Jena 2013 – wissenschaftliches Programm

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EP: Fachverband Extraterrestrische Physik

EP 1: Astrophysik

EP 1.1: Hauptvortrag

Montag, 25. Februar 2013, 14:00–14:30, HS 9

Probing quasars with large surveys and long-term monitoring programs — •Helmut Meusinger — Thueringer Landessternwarte, Tautenburg, Germany

50 years after the discovery of quasars, the active galactic nuclei (AGN) community is in the midst of a flood of high-quality data from large surveys. AGNs are efficiently selected in the mid-IR, radio, and X-ray domain and optical surveys provide spectra for huge numbers of (largely unobscured) high-luminosity AGNs. A major contribution comes from the Sloan Digital Sky Survey (SDSS) with its excellent photometric and spectroscopic data, including multi-epoch photometry. Variations of the optical/UV flux density over time, one of the key characteristics of AGNs, have long been considered to provide insight into the geometry and physics of quasars. Statistical trends seem to support a picture where accretion in a standard disk is the dominant underlying process for the UV/optical quasar variability. Quantitative discrepancies between observed and predicted trends, however, imply modifications beyond the simplest model. Moreover, other processes contribute to the observed variability as well, including those on longer timescales. Extreme deviations from the mean quasar spectrum indicate peculiar spectral types that may hold important clues to quasar structure and evolution. Using a neural network for the selection of peculiar spectra and combining the results with near-IR, mid-IR, and radio data, the SDSS is shown to be uniquely suited to collect and study substantial samples of unusual and hitherto unknown quasar types.