Browsing by Author "Paolillo, M."

Now showing 1 - 18 of 18
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    A random forest-based selection of optically variable AGN in the VST-COSMOS field
    (2021) De Cicco, D.; Bauer, F. E.; Paolillo, M.; Cavuoti, S.; Sanchez-Saez, P.; Brandt, W. N.; Pignata, G.; Vaccari, M.; Radovich, M.
    Context. The survey of the COSMOS field by the VLT Survey Telescope is an appealing testing ground for variability studies of active galactic nuclei (AGN). With 54 r-band visits over 3.3 yr and a single-visit depth of 24.6 r-band mag, the dataset is also particularly interesting in the context of performance forecasting for the Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST).Aims. This work is the fifth in a series dedicated to the development of an automated, robust, and efficient methodology to identify optically variable AGN, aimed at deploying it on future LSST data.Methods. We test the performance of a random forest (RF) algorithm in selecting optically variable AGN candidates, investigating how the use of different AGN labeled sets (LSs) and features sets affects this performance. We define a heterogeneous AGN LS and choose a set of variability features and optical and near-infrared colors based on what can be extracted from LSST data.Results. We find that an AGN LS that includes only Type I sources allows for the selection of a highly pure (91%) sample of AGN candidates, obtaining a completeness with respect to spectroscopically confirmed AGN of 69% (vs. 59% in our previous work). The addition of colors to variability features mildly improves the performance of the RF classifier, while colors alone prove less effective than variability in selecting AGN as they return contaminated samples of candidates and fail to identify most host-dominated AGN. We observe that a bright (r less than or similar to 21 mag) AGN LS is able to retrieve candidate samples not affected by the magnitude cut, which is of great importance as faint AGN LSs for LSST-related studies will be hard to find and likely imbalanced. We estimate a sky density of 6.2x10(6) AGN for the LSST main survey down to our current magnitude limit.
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    A structure function analysis of VST-COSMOS AGN
    (2022) De Cicco, D.; Bauer, F. E.; Paolillo, M.; Sanchez-Saez, P.; Brandt, W. N.; Vagnetti, F.; Pignata, G.; Radovich, M.; Vaccari, M.
    Context. We present our sixth work in a series dedicated to variability studies of active galactic nuclei (AGN), based on the survey of the COSMOS field by the VLT Survey Telescope (VST). Its 54 r-band visits over 3.3 yr and single-visit depth of 24.6 r-band mag make this dataset a valuable scaled-down version that can help forecast the performance of the Rubin Observatory Legacy Survey of Space and Time (LSST).
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    Abundance ratios and IMF slopes in the dwarf elliptical galaxy NGC 1396 with MUSE
    (2016) Mentz, J. J.; La Barbera, F.; Peletier, R. F.; Falcon-Barroso, J.; Lisker, T.; van de Ven, G.; Loubser, S. I.; Hilker, M.; Sanchez-Janssen, R.; Napolitano, N.; Cantiello, M.; Capaccioli, M.; Norris, M.; Paolillo, M.; Smith, R.; Beasley, M. A.; Lyubenova, M.; Munoz, R.; Puzia, T.
    Deep observations of the dwarf elliptical (dE) galaxy NGC 1396 (M-V = -16.60, Mass similar to 4 x 10(8) M-circle dot), located in the Fornax cluster, have been performed with the Very Large Telescope/Multi Unit Spectroscopic Explorer spectrograph in the wavelength region from 4750 to 9350 angstrom. In this paper, we present a stellar population analysis studying chemical abundances, the star formation history (SFH) and the stellar initial mass function (IMF) as a function of galactocentric distance. Different, independent ways to analyse the stellar populations result in a luminosity-weighted age of similar to 6 Gyr and a metallicity [Fe/H]similar to -0.4, similar to other dEs of similar mass. We find unusually overabundant values of [Ca/Fe]similar to+0.1, and underabundant Sodium, with [Na/Fe] values around -0.1, while [Mg/Fe] is overabundant at all radii, increasing from similar to+0.1 in the centre to similar to+0.2 dex. We notice a significant metallicity and age gradient within this dwarf galaxy. To constrain the stellar IMF of NGC 1396, we find that the IMF of NGC 1396 is consistent with either a Kroupa-like or a top-heavy distribution, while a bottom-heavy IMF is firmly ruled out. An analysis of the abundance ratios, and a comparison with galaxies in the Local Group, shows that the chemical enrichment history of NGC 1396 is similar to the Galactic disc, with an extended SFH. This would be the case if the galaxy originated from a Large Magellanic Cloud-sized dwarf galaxy progenitor, which would lose its gas while falling into the Fornax cluster.
