Search

We present the first measurements of HI galaxy scaling relations from a blind survey at $z>0.15$. We perform spectral stacking of 9023 spectra of star-forming galaxies undetected in HI at $0.23, Comment: 12 pages, 5 figures. Accepted for publication in ApJ Letters on 30 July 2022

We present here a re-calibration of the photometric systems used in the Pantheon+ sample of Type Ia supernovae (SNe Ia) including those used for the SH0ES distance-ladder measurement of H$_0$. We utilize the large and uniform sky coverage of the public Pan-STARRS stellar photometry catalog to cross-calibrate against tertiary standards released by individual SN Ia surveys. The most significant updates over the `SuperCal' cross-calibration used for the previous Pantheon and SH0ES analyses are: 1) expansion of the number of photometric systems (now 25) and filters (now 105), 2) solving for all filter offsets in all systems simultaneously in order to produce a calibration uncertainty covariance matrix that can be used in cosmological-model constraints, and 3) accounting for the change in the fundamental flux calibration of the HST CALSPEC standards from previous versions on the order of $1.5\%$ over a $\Delta \lambda$ of 4000~\AA. The re-calibration of samples used for light-curve fitting has historically been decoupled from the retraining of the light-curve model. Here, we are able to retrain the SALT2 model using this new calibration and find the change in the model coupled with the change to the calibration of the light-curves themselves causes a net distance modulus change ($d\mu/dz$) of 0.04 mag over the redshift range $0, Comment: Published in ApJ. Comments welcome. Papers and data release here PantheonPlusSH0ES.github.io

We present the version of the point source catalogue of the XXL Survey that was used, in part, in the first series of XXL papers. In this paper we release, in our database in Milan and at CDS: (i) the X-ray source catalogue with 26056 objects in two areas of 25 deg2; (ii) the associated multiwavelength catalogues with candidate counterparts of the X-ray sources in the infrared, near-infrared, optical, and ultraviolet (plus spectroscopic redshift when available); and (iii) a catalogue of spectroscopic redshifts recently obtained in the southern XXL area. We also present the basic properties of the X-ray point sources and their counterparts. Other catalogues described in the second series of XXL papers will be released contextually, and will constitute the second XXL data release., Comment: 19 pages, 11 figures, part of A&A Special Issue "The XXL Survey: second series" https://www.aanda.org/component/toc/?task=topic&id=927

We present the results of a study of the AGN density in a homogeneous and well-studied sample of 167 bona fide X-ray galaxy clusters ($0.110^{42}$ erg cm$^{-1}$) in bright cluster galaxies, up to $6r_{500}$ radius. To study the mass dependence and the evolution of the AGN population, we further divided the sample into low- and high-mass clusters and two redshift bins (0.1-0.28 and 0.28-0.5). We detect a significant excess of X-ray AGNs, at the 95% confidence level, in low-mass clusters between $0.5r_{500}$ and 2$r_{500}$, which drops to the field value within the cluster cores ($r, Comment: Accepted for publication in Astronomy & Astrophysics, 10 pages

The XMM-XXL Survey spans two fields of $\rm 25$ deg$^2$ each observed for more than 6Ms with XMM, which provided a sample of tens of thousands of point sources with a flux limit of $\sim 2.2 \times 10^{-15}$ and $\sim 1.4 \times 10^{-14}$ erg s$^{-1}$ cm$^{2}$, corresponding to 50% of the area curve, in the soft band and hard band, respectively. In this paper we present the spatial clustering properties of $\sim 3100$ and $\sim 1900$ X-ray active galactic nuclei (AGNs) in the 0.5-2 and 2-10 keV bands, respectively, which have been spectroscopically observed with the AAOmega facility. This sample is 90% redshift complete down to an optical magnitude limit of $r\lesssim 21.8$. The sources span the redshift interval $0, Comment: accepted in A&A

Modern cosmological simulations rely heavily on feedback from active galactic nuclei (AGN) in order to stave off overcooling in massive galaxies and galaxy groups and clusters. An important independent test is whether or not the simulations capture the broad demographics of the observed AGN population. Here, we have used the cosmo-OWLS suite of cosmological hydrodynamical simulations to produce realistic synthetic catalogs of X-ray AGN out to $z$=3, with the aim of comparing the catalogs to the observed X-ray AGN population in the XXL survey and other recent surveys. We focused on the unabsorbed X-ray luminosity function (XLF), the Eddington ratio distribution, the black hole mass function, and the projected clustering of X-ray AGN. To compute the unabsorbed XLF of the simulated AGN, we used recent empirically-determined bolometric corrections. We show that the simulated AGN sample accurately reproduces the observed XLF over 3 orders of magnitude in X-ray luminosity in all redshift bins. To compare to the observed Eddington ratio distribution and the clustering of AGN, we produced detailed 'XMM-Newton-detected' catalogs of the simulated AGN. This requires the production of synthetic X-ray images extracted from light cones of the simulations that fold in the relevant instrumental effects of XMM-Newton. We apply a luminosity- and redshift-dependent obscuration function for the AGN and employ the same AGN detection algorithm as used for the real XXL survey. We demonstrate that the detected population of simulated AGN reproduces the observed Eddington ratio distribution and projected clustering from XXL quite well. We conclude that the simulations have a broadly realistic population of AGN and that our synthetic X-ray AGN catalogs should be useful for interpreting additional trends and as a helpful tool for quantifying AGN contamination in galaxy group and cluster X-ray surveys., Comment: 14 pages, accepted for publication in A&A

