L. E. Tacconi-Garman

L '-band AGPM vector vortex coronagraph's first light on VLT/NACO Discovery of a late-type companion at two beamwidths from an F0V star

Context. High contrast imaging has thoroughly combed through the limited search space accessible with first-generation ground-based adaptive optics instruments and the Hubble Space Telescope. Only a few objects were discovered, and many non-detections reported and statistically interpreted. The field is now in need of a technological breakthrough. nAims. Our aim is to open a new search space with first-generation systems such as NACO at the Very Large Telescope, by providing ground-breaking inner working angle (IWA) capabilities in the L′ band. The L′ band is a sweet spot for high contrast coronagraphy since the planet-to-star brightness ratio is favorable, while the Strehl ratio is naturally higher. nMethods. An annular groove phase mask (AGPM) vector vortex coronagraph optimized for the L′ band made from diamond subwavelength gratings was manufactured and qualified in the lab. The AGPM enables high contrast imaging at very small IWA, potentially being the key to unexplored discovery space. nResults. Here we present the installation and successful on-sky tests of an L-band AGPM coronagraph on NACO. Using angular differential imaging, which is well suited to the rotational symmetry of the AGPM, we demonstrated a ΔL′ > 7.5 mag contrast from an IWA ≃ 0.09 onwards, during average seeing conditions, and for total integration times of a few hundred seconds.

Molecular hydrogen excitation around active galactic nuclei

We report R ~ 3000 Very Large Telescope ISAAC K-band spectroscopy of the nuclei (i.e., central 100-300 pc) of nine galaxies hosting an active galactic nucleus. For five of these we also present spectra of the circumnuclear region out to 1 kpc. We have measured a number of molecular hydrogen lines in the ν = 1-0, 2-1, and 3-2 vibrational transitions, as well as the Brγ and He I recombination lines and the Na I stellar absorption feature. Although only three of the galaxies are classified as type 1 Seyfert galaxies in the literature, broad Brγ (FWHM 1000 km s-1) is seen in seven of the objects. The ν = 1-0 emission appears thermalized at temperatures T ~ 1000 K. However, the ν = 2-1 and ν = 3-2 emission show evidence of being radiatively excited by far-ultraviolet photons. The photodissociation region models that fit the data best are, as for the ultraluminous infrared galaxies in Davies et al., those for which the H2 emission arises in dense clouds illuminated by intense far-ultraviolet radiation. The Na I stellar absorption line is clearly seen in six of the nuclear spectra of these AGNs, indicating the presence of a significant population of late-type stars. It is possible that these stars are a result of the same episode of star formation that gave rise to the stars heating the photodissociation regions. It seems unlikely that the AGN is the dominant source of excitation for the near-infrared H2 emission: in two of the nuclear spectra H2 was not detected at all, and in general we find no evidence of suppression of the 2-1 S(3) line, which may occur in X-ray-irradiated gas. Our data do not reveal any significant difference between the nuclear and circumnuclear line ratios, suggesting that the physical conditions of the dominant excitation mechanism are similar both near the AGN and in the larger scale environment around it, and that star formation is an important process even in the central 100 pc around AGNs.

PAH emission variations within the resolved starbursts of NGC 253 and NGC 1808

In order to better characterise the usefulness of PAH emission as a tracer of star formation, we have undertaken a programme of 3 µm narrowband imaging of a sample of nearby template galaxies covering a wide range of metallicity, star formation activity, and nuclear activity. In the present paper we present first results of this programme: high spatial resolution images of PAH feature emission and the adjacent continuum emission from the central regions of the nearby starburst galax- ies NGC 253 and NGC 1808, taken with ISAAC at the VLT-UT1. Globally, the feature emission is seen to peak on the central starburst regions of both sources. On smaller scales, however, we see no general spatial correlation or anti-correlation between the PAH feature emission and the location of sites of recent star formation, suggesting that the degree to which PAH feature emission traces starburst activity is more complicated than previously hypothesized based on results from data with lower spatial resolution. We do find spatial correlations, though, when we consider the feature-to-continuum ratio, which is low at the positions of known super star clusters in NGC 1808 as well as at the position of the IR peak in NGC 253. We take this to imply a decrease in the efficiency of PAH emission induced by the star formation, caused either by mechanical energy input into the ISM, photoionisation of the PAH molecules, or photodissociation of the PAH molecules. All three hypotheses are dis- cussed. In addition, for the first time we present observations of PAH feature emission in the superwind of a starbursting system (NGC 253), providing strong support that winds are heavily mass-loaded and entrain substantial amounts of ambient ISM. We have also found a plausible connection between observed NaD absorption, H2, and PAHs above the plane of NGC 253. This observation has important implications for enriching galaxy halos and possibly the intergalactic medium with small dust grains.