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    Astroinformatics-based search for globular clusters in the Fornax Deep Survey
    (2019) Angora, Giuseppe; Brescia, Massimo; Cavuoti, Stefano; Paolillo, M.; Longo, Giuseppe; Cantiello, M.; Capaccioli, M.; D'Abrusco, Raffaele; D'Ago, Giuseppe; Puzia, Thomas H.; Hilker, Michael; Iodice, Enrichetta; Mieske, Steffen; Napolitano, Nicola R.; Peletier, R.; Pota, Vincenzo; Riccio, Giuseppe; Spavone, Marilena
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    Ensemble power spectral density of SDSS quasars in UV/optical bands
    (2024) Petrecca, V.; Papadakis, I. E.; Paolillo, M.; De Cicco, D.; Bauer, F. E.
    Context. Quasar variability has proven to be a powerful tool to constrain the properties of their inner engine and the accretion process onto supermassive black holes. Correlations between UV/optical variability and physical properties have been long studied with a plethora of different approaches and time-domain surveys, although the detailed picture is not yet clear. Aims. We analysed archival data from the SDSS Stripe-82 region to study how the quasar power spectral density (PSD) depends on the black hole mass, bolometric luminosity, accretion rate, redshift, and rest-frame wavelength. We developed a model-independent analysis framework that could be easily applied to upcoming large surveys such as the Legacy Survey of Space and Time (LSST). Methods. We used light curves of 8042 spectroscopically confirmed quasars, observed in at least six yearly seasons in five filters ugriz. We split the sample into bins of similar physical properties containing at least 50 sources, and we measured the ensemble PSD in each of them. Results. We find that a simple power law is a good fit to the power spectra in the frequency range explored. Variability does not depend on the redshift at a fixed wavelength. Instead, both PSD amplitude and slope depend on the black hole mass, accretion rate, and rest-frame wavelength. We provide scaling relations to model the observed variability as a function of the physical properties, and discuss the possibility of a universal PSD shape for all quasars, where frequencies scale with the black hole mass, while normalization and slope(s) are fixed (at any given wavelength and accretion rate).
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    Globular cluster scale sizes in giant galaxies: orbital anisotropy and tidally underfilling clusters in M87, NGC 1399 and NGC 5128
    (2016) Webb, J.; Sills, A.; Harris, W.; Gomez, M.; Paolillo, M.; Woodley, K.; Puzia, Thomas H.
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    Long-term x-ray variability of typical active galactic nuclei in the distant universe.
    (2016) Yang, G.; Kim, Sam; Brandt, W N.; Bauer, Franz Erik; Schulze, Steve.; Luo, B.; Xue, Y. Q.; Sun, M. Y.; Zheng, X. C.; Paolillo, M.; Shemmer, O.
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    Luminosity function of low-mass X-ray binaries in the globular cluster system of NGC 1399
    (2014) D’Ago, Giuseppe; Paolillo, M.; Fabbiano, G.; Puzia, Thomas H.; Maccarone, T.J.; Kundu, A.; Goudfrooij, P.; Zepf, S.E.