Galaxy clusters trace the highest density peaks in the large-scale structure of the Universe. Their clustering provides a powerful probe that can be exploited in combination with cluster mass measurements to strengthen the cosmological constraints provided by cluster number counts. We investigate the spatial properties of a homogeneous sample of X-ray selected galaxy clusters from the XXL survey, the largest programme carried out by the XMM-Newton satellite. The measurements are compared to $\Lambda$-cold dark matter predictions, and used in combination with self-calibrated mass scaling relations to constrain the effective bias of the sample, $b_{eff}$, and the matter density contrast, $\Omega_{\rm M}$. We measured the angle-averaged two-point correlation function of the XXL cluster sample. The analysed catalogue consists of $182$ X-ray selected clusters from the XXL second data release, with median redshift $\langle z \rangle=0.317$ and median mass $\langle M_{500} \rangle\simeq1.3\cdot10^{14} M_\odot$. A Markov chain Monte Carlo analysis is performed to extract cosmological constraints using a likelihood function constructed to be independent of the cluster selection function. Modelling the redshift-space clustering in the scale range $10, Comment: 10 pages, 10 figures. Accepted for publication in Astronomy & Astrophysics

Context. The XXL Survey is the largest survey carried out by the XMM-Newton satellite and covers a total area of 50 square degrees distributed over two fields. It primarily aims at investigating the large-scale structures of the Universe using the distribution of galaxy clusters and active galactic nuclei as tracers of the matter distribution. Aims. This article presents the XXL bright cluster sample, a subsample of 100 galaxy clusters selected from the full XXL catalogue by setting a lower limit of $3\times 10^{-14}\,\mathrm{erg \,s^{-1}cm^{-2}}$ on the source flux within a 1$^{\prime}$ aperture. Methods. The selection function was estimated using a mixture of Monte Carlo simulations and analytical recipes that closely reproduce the source selection process. An extensive spectroscopic follow-up provided redshifts for 97 of the 100 clusters. We derived accurate X-ray parameters for all the sources. Scaling relations were self-consistently derived from the same sample in other publications of the series. On this basis, we study the number density, luminosity function, and spatial distribution of the sample. Results. The bright cluster sample consists of systems with masses between $M_{500}=7\times 10^{13}$ and $3\times 10^{14} M_\odot$, mostly located between $z=0.1$ and 0.5. The observed sky density of clusters is slightly below the predictions from the WMAP9 model, and significantly below the predictions from the Planck 2015 cosmology. In general, within the current uncertainties of the cluster mass calibration, models with higher values of $\sigma_8$ and/or $\Omega_m$ appear more difficult to accommodate. We provide tight constraints on the cluster differential luminosity function and find no hint of evolution out to $z\sim1$. We also find strong evidence for the presence of large-scale structures in the XXL bright cluster sample and identify five new superclusters., Comment: Accepted by A&A, 25 pages, 17 figures, 7 tables. The XXL-100-GC Master catalogue is available from the XXL Milan database (http://cosmosdb.iasf-milano.inaf.it/XXL/) and through the CDS (cdsarc.u-strasbg.fr)

We present a catalogue containing the redshifts of 3,660 X-ray selected targets in the XXL southern field. The redshifts were obtained with the AAOmega spectrograph and 2dF fibre positioner on the Anglo-Australian Telescope. The catalogue contains 1,515 broad line AGN, 528 stars, and redshifts for 41 out of the 49 brightest X-ray selected clusters in the XXL southern field., Comment: 8 pages, 4 figures, PASA in press

We present spectra of high-redshift supernovae (SNe) that were taken with the Subaru low resolution optical spectrograph, FOCAS. These SNe were found in SN surveys with Suprime-Cam on Subaru, the CFH12k camera on the Canada-France-Hawaii Telescope (CFHT), and the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope (HST). These SN surveys specifically targeted z>1 Type Ia supernovae (SNe Ia). From the spectra of 39 candidates, we obtain redshifts for 32 candidates and spectroscopically identify 7 active candidates as probable SNe Ia, including one at z=1.35, which is the most distant SN Ia to be spectroscopically confirmed with a ground-based telescope. An additional 4 candidates are identified as likely SNe Ia from the spectrophotometric properties of their host galaxies. Seven candidates are not SNe Ia, either being SNe of another type or active galactic nuclei. When SNe Ia are observed within a week of maximum light, we find that we can spectroscopically identify most of them up to z=1.1. Beyond this redshift, very few candidates were spectroscopically identified as SNe Ia. The current generation of super red-sensitive, fringe-free CCDs will push this redshift limit higher., 19 pages, 26 figures. PASJ in press. see http://www.supernova.lbl.gov/2009ClusterSurvey/ for additional information pertaining to the HST Cluster SN Survey

[Abridged] XMMU J2235.3-2557 is one of the most distant X-ray selected clusters, spectroscopically confirmed at z=1.39. We characterize the galaxy populations of passive members, the thermodynamical properties of the hot gas, its metal abundance and the total mass of the system using imaging data with HST/ACS (i775 and z850 bands) and VLT/ISAAC (J and K_s bands), extensive spectroscopic data obtained with VLT/FORS2, and deep Chandra observations. Out of a total sample of 34 spectroscopically confirmed cluster members, we selected 16 passive galaxies within the central 2' (or 1 Mpc) with ACS coverage, and inferred star formation histories for a sub-sample of galaxies inside and outside the core by modeling their spectro-photometric data with spectral synthesis models, finding a strong mean age radial gradient. Chandra data show a regular elongated morphology, closely resembling the distribution of core galaxies, with a significant cool core. We measure a global X-ray temperature of kT=8.6(-1.2,+1.3) keV (68% c.l.). By detecting the rest-frame 6.7 keV Iron K line, we measure a metallicty Z= 0.26(+0.20,-0.16) Zsun. In the likely hypothesis of hydrostatic equilibrium, we obtain a total mass of Mtot(1, with a baryonic content, both its galaxy population and intra-cluster gas, in a significantly advanced evolutionary stage at 1/3 of the current age of the Universe., Comment: 9 pages, 8 figures, accepted for publication in A&A (v2: typos/language style corrections, updated references)

