Context. The halo of NGC 891 has been the subject of studies for more than a decade. One of its most striking features is the large asymmetry in Ha emission. In this letter, we will take a quantitative look at this asymmetry at different wavelengths for the first time.
Aims. We suggest that NGC 891 is intrinsically almost symmetric and the large asymmetry in Ha emission is mostly due to dust attenuation. We will quantify the additional optical depth needed to cause the observed asymmetry in this model.
Methods. By comparing large strips on the North East side of the galaxy with strips covering the same area in the South West we can quantify and analyze the asymmetry in the different wavelengths.
Results. From the 24 mu m emission we find that the intrinsic asymmetry in star formation in NGC 891 is small i.e., similar to 30%. The additional asymmetry in Ha is modeled as additional symmetric dust attenuation which extends up to similar to 40 '' (1.9 kpc) above the plane of the galaxy with a mid-plane value of tau = 0.8 and a scale height of 0.5 kpc
- galaxies : halos
- galaxies : ISM
- galaxies : spiral
- galaxies : structure
- NGC 891
- SPIRAL GALAXIES