The following document lists the file abstract/MDENNEFE_XGAL_01.abs
from catalogue VI/111.
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Spectroscopic follow-up has been undertaken of a sample of 244 galaxies detected both by Rosat and by Iras.While about 80% of the work is advanced,two facts are emerging at this stage : 1)A number of galaxies have X-luminosities larger then 10E43 ergs/s, that is in the range of Seyferts or quasars,and two orders of magnitude above normal galaxies.Yet the optical spectrum shows no sign of seyfert activity,but it shows characteristics of strong reddening.The detection of an eventual AGN has therefore to be searched in the far IR ,to penetrate the dust enshrouded central regions and is of critical importance for the interpretation of the soft X-ray excess. 2)The fraction of Narrow Line Seyfert 1 galaxies is much larger then in other samples.If these NLS1 are indeed Seyfert galaxies,then again the reason for the small width of the permitted lines lies in the existence of dust obscuring the central regions.There is however a challenging interpretation,that NLS1 can be produced by strong episodes of star formation alone. These two types of objects have therefore common problems and are key elements in the controversy about the nature of the central source in high-luminosity Iras galaxies.They have therefore been put together in this proposal (rather then separately as initially planned) as the techniques to analyse them will be the same:on one hand,search for the existence of a broad line region by observing hydrogen lines further in the IR were reddening is much lower;and use forbiden lines of the same element (here neon) to get the excitation class in avoiding the question of relative abundances.On the other hand,get the spectral energy distribution in the 10mu region to disantangle the various hot dust components being eventually present,use the PAH features (which are destroyed in a high energy environment) as diagnostics for the AGN,and determine the "true" reddening from the silicate absorption feature.