We use HAWK-I, the recently-commissioned near-IR imager on Yepun (VLT-UT4), to obtain wide-field, high-resolution images of the X-ray luminous galaxy cluster XMMU J2235.3-2557 in the J and Ks bands, and we use these images to build a colour-magnitude diagram of cluster galaxies. Galaxies in the core of the cluster form a tight red sequence with a mean J-Ks colour of 1.9 (Vega system). The intrinsic scatter in the colour of galaxies that lie on the red sequence is similar to that measured for galaxies on the red sequence of the Coma cluster. The slope and location of the red sequence can be modelled by passively evolving the red sequence of the Coma cluster backwards in time. Using simple stellar population (SSP) models, we find that galaxies in the core of XMMU J2235.3-2557 are, even at z=1.39, already 3 Gyr old, corresponding to a formation redshift of z ~ 4. Outside the core, the intrinsic scatter and the fraction of galaxies actively forming stars increase substantially. Using SSP models, we find that most of these galaxies will join the red sequence within 1.5 Gyr. The contrast between galaxies in the cluster core and galaxies in the cluster outskirts indicates that the red sequence of XMMU J2235.3-2557 is being built from the dense cluster core outwards., Comment: 9 pages, 2 figures. To appear in A&A

We present the K-band luminosity-halo mass relation, $L_{K,500}-M_{500,WL}$, for a subsample of 20 of the 100 brightest clusters in the XXL Survey observed with WIRCam at the Canada-France-Hawaii Telescope (CFHT). For the first time, we have measured this relation via weak-lensing analysis down to $M_{500,WL} =3.5 \times 10^{13}\,M_\odot$. This allows us to investigate whether the slope of the $L_K-M$ relation is different for groups and clusters, as seen in other works. The clusters in our sample span a wide range in mass, $M_{500,WL} =0.35-12.10 \times 10^{14}\,M_\odot$, at $0, Comment: A&A, in press

Aims. The first star forming galaxies in the early universe should be copious Lya emitters and may play a significant role in ionizing the intergalactic medium (IGM). It has been proposed that the luminosity function of Lya emitting galaxies beyond z ∼ 6 may be used to constrain the neutral fraction of the IGM during this epoch. In this work we report on a search for Lya emitters at redshift 8.8. Methods. We performed a narrow band imaging programme using ISAAC at the ESO VLT. Seven fields, covering a total area of 31 sq. arcmin and for which optical and broad band infra-red images have been obtained in the GOODS survey, were imaged to a limiting flux (respectively luminosity) of -1.3 x 10 -17 erg s -1 cm -2 (respectively ∼1.3 x 10 43 erg s -1 ) in a narrow band filter centered in a region of low OH sky emission at 1.19 μm. Candidate Lya emitters are objects that are detected in the ISAAC NB images and undetected in the visible broad band images. Results. No z = 8.8 Lya emitting galaxies were detected to a limit approaching recent estimates of the luminosity function at z ∼ 6. Our results do suggest, however, that detections or substantial constraints could be achieved by this method in the near future with larger field instruments planned for various telescopes.

We expand upon the results of Close et al. 2005 regarding the young, low-mass object AB Dor C and its role as a calibration point for theoretical tracks. We present an improved spectral reduction and a new orbital solution with two additional epochs. Our improved analysis confirms our spectral type of M8 (+/- 1) and mass of 0.090+/-0.003 solar masses for AB Dor C. Comparing the results for AB Dor C with other young, low-mass objects with dynamical masses we find a general trend where current evolutionary models tend to over-predict the temperature (or under-predict the mass) for low mass stars and brown dwarfs. Given our precision, there is a ~99% chance that the mass of AB Dor C is underestimated by the DUSTY tracks in the HR diagram., 7 pages, 10 figures, proceedings for the workshop "Ultralow-mass star formation and evolution", to be published in Astronomische Nachrichten - Astronomical Notes

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., Comment: Accepted in A&A Letters

We present a first high contrast 1.575 micron surface map of Titan, that is haze corrected by simultaneously imaging the stratospheric layer. At visible and most near-infrared wavelengths, the methane rich atmosphere completely obscures the surface; only in a few narrow wavelength windows does the atmosphere become optically thin. One of the most convenient windows (Griffith et al. 2003) lies at 1.58 μm, adjacent to the methane absorption feature at 1.62 μm. Our data span seven consecutive nights, resulting in phase coverage of 275° in longitude. The images were taken with NAOS-CONICA adaptive optics system at the VLT, using the recently commissioned Simultaneous Differential Imager mode (SDI). The combination of adaptive optics and simultaneous imaging through three filters sampling the methane absorption at 1.6 micron reveals extraordinary details of Titan's surface. Providing views of Titan's surface at high resolution (60 mas) is of particular topical importance, since the Cassini-Huygens mission is currently approaching the Saturn system and the Huygens probe will enter Titan's atmosphere in early 2005.

We report optical and infrared spectroscopic observations of the Type Ia SN 1999ee and the Type Ib/c SN 1999ex, both of which were hosted by the galaxy IC 5179. For SN 1999ee we obtained a continuous sequence with an unprecedented wavelength and temporal coverage beginning 9 days before maximum light and extending through day 42. Before maximum light SN 1999ee displayed a normal spectrum with a strong Si II 6355 absorption, thus showing that not all slow-declining SNe are spectroscopically peculiar at these evolutionary phases. A comparative study of the infrared spectra of SN 1999ee and other Type Ia supernovae shows that there is a remarkable homogeneity among the Branch-normal SNe Ia during their first 60 days of evolution. SN 1991bg-like objects, on the other hand, display spectroscopic peculiarities at infrared wavelengths. SN 1999ex was characterized by the lack of hydrogen lines, weak optical He I lines, and strong He I 10830,20581, thus providing an example of an intermediate case between pure Ib and Ic supernovae. We conclude therefore that SN 1999ex provides first clear evidence for a link between the Ib and Ic classes and that there is a continuous spectroscopic sequence ranging from the He deficient SNe Ic to the SNe Ib which are characterized by strong optical He I lines.

