Modelling clumpy! galactic disks

Transcription

1 Modelling clumpy! galactic disks Simone Bianchi INAF-Osservatorio Astrofisico di Arcetri, Firenze with TRADING! Transfer of RAdiation through Dust IN Galaxies (Bianchi 2008)

2 Radiative Transfer models" for a spiral (disk) galaxy Smooth exponential stellar disk + spheroidal bulge i = 90 i = 85 + smooth exponential dust disk MC model for dust extinction" Bianchi, Ferrara & Giovanardi (1996)

3 Real galaxies vs models" (Kylafis & Bahcall 1984; Xilouris et al. 1997,1998,1999; " Baes et al. 2010; de Looze et al. 2012; De Geyter et al. 2013) V band NGC other objects Bianchi (2007) model K band model

4 From dust absorption to dust emission NGC 6946 (Bianchi et al. 2000) Stellar SED Absorbed energy -> Temperature map -> Dust emission Dust emission SED Dust emission is typically 30% of the Bolometric Luminosity (Popescu & Tuffs 2002; Davies et al. 2012) high τ V is needed for the energy balance Energy balance problem confirmed in may spirals (Popescu et al. 2000; Baes et al. 2010; de Looze et al 2012)

5 Clumping of dust: a solution? (Bianchi et al. 1999; Misiriotis & Bianchi 2002) I obs / I o (V Band) Clumpy disks are more transparent Clumps as MW molecular clouds A grid is required! 75% of dust in clumps What if the heating source is within a cloud? Homogeneous Radial Profile of an Edge-On Disk (τ V =2)

6 TRADING features Continuum RT in a dusty medium Monte Carlo code An adaptive grid for dust Stellar emission from diffuse/point-like sources of different spectra Thermal & stochastic dust emission from a distribution of grain sizes and material (Draine & Li 2007) Dust self-absorption.

7 RT and the Monte Carlo Method (details on Steinacker, Baes & Gordon 2013) The path of a phothon through dust Emission from stars Extinction: scattering or absorption? Out of dust: observed Several images

8 RT and the Monte Carlo Method (details on Steinacker, Baes & Gordon 2013) The path of a phothon through dust Extinction: scattering and absorption! Optimizations Photon weights Forced Scattering (Cashwell & Everett 1959) Peeling-off (Yusef-Zadeh et al. 1984) Continuous Absorption (Lucy 1999)

9 RT and the Monte Carlo Method (details on Steinacker, Baes & Gordon 2013) Emission from dust Local ISRF J λ = W λ /(4π κ λ ) j λ Dust Emission Coefficient Thermal & Stochastic heating Absorbed energy Mean absorption coefficient Dust self absorption (iteratively) l.o.s. integration Scheme similar to other MCs (DIRTY, Misselt et al. 2001; SKIRT, Baes et al. 2011)

10 TRADING: an adaptive grid " for a clumpy medium 3-D Tree structure: a regular Octree Finer grid on a denser (more opaque) spot Clumps of different size Resolution within the clump Neighbour cells found with the bookkeeping method (as defined by Saft et al. 2013) GMC: D 100 pc Disk: D 20 kpc

11 Model of an NGC891-like galaxy! seen at i=86 (Bianchi 2008) B, V, R B, V, R 70µm, 160µm, 850µm

12 Modelling NGC891! Bianchi 2008; Bianchi & Xilouris 2011 Is the model consistent with optical-nir images? Galaxy parameters from optical fits of Xilouris et al. (1999) Add enough dust to match thermal SED Model in K-band 2-MASS Ks-band Is the model consistent with FIR/submm maps? Herschel-SPIRE

13 Modelling NGC4244! Holwerda et al SPIRE SPIRE 250 & 500um Galaxy parameters from optical fits of MacLachlan et al. (2012) SDSS-r & IRAC 3.6um

14 The ISRF around NGC891! Bocchio et al Optical SED at R=12 kpc for z=0, 2, 5, 10, 15, 20 kpc compared to the LISRF (Mathis et al. 1983) Strength of the ISRF on a galactic meridian plane. Red contours refer to an ISRF 10, 1 and 0.1x the LISRF.

15 The dust model TRADING works with a distribution of grain sizes and materials Draine & Li (2007) model 4 materials and a total of 50 grains Thermal emission for a 0.01 μm Stochastic emission for smaller grains Method of Guhathakurta & Draine (1989) N=80 temperature bins

16 Not only disks! Optical: dust extinction FIR: dust emission

17 The spectral energy distribution of z 6 quasars: the case of SDSS J Schneider et al, submitted

18 Ivezic et al Checking the code Pascucci et al. 2004

19 Galactic disk geometry Benchmarking TRADING with SKIRT (+ DIRTY & CRT not shown) TRADING τ 1µm =1 τ 1µm = TRADING - SKIRT

20 TRADING features Continuum RT in a dusty medium Monte Carlo code An adaptive grid for dust Stellar emission from diffuse/point-like sources of different spectra Thermal & stochastic dust emission from a distribution of grain sizes and material (Draine & Li 2007) Dust self-absorption.