sim$10$\au$, including the effects of gas turbulence and magnetic fields. We ran two simulations with an initial turbulent gas core of one solar mass each and two different initial turbulent Mach numbers, M = 0.1 and M=0.2, for 6500yr after protostar formation.…
During the early phases of low-mass star formation, episodic accretion causes the ejection of high-velocity outflow bullets, which carry a fossil record of the driving protostar's accretion history. We present 44 SPH simulations of $1\,\mathrm{M}_{\odot}$ cores, covering a wide range of initial conditions, and follow the cores for five free-fall times. Individual protostars are represented by sink particles, and the sink particles launch episodic outflows using a subgrid model. The Optics algorithm is used to identify individual episodic bullets within the outflows. The parameters of the overa…
We report multi-epoch VLBI H$_2$O maser observations towards the compact cluster of YSOs close to the Herbig Be star LkH$α$ 234. This cluster includes LkH$α$ 234 and at least nine more YSOs that are formed within projected distances of $\sim$10 arcsec ($\sim$9,000 au). We detect H$_2$O maser emission towards four of these YSOs. In particular, our VLBI observations (including proper motion measurements) reveal a remarkable very compact ($\sim$0.2 arcsec = $\sim$180 au), bipolar H$_2$O maser outflow emerging from the embedded YSO VLA 2. We estimate a kinematic age of $\sim$40 yr for this bipolar…
In the last twenty years, the topic of episodic accretion has gained significant interest in the star formation community. It is now viewed as a common, though still poorly understood, phenomenon in low-mass star formation. The FU Orionis objects (FUors) are long-studied examples of this phenomenon. FUors are believed to undergo accretion outbursts during which the accretion rate rapidly increases from typically $10^{-7}$ to a few $10^{-4}$ $M_\odot$ yr$^{-1}$, and remains elevated over several decades or more. EXors, a loosely defined class of pre-main sequence stars, exhibit shorter and repe…
Protostars grow in mass by accreting material through their discs, and this accretion is initially their main source of luminosity. The resulting radiative feedback heats the environments of young protostars, and may thereby suppress further fragmentation and star formation. There is growing evidence that the accretion of material onto protostars is episodic rather than continuous; most of it happens in short bursts that last up to a few hundred years, whereas the intervals between these outbursts of accretion could be thousands of years. We have developed a model to include the effects of epi…
We present the latest development of the disk gravitational instability and fragmentation model, originally introduced by us to explain episodic accretion bursts in the early stages of star formation. Using our numerical hydrodynamics model with improved disk thermal balance and star-disk interaction, we computed the evolution of protostellar disks formed from the gravitational collapse of prestellar cores. In agreement with our previous studies, we find that cores of higher initial mass and angular momentum produce disks that are more favorable to gravitational instability and fragmentation, …
Using zoom-simulations carried out with the adaptive mesh-refinement code RAMSES with a dynamic range of up to $2^{27} \approx 1.34 \times 10^8$ we investigate the accretion profiles around six stars embedded in different environments inside a (40 pc)$^3$ giant molecular cloud, the role of mass infall and disc instabilities on the accretion profile, and thus on the luminosity of the forming protostar. Our results show that the environment in which the protostar is embedded determines the overall accretion profile of the protostar. Infall on to the circumstellar disc may trigger gravitational d…
ALMA-QUARKS view of W49N: Multipolar episodic outflow associated with the most energetic Galactic water maser
Shanghai Astronomical Observatory, Chinese Academy of Sciences（中国科学院上海天文台）；University of Chinese Academy of Sciences（中国科学院大学）；State Key Laboratory of Radio Astronomy and Technology, Shanghai Astronomical Observatory, Chinese Academy of Sciences（中国科学院上海天文台射电天文与技术国家重点实验室）；Max Planck Institute for Astronomy（马克斯·普朗克天文学研究所）；Xinjiang Astronomical Observatory, Chinese Academy of Sciences（中国科学院新疆天文台）；Institute of Astronomy, Graduate School of Science, The University of Tokyo（东京大学大学院理学系研究科天文学专攻）
