Loading in 5 sec....

Efficient Monte Carlo continuum radiative transfer with SKIRTPowerPoint Presentation

Efficient Monte Carlo continuum radiative transfer with SKIRT

- By
**halil** - Follow User

- 140 Views
- Uploaded on

Download Presentation
## PowerPoint Slideshow about ' Efficient Monte Carlo continuum radiative transfer with SKIRT' - halil

**An Image/Link below is provided (as is) to download presentation**

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript

Efficient Monte Carlo continuum radiative transfer with SKIRT

Maarten Baes

2nd East-Asia Numerical Astrophysics Meeting, Daejeon, Korea3 November 2006

Why continuum radiative transfer…

- the ISM is extremely dusty

- dust strongly affects the radiation field at all wavelengths - X-ray: scattering - UV and optical: extinction - IR and submm: emission

Detailed continuum radiative transfer simulations are necessary to investigate the effect of dust on observable properties of all dusy systems…

- we take into account the effects of - extinction

- condition of thermal equilibrium:

- we take into account the effects of - extinction - multiple anisotropic scattering

- condition of thermal equilibrium:

- we take into account the effects of - extinction - multiple anisotropic scattering - thermal dust re-emission, assuming thermal equilibrium

- condition of thermal equilibrium:

- we take into account the effects of - extinction - multiple anisotropic scattering - thermal dust re-emission, assuming thermal equilibrium - multiple dust grain populations

- condition of thermal equilibrium:

- the radiation field is reconstructed by classifying the photons by position, propagation direction, wavelength…

- probabilisitic technique >< deterministic technique

- RT simulations in which a large number of photons are followed individually through the dusty medium

- the trajectory of each photon is determined by (pseudo) random numbers

Monte Carlo radiative transfer

- ADVANTAGES
- conceptually simple, natural treatment of emission, absorption and scattering
- all geometries possible (3D simulations)
- rather economic in memory → large grids are possible
- very flexible: multiple anisotropic scattering, polarization, kinematics, dust clumping…

- DISADVANTAGES
- Poisson noise
- error analysis is difficult
- accuracy goes as N-1/2→ efficiency !?

SKIRT

- Stellar Kinematics Including Radiative Transfer
- allows all geometries for sources and sinks: dust cells
- several dust cell geometries: spherical, cylindrical, cuboidal,…

SKIRT

- strongly optimized through the use of deterministic elements
- forced (first) scattering Witt 1977
- peeling-off technique Yusef-Zadeh et al. 1984
- continuous absorption Lucy 1999
- partlypolychromatic photon packages Baes 2006, MNRAS, submitted

- computing power: dedicated cluster with 16 x 2 Gb memory

- two major modes:
- LTE → modelling the dust temperature distribution and the SED of dusty systems
- KINE → modelling the observed kinematics of dusty galaxies

SKIRT in LTE mode

- LTE radiative transfer:
- radiative equilibrium: energy absorbed = energy emitted
- the absorbed energy determines the dust temperature

- frequency distribution adjustment techniqueBjorkman & Wood 2001 Baes et al. 2005, NewA, 10, 523
- no iteration is necessary
- immediate re-emission: guaranteed flux conservation
- works with all optical depths

- polychromatic photon packages: very efficient

1D benchmark tests

- Ivezić et al. (1997) benchmark tests
- star + spherical envelope
- V-band optical depths 1-1000

Polychromatic photon packages

(re-)emissioneach photon package initially contains photons of all wavelengths

exitif it leaves the galaxy: contribution to the SED at all wavelengths

scatteringloss of polychromatism

minimal computational overheadsignificant gain in efficiency

Baes 2006, MNRAS, submitted

2D benchmark tests

- Pascucci et al. (2004) benchmark tests
- star + axisymmetric envelope
- V-band optical depths 0.1-100

Efficiency of Monte Carlo RT

- “common wisdom” about Monte Carlo RT: numerically demanding
- comparison between SKIRT and other codes used in Pascucci et al.

SKIRT 2D: 2.5 MBySKIRT 3D: 58 MBy

MC RT codes can be very efficient when modern optimization techniques are used.

Limited memory usage is extra advantage when moving to 3D

Baes 2006, MNRAS, submitted

Application 1: Circumstellar discs

- large homogeneous survey of post-AGB stars - they all seem to be binary systems - they have a MIR excess due to dust starting at the sublimation temperature - MIR-submm SED and VLTI data suggest circumbinary discs

Application 1: Circumstellar discs

- question: how do the temperature distribution and the emerging radiation field depend on the structure of the circumstellar medium ?

density temperature

We can see some systematic effects, but in general the structure of the dust temperature distribution is rather insensitive to the structure of the ISM.

Application 2: spiral galaxy atlas

- simulation of a large set of spiral galaxy models
- - images at various inclinations and passbands - global and spatially resolved spectral energy distributions- attenuation maps- dust temperature distributions

- scientific goals
- - investigate the systematic effects of physical parameters on the observables (luminosity, dust content, bulge-to-disc ratio, inclination…)
- - construct an optimized galaxy dust mass estimator for IRAS, Spitzer, Akari,… data
- - provide a database for statistical / cosmological applications

Spitzer MIPS 160 μm images

Conclusions

- SKIRT = efficient 3D Monte Carlo radiative transfer code

- 2 modes: LTE and KINE

- uses efficient optimization techniques

- reproduces the 1D and 2D benchmark test easily

- ready to go….
- - models for circumbinary discs around post-AGB stars - atlas of dusty spiral galaxy models - simulations of accretion discs in the centre of AGNs - kinematics of dusty galaxies and galactic nuclei

- your radiative transfer problem ???

EANAM 2008China

EANAM 2004Japan

EANAM 2012Belgium!

EANAM 2006Korea

EANAM 2010Iran ?

See you there !

Download Presentation

Connecting to Server..