Adaptive Optics Discovery of Supernova 2004ip in the Nuclear Regions of the Luminous Infrared Galaxy IRAS 18293-3413

The thesis focuses on two case studies of the host galaxies of the quasi-stellar objects (QSOs) I Zw 1 and 3C 48. The studies are motivated by the hypothesis that ultra-luminous infrared galaxies (ULIRGs) might represent the early stage of QSO evolution (Sanders et al. 1988). According to this hypothesis, galaxy mergers and interactions trigger gas inflow which is followed by starburst activity and by the formation of an active nucleus. As likely transitionary objects between the ultra-luminous infrared stage and the QSO stage, I Zw 1 and 3C 48 are promising candidates to investigate the active nucleus, the starburst, and the merger properties as the essential links between all stages of the proposed evolutionary sequence. The case study of I Zw 1 has an observational focus and is based on near-infrared (NIR) imaging and spectroscopy, carried out with ISAAC (Infrared Spectrometer and Array Camera) at the Very Large Telescope of the European Southern Observatory (ESO) on Cerro Paranal in Chile. The two-armed spiral host galaxy of I Zw 1 shows two bright knots in the north and in the west of the optical disk region, respectively. Here, the new ISAAC spectra indicate that the northern object is a projected foreground star, as previously assumed but recently challenged. In the surroundings of the western source, the ISAAC J-band image displays tidal features. This gives further support for the scenario that I Zw 1 is presently in a minor merger process with this source. The new spectra and the NIR colors of the western source indicate an old stellar population. The host of I Zw 1 is analyzed in a one-dimensional structural decomposition into bulge, disk, and halo components, which results in mean J-band mass-to-light ratios. The latter indicate a young mean stellar population in the bulge component, while the disk ratios agree with those of normal spiral galaxies. Such a scenario of younger stellar populations in the central region of the I Zw 1 host is also plausible from a two-color analysis. The nuclear ISAAC spectrum of I Zw 1 basically confirms previous results, by showing hydrogen emission lines and indications of extremely blueshifted high-excitation lines. The case study of 3C 48 is the numerical focus of this thesis and based on simulations with multi-particle methods. The aim is to investigate the major merger scenario for 3C 48 by reproducing a 3C 48 model. Such a model is found for a certain projection angle during the inclined merger of two equal-mass spiral galaxies. It inspirits a new idea for the problem of the apparently missing second tidal tail in 3C 48. For the derived projection angle, this tidal tail is located in front of the main body of the modeled host galaxy and is likely to be missed in observations. In the model, both galaxy centers are still separated. This leaves room to interpret the known second luminosity peak, north-east of the QSO in 3C 48, as the center of the galaxy merging with 3C 48. A central gas accumulation and a complex system of gas lanes develop in the simulation with a non-gravitating gas component added. Both results qualitatively agree with the known distribution of molecular gas in 3C 48. The new results about I Zw 1 and 3C 48 complement the existing assumption that both are likely transitionary objects in the evolutionary sequence.

We report the discovery of a confirmed supernova (SN) and a supernova-candidate in near-infrared images from the ALTAIR/NIRI adaptive optics system on the Gemini-North Telescope and NICMOS on the Hubble Space Telescope. The Gemini images were obtained as part of a near-infrared K-band search for highly-obscured SNe in the nuclear regions of luminous infrared galaxies. SN 2008cs apparent in the Gemini images is the first SN discovered using laser guide star adaptive optics. It is located at 1500 pc projected distance from the nucleus of the luminous infrared galaxy IRAS 17138-1017. The SN luminosity, JHK colors and light curve are consistent with a core-collapse event suffering from a very high host galaxy extinction of 15.7 +- 0.8 magnitudes in V-band which is to our knowledge the highest yet measured for a SN. The core-collapse nature of SN 2008cs is confirmed by its radio detection at 22.4 GHz using our Very Large Array observations 28 days after the SN discovery, indicating a prominent interaction of the SN ejecta with the circumstellar medium. An unconfirmed SN apparent in the NICMOS images from 2004 is located in the same galaxy at 660 pc projected distance from the nucleus and has a lower extinction.