We investigate various galaxy population properties of the massive X-ray luminous galaxy cluster XDCP J0044.0-2033 at z=1.58, which constitutes the most extreme matter density peak at this redshift currently known. We analyze deep VLT/HAWK-I NIR data in the J- and Ks-bands, complemented by Subaru imaging in i and V, Spitzer observations at 4.5 micron, and new spectroscopic observations with VLT/FORS2. We detect a cluster-associated excess population of about 90 galaxies, which follows a centrally peaked, compact NFW galaxy surface density profile with a concentration of c200~10. Based on the Spitzer 4.5 micron imaging data, we measure a stellar mass fraction of fstar,500=(3.3+-1.4)% consistent with local values. The total J- and Ks-band galaxy luminosity functions of the core region yield characteristic magnitudes J* and Ks* consistent with expectations from simple z_f=3 burst models. However, a detailed look at the morphologies and color distributions of the spectroscopically confirmed members reveals that the most massive galaxies are undergoing a very active mass assembly epoch through merging processes. Consequently, the bright end of the cluster red-sequence is not in place, while at intermediate magnitudes [Ks*,Ks*+1.6] a red-locus population is present, which is then sharply truncated at magnitudes fainter than Ks*+1.6. The dominant cluster core population comprises post-quenched galaxies transitioning towards the red-sequence at intermediate magnitudes, while additionally a significant blue cloud population of faint star-forming galaxies is present even in the densest central regions. Our observations lend support to the scenario in which the dominant effect of the dense z~1.6 cluster environment is an accelerated mass assembly timescale through merging activity that is responsible for driving core galaxies across the mass quenching threshold of log(Mstar/Msun)~10.4., Comment: 23 pages, 19 color figures, accepted for publication in A&A, v2 matches journal version

We report the detection with ROSAT of a transient X-ray source at R.A. 17h44m331 and decl. -28°44'29'' (J2000), which we identify with the transient bursting pulsar GRO J1744-28. We have made K-band observations of the X-ray source at ESO and the US Naval Observatory, Flagstaff Station. A K-band counterpart of this transient previously identified by us on an image taken 1996 February 8 by Blanco et al. is found to be detected during only two (of seven) short exposures of which this image is composed. We cannot definitely reject the reality of this variable object but feel that it is not possible to rule out an instrumental effect. The lack of a persistent K-band counterpart of GRO J1744-28 is consistent with the idea that the low-energy emission from this object is dominated by reprocessing of X-rays in an accretion disk.

We present new results on the two-point angular correlation function of galaxies. The results have been determined from two large-format CCD surveys, covering 13 deg2 in total. At all magnitudes the two-point correlation function is well described by a power law with an index, J, equal to - 0.8. The amplitude of the correlation function decreases with increasing magnitude; however, the precise behaviour is not reproduced in models that include reasonable amounts of clustering evolution. We also present new data on the I-band galaxy number counts. A model that fits the count data well is a model that has a cosmological constant and a local galaxy number density equal to 1.76 x 1O-2(Ho/100)3 Mpc-3 •

Many galaxies are thought to have supermassive black holes at their centres-more than a million times the mass of the Sun. Measurements of stellar velocities and the discovery of variable X-ray emission have provided strong evidence in favour of such a black hole at the centre of the Milky Way, but have hitherto been unable to rule out conclusively the presence of alternative concentrations of mass. Here we report ten years of high-resolution astrometric imaging that allows us to trace two-thirds of the orbit of the star currently closest to the compact radio source (and massive black-hole candidate) Sagittarius A*. The observations, which include both pericentre and apocentre passages, show that the star is on a bound, highly elliptical keplerian orbit around Sgr A*, with an orbital period of 15.2 years and a pericentre distance of only 17 light hours. The orbit with the best fit to the observations requires a central point mass of (3.7 +/- 1.5) x 10(6) solar masses (M(*)). The data no longer allow for a central mass composed of a dense cluster of dark stellar objects or a ball of massive, degenerate fermions.

We use three years of data from the Supernova Legacy Survey (SNLS) to study the general properties of core-collapse and type Ia supernovae. This is the first such study using the "rolling search" technique which guarantees well-sampled SNLS light curves and good efficiency for supernovae brighter than $i^\prime\sim24$. Using host photometric redshifts, we measure the supernova absolute magnitude distribution down to luminosities $4.5 {\rm mag}$ fainter than normal SNIa. Using spectroscopy and light-curve fitting to discriminate against SNIa, we find a sample of 117 core-collapse supernova candidates with redshifts $z, accepted Astronomy and Astrophysics

The recent robust and homogeneous analysis of the world's supernova distance-redshift data, together with cosmic microwave background and baryon acoustic oscillation data, provides a powerful tool for constraining cosmological models. Here we examine particular classes of scalar field, modified gravity, and phenomenological models to assess whether they are consistent with observations even when their behavior deviates from the cosmological constant Lambda. Some models have tension with the data, while others survive only by approaching the cosmological constant, and a couple are statistically favored over LCDM. Dark energy described by two equation of state parameters has considerable phase space to avoid Lambda and next generation data will be required to constrain such physics., Comment: 32 pages, 19 figures

