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AST 386S





Fe Abundance Results and the Relation to Fe II Emission in Quasars

Active galactic nuclei have significant Fe II emission from the BLR, and the strength of the Fe II emission differs greatly from object to object. Do differing Fe abundances among AGNs play a significant role in the observed variations? Using a sample of AGN spectra from the Sloan Digital Sky Survey in the redshift range of 0.2 < z < 0.35, we measure the Fe/Ne abundance of the NLR using the [Fe VII]/[Ne V] line intensity ratio. We find no significant difference in the abundance of Fe in the NLR as a function of Fe II/Hbeta. Assuming the Fe abundance is the same in the NLR and the BLR, these results support the idea that the Fe II emission strength from varies from object to object due to differences in excitation conditions rather than differences in the abundance of Fe.



Cats, Dogs, Hair, A Hero, And More: New Milky Way Satellite Discoveries In The SDSS

In less than a decade of operation, the Sloan Digital Sky Survey (SDSS) has surveyed one-quarter of the sky to unprecedented depth, yielding scores of new discoveries. Among these are ten new dwarf satellite galaxies in the vicinity of the Milky Way, more than doubling the number known before the SDSS era. The extreme sensitivity of the survey to low surface brightness objects probes a regime in the mass-to-light ratio of galaxies previously inaccessible. I will review the techniques by which the new discoveries were made and provide some context in which to place them, including how expanding the discovery space of dwarf galaxies affects models of galaxy formation and assembly in Lambda-CDM cosmologies. Follow-up observations of the dwarf galaxy candidates reveal some objects that blur the lines of distinction between the lowest-mass galaxies and the largest globular clusters. The census of dwarf Milky Way satellite objects is clearly incomplete, and I will comment on how the next generation of large areal surveys will help fully characterize this population.



Tidal Tales of Minor Mergers: Star Formation in the Tidal Debris of Minor Mergers

How does the tidal debris of minor galaxy mergers contribute to structures in spiral galaxies or in the intergalactic medium? While major mergers are known to create structures such as tidal dwarf galaxies and star clusters within their tidal debris, little is known about minor mergers (mass ratios between a dwarf galaxy and disk galaxy of less than one-third) and their tidal debris. This work surveys 15 minor mergers using optical and infrared imaging to characterize star formation in their tidal debris. For example, NGC 2782, a minor merger having a mass ratio of 0.25 that occurred ~200 Myr ago, has a population of young star clusters which formed along both tidal tails. In particular, the presence of young clusters in the Western tail is unexpected due to the lack of molecular gas observed in previous studies. Also, the star cluster populations of each tidal tail have very different masses with the Western tail having smaller mass clusters. This result has implications for the wider field of star formation, suggesting that star cluster formation is a common outcome of minor mergers regardless of gas content in the tidal debris. However, the properties of the star clusters formed may be dependent on local properties such as metallicity, gas pressure density, gas content, etc. Even if minor mergers contribute less tidal debris per interaction than major mergers, they are more common and possibly contribute structure to all types of galaxies and to the intergalactic medium throughout the history of the universe.



Quasars with a Kick

Recent simulations of merging black holes with spin give recoil velocities from gravitational radiation up to several thousand km/s. A recoiling supermassive black hole can retain the inner part of its accretion disk, providing fuel for a continuing QSO phase lasting millions of years as the hole moves away from the galactic nucleus. Observational manifestations include QSOs displaced from the galactic nucleus, an x-ray flare from the reforming disk, and QSO emission lines shifted in velocity from the host galaxy. We discuss candidate QSOs from the Sloan Digital Sky Survey that have broad emission lines shifted by more than 1000 km/s relative to the narrow lines.


13 April 2007
Astronomy Program · The University of Texas at Austin · Austin, Texas 78712
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