The work presented in my thesis covers two aspects of modern astronomy: Observations and instrumentation. Part I of this thesis addresses the design, the development and the qualification of the Low Resolution Spectroscopy Double Prism Assembly (LRSDPA). From an instrumentational point of view, the purpose of the LRSDPA is to make an integration of two prisms, made of Germanium and Zincsulfide, into the imaging module of the mid infrared instrument of the James Webb Space Telescope possible. My design of the LRSDPA answers to several challenging specifications, joining together available envelope, mechanical, thermal, optical and alignment aspects. Both prisms are mounted separately onto a holder via a semi-kinematic interface. The Aluminium components of the demonstration, qualification and flight model all have been manufactured at the mechanical workshop of the 1st Institute of Physics. As it is demanded of all space equipment, the function and performance of the LRSDPA has to be thoroughly demonstrated. The qualification campaign that was conducted in collaboration with the Centre Spatial de Liege, has just been brought to a successful finish. A brief introduction to the James Webb Space Telescope and its mid infrared instrument are given in Chapters 1 and 2. Chapter 3 then describes in detail the scientific capabilities, the design and the qualification of the LRSDPA. The low resolution spectroscopy mode will provide prism slit spectroscopy at a resolution of R=100 and cover the wavelength range from 5µm-10µm. This mode is particularly aiming at spectroscopic analyses of very low surface brightness objects, such as the first light-emitting galaxies that re-ionized the universe shortly after the big bang. This scenario of re-ionization is supposed to happen shortly after the big bang, at redshifts of z=10-15. At these redshifts, the mid infrared wavelength domain gets in particular interesting, because it covers the rest-frame optical and near infrared wavelengths. Near infrared characteristics are also well suited to investigate key properties of host galaxies of active galactic nuclei (AGN), which constitute part II of my thesis. The study of host galaxies of quasi-stellar objects (QSO) is handicapped by the bright nucleus outshining its host, even with state-of-the-art telescopes. Untangling the host from the nucleus is easier for closer AGN, and in the near infrared wavelengths, the contrast in spectral energy distributions of active nucleus and host galaxy favor the detection of the host. For these reasons, we have created a nearby type I AGN sample optimized for near infrared studies, with a redshift limit of z<0.06. Chapter 4 gives a short introduction to the background motivating the selection of this sample. In Chapter 5, I present large scale, near infrared, seeing limited slit spectroscopy and imaging of nine of these AGN, carried out with ISAAC, mounted at the very large telescope (VLT) of the European Southern Observatory. Hydrogen recombination lines are observed in seven of the nine sources of which five show a broad component. In three sources, extended 1-0S(1) rotational-vibrational molecular hydrogen emission is detected. Stellar CO absorption is seen in four sources. In one of these objects, an upper limit of the central mass can be determined from the stellar velocity field. H- and Ks-band imaging allow me to determine the morphology class of the host galaxies. Colors (with supplementary J-band 2micron all sky survey images) show that the four galaxies with detected CO absorption are characterized by an overall strong stellar contribution. After removal of the nuclear point source, the host galaxies show colors typical for non-active spiral galaxies. In chapter 6, I analyze the central kiloparsec of another source included in this sample, HE 0036-5133, using adaptive optics and SINFONI, the integral field near infrared spectrograph of the VLT. This source is mostly famous for its extremely soft X-ray radiation and an X-ray outburst detected during the ROSAT all sky survey in 1990. With the help of different extinction maps and equivalent widths of various stellar absorption lines, the data reveals a deeply hidden nuclear bar and enhanced nuclear star formation, but no prominent sign of extreme QSO-like nuclear activity. In addition, the data supports that the origin of the soft X-ray core is caused by an absent hard X-ray source, rather than a deeply embedded hard X-ray source.

We present new near-infrared (NIR) Keck and Very Large Telescope (VLT) spectroscopic data on the stellar dynamics in late-stage, ultraluminous infrared galaxy (ULIRG) mergers. We now have information on the structural and kinematic properties of 18 ULIRGs, eight of which contain QSO-like active galactic nuclei (AGNs). The host properties (σ, reff, μeff, MK) of AGN-dominated and star formation dominated ULIRGs are similar. ULIRGs fall remarkably close to the fundamental plane of early-type galaxies. They populate a wide range of the plane, are on average similar to L* rotating ellipticals, but are well offset from giant ellipticals and optically/UV-bright, low-z QSOs/radio galaxies. ULIRGs and local QSOs/radio galaxies are very similar in their distributions of bolometric and extinction-corrected NIR luminosities, but ULIRGs have smaller effective radii and velocity dispersions than the local QSO/radio galaxy population. Hence, their host masses and inferred black hole masses are correspondingly smaller. The latter are more akin to those of local Seyfert galaxies. ULIRGs thus resemble local QSOs in their NIR and bolometric luminosities because they are (much more) efficiently forming stars and/or feeding their black holes, and not because they have QSO-like, very massive black holes. We conclude that ULIRGs as a class cannot evolve into optically bright QSOs. They will more likely become quiescent, moderate mass field ellipticals or, when active, might resemble the X-ray-bright, early-type galaxies that have recently been found by the Chandra observatory.

