Pietro Schipani

VEGAS: A VST Early-type GAlaxy Survey - I. Presentation, wide-field surface photometry, and substructures in NGC 4472

We present the VST Early-type GAlaxy Survey (VEGAS), which is designed to obtain deep multiband photometry in g, r, i, of about one hundred nearby galaxies down to 27.3, 26.8, and 26 mag/arcsec^2 respectively, using the ESO facility VST/OmegaCAM. The goals of the survey are 1) to map the light distribution up to ten effective radii, r_e, 2) to trace color gradients and surface brightness fluctuation gradients out to a few r_e for stellar population characterization, and 3) to obtain a full census of the satellite systems (globular clusters and dwarf galaxies) out to 20% of the galaxy virial radius. The external regions of galaxies retain signatures of the formation and evolution mechanisms that shaped them, and the study of nearby objects enables a detailed analysis of their morphology and interaction features. To clarify the complex variety of formation mechanisms of early-type galaxies (ETGs), wide and deep photometry is the primary observational step, which at the moment has been pursued with only a few dedicated programs. The VEGAS survey has been designated to provide these data for a volume-limited sample with exceptional image quality. In this commissioning photometric paper we illustrate the capabilities of the survey using g- and i-band VST/OmegaCAM images of the nearby galaxy NGC 4472 and of smaller ETGs in the surrounding field. Our surface brightness profiles reach rather faint levels and agree excellently well with previous literature. Genuine new results concern the detection of an intracluster light tail in NGC 4472 and of various substructures at increasing scales. We have also produced extended (g-i) color profiles. The VST/OmegaCAM data that we acquire in the context of the VEGAS survey provide a detailed view of substructures in the optical emission from extended galaxies, which can be as faint as a hundred times below the sky level.

Supernova rates from the SUDARE VST-OmegaCAM search: I. Rates per unit volume

Aims. We describe the observing strategy, data reduction tools, and early results of a supernova (SN) search project, named SUDARE, conducted with the ESO VST telescope, which is aimed at measuring the rate of the different types of SNe in the redshift range 0.2 < z < 0.8. Methods. The search was performed in two of the best studied extragalactic fields, CDFS and COSMOS, for which a wealth of ancillary data are available in the literature or in public archives. We developed a pipeline for the data reduction and rapid identification of transients. As a result of the frequent monitoring of the two selected fields, we obtained light curve and colour information for the transients sources that were used to select and classify SNe by means of an especially developed tool. To accurately characterise the surveyed stellar population, we exploit public data and our own observations to measure the galaxy photometric redshifts and rest frame colours. Results. We obtained a final sample of 117 SNe, most of which are SN Ia (57%) with the remaining ones being core collapse events, of which 44% are type II, 22% type IIn and 34% type Ib/c. To link the transients, we built a catalogue of ~1.3 × 105 galaxies in the redshift range 0 < z ≤ 1, with a limiting magnitude KAB = 23.5 mag. We measured the SN rate per unit volume for SN Ia and core collapse SNe in different bins of redshifts. The values are consistent with other measurements from the literature. Conclusions. The dispersion of the rate measurements for SNe-Ia is comparable to the scatter of the theoretical tracks for single degenerate (SD) and double degenerate (DD) binary systems models, therefore it is not possible to disentangle among the two different progenitor scenarios. However, among the three tested models (SD and the two flavours of DD that either have a steep DDC or a wide DDW delay time distribution), the SD appears to give a better fit across the whole redshift range, whereas the DDC better matches the steep rise up to redshift ~1.2. The DDW instead appears to be less favoured. Unlike recent claims, the core collapse SN rate is fully consistent with the prediction that is based on recent estimates of star formation history and standard progenitor mass range.

Active optics primary mirror support system for the 2.6 m VST telescope.

The Very Large Telescope Survey Telescope (VST) is equipped with an active optics system in order to correct low-order aberrations. The 2.6 m primary mirror is supported both axially and laterally and is surrounded by several safety devices for earthquake protection. We describe the mirror support system and discuss the results of the qualification test campaign.

