We tackle the long-standing question “what is the relevance of major mergers and interactions as triggering mechanisms for AGN activity?” We study a sample of 83 quasars over z ~ 0.3-1.0 with high-resolution HST/ACS imaging in the F814W (broad I) band in the COSMOS field (Scoville et al. 2007), detected by their X-ray emission in the XMM-Newton

Recent analysis of the Milky Way's satellite galaxies reveals that these objects share a common central mass density, even though their luminosities range over five orders of magnitude. This observation can be understood in the context of galaxy formation theory by quantifying the factors which restrict the central mass density to a small range

We investigate the relationship between R Coronae Borealis (RCB) stars and hydrogen-deficient carbon (HdC) stars by measuring precise 16O/18O ratios for five cool RCB stars. The 16O/18O ratios are derived by spectrum synthesis from high-resolution (R ~ 50, 000) K-band spectra. Lower limits to the 16O/17O and 14N/15N ratios as well as Na and S

We present results from a survey of nearby AGN using the adaptive optics assisted integral-field spectrometer SINFONI on the VLT. These data enable us to study at high angular resolution (~ 0.″08) the distribution and kinematics of the low-ionization gas traced by the BrΓλ2.17 μm recombination line and [Si vi] λ 1.96 μm, [Al ix] λ 2.04 μm, and [Ca

We present a method that we developed to discern where the optical microvariability (OM) in quasars originates: in the accretion disk (related to thermal processes) or in the jet (related to non-thermal processes). Analyzing nearly simultaneous observations in three different optical bands of continuum emission, we are able to determine the origin

We present deep, accurate, and homogeneous multiband optical (U, B, V, I) photometry of the Carina dwarf spheroidal galaxy, based on more than 4000 individual CCD images from three different ground-based telescopes. Special attention was given to the photometric calibration, and the precision for the B, V, and I bands is generally better than 0.01