Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new user3D AMR simulations of G2 as an outflow
63
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We study the evolution of G2 in a textit{Compact Source Scenario}, where G2 is the outflow from a low-mass central star moving on the observed orbit. This is done through 3D AMR simulations of the hydrodynamic interaction of G2 with the surrounding hot accretion flow. A comparison with observations is done by means of mock position-velocity (PV) diagrams. We found that a massive ($dot{M}_mathrm{w}=5times 10^{-7} ;M_{odot} ; mathrm{yr^{-1}}$) and slow ($v_mathrm{w}=50 ;mathrm{km; s^{-1}}$) outflow can reproduce G2s properties. A faster outflow ($v_mathrm{w}=400 ;mathrm{km; s^{-1}}$) might also be able to explain the material that seems to follow G2 on the same orbit.
rate research
Read More
The nature of the gaseous and dusty cloud G2 in the Galactic Centre is still under debate. We present three-dimensional hydrodynamical adaptive mesh refinement (AMR) simulations of G2, modeled as an outflow from a compact source moving on the observed orbit. The construction of mock position-velocity (PV) diagrams enables a direct comparison with observations and allow us to conclude that the observational properties of the gaseous component of G2 could be matched by a massive ($dot{M}_mathrm{w}=5times 10^{-7} ;M_{odot} mathrm{yr^{-1}}$) and slow ($50 ;mathrm{km ;s^{-1}}$) outflow, as observed for T Tauri stars. In order for this to be true, only the material at larger ($>100 ;mathrm{AU}$) distances from the source must be actually emitting, otherwise G2 would appear too compact compared to the observed PV diagrams. On the other hand, the presence of a central dusty source might be able to explain the compactness of G2s dust component. In the present scenario, 5-10 years after pericentre the compact source should decouple from the previously ejected material, due to the hydrodynamic interaction of the latter with the surrounding hot and dense atmosphere. In this case, a new outflow should form, ahead of the previous one, which would be the smoking gun evidence for an outflow scenario.
We investigate the origin and fate of the recently discovered gas cloud G2 close to the Galactic Center. Our hydrodynamical simulations focussing on the dynamical evolution of the cloud in combination with currently available observations favor two scenarios: a Compact Cloud which started around the year 1995 and a Spherical Shell of gas, with an apocenter distance within the disk(s) of young stars and a radius of a few times the size of the Compact Cloud. The former is able to explain the detected signal of G2 in the position-velocity diagram of the Br gamma emission of the year 2008.5 and 2011.5 data. The latter can account for both, G2s signal as well as the fainter extended tail-like structure G2t seen at larger distances from the black hole and smaller velocities. In contrast, gas stripped from a compact cloud by hydrodynamical interactions is not able to explain the location of the detected G2t emission in the observed position-velocity diagrams. This favors the Spherical Shell Scenario and might be a severe problem for the Compact Cloud as well as the so-called Compact Source Scenario. From these first idealized simulations we expect a roughly constant feeding of the supermassive black hole through a nozzle-like structure over a long period, starting shortly after the closest approach in 2013.51 for the Compact Cloud. If the matter accretes in the hot accretion mode, we do not expect a significant boost of the current activity of Sgr A* for the Compact Cloud model, but a boost of the average infrared and X-ray luminosity by roughly a factor of 80 for the Spherical Shell scenario with order of magnitude variations on a timescale of a few months. The near-future evolution of the cloud will be a sensitive probe of the conditions of the gas distribution in the milli-parsec environment of the massive black hole in the Galactic Center.
We present 3D, adaptive mesh refinement simulations of G2, a cloud of gas moving in a highly eccentric orbit towards the galactic center. We assume that G2 originates from a stellar wind interacting with the environment of the Sgr A* black hole. The stellar wind forms a cometary bubble which becomes increasingly elongated as the star approaches periastron. A few months after periastron passage, streams of material begin to accrete on the central black hole with accretion rates $dot{M} sim 10^{-8}$ M$_odot$ yr$^{-1}$. Predicted Br$gamma$ emission maps and position-velocity diagrams show an elongated emission resembling recent observations of G2. A large increase in luminosity is predicted by the emission coming from the shocked wind region during periastron passage. The observations, showing a constant Br$gamma$ luminosity, remain puzzling, and are explained here assuming that the emission is dominated by the free-wind region. The observed Br$gamma$ luminosity ($sim 8 times 10^{30}$ erg s$^{-1}$) is reproduced by a model with a $v_w=50$ km s$^{-1}$ wind velocity and a $10^{-7}$ M$_odot$ yr$^{-1}$ mass loss rate if the emission comes from the shocked wind. A faster and less dense wind reproduces the Br$gamma$ luminosity if the emission comes from the inner, free wind region. The extended cometary wind bubble, largely destroyed by the tidal interaction with the black hole, reforms a few years after periastron passage. As a result, the Br$gamma$ emission is more compact after periastron passage.
Recent observations have revealed that starburst galaxies can drive molecular gas outflows through stellar radiation pressure. Molecular gas is the phase of the interstellar medium from which stars form, so these outflows curtail stellar mass growth in galaxies. Previously known outflows, however, involve small fractions of the total molecular gas content and are restricted to sub-kiloparsec scales. It is also apparent that input from active galactic nuclei is in at least some cases dynamically important, so pure stellar feedback has been considered incapable of aggressively terminating star formation on galactic scales. Extraplanar molecular gas has been detected in the archetype starburst galaxy M82, but so far there has been no evidence that starbursts can propel significant quantities of cold molecular gas to the same galactocentric radius (~10 kpc) as the warmer gas traced by metal absorbers. Here we report observations of molecular gas in a compact (effective radius 100 pc) massive starburst galaxy at z=0.7, which is known to drive a fast outflow of ionized gas. We find that 35 per cent of the total molecular gas is spatially extended on a scale of approximately 10 kpc, and one third of this has a velocity of up to 1000 km/s. The kinetic energy associated with this high-velocity component is consistent with the momentum flux available from stellar radiation pressure. This result demonstrates that nuclear bursts of star formation are capable of ejecting large amounts of cold gas from the central regions of galaxies, thereby strongly affecting their evolution.
We present the first ab initio cosmological simulations of a CR7-like object which approximately reproduce the observed line widths and strengths. In our model, CR7 is powered by a massive ($3.23 times 10^7$ $M_odot$) black hole (BH) the accretion rate of which varies between $simeq$ 0.25 and $simeq$ 0.9 times the Eddington rate on timescales as short as 10$^3$ yr. Our model takes into account multi-dimensional effects, X-ray feedback, secondary ionizations and primordial chemistry. We estimate Ly-$alpha$ line widths by post-processing simulation output with Monte Carlo radiative transfer and calculate emissivity contributions from radiative recombination and collisional excitation. We find the luminosities in the Lyman-$alpha$ and He II 1640 angstrom lines to be $5.0times10^{44}$ and $2.4times10^{43}$ erg s$^{-1}$, respectively, in agreement with the observed values of $>$ $8.3times10^{43}$ and $2.0times10^{43}$ erg s$^{-1}$. We also find that the black hole heats the halo and renders it unable to produce stars as required to keep the halo metal free. These results demonstrate the viability of the BH hypothesis for CR7 in a cosmological context. Assuming the BH mass and accretion rate that we find, we estimate the synchrotron luminosity of CR7 to be $P simeq 10^{40} - 10^{41}$ erg s$^{-1}$, which is sufficiently luminous to be observed in $mu$Jy observations and would discriminate this scenario from one where the luminosity is driven by Population III stars.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
