We have observed Centaurus A with the Mid-Infrared Interferometric Instrument (MIDI) at the Very Large Telescope Interferometer at resolutions of 7–15 mas (at 12.5 μm) and filled gaps in the (u, v) coverage in comparison to earlier measurements. We are now able to describe the nuclear emission in terms of geometric components and derive their parameters by fitting models to the interferometric data. With simple geometrical models, the best fit is achieved for an elongated disk with flat intensity profile with diameter 76 ± 9 × 35 ± 2 mas (1.41 ± 0.17 × 0.65 ± 0.03 pc) whose major axis is oriented at a position angle (PA) of 10.1 ± 2.2° east of north. A point source contributes 47 ± 11% of the nuclear emission at 12.5 μm. There is also evidence that neither such a uniform nor a Gaussian disk are good fits to the data. This indicates that we are resolving more complicated small-scale structure in active galactic nuclei with MIDI, as has been seen in Seyfert galaxies previously observed with MIDI. The PA and inferred inclination i = of the dust emission are compared with observations of gas and dust at larger scales.

One of the key predictions of hierarchical galaxy formation models is that a significant fraction of elliptical galaxies form in late merging events. One of the most important diagnostics of such an assembly is the existence of blue spheroidal galaxies, which have spheroid-dominated morphologies and blue colors indicating recent star formation, as an intermediate step in the evolution of elliptical galaxies.

We observed four nearby AGN with MIDI at the VLTI to investigate the mid-infrared emission from these sources. With our measurements we resolve the dusty structure around the nucleus of the Circinus galaxy. We find two dust components: a hot, small elongated structure with a size of 0.4 pc and a cooler, almost round component with a size of 1.9 pc. We interpret the emission to be originating in a geometrically thick dusty torus oriented perpendicular to the ionisation cone. Hence our finding nicely confirms the unified picture. We also observed the nucleus of Centaurus A and find that 70% of the mid infrared flux originates from an unresolved source with a size of less than 0.2 pc. In this case, the majority of the emission comes from a synchrotron source at the base of the radio jet. Two further galaxies, Mrk 1239 (Seyfert 1) and MCG -05-23-016 (Seyfert 2), also show unresolved mid infrared sources limiting the size of the dust distribution to less than 5 and 2 pc respectively.

We study the dark matter halos of galaxies with galaxy-galaxy lensing using the COMBO-17 survey. This survey offers an unprecedented data set for studying lens galaxies at $z=0.2-0.7$ including redshift information and spectral classification from 17 optical filters for objects brighter than $R=24$. So far, redshifts and classification for the lens galaxies have mainly been available for local surveys like the Sloan Digital Sky Survey (SDSS). Further, redshifts for the source galaxies have typically not been available at all but had to be estimated from redshift probability distribution which – for faint surveys – even had to be extrapolated.

To study the dark matter halos we parametrize the lens galaxies as singular isothermal spheres (SIS) or by Navarro-Frenk-White (NFW) profiles. In both cases we find a dependence of the velocity dispersion or virial radius, respectively, on lens luminosity and colour. For the SIS model, we are able to reproduce the Tully-Fisher/Faber-Jackson relation on a scale of $150h^{-1}~\mathrm{kpc}$. For the NFW profile we also calculate virial masses, mass-to-light ratios and rotation velocities.

Finally, we investigate differences between the three survey fields used here.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present our cosmic shear analysis of the Galaxy Evolution from Morphology and SEDs (GEMS) survey. Imaged with the Advanced Camera for Surveys (ACS) on HST, GEMS provides high resolution imaging spanning some 800 square arcmins in the Chandra Deep Field South (CDFS). We discuss the benefits of using space-based data for weak lensing studies and show that the ACS is a very powerful instrument in this regard. We find that we are not limited by systematic errors arising from the anisotropic ACS point spread function distortion and use our cosmic shear results to place joint constraints on the matter density parameter $\Omega_m$ and the amplitude of the matter power spectrum $\sigma_8$, finding $\sigma_8(\Omega_m/0.3)^{0.62}=0.73 \pm 0.12$.

To investigate the impact of atmospheric seeing on weak lensing analysis we compare the shear measured from CDFS galaxies resolved by the COMBO-17 survey and imaged by GEMS. We find good agreement between the two surveys and a higher dispersion in the intrinsic ellipticity distribution of COMBO-17. This dispersion implies that a space-based cosmic shear analysis would yield higher signal-to-noise results compared to a ground-based cosmic shear analysis of the same galaxy sample.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We have taken N-band spectra of the nuclear dust regions of NGC 1068 with the newly commissioned Mid-InfrareD-Interferometer (MIDI), with a spatial resolution of ∼10 milliarcsec (∼1 pc). We resolve the near-nuclear emission into a warm component (∼300 K) 2.1×3.4 pc in size and a smaller hot component. We see a strong silicate absorption in front of the central component that differs in form from normal olivine-type profiles. This thick dust structure cannot be supported for the length of the active phase of the AGN by gas pressure or turbulent motions.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

First results from the AGN-Heidelberg program aimed at spatially resolving the central pc region of the closest Active Galactic Nuclei are presented. The core region of prototype active nuclei are clearly unveiled at IR waves and at distances from the nucleus – few pc- where circumnuclear starforming regions appear not to be present. Within that perspective, classical active nuclei as Circinus and NGC 1097, reveal with unprecedented detail clear channels of material being driven to the core whereas others as Centaurus A and NGC 5506, show a “clean” core environment. At the very center, a central compact region of ∼2 pc scale is resolved in Circinus but not in the other cases challenging thus the universal presence of the putative obscuring torus.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html