On the Reddening in X‐Ray–absorbed Seyfert 1 Galaxies

There are several Seyfert galaxies for which there is a discrepancy betweenthe small column of neutral hydrogen deduced from X-ray observations and themuch greater column derived from the reddening of the optical/UV emission linesand continuum. The standard paradigm has the dust within the highly ionized gaswhich produces O~VII and O~VIII absorption edges (i.e., a ``dusty warmabsorber''). We present an alternative model in which the dust exists in acomponent of gas in which hydrogen has been stripped, but which is at too lowan ionization state to possess significant columns of O~VII and O~VIII (i.e, a``lukewarm absorber''). The lukewarm absorber is at sufficient radial distanceto encompass much of the narrow emission-line region, and thus accounts for thenarrow-line reddening, unlike the dusty warm absorber. We test the model byusing a combination of photoionization models and absorption edge fits toanalyze the combined ROSAT/ASCA dataset for the Seyfert 1.5 galaxy, NGC 3227.We show that the data are well fit by a combination of the lukewarm absorberand a more highly ionized component similar to that suggested in earlierstudies. We predict that the lukewarm absorber will produce strong UVabsorption lines of N V, C IV, Si IV and Mg II. Finally, these resultsillustrate that singly ionized helium is an important, and often overlooked,source of opacity in the soft X-ray band (100 - 500 eV).Comment: 17 pages, Latex, includes 1 figure (encapsulated postscript), one additional table in Latex (landscape format), to appear in the Astrophysical Journa