arXiv subjects

Paolo Ciliegi

Publications and source records attributed to Paolo Ciliegi.

32 records · Page 2Linked to original sources

arXiv2016

Stellar photometry with Multi Conjugate Adaptive Optics

We overview the current status of photometric analyses of images collected with Multi Conjugate Adaptive Optics (MCAO) at 8-10m class telescopes that operated, or are operating, on sky. Particular attention will be payed to resolved stellar population studies. Stars in crowded stellar systems, such as globular clusters or in nearby galaxies, are ideal test particles to test AO performance. We will focus the discussion on photometric precision and accuracy reached nowadays. We briefly describe our project on stellar photometry and astrometry of Galactic globular clusters using images taken with GeMS at the Gemini South telescope. We also present the photometry performed with DAOPHOT suite of programs into the crowded regions of these globulars reaching very faint limiting magnitudes Ks ~21.5 mag on moderately large fields of view (~1.5 arcmin squared). We highlight the need for new algorithms to improve the modeling of the complex variation of the Point Spread Function across the field of view. Finally, we outline the role that large samples of stellar standards plays in providing a detailed description of the MCAO performance and in precise and accurate colour{magnitude diagrams.

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arXiv2016

The numerical simulation tool for the MAORY multiconjugate adaptive optics system

The Multiconjugate Adaptive Optics RelaY (MAORY) is and Adaptive Optics module to be mounted on the ESO European-Extremely Large Telescope (E-ELT). It is a hybrid Natural and Laser Guide System that will perform the correction of the atmospheric turbulence volume above the telescope feeding the Multi-AO Imaging Camera for Deep Observations Near Infrared spectro-imager (MICADO). We developed an end-to-end Monte- Carlo adaptive optics simulation tool to investigate the performance of a the MAORY and the calibration, acquisition, operation strategies. MAORY will implement Multiconjugate Adaptive Optics combining Laser Guide Stars (LGS) and Natural Guide Stars (NGS) measurements. The simulation tool implements the various aspect of the MAORY in an end to end fashion. The code has been developed using IDL and uses libraries in C++ and CUDA for efficiency improvements. Here we recall the code architecture, we describe the modeled instrument components and the control strategies implemented in the code.

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arXiv2015

The XXL Survey XI: ATCA 2.1 GHz continuum observations

We present 2.1 GHz imaging with the Australia Telescope Compact Array (ATCA) of a 6.5 deg^2 region within the XXM-Newton XXL South field using a band of 1.1-3.1 GHz. We achieve an angular resolution of 4.7" x 4.2" in the final radio continuum map with a median rms noise level of 50 uJy/beam. We identify 1389 radio sources in the field with peak S/N >=5 and present the catalogue of observed parameters. We find that 305 sources are resolved, of which 77 consist of multiple radio components. These number counts are in agreement with those found for the COSMOS-VLA 1.4 GHz survey. We derive spectral indices by a comparison with the Sydney University Molongolo Sky Survey (SUMSS) 843MHz data. We find an average spectral index of -0.78 and a scatter of 0.28, in line with expectations. This pilot survey was conducted in preparation for a larger ATCA program to observe the full 25 deg^2 southern XXL field. When complete, the survey will provide a unique resource of sensitive, wide-field radio continuum imaging with complementary X-ray data in the field. This will facilitate studies of the physical mechanisms of radio-loud and radio-quiet AGNs and galaxy clusters, and the role they play in galaxy evolution. The source catalogue is publicly available online via the XXL Master Catalogue browser and the Centre de Données astronomiques de Strasbourg (CDS).

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arXiv2015

A method for space-variant deblurring with application to adaptive optics imaging in astronomy

Images from adaptive optics systems are generally affected by significant distortions of the point spread function (PSF) across the field of view, depending on the position of natural and artificial guide stars. Image reduction techniques circumventing or mitigating these effects are important tools to take full advantage of the scientific information encoded in AO images. The aim of this paper is to propose a method for the deblurring of the astronomical image, given a set of samples of the space-variant PSF. The method is based on a partitioning of the image domain into regions of isoplanatism and on applying suitable deconvolution methods with boundary effects correction to each region. The effectiveness of the boundary effects correction is proved. Moreover, the criterion for extending the disjoint sections to partially overlapping sections is validated. The method is applied to simulated images of a stellar system characterized by a spatially variable PSF. We obtain good photometric quality, and therefore good science quality, by performing aperture photometry on the deblurred images. The proposed method is implemented in IDL in the Software Package "Patch", which is available on http://www.airyproject.eu.