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    Properties of intra-cluster low-mass X-ray binaries in Fornax globular clusters
    (2022) Riccio, G.; Paolillo, M.; Cantiello, M.; D'Abrusco, R.; Jin, X.; Li, Z.; Puzia, T.; Mieske, S.; Prole, D. J.; Iodice, E.; D'Ago, G.; Gatto, M.; Spavone, M.
    Aims. We present a study of the intra-cluster population of low-mass X-ray binaries (LMXB) residing in globular clusters (GC) in the central 1 deg(2) of the Fornax galaxy cluster. Differently from previous studies, which were restricted to the innermost regions of individual galaxies, this work is aimed at comparing the properties of the intra-cluster population of GC-LMXBs with those of the host galaxy. Methods. The data used in this work are a combination of the VLT Survey Telescope (VST) and Chandra observations. We performed a cross-match between the optical and the X-ray catalogue in order to identify the LMXBs residing in GCs. We divided the GC-LMXBs into host-galaxy and intra-cluster objects based on their distance from the nearest galaxy in terms of effective radius (R-eff). We found 82 intra-cluster GC-LMXBs and 86 objects that are hosted in galaxies. As the formation of LMXBs also depends on the host GC colour, we performed a Gaussian mixture model to divide the population into red and blue GCs. Results. As has been found for the innermost regions of galaxies, LMXBs tend to form in red and bright GCs in intra-cluster space as well. We find, however, that the likelihood of a red GC to host an LMXB decreases with galactocentric distance, but it remains approximately constant for the blue GC population. Investigating the X-ray properties of the LMXBs residing in GCs, we find a difference in the X-ray luminosity function between the intra-cluster and host-galaxy sample: both follow a power-law down to similar to 8.5 x 10(37) erg s(-1), which is consistent with field LMXBs for the intra-cluster sample, while the latter agree with previous estimates for LMXBs in GCs. We observe a deficiency of bright LMXBs in blue intra-cluster GCs, however. This might indicate a lack of black hole binaries in metal-poor systems. We further investigated the spectral properties of the GC-LMXBs through their hardness-ratio. We detect a tentative difference in the hardness ratio of two populations, where the intra-cluster GC-LMXBs appear to have harder spectra than the host-galaxy objects. We find the same trend when we compare red and blue GC-LMXBs: the spectra of the blue sample are harder spectra than those of the red sample. This result could suggest a relation between the spectral properties of LMXBs and the host GC colour and therefore its metallicity. We discuss the possibilities of spatial biases due to uncertainties in the X-ray spectral response correction and due to contamination by background active galactic nuclei.
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    THE 4 Ms CHANDRA DEEP FIELD-SOUTH NUMBER COUNTS APPORTIONED BY SOURCE CLASS: PERVASIVE ACTIVE GALACTIC NUCLEI AND THE ASCENT OF NORMAL GALAXIES
    (2012) Lehmer, B. D.; Xue, Y. Q.; Brandt, W. N.; Alexander, D. M.; Bauer, F. E.; Brusa, M.; Comastri, A.; Gilli, R.; Hornschemeier, A. E.; Luo, B.; Paolillo, M.; Ptak, A.; Shemmer, O.; Schneider, D. P.; Tozzi, P.; Vignali, C.