Medium resolution 2.3

The Galactic open cluster Westerlund 1 was found only a few years ago to be much more massive than previously thought, with evidence suggesting its mass to be in excess of ∼10 5 M� , in the range spanned by young extragalactic star clusters. Unlike those clusters, its proximity makes spatially resolved studies of its stellar population feasible. It is therefore an ideal template for a young, massive star cluster, permitting direct comparison of its properties with measurements of velocity dispersion and dynamical mass for spatially unresolved extragalactic clusters. To this end, we used the long slit near-infrared spectrograph VLT/ISAAC to observe the CO bandhead region near 2.29 µm, scanning the slit across the cluster centre during the integration. Spatially collapsing the spectra along the slit results in a single co-added spectrum of the cluster, comparable to what one would obtain in the extragalactic cluster context. This spectrum was analysed in the same way as the spectra of almost point-like extragalactic clusters, using red superiant cluster members as velocity templates. We detected four red supergiants that are included in the integrated spectrum, and our measured velocity dispersion is 5.8 km s −1 . Together with the cluster size of 0.86 pc, derived from archival near-infrared SOFI-NTT images, this yields a dynamical mass of 6.3 × 10 4 M� .

{\mathsf \mu}

Current stellar population models have arguably the largest uncertainties in the near-IR wavelength range, partly due to a lack of large and well calibrated empirical spectral libraries. In this paper we present a project whose aim it is to provide the first library of luminosity weighted integrated near-IR spectra of globular clusters to be used to test the current stellar population models and serve as calibrators for future ones. Our pilot study presents spatially integrated K-band spectra of three old (≥10 Gyr) and metal poor ([Fe/H] ∼− 1.4), and three intermediate age (1–2 Gyr) and more metal rich ([Fe/H] ∼− 0.4) globular clusters in the LMC. We measured the line strengths of the Na i ,C ai and 12 CO (2–0) absorption features. The Na i index decreases with increasing age and decreasing metallicity of the clusters. The DCO index, used to measure the 12 CO (2–0) line strength, is significantly reduced by the presence of carbon-rich TP-AGB stars in the globular clusters with age ∼1 Gyr. This is in contradiction to the predictions of the stellar population models of Maraston (2005, MNRAS, 362, 799). We find that this disagreement is due to the different CO absorption strength of carbon-rich Milky Way TP-AGB stars used in the models and the LMC carbon stars in our sample. For globular clusters with age ≥ 2G yr we fi ndDCO index measurements consistent with the model predictions.

m spectroscopy of the massive Galactic open cluster Westerlund 1

Context. The rest-frame near-IR spectra of intermediate age (1-2 Gyr) stellar populations are dominated by carbon based absorption features offering a wealth of information. Yet, spectral libraries that include the near-IR wavelength range do not sample a suffi ciently broad range of ages and metallicities to allow for accurate calibration of stellar population models and thus the interp retation of the observations. Aims. In this paper we investigate the integrated J- and H-band spectra of six intermediate age and old globular clusters in the Large Magellanic Cloud (LMC). Methods. The observations for six clusters were obtained with the SINFONI integral field spectrograph at the ESO VLT Yepun telescope, covering the J (1.09− 1.41µm) and H-band (1.43− 1.86µm) spectral range. The spectral resolution is 6.7 A in J and 6.6 A in H-band (FWHM). The observations were made in natural seeing, covering the central 24 ′′ × 24 ′′ of each cluster and in addition sampling the brightest eight red giant branch (RGB) and asymptotic giant branch (AGB) star candidates within the clusters’ tidal radii. Targeted clusters cover the ages of∼1.3 Gyr (NGC 1806, NGC 2162), 2 Gyr (NGC 2173) and∼13 Gyr (NGC 1754, NGC 2005, NGC 2019). Results. H-band C2 and K-band 12 CO (2‐0) feature strengths for the LMC globular clusters are compared to the models of Maraston (2005). C2 is reasonably well reproduced by the models at all ages, while 12 CO (2‐0) shows good agreement for older (age≥ 2 Gyr) populations, but the younger (1.3 Gyr) globular clusters do not follow the models. We argue that this is due to the fact that the empirical calibration of the models relies on only a few Milky Way carbon star spectra, which show different 12 CO (2‐0) index strengths than the LMC stars. The C2 absorption feature strength correlates strongly with age. It is present essentially only in populations that have 1-2 Gyr old stars, while its value is consistent with zero for older populations. The distinct spectral energy distribut ion observed for the intermediate age globular clusters in the J- and H-bands agrees well with the model predictions of Maraston for the contribution from the thermally pulsing asymptotic giant branch phase. Conclusions. In this pilot project we present an empirical library of six L MC globular cluster integrated near-IR spectra that are useful for testing stellar population models in this wavele ngth regime. We show that the H-band C2 absorption feature and the J-, H-band spectral shape can be used as an age indicator for intermediate age stellar populations in integrated spectra of st ar clusters and galaxies.