The formation of SMSs is a potential pathway to seed SMBHs in the early universe. A critical issue for forming SMSs is stellar UV feedback, which may limit the stellar mass growth via accretion. In this paper we study the evolution of an accreting SMS and its UV emissivity under conditions of realistic variable accretion from a self-gravitating circumstellar disc. First we conduct a 2D hydrodynamical simulation to follow the long-term protostellar accretion until the stellar mass exceeds $10^4~M_\odot$. The disc fragments due to gravitational instability, creating a number of small clumps that…
Very low-mass Class I protostars have been investigated very little thus far. Variability of these young stellar objects (YSOs) and whether or not they are capable of strong episodic accretion is also left relatively unstudied. We investigate accretion variability in IRS54, a Class I very low-mass protostar with a mass of M$_{\star}$ ~ 0.1 - 0.2 M$_{\odot}$. We obtained spectroscopic and photometric data with VLT/ISAAC and VLT/SINFONI in the near-infrared ($J$, $H$, and $K$ bands) across four epochs (2005, 2010, 2013, and 2014). We used accretion-tracing lines (Pa$β$ and Br$γ$) and outflow-tra…
Episodic accretion has been used to explain the wide range of protostellar luminosities, but its origin and influence on the star forming process are not yet fully understood. We present an ALMA survey of N$_2$H$^+$ ($1-0$) and HCO$^+$ ($3-2$) toward 39 Class 0 and Class I sources in the Perseus molecular cloud. N$_2$H$^+$ and HCO$^+$ are destroyed via gas-phase reactions with CO and H$_2$O, respectively, thus tracing the CO and H$_2$O snowline locations. A snowline location at a much larger radius than that expected from the current luminosity suggests that an accretion burst has occurred in …
3D simulations of high mass young stellar object (HMYSO) growth show that their circumstellar discs fragment onto multiple self-gravitating objects. Accretion of these by HMYSO may explain episodic accretion bursts discovered recently. We post-process results of a previous 3D simulation of a HMYSO disc with a 1D code that resolves the disc and object dynamics down to the stellar surface. We find that burst-like deposition of material into the inner disc seen in 3D simulations by itself does not always signify powerful accretion bursts. Only high density post-collapse clumps crossing the inner …
The earliest phases of star formation are characterised by intense mass accretion from the circumstellar disk to the central star. One group of young stellar objects, the FU Orionis-type stars exhibit accretion rate peaks accompanied by bright eruptions. The occurrence of these outbursts might solve the luminosity problem of protostars, play a key role in accumulating the final star mass, and have a significant effect on the parameters of the envelope and the disk. In the framework of the Structured Accretion Disks ERC project, we are conducting a systematic investigation of these sources with…
Rotating outflows from protostellar disks might trace extended magneto-hydrodynamic (MHD) disk winds (DWs), providing a solution to the angular momentum problem in disk accretion for star formation. In the jet system HH 212, a rotating outflow was detected in SO around an episodic jet detected in SiO. Here we spatially resolve this SO outflow into three components: a collimated jet aligned with the SiO jet, the wide-angle disk outflow, and an evacuated cavity in between created by a large jet-driven bowshock. Although it was theoretically predicted before, it is the first time that such a jet-…
Protostars likely accrete material at a highly time variable rate, however, measurements of accretion variability from the youngest protostars are rare, as they are still deeply embedded within their envelopes. Sub-mm/mm observations can trace the thermal response of dust in the envelope to accretion luminosity changes, allowing variations in the accretion rate to be quantified. In this paper, we present contemporaneous sub-mm/mm light curves of variable protostars in Serpens Main, as observed by the ALMA ACA, SMA, and JCMT. The most recent outburst of EC 53 (V371 Ser), an $\sim 18$ month peri…
Episodic accretion is an important process in the evolution of young stars and their environment. The observed strong luminosity bursts of young stellar objects likely have a long lasting impact on the chemical evolution of the disk and envelope structure. We want to investigate observational signatures of the chemical evolution in the post-burst phase for embedded sources. With such signatures it is possible to identify targets that experienced a recent luminosity burst. We present a new model for episodic accretion chemistry based on the 2D, radiation thermo-chemical disk code ProDiMo. We ha…