Shapley Supercluster Survey: Galaxy evolution from filaments to cluster cores

The research leading to these results has received funding from the European Community’s Seventh Framework Programme (FP7/2007–13) under grant agreement number 312430 (OPTICON; PI: P. Merluzzi) and PRIN-INAF 2011 ‘Galaxy evolution with the VLT Surveys Telescope (VST)’ (PI A. Grado). CPH was funded by CONICYT Anillo project ACT-1122. N.Okabe is supported by a Grant-in-Aid from the Ministry of Education, Culture, Sports, Science and Technology of Japan (26800097) and by World Premier International Research Center Initiative (WPI Initiative), MEXT, Japan.

Removing static aberrations from the active optics system of a wide-field telescope

The wavefront sensor in active and adaptive telescopes is usually not in the optical path toward the scientific detector. It may generate additional wavefront aberrations, which have to be separated from the errors due to the telescope optics. The aberrations that are not rotationally symmetric can be disentangled from the telescope aberrations by a series of measurements taken in the center of the field, with the wavefront sensor at different orientation angles with respect to the focal plane. This method has been applied at the VLT Survey Telescope on the ESO Paranal observatory.

VIMOS and NIRMOS multi-object spectrographs for the ESO VLT

The VIRMOS consortium of French and Italian Institutes is manufacturing 2 wide field imaging multi-object spectrographs for the European Southern Observatory Very Large Telescope, with emphasis on the ability to carry over spectroscopic surveys of large numbers of sources. The Visible Multi-Object Spectrograph, VIMOS, is covering the 0.37 to 1 micron wavelength domain, with a full field of view of 4 by 7 by 8 arcmin2 in imaging and MOS mode. The Near IR Multi-Object Spectrograph, NIRMOS, is covering the 0.9 to 1.8 microns wavelength range, with afield of view 4 by 6 by 8 arcmin2 in MOS mode. The spectral resolution for both instrument scan reach up to R equals 5000 for a 0.5 arcsec wide slit. Multi-slit masks are produced by a dedicated Mask Manufacturing Machine cutting through thin Invar sheets and capable of producing 4 slit masks approximately 300 by 300 mm each with approximately slits 5.7 mm long in less than one hour. Integral field spectroscopy is made possible in VIMOS by switching in the beam specially build masks fed by 6400 fibers coming form a 54 by 54 arcsec2 integral field head with a 80 by 80 array of silica micro-lenses. NIRMOS has a similar IFS unit with a field of 30 by 30 arcmin2. These instruments are designed to offer very large multiplexing capabilities. In MOS mode, about 1000 objects can be observed simultaneously with VIMOS, with a S/N equals 10 obtained on galaxies with I equals 24 in one hour, and approximately 200 objects can be observed simultaneously with NIRMOS, with a S/N equals 10 obtained don galaxies with J equals 22, H equals 20.6 in 1h at Req equals 200. We present here the status of VIMOS, currently under final integration, with expected first light in the summer 2000, together with the final design of NIRMOS presented at the Final Design Review. The VLT-VIRMOS deep redshift survey of more with the final design of NIRMOS presented at the Final Design Review. The VLT-VIRMOS deep redshift survey of more than 150000 galaxies over the redshift range 0 < z < 5 will be undertaken based on 120 guaranteed nights awarded to the project.

VST project: technical overview

The VST (Very Large Telescope Survey Telescope) is an 2.6 m class Alt-Az telescope which will be installed in the European Southern Observatory (ESO) Paranal site, Chile. It has been designed by the Technology Working Group of the Astronomical Observatory of Capodimonte, Italy. The VST is an 1 degree(s) X 1 degree(s) wide-field imaging facility planned to supply databases for the ESO VLT science and carry out stand-alone observations in the UV to I spectral range starting in the year 2001. All the solutions adopted in the VST design comply to the ESO VLT standards. This paper reports a technical overview of the telescope design.

