Feeding Monsters – A Study of Active Galaxies

We present new interferometric observations of the molecular gas distribution and kinematics in the nuclei of different active galaxies at high angular resolution and high sensitivity carried out with the IRAM Plateau de Bure interferometer (PdBI). The observations cover galaxies in a redshift range of 0.03–1.4. We have so far observed five different active galaxies: NGC3718, NGC1068, HE1029–1831, 3C48 and Q0957+561. The first two objects belong to the NUGA (NUclei of GAlaxies) project – an international collaboration mainly between Spain, France and Germany – containing about 30 Seyfert and LINER galaxies. Both are at the same distance of 14Mpc and show a warped gas and dust disk. The new mosaic map of NGC3718 corrected for short-spacing effects with IRAM 30 m observations well demonstrates the existence of the warped gas disk with several secondary maxima in the projected gas distribution caused by orbit crowding effects. Based on these new data we have improved recent simulations of the warped disk in NGC3718. HE1029–1831 and 3C48 are nearby QSOs. HE1029–1831 is taken out of the Cologne nearby QSO sample. The maps of the integrated CO(1–0) and CO(2–1) emission clearly show that the molecular gas is mostly related to the central bulge with a non-negligible fraction distributed along the bar known from optical observations. Our new CO data of 3C48 unveil new information about the kinematics of its molecular gas complementing and improving further studies based on previous infrared observations and detailed multi-particle simulations. Finally, new measurements of the CO(1–0) line in Q0957+561 – a highly-red-shifted, gravitationally lensed quasar – will be presented as a link to earlier evolutionary stages of active galaxies and their hosts.     

Why chromatic imaging matters

During the last two decades, the first generation of beam combiners at the Very Large Telescope Interferometer has proved the importance of optical interferometry for high-angular resolution astrophysical studies in the near- and mid-infrared. With the advent of 4-beam combiners at the VLTI, the u ? v coverage per pointing increases significantly, providing an opportunity to use reconstructed images as powerful scientific tools. Therefore, interferometric imaging is already a key feature of the new generation of VLTI instruments, as well as for other interferometric facilities like CHARA and JWST. It is thus imperative to account for the current image reconstruction capabilities and their expected evolutions in the coming years. Here, we present a general overview of the current situation of optical interferometric image reconstruction with a focus on new wavelength-dependent information, highlighting its main advantages and limitations. As an Appendix we include several cookbooks describing the usage and installation of several state-of-the art image reconstruction packages. To illustrate the current capabilities of the software available to the community, we recovered chromatic images, from simulated MATISSE data, using the MCMC software SQUEEZE. With these images, we aim at showing the importance of selecting good regularization functions and their impact on the reconstruction.     

New active galactic nuclei science cases with interferometry

Infrared (IR) interferometry has made widely recognised contributions to the way we look at the dusty environment of supermassive black holes on parsec scales. It finally provided direct evidence for orientation-dependent unification of active galaxies, however it also showed that the classical “torus” picture is oversimplified. New scientific opportunities for AGN have been suggested, and will soon be carried out, focusing on the dynamical aspects of spectrally and spatially resolved interferometry, as well as the potential to employ interferometry for cosmology. This will open interferometry to new scientific communities.     

The planet formation imager

The Planet Formation Imager (PFI, www.planetformationimager.org) is a next-generation infrared interferometer array with the primary goal of imaging the active phases of planet formation in nearby star forming regions. PFI will be sensitive to warm dust emission using mid-infrared capabilities made possible by precise fringe tracking in the near-infrared. An L/M band combiner will be especially sensitive to thermal emission from young exoplanets (and their disks) with a high spectral resolution mode to probe the kinematics of CO and H₂O gas. In this paper, we give an overview of the main science goals of PFI, define a baseline PFI architecture that can achieve those goals, point at remaining technical challenges, and suggest activities today that will help make the Planet Formation Imager facility a reality.     

