Discovery of narrow X-ray absorption lines from NGC 3783 with the Chandra high energy transmission grating spectrometer

We present the first grating-resolution X-ray spectra of the Seyfert 1 gala xy NGC 3783, obtained with the High Energy Transmission Grating Spectromete r on the Chandra X-Ray Observatory. These spectra reveal many narrow absorp tion lines from the H-like and He-like ions of O, Ne, Mg, Si, S, and Ar as well as Fe XVII-Fe XXI L-shell lines. We have also identified several weak emission lines, mainly from O and Ne. The absorption lines are blueshifted by a mean velocity of approximate to 440 +/- 200 km s(-1) and are not resol ved, indicating a velocity dispersion within the absorbing gas of a few hun dred kilometers per second or less. We measure the lines' equivalent widths and compare them with the predictions of photoionization models. The best- fitting model has a microturbulence velocity of 150 km s(-1) and a hydrogen column density of 1.3 x 10(22) cm(-2). The measured blueshifts and inferre d velocity dispersions of the X-ray absorption lines are consistent with th ose of the strongest UV absorption lines observed in this object. However, simple models that propose to strictly unify the X-ray and UV absorbers hav e difficulty explaining simultaneously the X-ray and UV absorption-line str engths.