Ultraluminous infrared galaxies (ULIRGs) are the most luminous galaxies in the local universe, with power outputs above 10^12 times that of our sun. Almost all ULIRGs are found to be associated with collisions between large, gas-rich galaxies. With most of the energy output emerging at far-infrared wavelengths, these galaxies are understood to be extremely dusty. As such, the nature of the power source within the dust shroud is not clearly understood. The two most likely explanations involve either a massive burst of star formation or the presence of an active galactic nucleus (AGN) in the form of a dust-enshrouded quasar. This work presents two separate approaches to investigating the nature of ultraluminous infrared galaxies. The first is a spectrosciopic survey of 33 ULIRGs in the near-infrared band around a wavelength of 2 microns, where dust extinction is much less severe than in visible light. The aim of this study is to search for evidence of buried AGN, as indicated by velocity-broadened hydrogen recombination lines as well as the presence of the high excitation [Si VI] emission line. This survey finds that signs of AGN are rare in ULIRGs, with the most natural conclusion being that the majority of ULIRGs are powered by starburst phenomena. The second approach presented involves the design, construction, and use of a novel instrument built specifically to study the spatial and kinematical properties of gas within the morphologically complex ULIRGs. A single long slit is generally not capable of capturing the rich phenomenology found in the complex environments of ULIRGs. Data from the Palomar Integral Field Spectrograph reveals that several ULIRGs are found to exist at times very early in the galaxy encounter process. The possibility that ultraluminous activity may develop so early in the merger history suggests a non-trivial luminosity evolution among galaxy mergers, wherein the less powerful class of luminous infrared galaxies may represent a different phase of the same overall phenomenon.

An Adaptive Optic (AO) system is a fundamental requirement of 8m-class telescopes. We know that in order to obtain the maximum possible resolution allowed by these telescopes we need to correct the atmospheric turbulence. Thanks to adaptive optic systems we are able to use all the effective potential of these instruments, drawing all the information from the universe sources as best as possible. In an AO system there are two main components: the wavefront sensor (WFS) that is able to measure the aberrations on the incoming wavefront in the telescope, and the deformable mirror (DM) that is able to assume a shape opposite to the one measured by the sensor. The two subsystem are connected by the reconstructor (REC). In order to do this, the REC requires a “common language between these two main AO components. It means that it needs a mapping between the sensor-space and the mirror-space, called an interaction matrix (IM). Therefore, in order to operate correctly, an AO system has a main requirement: the measure of an IM in order to obtain a calibration of the whole AO system. The IM measurement is a 'mile stone' for an AO system and must be done regardless of the telescope size or class. Usually, this calibration step is done adding to the telescope system an auxiliary artificial source of light (i.e a fiber) that illuminates both the deformable mirror and the sensor, permitting the calibration of the AO system. For large telescope (more than 8m, like Extremely Large Telescopes, ELTs) the fiber based IM measurement requires challenging optical setups that in some cases are also impractical to build. In these cases, new techniques to measure the IM are needed. In this PhD work we want to check the possibility of a different method of calibration that can be applied directly on sky, at the telescope, without any auxiliary source. Such a technique can be used to calibrate AO system on a telescope of any size. We want to test the new calibration technique, called “sinusoidal modulation technique”, on the Large Binocular Telescope (LBT) AO system, which is already a complete AO system with the two main components: a secondary deformable mirror with by 672 actuators, and a pyramid wavefront sensor. My first phase of PhD work was helping to implement the WFS board (containing the pyramid sensor and all the auxiliary optical components) working both optical alignments and tests of some optical components. Thanks to the “solar tower” facility of the Astrophysical Observatory of Arcetri (Firenze), we have been able to reproduce an environment very similar to the telescope one, testing the main LBT AO components: the pyramid sensor and the secondary deformable mirror. Thanks to this the second phase of my PhD thesis: the measure of IM applying the sinusoidal modulation technique. At first we have measured the IM using a fiber auxiliary source to calibrate the system, without any kind of disturbance injected. After that, we have tried to use this calibration technique in order to measure the IM directly “on sky”, so adding an atmospheric disturbance to the AO system. The results obtained in this PhD work measuring the IM directly in the Arcetri solar tower system are crucial for the future development: the possibility of the acquisition of IM directly on sky means that we are able to calibrate an AO system also for extremely large telescope class where classic IM measurements technique are problematic and, sometimes, impossible. Finally we have not to forget the reason why we need this: the main aim is to observe the universe. Thanks to these new big class of telescopes and only using their full capabilities, we will be able to increase our knowledge of the universe objects observed, because we will be able to resolve more detailed characteristics, discovering, analyzing and understanding the behavior of the universe components.

