Dusty tori have been suggested to play a crucial role in determining the physical characteristics of active galactic nuclei (AGN), but investigation of their properties has stalled for lack of high resolution mid-IR imaging. Recently, a long-awaited breakthrough in this field was achieved: NGC 1068, a nearby AGN, was the first extragalactic object to be observed with a mid-IR interferometer, thereby obtaining the needed angular resolution to study the alleged torus. The instrument used was MIDI mounted on the ESO's VLT interferometer. The resulting 8-13 micron interferometric spectra indicated the presence of a thick (3 x 4 parsec) configuration of warm dust surrounding a hot ~1 pc component, marginally elongated in the direction perpendicular to the main orientation of the warm component. The structure of the 10 micron "silicate" absorption feature hinted at the presence of non-typical dust.
In this proceeding, first the field of AGN research is briefly reviewed, with an emphasis on models of dusty tori. Second, the general properties of the key object NGC 1068 are discussed. Third, the MIDI data set is presented together with a first attempt to interpret this data in the context of tori models. Fourth, preliminary MIDI interferometric spectra of the nucleus of the nearby starbursting galaxy Circinus are presented. The apparent observed absence of both a hot component as well as a sharp absorption feature suggest that we view the torus more edge-on than is the case for NGC 1068. Finally, we briefly discuss the prospects of ESA's Darwin mission for observing nearby and distant AGN. The required capabilities for Darwin's first goal -- the search for and subsequent characterization of earth-like planets orbiting nearby stars -- are such that for its second goal -- high resolution astrophysical imaging -- the sensitivity will be similar to JWST and the angular resolution 1-2 orders better. This will allow detailed mapping of tori of low luminosity AGN such as NGC 1068 up to redshifts of 1 - 2 and more luminous AGN up to redshift of 10 and beyond.
ESA's DARWIN will be an interferometric mission carrying out high-resolution astrophysical observations as well as the detection/characterization of earthlike exoplanets. In this paper, the current status and development perspectives of the Darwin imaging mode are discussed. First, overall system aspects are addressed including expected sensitivity, and baseline reconfiguration needs. Subsequently, the current instrumental concept is reviewed. This is based on a phase-referencing architecture supporting simultaneous observation of the science object, and an off-axis reference target for OPD stabilization purposes. The reference and science beams are wavelength-multiplexed and propagate along a common path through the interferometer. The viability of the cophasing approach is discussed, with emphasis on crosstalk control for multiplexed beam transfer, real-time compensation of the astrometric OPD, and associated metrology requirements. Studies have shown that imaging capabilities can be implemented within the current nulling beam combiner concept, which avoids the complexity and cost of developing a dedicated imaging beam combiner spacecraft. However, this approach has important drawbacks for the imaging mission
The start of NEVEC was initiated by the opportunity in the Netherlands to reinstate instrumental efforts in astronomy through a funding program for 'Top Research Schools,’ which brought about the creation of NOVA. The fact that considerable experience exists in Radio Astronomical imaging through interferometry (the Westerbork Synthesis Radio Telescope started in 1970), and the relatively small size at the time of ESO's VLTI Team made it opportune to aim for a win-win situation through collaboration. So presently an MOU between ESO and NOVA is in force, which stipulates that 10 out of the 18 man-years funded by NOVA for NEVEC until 2005 [new personnel, in university setting (Leiden) but on project money] shall be used on tasks that are mutually agreed between NOVA and ESO.
The tasks presently are found in the domain of observing modes, calibration and modeling, as well as contributing to the commissioning of new instruments and thinking about future instruments. Another task, outside these 10 FTE, has been the data handling and analysis software for MIDI, and again contributing to its commissioning. Delivery of the first operational version in Heidelberg has just taken place (summer 2002) contributing to the successful Preliminary Acceptance in Europe for MIDI on September 10, 2002. The actual state of 'products and deliveries' and the future outlook are reviewed.
We have obtained ultradeep Js, H and Ks near-infrared imaging of the Hubble Deep Field South WFPC2 field with the ISAAC camera on the VLT. The total integration time of 100 hours resulted in the deepest ground-based infrared observations to date and the deepest Ks-band data ever taken. This depth allows us to determine the spectral energy distributions of the high-redshift galaxies with unprecendented accuracy. Together with existing optical observations, we use the multicolor data to select high-redshift galaxies by their rest-frame optical light, and study their statistical properties and morphologies. We find a wide variety of morphologies: some are large in the rest-frame optical and resemble normal spiral galaxies, others are barely detected in the observers optical and have red NIR colors. The latter belong to a new population of galaxies at redshifts z>2, that is notably absent in the HDF-North. The spectral energy distributions of many of such red galaxies show distinct breaks, which we identify as the balmer break/4000 Angstrom break, and their contribution to the stellar mass density is estimated to be substantial. At redshift z~3, we find a clear excess of superluminious galaxies (> 5 L*B(z=0)), which is consistent with 1 magnitude of luminosity evolution. Overall, the results show the necessity of deep near-infrared imaging to obtain a full census of the high redshift universe.
High redshift radio galaxies are great cosmological tools for pinpointing the most massive objects in the early Universe: massive forming galaxies, active super-massive black holes and proto-clusters. We report on deep narrow-band imaging and spectroscopic observations of several z > 2 radio galaxy fields to investigate the nature of giant Ly-α nebulae centered on the galaxies and to search for over-dense regions around them. We discuss the possible implications for our understanding of the formation and evolution of massive galaxies and galaxy clusters.
In this review, we will first briefly discuss the imaging performance of the missions, with an emphasis on the Darwin mission. We will then discuss how these space interferometers will contribute in a very significant way to our understanding of the formation and evolution of planets, stars, galaxies and supermassive black-holes located at the centers of most or possibly even all galaxies.
The mid-infrared interferometric instrument (MIDI) is planned to become operative at the ESO Very Large Telescope Interferometer (VLTI) during the year 2001. The first version of MIDI is designed for use of two telescope beams at 10 micrometers wavelength. We here present an overview of some of the scientific objectives. The preparatory work under progress, before first VLTI observations, consists in studying the feasibility of different astrophysical projects (expected visibility, required absolute accuracy of the measurement, required observing time, procedure of observation, and VLTI baseline configuration). As examples we will discuss the observations of disks around young stellar objects, of active galactic nuclei, of extrasolar planets and of some evolved stars.
We present the main results of a project aimed at understanding the nature of extremely red galaxies (ERGs) and their role in galaxy formation and evolution. The paper is focused on recent near-IR spectroscopy of ERGs made with the ESO VLT-UT1 equipped with ISAAC. Neither strong emission lines nor continuum breaks were detected in their near-IR spectra. The optical to near-IR spectral energy distributions of the observed ERGs suggest that 0.8 < z < 1.8 and that most of them are passively evolving elliptical galaxies. The main results of complementary HST and sub mm observations are also presented. Finally, we discuss what the present result tell us about the nature of ERGs and on their relation with the problem of the formation and evolution of elliptical galaxies.