We present a weak-lensing analysis of the z=1.4 galaxy cluster XMMU J2235.3-2557, based on deep Advanced Camera for Surveys images. Despite the observational challenge set by the high redshift of the lens, we detect a substantial lensing signal at the >~ 8 sigma level. This clear detection is enabled in part by the high mass of the cluster, which is verified by our both parametric and non-parametric estimation of the cluster mass. Assuming that the cluster follows a Navarro-Frenk-White mass profile, we estimate that the projected mass of the cluster within r=1 Mpc is (8.5+-1.7) x 10^14 solar mass, where the error bar includes the statistical uncertainty of the shear profile, the effect of possible interloping background structures, the scatter in concentration parameter, and the error in our estimation of the mean redshift of the background galaxies. The high X-ray temperature 8.6_{-1.2}^{+1.3} keV of the cluster recently measured with Chandra is consistent with this high lensing mass. When we adopt the 1-sigma lower limit as a mass threshold and use the cosmological parameters favored by the Wilkinson Microwave Anisotropy Probe 5-year (WMAP5) result, the expected number of similarly massive clusters at z >~ 1.4 in the 11 square degree survey is N ~ 0.005. Therefore, the discovery of the cluster within the survey volume is a rare event with a probability < 1%, and may open new scenarios in our current understanding of cluster formation within the standard cosmological model., Accepted to ApJ for publication. 40 pages and 14 figures

Aim: We present new extraction and identification techniques for supernova (SN) spectra developed within the Supernova Legacy Survey (SNLS) collaboration. Method: The new spectral extraction method takes full advantage of photometric information from the Canada-France-Hawai telescope (CFHT) discovery and reference images by tracing the exact position of the supernova and the host signals on the spectrogram. When present, the host spatial profile is measured on deep multi-band reference images and is used to model the host contribution to the full (supernova + host) signal. The supernova is modelled as a Gaussian function of width equal to the seeing. A chi-square minimisation provides the flux of each component in each pixel of the 2D spectrogram. For a host-supernova separation greater than, Comment: 27 pages, 18 Figures, 1 Table. Accepted for publication in A&A

We present observations of SCP 06F6, an unusual optical transient discovered during the Hubble Space Telescope Cluster Supernova Survey. The transient brightened over a period of ~100 days, reached a peak magnitude of ~21.0 in both i_775 and z_850, and then declined over a similar timescale. There is no host galaxy or progenitor star detected at the location of the transient to a 3 sigma upper limit of i_775 = 26.4 and z_850 = 26.1, giving a corresponding lower limit on the flux increase of a factor of ~120. Multiple spectra show five broad absorption bands between 4100 AA and 6500 AA and a mostly featureless continuum longward of 6500 AA. The shape of the lightcurve is inconsistent with microlensing. The transient's spectrum, in addition to being inconsistent with all known supernova types, is not matched to any spectrum in the Sloan Digital Sky Survey (SDSS) database. We suggest that the transient may be one of a new class., 5 pages, 4 figures. Accepted for publication in ApJ. Data are available at http://supernova.lbl.gov/2006Transient/

The ESO Very Large Telescope Interferometer (VLTI) offers access to the four 8 m Unit Telescopes (UT) and the four 1.8 m Auxiliary Telescopes (AT) of the Paranal Observatory located in the Atacama Desert in northern Chile. The fourth AT has been delivered to operation in December 2006, increasing the flexibility and simultaneous baselines access of the VLTI. Regular science operations are now carried on with the two VLTI instruments, AMBER and MIDI. The FINITO fringe tracker is now used for both visitor and service observations with ATs and will be offered on UTs in October 2008, bringing thus the fringe tracking facility to VLTI instruments. In parallel to science observations, technical periods are also dedicated to the characterization of the VLTI environment, upgrades of the existing systems, and development of new facilities. We will describe the current status of the VLTI and prospects on future evolution.

International audience; We have developed an PSF reconstruction algorithm for the NAOS adaptive optics system that is coupled with CONICA at ESO/VLT. We have modified the algorithm of Véran et al. (1997), originally written for PUEO at CFHT, to make use of the specific real-time wavefront-related data that observers with NACO receive together with their scientific images. In addition, we use the Vii algorithm introduced by Clénet et al. (2006) and Gendron et al. (2006) instead of the Uij algorithm originally used by Véran et al. (1997). Until now, tests on NAOS has been undertaken during technical time thanks to the NACO team at Paranal. A first test has been successfully performed to calibrate the orientation of reconstructed PSFs with respect to NACO images. We have also obtained two sets of PSF reconstruction test data with NACO in November 2006 and September 2007 to reconstruct PSFs. Discrepancies exist between the observed and reconstructed PSFs: their Strehl ratios are ~31% and ~39% respectively in Nov. 2006, ~31% and ~19% respectively in Sept. 2007. These differences may be at least partly explained by reconstructions that either did not account for the aliasing contribution or poorly estimated the noise contribution with the available noise information at that time. We have additionally just started to test our algorithm using the AO bench Sésame, at LESIA. Results are promising but need to be extended to a larger set of atmospheric conditions or AO correction qualities.

After about 15 years of operation with astronomical instruments, adaptive optics has now reached maturity: it is routinely used at several large telescopes and transparent for the astronomer. Though, adaptive optics assisted images have specificities compared to seeing-limited images, such as their point spread function profile or spatial/temporal variability, that I review in the following. Adaptive optics imaging, unlike seeing-limited imaging, offers the possibility to calibrate the PSF simultaneously to the scientific observations, using real-time measurements of the adaptive optics system itself. I introduce here this PSF reconstruction and review the different PSF reconstruction algorithms developed till now, in particular the one for NAOS.