Understanding limitations of adaptive optics (AO) systems is crucial when designing new systems. In particular, analyzing the potential of different controllers is of great interest for the upcoming AO systems of the very large telescopes (VLTs) and extremely large telescopes (ELTs). This paper thus details a complete error budget assessment formalism, based on analytic formulas involving the disturbance temporal power spectral density (PSD) and the controller transfer function, and is applicable to any linear controller. This formalism is presented here for the special case of classical AO systems, but can be extended to any closed- or open-loop, single- or multi-conjugated AO configuration. Special attention is paid to the "control-dependent" errors, the importance of which is directly related to the type of control used in the AO system. The proposed method is applied to a NAOS/VLT-type single conjugated AO system, using disturbance PSD derived from a simulated turbulence trajectory or estimated from wavefront sensor measurements, enabling the construction of detailed error budgets for an integrator and different linear quadratic Gaussian controllers. Application to ELT-sized systems is discussed in the conclusion.

We have studied the dynamics and masses of a sample of 10 nearby luminous and ultraluminous infrared galaxies (LIRGs and ULIRGs, respectively) using 2.3 μm 12CO-absorption line spectroscopy and near-infrared H- and Ks-band imaging. By combining velocity dispersions derived from the spectroscopy, disk scale lengths obtained from the imaging, and a set of likely model density profiles, we calculate dynamical masses for each LIRG. For the majority of the sample, it is difficult to reconcile our mass estimates with the large amounts of gas derived from millimeter observations and from a standard conversion between 12CO emission and H2 mass. Our results imply that LIRGs do not have huge amounts of molecular gas (1010-1011 M☉) at their centers and support previous indications that the standard conversion of 12CO to H2 probably overestimates the gas masses and cannot be used in these environments. This in turn suggests much more modest levels of extinction in the near-infrared for LIRGs than previously predicted (AV ~ 10-20 vs. AV ~ 100-1000). The lower gas mass estimates indicated by our observations imply that the star formation efficiency in these systems is very high and is triggered by cloud-cloud collisions, shocks, and winds rather than by gravitational instabilities in circumnuclear gas disks.

We present the results of L-band spectroscopical observations of local bright Ultraluminous Infrared Galaxies (ULIRGs), performed with the Infrared Spectrometer And Array Camera (ISAAC) at the Very Large Telescope. The excellent sensitivity of the telescope and of the instrument provided spectra of unprecedented quality for this class of objects, which allowed a detailed study of the active galactic nucleus (AGN)/starburst contribution to the energy output, and of the composition of the circumnuclear absorber. We discuss the L-band spectral features of seven single sources, and the statistical properties of a complete sample of 15 sources obtained combining our observations with other published 3–4 μm spectra. Our main results are as follows. (i) When a spectral indicator suggesting the presence of an AGN (low equivalent width of the 3.3-μm emission line, steep λ–fλ spectrum, presence of an absorption feature at 3.4 μm) is found, the AGN is always confirmed by independent analysis at other wavelengths. Conversely, in all known AGNs at least one of the above indicators is present. (ii) Two new diagnostic diagrams are proposed combining the above indicators, in which starbursts and AGNs are clearly and completely separated. (iii) The above diagnostic techniques are possible with spectra of relatively low quality, which can be obtained for several tens of ULIRGs with currently available telescopes. This makes L-band spectroscopy the current best tool to disentangle AGN and starburst contributions in ULIRGs. (iv) The L-band properties of ULIRGs are heterogeneous. However, we show that all the spectral differences among ULIRGs can be reproduced starting from pure intrinsic AGN and starburst spectra and two varying parameters: the amount of dust extinction of the AGN component, and the relative AGN/starburst contribution to the bolometric luminosity. (v) Using the above decomposition model, we show that AGNs in ULIRGs have a low dust-to-gas ratio and a dust extinction curve different from Galactic. (vi) The estimate of the presence and contribution of AGNs in a complete sample shows that AGNs are hosted by approximately two-thirds of ULIRGs, but their energetic contribution is relevant (>30 per cent of the bolometric luminosity) only in ∼20 per cent of the sample.

