Query : 1998A&A...339...19S

1998A&A...339...19S - Astronomy and Astrophysics, volume 339, 19-33 (1998/11-1)

FIR and C+ emissions of spiral galaxies disks. The example of NGC 6946.


Abstract (from CDS):

We present numerical simulations of radiative transfer in the spiral galaxy NGC 6946. The interstellar medium is represented as a two phases medium, with molecular clouds and a smooth diffuse phase. The molecular gas distribution is calculated in a self-consistent way from the distribution of an ensemble of molecular clouds evolving in the gravitational potential of NGC 6946. We simulate star formation by creating OB associations in molecular clouds. The transfer of UV radiation is calculated in the clumpy interstellar medium, to determine the local UV illumination of molecular clouds. We compute the emergent intensity in the UV continuum (912-2000Å), in the Hα and C+ 2P3/2-2P1/2 lines as well as in the continuum at far infrared wavelengths, 60, 100 & 200µm. It is possible to obtain a consistent picture of this galaxy with a global star formation rate of 4M/yr (for stars with masses in the range 2-60M) occuring mostly in the spiral arms. The close spatial association of massive stars and molecular clouds has a profound impact on the transfer of UV radiation in the galactic disk and on the dust emission. The median distance travelled by UV photons is about 120pc. However, when they have escaped from the vicinity of their parent OB associations, UV photons may travel quite far in the disk, up to 1kpc. The UV opacity of the model spiral galaxy disk, observed face-on, is 0.8 at 1000Å and 0.7 at 2000Å. For radii less than 4kpc, the C+ 158µm line is mostly produced in photodissociation regions at the surfaces of molecular clouds. The C+ emission from diffuse atomic gas accounts for about 20% of the total. It becomes significant at large distance from the nucleus (r≥4kpc). Molecular clouds and diffuse atomic gas have almost equal contributions to the total far infrared emission from 60 to 200µm. As a whole, 72% of the 60-200µm FIR emission can be attributed to dust grains heated by the UV radiation of massive stars and 28% by the radiation field of the old stellar population.

Abstract Copyright:

Journal keyword(s): ISM: molecules - ISM: dust, extinction - galaxies: individual: NGC 6946 - galaxies: ISM

CDS comments: In abstract, figure captions and text, there are a few misprints "NGC946" instead of NGC 6946.

Simbad objects: 4

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Number of rows : 4
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
1 NGC 891 H2G 02 22 32.907 +42 20 53.95 11.08 10.81 9.93 7.86   ~ 1592 2
2 M 51 GiP 13 29 52.698 +47 11 42.93   9.26 8.36 8.40   ~ 4061 4
3 M 101 GiP 14 03 12.583 +54 20 55.50   8.46 7.86 7.76   ~ 2701 2
4 NGC 6946 H2G 20 34 52.332 +60 09 13.24   10.5       ~ 2372 2

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