We present our survey for optically faint variable objects using multi-epoch (8-10 epochs over 2-4 years) $i'$-band imaging data obtained with Subaru Suprime-Cam over 0.918 deg$^2$ in the Subaru/XMM-Newton Deep Field (SXDF). We found 1040 optically variable objects by image subtraction for all the combinations of images at different epochs. This is the first statistical sample of variable objects at depths achieved with 8-10m class telescopes or HST. The detection limit for variable components is $i'_{\rm{vari}}\sim25.5$ mag. These variable objects were classified into variable stars, supernovae (SNe), and active galactic nuclei (AGN), based on the optical morphologies, magnitudes, colors, and optical-mid-infrared colors of the host objects, spatial offsets of variable components from the host objects, and light curves. Detection completeness was examined by simulating light curves for periodic and irregular variability. We detected optical variability for $36\pm2%$ ($51\pm3%$ for a bright sample with $i'150$ kpc from the Galactic center., 18 pages, 17 figures, accepted for publication in ApJ

Gravitational lens modeling is presented for the first discovered example of a three-component source for which each component is quadruply imaged. The lens is a massive galaxy member of the cluster Cl J0152.7-1357 at z ~ 0.84. Taking advantage of this exceptional configuration and of the excellent angular resolution of the HST/ACS, we measure the properties of the lens. Several parametric macroscopic models were developed for the lens galaxy, starting from pointlike to extended image models. For a lens model in terms of a singular isothermal sphere with external shear, the Einstein radius is found to be R_{E} = (9.54 +/- 0.15) kpc. The external shear points to the cluster's northern mass peak. The unknown redshift of the source is determined to be higher than 1.9 and lower than 2.9. Our estimate of the lensing projected total mass inside the Einstein radius, M_{len}(R < 9.54 kpc), depends on the source distance and lies between 4.6 and 6.2 x 10^{11} M_{Sun}. This result turns out to be compatible with the dynamical estimate based on an isothermal model. By considering the constraint on the stellar mass-to-light ratio that comes from the evolution of the Fundamental Plane, we can exclude the possibility that at more than 4 sigma level the total mass enclosed inside the Einstein ring is only luminous matter. Moreover, the photometric-stellar mass measurement within the Einstein radius gives a minimum value of 50% (1 sigma) for the dark-to-total matter fraction. The lensing analysis has allowed us to investigate the distribution of mass of the deflector, also providing some interesting indications on scales that are larger and smaller than the Einstein radius of the lens galaxy. The combination of different diagnostics has proved to be essential in determining quantities that otherwise would have not been directly measurable with the current data., 10 pages, 9 figures, accepted by Astronomy & Astrophysics

Timmes, Brown & Truran found that metallicity variations could theoretically account for a 25% variation in the mass of 56Ni synthesized in Type Ia supernovae (SNe Ia), and thus account for a large fraction of the scatter in observed SN Ia luminosities. Higher-metallicity progenitors are more neutron-rich, producing more stable burning products relative to radioactive 56Ni. We develop a new method for estimating bolometric luminosity and 56Ni yield in SNe Ia and use it to test the theory with data from the Supernova Legacy Survey. We find that the average 56Ni yield does drop in SNe Ia from high metallicity environments, but the theory can only account for 7%--10% of the dispersion in SN Ia 56Ni mass, and thus luminosity. This is because the effect is dominant at metallicities significantly above solar, whereas we find that SN hosts have predominantly subsolar or only moderately above-solar metallicities. We also show that allowing for changes in O/Fe with the metallicity [Fe/H] does not have a major effect on the theoretical prediction of Timmes, Brown & Truran, so long as one is using the O/H as the independent variable. Age may have a greater effect than metallicity -- we find that the luminosity weighted age of the host galaxy is correlated with 56Ni yield, and thus more massive progenitors give rise to more luminous explosions. This is hard to understand if most SNe Ia explode when the primaries reach the Chandrasekhar mass. Finally, we test the findings of Gallagher et al., that the residuals of SNe Ia from the Hubble diagram are correlated with host galaxy metallicity, and we find no such correlation., ApJ, accepted, 34 pages, 11 figures, apologies for one column format -- necessary for the equations

We present results from an extensive spectroscopic survey, carried out with VLT FORS, and from an extensive multiwavelength imaging data set from the HST Advanced Camera for Surveys and ground based facilities, of the cluster of galaxies RDCS J1252.9-2927. We have spectroscopically confirmed 38 cluster members in the redshift range 1.22 < z < 1.25. A cluster median redshift of z=1.237 and a rest-frame velocity dispersion of 747^{+74}_{-84} km/s are obtained. Using the 38 confirmed redshifts, we were able to resolve, for the first time at z > 1, kinematic structure. The velocity distribution, which is not Gaussian at the 95% confidence level, is consistent with two groups that are also responsible for the projected east-west elongation of the cluster. The groups are composed of 26 and 12 galaxies with velocity dispersions of 486^{+47}_{-85} km/s and 426^{+57}_{-105} km/s, respectively. The elongation is also seen in the intracluster gas and the dark matter distribution. This leads us to conclude that RDCS J1252.9-2927 has not yet reached a final virial state. We extend the analysis of the color-magnitude diagram of spectroscopic members to more than 1 Mpc from the cluster center. The scatter and slope of non-[OII]-emitting cluster members in the near-IR red sequence is similar to that seen in clusters at lower redshift. Furthermore, most of the galaxies with luminosities greater than ~ K_s*+1.5 do not show any [OII], indicating that these more luminous, redder galaxies have stopped forming stars earlier than the fainter, bluer galaxies. Our observations provide detailed dynamical and spectrophotometric information on galaxies in this exceptional high-redshift cluster, delivering an in-depth view of structure formation at this epoch only 5 Gyr after the Big Bang., 29 pages. 16 figures. ApJ accepted. Tables 2,3 and 5, figure 1 and the full figure 5 will be available in the paper and electronic editions from ApJ. v2: minor corrections to the abstract and text to match the Journal's version

The ESO VLT Interferometer (VLTI) is a general-user facility and is operated in service mode (SM) for a large part of the available time. An important aspect of this SM observing mode is the definition of a set of critical observing conditions that must be met at the time of executing the requested observation. There are a number of observing constraints that are specific to interferometric observations, such as the choice of the array configuration and the hour angle at time of observation, which is processed during the scheduling. On the other hand, classical constraints such as the regular seeing or the lunar illumination are less critical for observations using VLTI instruments than for those using classical VLT instruments. In particular, the use of the adaptive optics system MACAO for VLTI observations employing the Unit Telescopes (UTs) ensures a very good image quality even for moderate environmental conditions. However, the exact dependence between environmental conditions, the performance of the MACAO systems, the wavefront quality at the interferometric instruments, and the accuracy of the final visibility, are not yet known in much detail. In order to investigate this dependence we have started to monitor routinely the environmental conditions, the quality of the MACAO systems, the quality of the acquisition images, and the final data product for all VLTI observations since June 2005. Here, we present the details of this study, as well as first statistics and results.