Integrated K -band spectra of old and intermediate-age globular clusters in the Large Magellanic Cloud

We report on new high-resolution near-infrared images of the gravitationally lensed radio source PKS1830-211, a quasar at z=2.507. These adaptive optics observations, taken with the Very Large Telescope (VLT), are further improved through image deconvolution. They confirm the presence of a second object along the line of sight to the quasar, in addition to the previously known spiral galaxy. This additional object is clearly extended in our images. However, its faint luminosity does not allow to infer any photometric redshift. If this galaxy is located in the foreground of PKS1830-211, it complicates the modeling of this system and decreases the interest in using PKS1830-211 as a means to determine H0 via the time delay between the two lensed images of the quasar.

Integrated J- and H-band spectra of globular clusters in the LMC: implications for stellar population models and galaxy age dating ⋆

CRIRES is a cryogenic, pre-dispersed, infrared Echelle spectrograph designed to provide a nominal resolving power ν/Δν of 105 between 1000 and 5000 nm for a nominal slit width of 0.2. The CRIRES installation at the Nasmyth focus A of the 8-m VLT UT1 (Antu) marks the completion of the original instrumentation plan for the VLT. A curvature sensing adaptive optics system feed is used to minimize slit losses and to provide 0.2 spatial resolution along the slit. A mosaic of four Aladdin InSb-arrays packaged on custom-fabricated ceramic boards has been developed. It provides for an effective 4096 × 512 pixel focal plane array to maximize the free spectral range covered in each exposure. Insertion of gas cells is possible in order to measure radial velocities with high precision. Measurement of circular and linear polarization in Zeeman sensitive lines for magnetic Doppler imaging is foreseen but not yet fully implemented. A cryogenic Wollaston prism on a kinematic mount is already incorporated. The retarder devices will be located close to the Unit Telescope focal plane. Here we briefly recall the major design features of CRIRES and describe the commissioning of the instrument including a report of extensive testing and a preview of astronomical results.

Confirmation of two extended objects along the line of sight to PKS 1830-211 with ESO-VLT adaptive optics imaging

We report on Galactic Center L-band observations made during NAOS/CONICA Science Verification. Colors of the inner 2 stars reveal an infrared excess of S2, the closest star to the black hole, that could sign the first thermal infrared detection of Sgr A*. A multi-wavelength maximum likelihood analysis has allowed us to eliminate all but two of the candidates for gravitational lensing proposed by Alexander (2001). Our observations of the thin and intersecting structures ofthe Northern Arm could trace several shocks heating the neighbooring dust rather than a stream of matter in orbit around the central mass as previously thought.

CRIRES: commissioning and first science results

The European Southern Observatory (ESO) is in the process of creating a central access point for all services offered to its user community via the Web. That gateway, called the User Portal, will provide registered users with a personalized set of service access points, the actual set depending on each users privileges. Correspondence between users and ESO will take place by way of profiles, that is, contact information. Each user may have several active profiles, so that an investigator may choose, for instance, whether their data should be delivered to their own address or to a collaborator. To application developers, the portal will offer authentication and authorization services, either via database queries or an LDAP server. The User Portal is being developed as a Web application using Java-based technology, including servlets and JSPs.