In October 2002 NAOS-CONICA, one of the most powerful adaptive optics systems was offered to the astronomical community. The instrument is installed at the Very Large Telescope in Chile and operated by the European Southern Observatory. The adaptive optics system NAOS corrects for atmospheric turbulence and provides the near-infrared multi-mode camera and spectrograph CONICA with diffraction limited images. Development of NAOS was achieved by a French consortium, while CONICA was developed by a German consortium under the leadership of the Max-Planck-Institut fur Astronomie, Heidelberg. In the context of this PhD thesis several critical contributions to the successful commissioning were made. The major test and calibration results obtained on the way to First Light, i.e., during the laboratory, integration and commissioning periods are presented. They cover cryogenics, mechanics, optics and detector characteristics of CONICA. A major achievement was the development and implementation of a technique for the calibration of static optical aberrations. Since the instrument is designed to achieve absolute Strehl ratios higher than 70%, even the accumulation of residual static wavefront perturbations arising from optical components in the imaging path, critically affect the overall performance. The technique has been completely implemented for the instrument, and the adaptive optics system automatically corrects the static aberrations according to the different instrument configurations. The presented technique will be of great importance for future adaptive optics systems. Particular attention is payed to the calibration of CONICA's high resolution imaging spectroscopy mode, realized by a cold tunable Fabry-Perot interferometer. A detailed guideline is given of how to process a phase-shift map and the capabilities for 3-dimensional structure analysis are demonstrated at Eta Carinae. A first, high-spatial resolution velocity map is created.

The aim of the Spectro-Polarimetric High-contrast Exoplanet Research (SPHERE) instrument is to detect extremely faint astronomical sources (i.e., giant extra-solar planets, disks etc …) in the vicinity of bright stars. The detection capabilities of an exoplanet hunter are largely controlled by its adaptive optics (AO) system. Better AO correction provides improved coronagraph extinction and fewer starlight residuals. The challenging SPHERE science goals require a very high performance AO system to feed a quasi-perfect flat wave front, corrected for atmospheric turbulence and internal defects, to the scientific instruments. In May 2014 SPHERE was installed on the third unit telescope (Melipal) of the Very Large Telescope (VLT) in Chile. The results obtained over 3 years of operations essentially nicely confirm the AO predictions made at the time of the design phase and the corresponding performance budget analysis to cover various operation conditions in terms of target brightness and turbulence conditions. This is a strong basis to propose a realistic SPHERE AO upgrade. The SPHERE upgrade project intends to push the ultimate performance of SPHERE in terms of both final contrast and sensitivity (especially towards redder and fainter stars), thus allowing to address new science cases and to offer new detection or characterisation modes such as the coupling with high spectral resolution spectrographs, either in the infrared or in the visible. To do so, we have to address several tasks: • The main AO loop has to be accelerated (up to 3 kHz) and efficient predictive control laws have to be implemented in order to significantly reduce the temporal effects; • The main wave front sensor scheme has to be revisited in order to make the system more sensitive and make possible to work on very red stars. It will be achieved by adding to the current Visible Spatially Filtered Shack-Hartman an IR-Pyramid counterpart; • The NCPA correction and the system ability to create and stabilize dark-hole during an entire observation block has to be developed in order to get rid of the residual quasi-static speckles and residual diffraction patterns. This will be done thanks to the combination of very accurate coronagraphic wave front sensors (COFFEE and ZELDA). This presentation will detail the various system studies and trade-off choices which have led to the new concept of the SPHERE upgrade. A preliminary design of the new AO loop and its main components (IR pyramid, RTC, post-coronographic WFS) will be presented. We will show that the proposed SPHERE upgrade development can be achieved in a timely manner without affecting the current SPHERE configuration and for a reasonable cost. Finally, an AIT concept minimizing the down-time of the instrument will be described. At each stage of the project, special attention will be paid to ensure that the initial capabilities and performance of SPHERE are not be jeopardized by the proposed SPHERE upgrade developments.