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arXiv2015

The environment of radio sources in the VLA-COSMOS Survey field

Several problems regarding the process of galaxy formation are still open. One of them is the role played by AGN phenomena in contributing to galaxy build-up and to Star Formation (SF) quenching. On the other hand, the theory of AGN formation predicts these phenomena to be correlated with the host-galaxy environment, thus opening for links between SF quenching, environment and AGN phenomena in the galaxy formation paradigm. This work is focused on the study of the correlation between environmental density and radio AGN presence. Using data from the photometric COSMOS survey and the radio 1.4GHz VLA-COSMOS, a sample of radio AGNs has been defined. The environment has been studied throughout the use of the richness distributions inside a parallelepipedon with base side of 1 Mpc and height proportional to the photometric redshift precision. Richness distributions have been compared as a function of both the redshift and the relative evolution of the stellar masses of galaxies and AGN hosts up to $z=2$. Radio AGNs are always located in environments that are significantly denser than those around galaxies in which radio emission is absent. Therefore, the environment seems to enhance the probability of a galaxy to host a radio AGN. Moreover, a distinction between high power and low power radio AGNs leads to the conclusion that the significance in the environmental effect is maintained only for low power radio sources. By studying the evolution of stellar masses it is possible to conclude that radio AGN presence is a phenomenon related to quiescent galaxies up to $z=2$, with a significant increase of the fraction of quiescent galaxies hosting a radio AGN with decreasing redshift. Hints of an environmental effect are present. The results found with this work lead to conclude that denser environments play a significant role in enhancing the probability of a galaxy to host a low power radio AGN.

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arXiv2015

Synergistic science with Euclid and SKA : the nature and history of Star Formation

We explored the impact of the synergy between the Euclid near-infrared photometric surveys and the SKA radio continuum surveys on the studies of the cosmic star formation. The Euclid satellite is expected to perform a Wide and Deep photometric surveys to an infrared limit of H ~ 24 and H ~ 26 respectively and a spectroscopy survey with a flux limit of $\sim 3 \times 10^{-16}$ erg cm$^{-2}$ s$^{-1}$ in the Halpha line. Combining the H band Euclid selected samples with the ground based ancillary data (fundamental for the SFR estimation) we will be able to detect the star forming galaxies down to SFRs of order of unit to z ~ 2 and down to SFR ~ 10 to z ~ 3, sampling the majority of the star forming galaxies up to z ~3 and beyond and placing definitive constraints on the star formation history of the universe at z<4-5 (is there a peak a z ~2 or a plateau at 1 <z <5 ?) and on the galaxies evolution models. The only tools able to provide a accurate dust-free calculation of their SFR are the SKA continuum surveys. The observational parameters of the Deep Tier SKA1 reference survey (a 0.2- 0.5 arcsec resolution and a 5 sigma detection limit of 1 microJy over 30 deg2 at Band 1/2 ) are the perfect complement of the Euclid survey. We showed, in fact, that with this kind of SKA survey we will be able to determine a dust unbiased SFR for a huge fraction (~85 %) of the Euclid SFG providing strong constraints on the star formation history of the Universe.

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arXiv2014

New insights from deep VLA data on the potentially recoiling black hole CID-42 in the COSMOS field

