AAS 197, January 2001
Session 38. Gas in External Galaxies
Display, Tuesday, January 9, 2001, 9:30am-7:00pm, Exhibit Hall

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[38.01] STIS Echelle Observations of NGC 4151. III. Interstellar Medium

A.C. Danks (RPSC, GSFC), G.L. Vieira, W. Landsman (RITSS, GSFC), D.M. Crenshaw, S.B. Kraemer (CUA, GSFC), J.B. Hutchings (DAO), T.R. Gull (GSFC), M.E. Kaiser (JHU), C.H. Nelson, D. Weistrop (UNLV)

We present ultraviolet spectroscopic observations of NGC 4151 taken with the Space Telescope Imaging Spectrograph (STIS). The observations were obtained 19-20 July 1999 in the modes E140M (R~ 45,000) and E230M (R~ 30,000), covering the wavelength range 1140-1690Åand 1610-3070Å respectively.

The data are compared with the earlier GHRS spectra reported by Weyman et al. (Ap.J. 1997, 483,717) and with a slitless STIS spectrum obtained in May 1997. The velocity components identified by Weyman et al. as A (-587km/s), B (-31km/s), C (139km/s), D (broad 411km/s), E (broad 710km/s), E' (786km/s), F (972km/s) and F' (1032km/s) are all present. The feature A' (-652 to -716km/s) is instead tentatively identified with the CO (0,0) band at 1544.45Åin the Galactic component. Two new features are identified, which we designate E"(859km/s) and G (1105km/s).

Since 1992, the Si II 1526Åand Si II* 1533Åfeatures have diminished greatly in the A component, but have grown in strength in the E' component.For the E' component we derive information on the excitation mechanism using the ratios of Si II* (1533)/Si II (1526) and Si II* (1309)/ Si II (1304) . In the Mg II doublet region, components A, B, C, D, E, E', E" and F are present, and the A component are seen to weaken while component E' strengths.

The high ionization lines Si IV, C IV and N V are unsaturated in the Galactic B component yielding log N sin|b| values of 13.6, 14.07 and 13.6 respectively. These values compare favorably to the Galactic average values of 13.56, 14.08 and 13.40 given by Sembach et al. (Ap.J. 1999, 524,98). The ratios of N (C IV)/N (Si IV) and N (C IV)/N (N V) are found to be 2.94 and 2.96 respectively, falling in the cooling fountain range (Benjamin and Shapiro 1999, ApJS, submitted). These values are comparable to those found for PKS 2155-304 lying at the opposite Galactic Pole. This work was supported by NASA through the STIS GTO funding.

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