On the reddening in X-ray-absorbed Seyfert 1 galaxies

There are several Seyfert galaxies for which there is a discrepancy between the small column of neutral hydrogen deduced from X-ray observations and t he much greater column derived from the reddening of the optical/UV emissio n lines and continuum. The standard paradigm has the dust within the highly ionized gas that produces O VII and O wr absorption edges (i.e., a "dusty warm absorber"). We present an alternative model in which the dust exists i n a component of gas in which hydrogen has been stripped, but which is at t oo low an ionization state to possess significant columns of O VII and O VI II (i.e., a "lukewarm absorber"). The lukewarm absorber is at sufficient ra dial distance to encompass much of the narrow emission line region and thus accounts for the narrow-line reddening, unlike the dusty warm absorber. We test the model by using a combination of photoionization models and absorp tion edge fits to analyze the combined ROSAT/ASCA dataset for the Seyfert 1 .5 galaxy, NGC 3227. We show that the data are well fitted by a combination of the lukewarm absorber and a more highly ionized component similar to th at suggested in earlier studies. We predict that the lukewarm absorber will produce strong UV absorption lines of N V, C IV, Si IV, and Mg II. Finally , these results illustrate that singly ionized helium is an important, and often overlooked, source of opacity in the soft X-ray band (100-500 eV).