Efficient monte carlo continuum radiative transfer with skirt
Download
1 / 26

Efficient Monte Carlo continuum radiative transfer with SKIRT - PowerPoint PPT Presentation


  • 142 Views
  • Uploaded on

Efficient Monte Carlo continuum radiative transfer with SKIRT. Maarten Baes. 2 nd East-Asia Numerical Astrophysics Meeting, Daejeon, Korea 3 November 2006. Brussels. Why continuum radiative transfer…. the ISM is ex t remely dus t y.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
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
Efficient Monte Carlo continuum radiative transfer with SKIRT

Maarten Baes

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



Efficient monte carlo continuum radiative transfer with skirt

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…


Efficient monte carlo continuum radiative transfer with skirt

Radiative transfer equation

  • we take into account the effects of - extinction

  • condition of thermal equilibrium:


Efficient monte carlo continuum radiative transfer with skirt

Radiative transfer equation

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

  • condition of thermal equilibrium:


Efficient monte carlo continuum radiative transfer with skirt

Radiative transfer equation

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

  • condition of thermal equilibrium:


Efficient monte carlo continuum radiative transfer with skirt

Radiative transfer equation

  • 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:


Monte carlo radiative transfer

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

Monte Carlo radiative transfer

  • 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 transfer1
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

Steinacker et al. 2003

SKIRT

  • Stellar Kinematics Including Radiative Transfer

  • allows all geometries for sources and sinks: dust cells

  • several dust cell geometries: spherical, cylindrical, cuboidal,…


Skirt1
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
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
1D benchmark tests

  • Ivezić et al. (1997) benchmark tests

    • star + spherical envelope

    • V-band optical depths 1-1000


Polychromatic photon packages
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
2D benchmark tests

  • Pascucci et al. (2004) benchmark tests

    • star + axisymmetric envelope

    • V-band optical depths 0.1-100


Efficient monte carlo continuum radiative transfer with skirt

SKIRT 2D

benchmark

SKIRT 3D vs benchmark


Efficiency of monte carlo rt
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


Efficient monte carlo continuum radiative transfer with skirt

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


Efficient monte carlo continuum radiative transfer with skirt

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.


Efficient monte carlo continuum radiative transfer with skirt

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


Efficient monte carlo continuum radiative transfer with skirt

Application 2: spiral galaxy atlas

Optical depth

Bulge luminosity

Bulge luminosity

Optical depth


Efficient monte carlo continuum radiative transfer with skirt

R-band images

Spitzer MIPS 160 μm images


Conclusions
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 ???


Efficient monte carlo continuum radiative transfer with skirt

Thank you…

EANAM 2008China

EANAM 2004Japan

EANAM 2012Belgium!

EANAM 2006Korea

EANAM 2010Iran ?

See you there !