Physics
Scientific paper
Sep 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004sptz.prop.3374k&link_type=abstract
Spitzer Proposal ID #3374
Physics
Scientific paper
According to the unified model for AGN, Seyfert 1.8 and 1.9 galaxies are viewed at inclinations between those of Seyfert 1s (face-on) and Seyfert 2s (edge-on) with respect to the source of obscuration, typically envisioned as a dusty torus. This view is supported by the weak broad emission-line components of the Balmer lines, with ratios that are consistent with significant (E(B-V} ~ 1 mag) reddening of the broad-line region. Mid-IR spectra are the only means with which to probe the circumnuclear gas in these intermediate Seyferts and constrain the physical structure of the torus, such as its size, scale height, and clumpiness. Seyfert 1.8s and 1.9s also tend to possess relatively weak high ionization narrow lines (e.g. [Fe~VII] 6087 A) compared to Seyfert 1s, suggesting that the dusty circumnuclear gas may also obscure the inner narrow line region. We request Spitzer IRS spectra of 12 Seyfert 1.8s and 1.9s in order to 1) determine the temperature of the dust, and hence its radial distance from the central engine, to test for a torus origin, 2) determine the scale height and clumpiness of the torus atmosphere via the silicate 10 feature and comparisons with clumpy torus models, and 3) penetrate the obscuring gas via mid-IR emission lines, such as [Ne~V] 14.3 microns and [O~IV] 25.9 microns, to reveal the hidden high-ionization inner narrow line region. We have selected targets with host galaxies that are close to face-on, to minimize contamination of the mid-IR spectra by dust in their galactic planes. Among the more than 60 Seyferts in the Spitzer/IRS reserved target catalog, there are only a handful of true Seyfert 1.8s and 1.9s, and all of these have inclined (b/a < 0.5 ) host galaxies.
Crenshaw Michael
Dietrich Matthias
Elitzur Moshe
Gull Theodore
Kraemer Steven
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