Variability-selected active galactic nuclei in the VST-SUDARE/VOICE survey of the COSMOS field

Optical variability has proven to be an effective way of detecting AGNs in imaging surveys, lasting from weeks to years. In the present work we test its use as a tool to identify AGNs in the VST multi-epoch survey of the COSMOS field, originally tailored to detect supernova events. We make use of the multi-wavelength data provided by other COSMOS surveys to discuss the reliability of the method and the nature of our AGN candidates. Our selection returns a sample of 83 AGN candidates; based on a number of diagnostics, we conclude that 67 of them are confirmed AGNs (81% purity), 12 are classified as supernovae, while the nature of the remaining 4 is unknown. For the subsample of AGNs with some spectroscopic classification, we find that Type 1 are prevalent (89%) compared to Type 2 AGNs (11%). Overall, our approach is able to retrieve on average 15% of all AGNs in the field identified by means of spectroscopic or X-ray classification, with a strong dependence on the source apparent magnitude. In particular, the completeness for Type 1 AGNs is 25%, while it drops to 6% for Type 2 AGNs. The rest of the X-ray selected AGN population presents on average a larger r.m.s. variability than the bulk of non variable sources, indicating that variability detection for at least some of these objects is prevented only by the photometric accuracy of the data. We show how a longer observing baseline would return a larger sample of AGN candidates. Our results allow us to assess the usefulness of this AGN selection technique in view of future wide-field surveys.

SUDARE-VOICE variability-selection of active galaxies in the Chandra Deep Field South and the SERVS/SWIRE region

Context. One of the most peculiar characteristics of Active Galactic Nuclei (AGN) is their variability over all wavelengths. This property has been used in the past to select AGN samples and is foreseen to be one of the detection techniques applied in future multi-epoch surveys, complementing photometric and spectroscopic methods. Aims. In this paper, we aim to construct and characterise an AGN sample using a multi-epoch dataset in the r band from the SUDAREVOICE survey. Methods. Our work makes use of the VST monitoring program of an area surrounding the Chandra Deep Field South to select variable sources. We use data spanning a six month period over an area of 2 square degrees, to identify AGN based on their photometric variability. Results. The selected sample includes 175 AGN candidates with magnitude r < 23 mag. We distinguish different classes of variable sources through their lightcurves, as well as X-ray, spectr oscopic, SED, optical and IR information overlapping with our survey. Conclusions. We find that 12% of the sample (21/175) is represented by SN. Of the remaining sources, 4% (6/154) are stars, while 66% (102/154) are likely AGNs based on the available diagnostics. We estimate an upper limit to the contamination of the variabili ty selected AGN sample≃ 34%, but we point out that restricting the analysis to the sources with available multi-wavelength ancillary information, the purity of our sample is close to 80% (102 AGN out of 128 non-SN sources with multi-wavelength diagnostics). Our work thus confirms the effi ciency of the variability selection method in agreement with our previous work on the COSMOS field; in addition we show that the variability approach is roughly consistent with the infrared selection.

The Fornax Deep Survey with VST. II. Fornax A: A Two-phase Assembly Caught in the Act

As part of the Fornax Deep Survey with the ESO VLT Survey Telescope, wepresent new g- and r-band mosaics of the SW group of the Fornax Cluster. It covers an area of 3 × 2 square degrees around the centralgalaxy NGC 1316. The deep photometry, the high spatial resolution ofOmegaCam, and the large covered area allow us to study the galaxystructure, trace stellar halo formation, and look at the galaxyenvironment. We map the surface brightness profile out to 33‧(˜200 kpc ˜ 15R e ) from the galaxy center, downto {μ }g˜ 31 {mag} arcsec-2 and {μ}r˜ 29 {mag} arcsec-2. This allow us toestimate the scales of the main components dominating the lightdistribution, which are the central spheroid, inside 5.‧5(˜33 kpc), and the outer stellar envelope. Data analysis suggeststhat we are catching in the act the second phase of the mass assembly inthis galaxy, since the accretion of smaller satellites is going on inboth components. The outer envelope of NGC 1316 still hosts the remnantsof the accreted satellite galaxies that are forming the stellar halo. Wediscuss the possible formation scenarios for NGC 1316, by comparing theobserved properties (morphology, colors, gas content, kinematics, anddynamics) with predictions from cosmological simulations of galaxyformation. We find that (I) the central spheroid could result from atleast one merging event (it could be a preexisting early-type diskgalaxy with a lower-mass companion) and (II) the stellar envelope comesfrom the gradual accretion of small satellites.