Warped accretion disks have attracted intensive attention because of their critical role on shaping the spin of supermassive massive black holes (SMBHs) through the Bardeen-Petterson effect, a general relativistic effect that leads to final alignments or anti-alignments between black holes and warped accretion disks. We study such alignment processes by explicitly taking into account the finite sizes of accretion disks and the episodic lifetimes of AGNs that delineate the duration of gas fueling onto accretion disks. We employ an approximate global model to simulate the evolution of accretion …
We aim at studying the causal link between the knotty jet structure in CARMA 7, a young Class 0 protostar in the Serpens South cluster, and episodic accretion in young protostellar disks. We used numerical hydrodynamics simulations to derive the protostellar accretion history in gravitationally unstable disks around solar-mass protostars. We compared the time spacing between luminosity bursts Δτ_mod, caused by dense clumps spiralling on the protostar, with the differences of dynamical timescales between the knots Δτ_obs in CARMA 7. We found that the time spacing between the bursts have a bi-mo…
Ejection activities in S255IR-SMA1 and AFGL 5142 were investigated by multi-epoch VLBI observations of 22 GHz water masers, tracing bowshocks leading collimated jets. The history of ejections, revealed by the 3D maser motions and supplemented by the literature, suggests that these massive stars formed by episodic accretion, inferred via the accretion-ejection connection. This contribution centers on the role of episodic accretion in overcoming the radiation pressure problem of massive star formation - with maser VLBI and single-dish observations providing essential observational tools.
In search for a synthetic understanding, a scenario for the evolution of the star formation rate and the chemical abundances in galaxies is proposed, combining gas infall from galactic halos, outflow of gas by supernova explosions, and an oscillatory star formation process. The oscillatory star formation model is a consequence of the modelling of the fractional masses changes of the hot, warm and cold components of the interstellar medium. The observed periods of oscillation vary in the range $(0.1-3.0)\times10^{7}$\,yr depending on various parameters existing from giant to dwarf galaxies. The…
We constrain the average episodic quasar lifetime (as in steady-state accretion) using two statistics of quasars that are recently turned off (i.e., dimmed by a large factor): 1) the fraction of turned-off quasars in a statistical sample photometrically observed over an extended period (e.g., $Δt=20$ yrs); 2) the fraction of massive galaxies that show 'orphan' broad MgII emission, argued to be short-lived echoes of recently turned-off quasars. The two statistics constrain the average episodic quasar lifetime to be hundreds to thousands of years. Much longer (or shorter) episodic lifetimes are …
We present a study of outflows at extremely early stages of high-mass star formation obtained from the ALMA Survey of 70 $μ\rm m$ dark High-mass clumps in Early Stages (ASHES). Twelve massive 3.6$-$70 $μ\rm m$ dark prestellar clump candidates were observed with the Atacama Large Millimeter/submillimeter Array (ALMA) in Band 6. Forty-three outflows are identified toward 41 out of 301 dense cores using the CO and SiO emission lines, yielding a detection rate of 14%. We discover 6 episodic molecular outflows associated with low- to high-mass cores, indicating that episodic outflows (and therefore…
The relation between the mass accretion rate onto the circumstellar disc and the rate of mass ejection by magnetically driven winds is investigated using three-dimensional magnetohydrodynamics simulations. Using a spherical cloud core with a varying ratio of thermal to gravitational energy, which determines the mass accretion rate onto the disc, to define the initial conditions, the outflow propagation for approximately 10^4 yr after protostar formation is then calculated for several cloud cores. The mass ejection rate and accretion rate are comparable only when the magnetic energy of the init…