Response of Pediastrum in German floodplain lakes to Late Glacial climate changes

Subfossil remains of the Pediastrum-algae group (Fam. Hydrodictyaceae) are frequently found in lake sediments, but very few studies have used them as palaeoclimate and palaeolimnological indicators. This study explored the species composition of Pediastrum assemblages in shallow floodplain lakes in northern Germany during two transitional periods from cold to temperate climate conditions (GS-2/GI-1 and GI-1/Holocene). We identified Pediastrum taxa to subspecies level and used multivariate statistics (constrained clustering, principal component analysis and redundancy analysis) to show that shifts in taxonomic composition reflected the strong Late Glacial climate oscillations. The Pediastrum assemblages indicate that climate amelioration already begun shortly before the main GS-2/GI-1 summer-temperature transition. In contrast to previous studies that identified trophic state as the main driver of change in Pediastrum species composition, we identified climate shifts and related factors as the major drivers of community change. Water depth and trophic state probably acted as secondary factors that were responsible for differences in Pediastrum response between the first and second investigated climate transitions. During cold periods, Pediastrum algae composition was controlled mainly by environmental variables, whereas during warm periods, Pediastrum assemblages may have been influenced to a greater extent by intra- and intergeneric competition. This study contributes to knowledge about ecological niches of Pediastrum species. Size-measurements on Pediastrum coenobia reveal that one response of Pediastrum algae to climate shifts probably was size change. Coenobia of Pseudopediastrum boryanum var. boryanum were significantly smaller during cold climate periods than during temperate periods. The shifts in Pediastrum species composition and coenobium size suggest this algae group has great potential for enabling palaeoecological and palaeoclimate inferences.     

The warped gas and dust lane in NGC 3718

We present the first observations of molecular line emission in NGC 3718 with the IRAM 30m and the Plateau de Bure Interferometer. This galaxy is an excellent example for a strongly warped gas disk harboring an active galactic nucleus (AGN). An impressive dust lane is crossing the nucleus and a warp is developing into a polar ring. The molecular gas content is found to be typical of an elliptical galaxy with a relatively low molecular gas mass content (∼ 4 × 10⁸ M _⊙). The molecular gas distribution is found to warp from the inner disk together with the HI distribution. The CO data were also used to improve the kinematic modeling in the inner part of the galaxy, based on the so-called tilted ring-model. The nature of NGC 3718 is compared with its northern sky `twin' Centaurus A and the possible recent swallowing of a small-size gas-rich spiral is discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Circumstellar disks and planets

We present a review of the interplay between the evolution of circumstellar disks and the formation of planets, both from the perspective of theoretical models and dedicated observations. Based on this, we identify and discuss fundamental questions concerning the formation and evolution of circumstellar disks and planets which can be addressed in the near future with optical and infrared long-baseline interferometers. Furthermore, the importance of complementary observations with long-baseline (sub)millimeter interferometers and high-sensitivity infrared observations is outlined.     

The path towards high-contrast imaging with the VLTI: the Hi-5 project

The development of high-contrast capabilities has long been recognized as one of the top priorities for the VLTI. As of today, the VLTI routinely achieves contrasts of a few 10^??3 in the near-infrared with PIONIER (H band) and GRAVITY (K band). Nulling interferometers in the northern hemisphere and non-redundant aperture masking experiments have, however, demonstrated that contrasts of at least a few 10^??4 are within reach using specific beam combination and data acquisition techniques. In this paper, we explore the possibility to reach similar or higher contrasts on the VLTI. After reviewing the state-of-the-art in high-contrast infrared interferometry, we discuss key features that made the success of other high-contrast interferometric instruments (e.g., integrated optics, nulling, closure phase, and statistical data reduction) and address possible avenues to improve the contrast of the VLTI by at least one order of magnitude. In particular, we discuss the possibility to use integrated optics, proven in the near-infrared, in the thermal near-infrared (L and M bands, 3-5 \(\upmu \)m), a sweet spot to image and characterize young extra-solar planetary systems. Finally, we address the science cases of a high-contrast VLTI imaging instrument and focus particularly on exoplanet science (young exoplanets, planet formation, and exozodiacal disks), stellar physics (fundamental parameters and multiplicity), and extragalactic astrophysics (active galactic nuclei and fundamental constants). Synergies and scientific preparation for other potential future instruments such as the Planet Formation Imager are also briefly discussed. This project is called Hi-5 for High-contrast Interferometry up to 5 μm.