Resolving the Intrinsic CivAbsorption in the Seyfert 1 Galaxy NGC 3516

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Abstract
We observed the Seyfert 1 galaxy NGC 3516 with the Goddard High Resolution Spectrograph on the Hubble Space Telescope, and obtained UV spectra at a resolution of λ/Δλ ≈ 20,000 in the redshifted C IV λ1549 region. The intrinsic C IV absorption in the core of the broad emission line is resolved for the first time into four distinct kinematic components, which are all blueshifted, relative to the systemic radial velocity of the host galaxy. Two components are narrow (~20 and ~30 km s-1 FWHM) and at small radial velocities (-90 and -30 km s-1, respectively), and could arise from the interstellar medium or halo of the host galaxy. The two broad components are centered at radial velocities of -380 and -150 km s-1, have widths of 130 and 210 km s-1 FWHM, respectively, and most likely arise in outflowing gas near the active nucleus. At the times of observation, 1995 April 24 and 1995 October 22, there was no evidence for the variable absorption component at a higher outflow velocity that disappeared some time after 1989 October. The cores of the broad C IV absorption components are very close to zero intensity, indicating that the absorption regions are extended enough to occult completely the broad C IV emitting region (which is ~9 light-days in extent). The total column density of the C IV absorption is substantially larger than that measured by Kriss et al. from contemporaneous Hopkins Ultraviolet Telescope (HUT) spectra, but we agree with their conclusion that the UV absorption is too strong to arise primarily from the X-ray warm absorber region. The GHRS observations, separated by six months, reveal no appreciable changes in the equivalent widths or radial velocities of any of the absorption components, although a change in the column density of either broad component at a level ≤25% cannot be ruled out, because the lines are highly saturated. At present, we know of two Seyfert galaxies, NGC 3516 and NGC 4151, with complex multiple absorption zones, which can remain stable in column density and velocity field over timescales of months to years.
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