Born in rapidly evolving mini-halos during the first billion years of the Universe, super- massive black holes (SMBH) feed from gas flows spanning many orders of magnitude, from the cosmic web in which they are embedded to their event horizon. As such, accretion onto SMBHs constitutes a formidable challenge to tackle numerically, and currently requires the use of sub-grid models to handle the flow on small, unresolved scales. In this paper, we study the impact of resolution on the accretion pattern of SMBHs initially inserted at the heart of dense galactic gas clouds, using a custom super-Lagr…
We present coupled stellar evolution (SE) and 3D radiation-hydrodynamic (RHD) simulations of the evolution of primordial protostars, their immediate environment, and the dynamic accretion history under the influence of stellar ionizing and dissociating UV feedback. Our coupled SE-RHD calculations result in a wide diversity of final stellar masses covering 10 Msun $\lesssim M_* \lesssim$ 1000 Msun. The formation of very massive ($\gtrsim$ 250 Msun) stars is possible under weak UV feedback, whereas ordinary massive (a few x 10 Msun) stars form when UV feedback can efficiently halt the accretion.…
It is well known that the Galactic bar drives a gas inflow into the Central Molecular Zone, which fuels star formation, accretion onto the central super-massive black hole, and large-scale outflows. This inflow happens mostly through two symmetrical dust-lanes, similar to those often seen in external barred galaxies. Here we use the fact that the Milky Way dust-lanes have been previously identified in $^{12}$CO datacubes and a simple geometrical model to derive the first observational determination of the mass inflow rate into the Central Molecular Zone. We find that the time-averaged inflow r…
Context. The process of mass accretion in the earliest phases of star formation is still not fully understood: Does the accretion rate smoothly decline with the age of the protostar or are there short, intermittent accretion bursts? Aims. We aim to explore whether or not the observed C$^{18}$O and N$_2$H$^+$ emission pattern towards the VeLLO IRAM 04191+1522 can be understood in the framework of a scenario where the emission is chemically tracing a past accretion burst. Methods.We used high-angular-resolution Plateau de Bure Interferometer (PdBI) observations of C$^{18}$O and N$_2$H$^+$ toward…
The evolution of protostellar outflows is investigated under different mass accretion rates in the range $\sim10^{-5}-10^{-2} {\rm M}_\odot$ yr$^{-1}$ with three-dimensional magnetohydrodynamic simulations. A powerful outflow always appears in strongly magnetized clouds with $B_0 \gtrsim B_{\rm 0, cr}$ $=10^{-4} (M_{\rm cl}/100 {\rm M}_\odot){\rm G}$, where $M_{\rm cl}$ is the cloud mass. When a cloud has a weaker magnetic field, the outflow does not evolve promptly with a high mass accretion rate. In some cases with moderate magnetic fields $B_0$ slightly smaller than $B_{\rm 0,cr}$, the outf…
We perform two-dimensional axially symmetric radiation-hydrodynamic simulations to assess the impact of outflows and radiative force feedback from massive protostars by varying when the protostellar outflow starts, the ratio of ejection to accretion rates, and the strength of the wide angle disk wind component. The star formation efficiency, i.e. the ratio of final stellar mass to initial core mass, is dominated by radiative forces and the ratio of outflow to accretion rates. Increasing this ratio has three effects: First, the protostar grows slower with a lower luminosity at any given time, l…
The Gaia Alert System issued an alert on 2020 August 28, on Gaia 20eae when its light curve showed a $\sim$4.25 magnitude outburst. We present multi-wavelength photometric and spectroscopic follow-up observations of this source since 2020 August and identify it as the newest member of the FUor/EXor family of sources. We find that the present brightening of Gaia 20eae is not due to the dust clearing event but due to an intrinsic change in the spectral energy distribution. The light curve of Gaia 20eae shows a transition stage during which most of its brightness ($\sim$3.4 mag) has occurred at a…
Understanding how material accretes onto the rotationally supported disk from the surrounding envelope of gas and dust in the youngest protostellar systems is important for describing how disks are formed. Magnetohydrodynamic simulations of magnetized, turbulent disk formation usually show spiral-like streams of material (accretion flows) connecting the envelope to the disk. However, accretion flows in these early stages of protostellar formation still remain poorly characterized due to their low intensity and possibly some extended structures are disregarded as being part of the outflow cavit…