We present deep 3 GHz VLA observations of the potentially recoiling black hole CID-42 in the COSMOS field. This galaxy shows two optical nuclei in the HST/ACS image and a large velocity offset of ~ 1300 km/s between the broad and narrow H beta emission line although the spectrum is not spacially resolved (Civano et al. 2010). The new 3 GHz VLA data has a bandwidth of 2 GHz and to correctly interpret the flux densities imaging was done with two different methods: multi-scale multi-frequency synthesis and spectral windows stacking. The final resolutions and sensitivities of these maps are 0.7" with rms = 4.6 muJy/beam and 0.9" with rms = 4.8 muJy/beam respectively. With a 7 sigma detection we find that the entire observed 3 GHz radio emission can be associated with the South-Eastern component of CID-42, coincident with the detected X-ray emission. We use our 3 GHz data combined with other radio data from the literature ranging from 320 MHz to 9 GHz, which include the VLA, VLBA and GMRT data, to construct a radio synchrotron spectrum of CID-42. The radio spectrum suggests a type I unobscured radio-quiet flat-spectrum AGN in the South-Eastern component which may be surrounded by a more extended region of old synchrotron electron population or shocks generated by the outflow from the supermassive black hole. Our data are consistent with the recoiling black hole picture but cannot rule out the presence of an obscured and radio-quiet SMBH in the North-Western component.

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arXiv2014

End to end numerical simulations of the MAORY multiconjugate adaptive optics system

MAORY is the adaptive optics module of the E-ELT that will feed the MICADO imaging camera through a gravity invariant exit port. MAORY has been foreseen to implement MCAO correction through three high order deformable mirrors driven by the reference signals of six Laser Guide Stars (LGSs) feeding as many Shack-Hartmann Wavefront Sensors. A three Natural Guide Stars (NGSs) system will provide the low order correction. We develop a code for the end-to-end simulation of the MAORY adaptive optics (AO) system in order to obtain high-delity modeling of the system performance. It is based on the IDL language and makes extensively uses of the GPUs. Here we present the architecture of the simulation tool and its achieved and expected performance.

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arXiv2014

The VLA-COSMOS Survey: V. 324 MHz continuum observations

We present 90 cm VLA imaging of the COSMOS field, comprising a circular area of 3.14 square degrees at 8.0"x6.0" angular resolution with an average rms of 0.5 mJy/beam. The extracted catalog contains 182 sources (down to 5.5sigma), 30 of which are multi-component sources. Using Monte Carlo artificial source simulations we derive the completeness of the catalog, and we show that our 90 cm source counts agree very well with those from previous studies. Using X-ray, NUV-NIR and radio COSMOS data to investigate the population mix of our 90 cm radio sample, we find that our sample is dominated by active galactic nuclei (AGN). The average 90-20 cm spectral index (S_nu~nu**alpha, where S_nu is the flux density at frequency nu, and alpha the spectral index) of our 90 cm selected sources is -0.70, with an interquartile range of -0.90 to -0.53. Only a few ultra-steep-spectrum sources are present in our sample, consistent with results in the literature for similar fields. Our data do not show clear steepening of the spectral index with redshift. Nevertheless, our sample suggests that sources with spectral indices steeper than -1 all lie at z>1, in agreement with the idea that ultra-steep-spectrum radio sources may trace intermediate-redshift galaxies (z>1).

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arXiv2007

Deep ATLAS Radio Observations of the ELAIS-S1/Spitzer Wide-Area Infrared Extragalctic field

We have conducted sensitive (1 sigma<30 uJy) 1.4 GHz radio observations with the Australia Telescope Compact Array of a field largely coincident with infrared observations of the Spitzer Wide-Area Extragalactic Survey. The field is centred on the European Large Area ISO Survey S1 region and has a total area of 3.9 deg. We describe the observations and calibration, source extraction, and cross-matching to infrared sources. Two catalogues are presented; one of the radio components found in the image and one of radio sources with counterparts in the infrared and extracted from the literature. 1366 radio components were grouped into 1276 sources, 1183 of which were matched to infrared sources. We discover 31 radio sources with no infrared counterpart at all, adding to the class of Infrared-Faint Radio Sources.

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arXiv2006

Deep ATLAS radio observations of the CDFS-SWIRE field

We present the first results from the Australia Telescope Large Area Survey (ATLAS), which consist of deep radio observations of a 3.7 square degree field surrounding the Chandra Deep Field South, largely coincident with the infrared Spitzer Wide-Area Extragalactic (SWIRE) Survey. We also list cross-identifications to infrared and optical photometry data from SWIRE, and ground-based optical spectroscopy. A total of 784 radio components are identified, corresponding to 726 distinct radio sources, nearly all of which are identified with SWIRE sources. Of the radio sources with measured redshifts, most lie in the redshift range 0.5-2, and include both star-forming galaxies and active galactic nuclei (AGN). We identify a rare population of infrared-faint radio sources which are bright at radio wavelengths but are not seen in the available optical, infrared, or X-ray data. Such rare classes of sources can only be discovered in wide, deep surveys such as this.

