National Observatory of Athens Modeling the ISM in the Milky Way Xilouris Manolis National Observatory of Athens with: Angelos Misiriotis University of Crete ESF Workshop (Ghent) – 14 May 2007

Milky Way NGC891 ESF Workshop (Ghent) – 14 May 2007

Scattered Intensities Optical/NIR extinction model - 9 free parameters Method: Scattered Intensities Kylafis & Bahcall, 1987, ApJ, 317, 637 Stellar disk Bulge Dust Stars: Dust: ESF Workshop (Ghent) – 14 May 2007

+ FIR/Submm emission model - 6 free parameters Emitted energy by diffuse dust Stellar disk Bulge Dust Absorbed energy + Emitted energy by HII regions Energy balance FIR/Submm emission ESF Workshop (Ghent) – 14 May 2007

( ESF Workshop (Ghent) – 14 May 2007

FIN THE FITTING PROCEDURE UGC 2048 (I-Band) Observation Model ESF Workshop (Ghent) – 14 May 2007

3D Radiative Transfer modeling of spiral galaxies Xilouris et al., 1999, A&A, 344, 868 ESF Workshop (Ghent) – 14 May 2007

) ESF Workshop (Ghent) – 14 May 2007

The COBE/DIRBE maps Mollweide projection of COBE/DIRBE maps 1.2 μm F.O.V. = 0.7 sq. degrees Sensitivity : ~ 0.1 MJy sr-1 @ 1.2 μm 1.1 MJy sr-1 @ 140μm Mollweide projection of COBE/DIRBE maps 1.2 μm 240 μm ESF Workshop (Ghent) – 14 May 2007

Results of the RT model COBE Observations Models Misiriotis et al., 2006, A&A, 459, 113 ESF Workshop (Ghent) – 14 May 2007

Vertical and Radial profiles ESF Workshop (Ghent) – 14 May 2007

Best fit model parameters Parameters for the dust Parameters for the stars Parameter Value ρw(0,0) 1.22×10-27 gr cm-3 hw 3.3 kpc zw 0.09 kpc ρc(0,0) 1.51×10-25 gr cm-3 hc 5.0 kpc zc 0.1 kpc Tc(0,0) 19.2 K hT 48 kpc zT 500 kpc Parameter 1.2 μm 2.2 μm ηdisk 5.49×10-38 9.94×10-38 erg s-1 cm-3 Hz-1 srad-1 hs 2.50 2.20 kpc zs 0.16 0.12 kpc ηbulge 2.07 ×10-38 2.07×10-35 erg s-1 cm-3 Hz-1 srad-1 Re 0.68 0.79 kpc a/b 0.61 0.63 hdust≈2 hs zdust≈0.6 zs Mc=7.0×107 M Mw=2.2×105 M ESF Workshop (Ghent) – 14 May 2007

Modeling the SED of the Milky Way (COBE/FIRAS) ESF Workshop (Ghent) – 14 May 2007

Milky Way in the Optical bands The B-V color excess for the sample of the Galactic Classical Cepheids (Fernie et al. 1995; x-axis) compared with the color excess along the same directions as derived from the model. ESF Workshop (Ghent) – 14 May 2007

Modeling the gas (H2 and HI) in the Milky Way Parameters for the gas Parameter Value ρH2(0,0) 4.06 cm-3 hH2 2.57 kpc zH2 0.08 kpc ρHI(0,0) 0.32 cm-3 hHI 18.24 kpc zHI 0.52 kpc Rt 2.75 kpc MH2=1.3×109 M MHI=8.2×109 M Mdust=7.0×107M } Mgas/Mdust=135

Star formation in the Milky Way <SFR>=2.7 M/yr <ε>=2.8% / 0.1 Gyr The star formation rate (SFR) and the star formation rate density (ΣSFR) as a function of radius in the MW. Points correspond to different star formation estimates taken from the literature. The SFR was calculated using the strong correlation between SFR and L100 found in Misiriotis et al., 2004, A&A, 417, 39. Star formation rate density as a function of gas surface density in the MW disk. M yr-1 ESF Workshop (Ghent) – 14 May 2007

CONCLUSIONS Parameters for the dust and the stellar distributions in the MW are derived by applying a 3D Radiative Transfer model to the COBE/DIRBE maps (1.2μm…240 μm). The conclusions follow the general trends found for distant spiral galaxies (Xilouris et al., 1999; Bianchi 2007). The model predicts very accurately the observed (COBE/FIRAS) Submm SED of the MW. The model predicts, on average, the optical extinction observed for a sample of Cepheids. The SFR as a function of galactocentric distance calculated by the model is in good agreement with various indicators of SFR found in the literature. An “internal” Schmidt law is found for the MW which has exactly the same characteristics as the “external” Schmidt law found for external galaxies indicating a universal gas-SFR behavior not only on large scales (for the galaxy as a whole) but also on small scales (within an individual galaxy). ESF Workshop (Ghent) – 14 May 2007