The JWST EXCELS survey: Outflows in 1.5 < z < 5 quiescent and recently quenched galaxies are likely relics from episodic AGN activity
University of Edinburgh（爱丁堡大学）；University of Nottingham（诺丁汉大学）；Universidad de Sevilla（塞维利亚大学）；University of St Andrews（圣安德鲁斯大学）；University of California, Los Angeles（加州大学洛杉矶分校）
利用JWST NIRSpec光谱研究1.8 ≤ z ≤ 4.6红移的13个后星暴和静止星系中的中性气体出流和吸积，发现出流与AGN活动相关，且出流速率远高于恒星形成率。
Detection of episodic Ultra-fast Outflows in the Low-luminosity quasar Mrk 205 using XMM-Newton data
Instituto de Astronomía, (IA-UNAM)（天文学研究所（UNAM））；INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna（博洛尼亚天文物理与空间科学研究所（INAF））；Instituto Nacional de Astrofísica, Óptica y Electrónica（国家天文学、光学和电子学研究所）；Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México（墨西哥国立自治大学核科学研究所）
Episodic accretion has been proposed as a solution to the long-standing luminosity problem in star formation; however, the process remains poorly understood. We present observations of line emission from N2H+ and CO isotopologues using the Atacama Large Millimeter/submillimeter Array (ALMA) in the envelopes of eight Very Low Luminosity Objects (VeLLOs). In five of the sources the spatial distribution of emission from N2H+ and CO isotopologues shows a clear anti-correlation. It is proposed that this is tracing the CO snow line in the envelopes: N2H+ emission is depleted toward the center of the…
Hub-filament systems and the growth of massive stars: episodic accretion, clustered environments, and projection effects
Nazarbayev University（纳扎尔巴耶夫大学）；Institut de Ciències del Cosmos (ICCUB), Universitat de Barcelona (UB)（巴塞罗那大学宇宙科学研究所）；Dartmouth College（达特茅斯学院）；University of Helsinki（赫尔辛基大学）；Kavli Institute for Astronomy and Astrophysics, Peking University（北京大学卡尔文天体物理研究所）
The growth of supermassive black holes (BHs) located at the centers of their host galaxies comes mainly from accretion of gas, but how to fuel them remains an outstanding unsolved problem in quasar evolution. This issue can be elucidated by quantifying the radiative efficiency parameter ($η$) as a function of redshift, which also provides constraints on the average spin of the BHs and its possible evolution with time. We derive a formalism to link $η$ with the luminosity density, BH mass density, and duty cycle of quasars, quantities we can estimate from existing quasar and galaxy survey data.…
We derive analytical expressions for the mass flow rates in and from accretion discs, taking into account the Eddington limit. This allows us to connect the basic properties of outflows with those of the accretion flow. As an example, we derive the radial surface density distribution in the accretion disc of Mrk 231.
Powerful outflows with a broad range of properties (such as velocity, ionization, radial scale and mass loss rate) represent a key feature of active galactic nuclei (AGN), even more so since they have been simultaneously revealed also in individual objects. Here we revisit in a simple analytical framework the recent remarkable cases of two ultraluminous infrared quasars, IRAS F11119+3257 and Mrk 231, which allow us to investigate the physical connection between multi-phase AGN outflows across the ladder of distance from the central supermassive black hole (SMBH). We argue that any major deviat…
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 growing evidence for energy-conserving outflows in powerful and luminous AGN supports the idea that high-velocity winds launched from the accretion disc evolve systematically after undergoing a shock with the ambient medium and that they are capable to expel enough mass and energy so as to produce feedback. This talk will give an overview of recent results on AGN ultra fast outflows, with focus on grating X-ray spectra of bright sources. I will review how UFO work, their observational properties and their relation with AGN outflows in other bands, what is their impact on the host galaxies …
We investigate the impact of gas accretion in streams on the evolution of disc galaxies, using magneto-hydrodynamic simulations including advection and anisotropic diffusion of cosmic rays generated by supernovae as the only source of feedback. Stream accretion has been suggested as an important galaxy growth mechanism in cosmological simulations and we vary their orientation and angular momentum in idealised setups. We find that accretion streams trigger the formation of galactic rings and enhanced star formation. The star formation rates and consequently the cosmic ray driven outflow rates a…