The ESO Very Large Telescope Interferometer (VLTI) is the first general-user interferometer that offers near- and mid-infrared long-baseline interferometric observations in service and visitor mode to the whole astronomical community. Over the last two years, the VLTI has moved into its regular science operation mode with the two science instruments, MIDI and AMBER, both on all four 8m Unit Telescopes and the first three 1.8m Auxiliary Telescopes. We are currently devoting up to half of the available time for science, the rest is used for characterization and improvement of the existing system, plus additional installations. Since the first fringes with the VLTI on a star were obtained on March 17, 2001, there have been five years of scientific observations, with the different instruments, different telescopes and baselines. These observations have led so far to more than 40 refereed publications. We describe the current status of the VLTI and give an outlook for its near future.

Adaptive optics (AO) allows one to derive the point spread function (PSF) simultaneously to the science image, which is a major advantage in post-processing tasks such as astrometry/photometry or deconvolution. Based on the algorithm of \citet{veran97}, PSF reconstruction has been developed for four different AO systems so far: PUEO, ALFA, Lick-AO and Altair. A similar effort is undertaken for NAOS/VLT in a collaboration between the group PHASE (Onera and Observatoire de Paris/LESIA) and ESO. In this paper, we first introduce two new algorithms that prevent the use of the so-called "$U\_{ij}$ functions" to: (1) avoid the storage of a large amount of data (for both new algorithms), (2) shorten the PSF reconstruction computation time (for one of the two) and (3) provide an estimation of the PSF variability (for the other one). We then identify and explain issues in the exploitation of real-time Shack-Hartmann (SH) data for PSF reconstruction, emphasising the large impact of thresholding in the accuracy of the phase residual estimation. Finally, we present the data provided by the NAOS real-time computer (RTC) to reconstruct PSF ({\em (1)} the data presently available, {\em (2)} two NAOS software modifications that would provide new data to increase the accuracy of the PSF reconstruction and {\em (3)} the tests of these modifications) and the PSF reconstruction algorithms we are developing for NAOS on that basis., Comment: 12 pages & 13 figures. To be published in the proceedings of the SPIE conference Advances in Adaptive Optics - Astronomical Telescopes & Instrumentation, 24-31 May 2006, Orlando

Context: Wide-field narrowband surveys are an efficient way of searching large volumes of high-redshift space for distant galaxies. Aims: We describe the Wide Field Imager Lyman-Alpha Search (WFILAS) over 0.74 sq. degree for bright emission-line galaxies at z~5.7. Methods: WFILAS uses deep images taken with the Wide Field Imager (WFI) on the ESO/MPI 2.2m telescope in three narrowband (70 A), one encompassing intermediate band (220 A) and two broadband filters, B and R. We use the novel technique of an encompassing intermediate band filter to exclude false detections. Images taken with broadband B and R filters are used to remove low redshift galaxies from our sample. Results: We present a sample of seven Lya emitting galaxy candidates, two of which are spectroscopically confirmed. Compared to other surveys all our candidates are bright, the results of this survey complements other narrowband surveys at this redshift. Most of our candidates are in the regime of bright luminosities, beyond the reach of less voluminous surveys. Adding our candidates to those of another survey increases the derived luminosity density by ~30%. We also find potential clustering in the Chandra Deep Field South, supporting overdensities discovered by other surveys. Based on a FORS2/VLT spectrum we additionally present the analysis of the second confirmed Lya emitting galaxy in our sample. We find that it is the brightest Lya emitting galaxy (1 x 10^-16 erg s^-1 cm^-2) at this redshift to date and the second confirmed candidate of our survey. Both objects exhibit the presence of a possible second Lya component redward of the line., Comment: 15 pages, accepted for publication in A&A Replaced with published version

We determined the K band luminosity function (LF) of cluster galaxies at redshift z~1.2, using near-infrared images of three X-ray luminous clusters at z=1.11,1.24,1.27. The composite LF was derived down to M*+4, by means of statistical background subtraction, and is well described by a Schechter function with K*=20.5 AB mag and alpha=-1. From the K band composite LF we derived the stellar mass function of cluster galaxies. Using available X-ray mass profiles we determined the M/L ratios of these three clusters, which tend to be lower than those measured in the local universe. With these data, no significant difference can be seen between the shapes of the cluster galaxies LF and the LF of field galaxies at similar redshift. We also found no significant evolution out to z ~1.2 in the bright (2. The results obtained in this work support and extend previous findings that most of the stars in bright galaxies were formed at high redshift, and that K-bright (M>10^11 Msun) galaxies were already in place at z ~ 1.2, at least in the central regions of X-ray luminous clusters. Together with recent results on the field galaxies stellar mass function, this implies that most of the stellar mass is already assembled in massive galaxies by z ~ 1, both in low and high density environments., Comment: 16 pages, 10 figures, to appear in A&A

