Resolved Spectroscopy of the Narrow‐Line Region in NGC 1068. II. Physical Conditions near the NGC 1068 “Hot Spot”

The physical conditions near the optical continuum peak (``hot spot'') in theinner narrow line region (NLR) of the Seyfert 2 galaxy, NGC 1068. Spectra weretaken with HST/STIS through the 0.1X52 arcsec slit, covering the full STIS 1200to 10000 Angstrom waveband, and are from a region that includes the hot spot,extending 0.2, or ~ 14 pc (for H= 75 km/sec/Mpc). Perhaps the most strikingfeature of these spectra is the presence of strong coronal emission lines,including [S XII] 7611 which has hitherto only been identified in spectra ofthe solar corona. There is an apparent correlation between ionization energyand velocity of the emission lines with respect to the systemic velocity of thehost galaxy, with the coronal lines blueshifted, most other high excitationlines near systemic, and some of the low ionization lines redshifted. From theresults of our modeling, we find that the emission-line gas consists of threeprincipal components: 1) one in which most of the strong emission-lines, suchas [O III] 5007, [Ne V] 3426, C IV 1550, arise, 2) a more tenuous, highlyionized component, which is the source of the coronal-line emission, and 3) acomponent, which is not co-planar with the other two, in which the lowionization and neutral lines, such as [N II] 6548 and [O I] 6300, are formed.The first two components are directly ionized by the EUV-Xray continuum emittedby the central source, while the low ionization gas is ionized by a combinationof highly absorbed continuum radiation and a small fraction of unabsorbedcontinuum scattered by free electrons associated with the hot spot. Thecombination of covering factor and Thomson optical depth of the high ionizationcomponents is insufficient to scatter the observed fraction of continuumradiation into our line-of-sight.Comment: 42 pages, Latex, includes 5 figures (postscript), to appear in the Astrophysical Journa