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arXiv2000

First detections of FIRBACK sources with SCUBA

The FIRBACK (Far InfraRed BACKground) survey represents the deepest extensive 170 micron images obtained by the ISO satellite. The sources detected comprise about 10% of the Cosmic IR Background (CIB) seen by COBE, and, importantly, were observed at a wavelength near the peak of the CIB. Detailed follow-up of these sources should help pin down the redshifts, Hubble types, and other properties of the galaxies which constitute this background. We have used the Submillimetre Common-User Bolometer Array (SCUBA) instrument on the James Clerk Maxwell Telescope (JCMT) to search for sub-mm emission from a sample of 10 galaxies which are bright at 170 microns and for which we had accurate radio positions. Statistically we detect this sample at both 450 microns (~4 sigma) and 850 microns (~ 7 sigma); individual objects are convincingly detected in four cases at 850 microns, and one case at 450 microns. Fits to simple spectral energy distributions suggest a range of low to moderate redshifts, perhaps z=0 to 1.5 for this FIRBACK sub-sample.

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arXiv1997

The X-ray flux and spectral variability of EMSS AGN

Fifteen ROSAT PSPC observations available in the public archive are analyzed in order to study time and spectral variability of the 12 EMSS AGN detected by ROSAT with more than 2000 net counts. Time variability was investigated on 13 different time scales, ranging from 400 s to 1 year. Of the 12 sources analyzed, only two do not show a significant variability on any time scale. On short time scale about 20 percent of AGN are seen as variable sources while on time scale greater than 100.000 s the fraction becomes greater than 50 percent. However one should bare in mind that the visibility function for variability is far from being uniform and that small amplitude variations can be detected more often on long time scale than on short time scale. Spectral variability was detected in only two sources. MS1158.6-0323 shows an hardening of the spectrum with increasing intensity while MS2254.9-3712 shows a softening of the spectrum with increasing intensity. Finally, for one source (MS1416.3-1257), the observed variability is not due to an intrinsic flux variation but, instead, to a variation in the column density along the line of sight. Since this variability has been observed on a time scale of about 3.9 days, it is probably associated to the broad line clouds.

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arXiv1996

The X-ray spectral properties of X-ray selected AGN : ROSAT spectra of EMSS AGN

Using a sample of 63 AGNs extracted from the $Einstein$ Extended Medium Sensitivity Survey (EMSS), we study the X-ray spectral properties of X-ray selected AGN in the 0.1$-$2.4 keV ROSAT band. These objects are all the EMSS AGN detected with more than 300 net counts in ROSAT PSPC images available from the public archive (as of May 31, 1995). A Maximum-Likelihood analysis is used to find the mean power-law spectral index $<α_p>$ and the intrinsic dispersion $σ_p$. We find $<α_p>$=1.42 with $σ_p$=0.44. This value is significantly steeper ($Δα\sim$0.4) than the mean $Einstein$/IPC spectral index obtained applying the ML analysis on the whole sample of EMSS AGN. This result shows that the soft excess already noted in optically selected AGN is present also in X-ray selected AGN. The relatively high value obtained for the intrinsic dispersion confirms that in the soft band AGN are characterized by a variety of spectral indices and the increase with respect to results obtained from the analysis of Einstein data ($Δσ_p \sim$0.16) suggests a further broadening of the spectral index distribution as one moves to softer energies. A comparison between the mean spectral index of Radio-quiet and Radio-loud subsamples shows that the mean index of the RL sample is flatter than that of RQ, both in the IPC ($Δα\sim$0.3) and in the PSPC ($Δα\sim$0.4) data. This suggests that the additional X-ray component in RL AGN dominates the X-ray emission of RL AGN over almost two decades of energy ($\sim$0.1$-$10 keV).

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