We present the results of an extensive spectroscopic survey of RX J0152.7-1357, one of the most massive distant clusters of galaxies known. Multi-object spectroscopy, carried out with FORS1 and FORS2 on the ESO Very Large Telescope (VLT), has allowed us to measure more than 200 redshifts in the cluster field and to confirm 102 galaxies as cluster members. The mean redshift of the cluster is $z=0.837 \pm 0.001$ and we estimate the velocity dispersion of the overall cluster galaxy distribution to be $\sim 1600 \mathrm{km \ s^{-1}}$. The distribution of cluster members is clearly irregular, with two main clumps that follow the X-ray cluster emission mapped by Chandra. A third clump of galaxies to the east of the central structure and at the cluster redshift has also been identified. The two main clumps have velocity dispersions of $\sim919$ and $\sim737 \mathrm{km s^{-1}}$ respectively, and the peculiar velocity of the two clumps suggests that they will merge into a single more massive cluster. A segregation in the star formation activity of the member galaxies is observed. All star forming galaxies are located outside the high-density peaks, which are populated only by passive galaxies. A population of red galaxies (belonging to the cluster red sequence) with clear post-starburst spectral features and [OII] ($\lambda$3727) emission lines is observed in the outskirts of the cluster. Two AGNs, which were previously confused with the diffuse X-ray emission from the intracluster medium in ROSAT and BeppoSAX observations, are found to be cluster members., Comment: 16 pages. 13 figures. Accepted for publication in Astronomy & Astrophysics. Tables 4 and 5 available in printed version. Corrected typos and missing references

An on-line estimation of turbulence parameters (r0, L0 and wind speed) and Adaptive Optics (AO) performance using NAOS [Nasmyth Adaptive Optics System] is presented. The method is based on the reconstruction of open-loop data from deformable mirror voltages and residual wavefront sensor slopes obtained in closed loop. This dedicated tool implemented in the real time computer of the NAOS system (first AO of the Very Large Telescope) allows without any loop opening to automatically monitor and display (every 15 seconds) both the atmospheric conditions and the system performance. We have validated the algorithm and tested its robustness on simulated and experimental data (both in laboratory and on sky). Using data obtained during more than two years of operations, statistical study on NAOS performance and turbulence characteristics are proposed. An on-line estimation of turbulence parameters (r0, L0 and wind speed) and Adaptive Optics (AO) performance is presented.

We present optical R-band light curves of the double gravitationally lensed quasar FBQ 0951+2635 from observations obtained at the Nordic Optical Telescope between March 1999 and June 2001. A time delay of 16 +/- 2 days (1 sigma) is determined from the light curves. New constraints on the lensing geometry are provided by the position and ellipticity of the lensing galaxy. For a (Omega_m, Omega_Lambda) = (0.3, 0.7) cosmology, the time delay yields a Hubble parameter of H_0 = 60^{+9}_{-7} (random, 1 sigma) +/- 2 (systematic) km/s/Mpc for a singular isothermal ellipsoid model and H_0 = 63^{+9}_{-7} (random, 1 sigma) +/- 1 (systematic) km/s/Mpc for a constant mass-to-light ratio model. In both models, the errors are mainly due to the time-delay uncertainties. Non-parametric models yield H_0 = 64^{+9}_{-7} (random, 1 sigma) +/- 14 (systematic) km/s/Mpc., Comment: 7 pages, 7 figures. Accepted for publication in A&A

36 pags., 13 figs., 31 tabs., 1 app., We report measurements of ΩM, ΩΛ w from 11 supernovae (SNe) at z ¼ 0:36 0:86 with high-quality light curves measured using WFPC2 on the Hubble Space Telescope (HST). This is an independent set of high-redshift SNe that confirms previous SN evidence for an accelerating universe. The high-quality light curves available from photometry on WFPC2 make it possible for these 11 SNe alone to provide measurements of the cosmological parameters comparable in statistical weight to the previous results. Combined with earlier Supernova Cosmology Project data, the new SNe yield a measurement of the mass density ΩM ¼ 0:25þ0:07 Ω0:06 ðstatisticalÞ Λ 0:04 (identified systematics), or equivalently, a cosmological constant of ΩΛ ¼ 0:75þ0:06 Ω0:07 ðstatisticalÞ Λ 0:04 (identified systematics), under the assumptions of a flat universe and that the dark energy equation-of-state parameter has a constant value w ¼ Ω1.When the SN results are combined with independent flat-universe measurements of ΩM from cosmic microwave background and galaxy redshift distortion data, they provide a measurement of w ¼ Ω1:05þ0:15 Ω0:20 ðstatisticalÞ Λ 0:09 (identified systematic), if w is assumed to be constant in time. In addition to high-precision light-curve measurements, the new data offer greatly improved color measurements of the high-redshift SNe and hence improved host galaxy extinction estimates. These extinction measurements show no anomalous negative E(BΩ) at high redshift. The precision of the measurements is such that it is possible to perform a host galaxy extinction correction directly for individual SNe without any assumptions or priors on the parent E(BΩV) distribution. Our cosmological fits using full extinction corrections confirm that dark energy is required with PðΩΛ > 0Þ > 0:99, a result consistent with previous and current SN analyses that rely on the identification of a low-extinction subset or prior assumptions concerning the intrinsic extinction distribution., Support for this work was provided by NASA through grants HST-GO-07336.01-A and HST-GO-08346.01-A from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. This work was supported in part by the Director, Office of Science,Office of High Energy and Nuclear Physics, of the US Department of Energy under Contract DE-AC03- 76SF000098, by the Center for Particle Astrophysics, an NSF Science and Technology Center operated by the University of California, Berkeley, under Cooperative Agreement AST 91-20005. This work was supported in part by a NASA LTSA grant to P. E. N., G. A., S. P., and S. E. D., and W. M. W.-V. was supported in part by a National Science Foundation Graduate Research Fellowship. A.G. is a Royal Swedish Academy Research Fellow supported by a grant from the Knut and Alice Wallenberg Foundation.

(Abridged) We present new results on the Hubble diagram of distant type Ia supernovae (SNe Ia) segregated according to the type of host galaxy. This makes it possible to check earlier evidence for a cosmological constant by explicitly comparing SNe residing in galaxies likely to contain negligible dust with the larger sample. The cosmological parameters derived from these SNe Ia hosted by presumed dust-free early-type galaxies supports earlier claims for a cosmological constant, which we demonstrate at 5 sigma significance, and the internal extinction implied is small even for late-type systems (A_B, MNRAS; post-referee version. 21 pages, 10 figures including 4 colour figures. Preprint also available at http://supernova.lbl.gov/