1. 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

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

3. 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

4. + 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

5. (
ESF Workshop (Ghent) – 14 May 2007

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

7. 3D Radiative Transfer modeling of spiral galaxies
Xilouris et al., 1999, A&A, 344, 868
ESF Workshop (Ghent) – 14 May 2007

8. )
ESF Workshop (Ghent) – 14 May 2007

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

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

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

12. 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

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

14. 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

15. 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

16. 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

17. 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