AAS 203rd Meeting, January 2004
Session 56 Seyfert, FRI and FRII Galaxies
Poster, Tuesday, January 6, 2004, 9:20am-6:30pm, Grand Hall

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[56.05] The EUV Continuum Shape and Strength of NLS1 Galaxies

M. Dietrich, D.M. Crenshaw (Georgia State University), S.B. Kraemer (Catholic University of America)

Narrow-Line Seyfert 1 galaxies (NLS1s) hold key information about the structure and evolution of active galactic nuclei (AGN), particularly the strength and intrinsic shape of the ionizing continuum. A characteristic feature of AGN, relating the X-ray and optical/UV regime, is the big blue bump (BBB), which may be associated with thermal accretion disk emission. The presence of the BBB which is located in the EUV range, is indicated by upturns in the far-UV and soft X-rays. The strength and location of the BBB likely depend on the black hole mass, the luminosity, and the accretion rate. However, the direct observation of the EUV range is extremely difficult due to Galactic absorption. But the strength and emission line ratios of a variety of emission lines in the optical and infrared that are sensitive to different parts of the ionizing continuum in the EUV can be used as tracers of the SED shape and strength. Therefore, NLS1s are excellently suited to investigate the strength and the location of the BBB since they show in general strong soft X-ray emission while classical broad-line Seyfert 1 galaxies may show only a small or no BBB. We observed a sample of 12 bright NLS1s in the optical regime using the CTIO 1.5 m telescope to measure emission lines with ionization potentials up to ~400 eV. These spectra have sufficient spectral resolution in the optical are used to separate the broad (BLR) and narrow line region (NLR) emission contributions. Accurate photoionization modeling of the NLR will be applied to map the shape and strength of the BBB and determine the gas metallicity. In contrast to modeling the BLR spectrum, the detailed study of the NLR emission avoids the serious uncertainties of radiative transfer that affect BLR photoionization models.

The author(s) of this abstract have provided an email address for comments about the abstract: dietrich@chara.gsu.edu

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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.