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Abstracts (11/01) Journal Club: "Infrared Fe II Emission in Narrow-line Seyfert 1 Galaxies" Randi Worhatch, University of Texas at Austin We obtained 0.8-2.4 micrometer spectra at a resolution of 320 km s-1 of four narrow-line Seyfert 1 galaxies in order to study the near-infrared properties of these objects. We focus on the analysis of the Fe II emission in that region and the kinematics of the low-ionization broad lines. We show that the 1 micrometer Fe II lines (lambda 9997, lambda 10501, lambda 10863, and lambda 11126) are the strongest Fe II lines in the observed interval. For the first time, primary cascade lines of Fe II arising from the decay of upper levels pumped by Lyman alpha fluorescence are resolved and identified in active galactic nuclei. Excitation mechanisms leading to the emission of the 1 micrometer Fe II features are discussed. A combination of Lyman alpha fluorescence and collisional excitation is found to be the main contributor. The flux ratio between near-IR Fe II lines varies from object to object, in contrast to what is observed in the optical region. A good correlation between the 1 micrometer and optical Fe II emission is found. This suggests that the upper z4F0 and z4D0 levels from which the bulk of the optical Fe II lines descend are mainly populated by the transitions leading to the 1 micrometer lines. The width and profile shape of Fe II lambda 11127, Ca II lambda 8642, and O I lambda 8446 are very similar but significantly narrower than PaB, giving strong observational support to the hypothesis that the regions where Fe II, Ca II, and O I are produced are cospatial, interrelated kinematically, and most probably located in the outermost portion of the broad-line region. (11/08) Constraining Galaxy Evolution with Bulge+Disk+Bar Decomposition Tim Weinzirl, University of Texas at Austin Structural decomposition of galaxies into bulge, disk, and bar components is important to address a number of scientific problems. Measuring bulge, disk, and bar structural parameters will set constraints on the violent and secular processes of galaxy assembly and recurrent bar formation and dissolution models. It can also help to quantify the fraction and properties of bulgeless galaxies (those systems having no bulge or only a relatively insignificant disky-pseudobulges), which defy galaxy formation paradigms requiring almost every disk galaxy to have a classical bulge at its core. Three-component bulge+disk+bar decomposition is demonstrated for NIR images of galaxies, with Hubble types S0 to Sm, from the Ohio State University Bright Spiral Galaxy Survey (OSUBSGS). Unlike most early studies, which attempt two-component bulge+disk decomposition, three-component bulge+disk+bar decomposition is performed with GALFIT. The importance of including the bar component is highlighted, as this can lower the bulge fractional luminosity ratio (B/T), often by a factor of two or more, and effectively change the Hubble type of a galaxy from early to late. Accordingly, the variation in the structure of bulges and B/T across the Hubble sequence for barred and unbarred galaxies is explored. |
13 April 2007
Astronomy Program · The University of Texas at Austin · Austin, Texas 78712
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Astronomy Program · The University of Texas at Austin · Austin, Texas 78712
prospective student inquiries: studentinfo@astro.as.utexas.edu
site comments: www@www.as.utexas.edu