Adaptive optics is one of the main features of the Very Large Telescope (VLT) of the European Southern Observatory (ESO) - an array of four 8 meter telescopes. These telescopes can be operated individually, in an incoherent and in a coherent interferometric beam combination mode. Each telescope will be equipped with adaptive optics systems for real-time correction of atmospheric turbulence effects. First results with a prototype system developed for the VLT demonstrated the feasibility and the significant gain of this technology for astronomical imaging. This paper describes the VLT adaptive optics system and its implementation program.

Context. Static and quasi-static aberrations represent a great limit for high-contrast imaging in large telescopes. Among them the most important ones are all the aberrations not corrected by the adaptive optics (AO) system, which are called non-common path aberrations (NCPA). Several techniques have been proposed to mitigate it. The typical approach is to set an offset on the AO system with exactly the opposite sign of the NCPA in order to correct for the aberrations introduced by all the optical components downstream the wave-front sensor (WFS) up to the science camera. An estimate of the NCPA can be obtained with a trial-and-error approach or by more sophisticated techniques of focal-plane wave-front sensing. Aims. In all cases, a fast procedure is desirable to limit the telescope downtime and to repeat, if needed, the correction procedure to cope with the temporal variation of the NCPA. Very recently, new approaches based on neural networks (NNs) have also been proposed as an alternative. Methods. In this work, through simulated images, we test the application of a supervised NN for the mitigation of NCPAs in high-contrast imaging at visible wavelengths and, in particular, we investigate the possibility of applying this method to fast imagers such as SHARK-VIS, the forthcoming visible-band high-contrast imager for the Large Binocular Telescope (LBT). Results. Preliminary results show a measurement accuracy of the NCPA of 2 nm root mean square (RMS) for each sensed Zernike mode in turbulence-free conditions, and 5 nm RMS per mode when the residual turbulence has a wave-front error (WFE) of approximately 42.5 nm RMS, a typical value during LBT AO system calibration. This measurement is sufficient to guarantee that, after correction, NCPA residuals in the system are negligible compared to the typical WFE &gt; 100 nm RMS of the best AO systems at large telescopes. Conclusions. Our simulations show this method is robust even in the presence of turbulence-induced aberrations that are not labelled in the training phase of the NN. The method could thus be used in a real-world setting by offloading a corrective static offset to the AO system of a telescope to mitigate the NCPA.

Imaging in ground-based astronomy is limited by transmission effects of the light caused by the turbulent atmosphere. Adaptive optics offers the possibility to overcome these limitations. The performance of adaptive optical systems and the requirements for their application in astronomy are discussed in order to give guidelines for the implementation of this technology in ESO’s Very Large Telescope (VLT). It is intended to equip each one of the four 8-meter telescopes of the VLT with an independent adaptive optical system. These systems will serve the individual Coude and the combined Coude foci. Currently a small scale prototype adaptive system is under development. The experience with this system will be used for an intermediate system which will serve as the final prototype for the VLT systems, requiring 150 to 200 subapertures. To solve the reference source problems, experiments to generate artificial reference stars by sending a laser pulse to the upper atmosphere are currently in preparation.

We present the results of infrared L-band (3-4 μm) and M-band (4-5 μm) Very Large Telescope (VLT) ISAAC spectroscopy of five bright ultraluminous infrared galaxies (ULIRGs) hosting an AGN. From our analysis we distinguish two types of sources: ULIRGs in which the AGN is unobscured (with a flat continuum and no absorption features at 3.4 and 4.6 μm), and those with highly obscured AGNs (with a steep, reddened continuum and absorption features due to hydrocarbons and CO). Starburst activity is also present in all of the sources, as inferred from the 3.3 μm PAH emission line. A strong correlation is found between continuum slope and CO optical depth, which suggests that deep carbon monoxide absorption is a common feature of highly obscured ULIRG AGNs. Finally, we show that the AGN dominates the 3-4 μm emission, even if its contribution to the bolometric luminosity is small.