We have obtained low-dispersion spectra of NGC 3227 with the Space Telescope Imaging Spectrograph ( STIS ) to study the intrinsic UV absorption and the reddening of the nucleus in this Seyfert 1 galaxy .
The UV spectra show a wealth of absorption lines at the systemic redshift that span a wide range in ionization state ( Mg I to N V ) .
The equivalent widths of the lines are consistent with our earlier prediction that a “ lukewarm absorber ” ( T _ { e } = 18,000 K at the ionized face ) with a substantial column of gas ( N _ { H } = 2 x 10 ^ { 21 } cm ^ { -2 } ) is present and likely responsible for the reddening of the nucleus .
The lukewarm absorber is also responsible for most of the absorption in the X-rays at energies less than 1 keV , although a more highly ionized “ warm absorber ” is needed to account for the O VII and O VIII ionization edges .
In addition , we require a small column ( N _ { H } = 5 x 10 ^ { 19 } cm ^ { -2 } ) of cold gas to match the strengths of the neutral and singly-ionized lines in the UV spectra .
NGC 3227 is the first Seyfert galaxy in which a strong link between the reddening and intrinsic UV absorption has been found .
By comparing our STIS UV and optical spectra with those of the unreddened Seyfert NGC 4151 , we have determined a reddening curve for the nuclear continuum source in NGC 3227 over the 1150 – 10,200 Å range .
The reddening curve does not show a 2200 Å bump , and is steeper in the UV than reddening curves derived for the Galaxy , LMC , and SMC , suggesting a preponderence of small dust grains near the nucleus .