    We present 0.5-2 keV, 2-8 keV, 4-8 keV, and 0.5-8 keV (hereafter soft, hard, ultra-hard, and full bands, respectively) cumulative and differential number-count (log N-log S) measurements for the recently completed approximate to 4 Ms Chandra Deep Field-South (CDF-S) survey, the deepest X-ray survey to date. We implement a new Bayesian approach, which allows reliable calculation of number counts down to flux limits that are factors of approximate to 1.9-4.3 times fainter than the previously deepest number-count investigations. In the soft band (SB), the most sensitive bandpass in our analysis, the approximate to 4 Ms CDF-S reaches a maximum source density of approximate to 27,800 deg(-2). By virtue of the exquisite X-ray and multiwavelength data available in the CDF-S, we are able to measure the number counts from a variety of source populations (active galactic nuclei (AGNs), normal galaxies, and Galactic stars) and subpopulations (as a function of redshift, AGN absorption, luminosity, and galaxy morphology) and test models that describe their evolution. We find that AGNs still dominate the X-ray number counts down to the faintest flux levels for all bands and reach a limiting SB source density of approximate to 14,900 deg(-2), the highest reliable AGN source density measured at any wavelength. We find that the normal-galaxy counts rise rapidly near the flux limits and, at the limiting SB flux, reach source densities of approximate to 12,700 deg(-2) and make up 46% +/- 5% of the total number counts. The rapid rise of the galaxy counts toward faint fluxes, as well as significant normal-galaxy contributions to the overall number counts, indicates that normal galaxies will overtake AGNs just below the approximate to 4 Ms SB flux limit and will provide a numerically significant new X-ray source population in future surveys that reach below the approximate to 4 Ms sensitivity limit. We show that a future approximate to 10 Ms CDF-S would allow for a significant increase in X-ray-detected sources, with many of the new sources being cosmologically distant (z greater than or similar to 0.6) normal galaxies.
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    The first detection of ultra-diffuse galaxies in the Hydra I cluster from the VEGAS survey
    (2020) Iodice, E.; Cantiello, M.; Hilker, M.; Rejkuba, M.; Arnaboldi, M.; Spavone, M.; Greggio, L.; Forbes, D. A.; D’Ago, Giuseppe; Mieske, S.; Spiniello, C.; La Marca, A.; Rampazzo, R.; Paolillo, M.; Capaccioli, M.; Schipani, P.
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    The fornax cluster VLT spectroscopic survey - I. VIMOS spectroscopy of compact stellar systems in the fornax core region
    (2018) Pota, V.; Napolitano, N.R.; Hilker, M.; Spavone, M.; Schulz, C.; Cantiello, M.; Totora, C.; Lodice, C.; Paolillo, M.; Órdenes Briceño, Yasna
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    The universal shape of the X-ray variability power spectrum of AGN up to z ∼ 3
    (2023) Paolillo, M.; Papadakis, I. E.; Brandt, W. N.; Bauer, F. E.; Lanzuisi, G.; Allevato, V.; Shemmer, O.; Zheng, X. C.; De Cicco, D.; Gilli, R.; Luo, B.; Thomas, M.; Tozzi, P.; Vito, F.; Xue, Y. Q.
    Aims. We study the ensemble X-ray variability properties of active galactic nuclei (AGN) over large ranges of timescale (20 ks <= T <= 14 yr), redshift (0 <= z less than or similar to 3), luminosity (10(40) erg s(-1) <= L-X <= 10(46) erg s(-1)), and black hole (BH) mass (10(6) <= M-circle dot <= 10(9)).
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    The XMM-SERVS survey: new XMM-Newton point-source catalogue for the XMM-LSS field
    (2018) Chen, C-T J.; Brandt, W. N.; Luo, B.; Ranalli, P.; Yang, G.; Alexander, D. M.; Bauer, Franz Erik; Kelson, D. D.; Lacy, M.; Nyland, K.; Tozzi, P.; Vito, F.; Cirasuolo, M.; Gilli, R.; Jarvis, M. J.; Lehmer, B. D.; Paolillo, M.; Schneider, D. P.|
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    Tracing the accretion history of supermassive black holes through X-ray variability: results from the Chandra Deep Field-South
    (2017) Paolillo, M.; Papadakis, I.; Brandt, W. N.; Luo, B.; Xue, Y. Q.; Tozzi, P.; Shemmer, O.; Allevato, V.; Bauer, Franz Erik; Comastri, A.
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    Variability and transient search in the SUDARE–VOICE field: a new method to extract the light curves
    (2020) Liu, D.; Deng, W.; Fan, Z.; Fu, L.; Covone, G.; Vaccari, M.; Radovich, M.; Capaccioli, M.; De Cicco, D.; Grado, A.; Marchetti, L.; Napolitano, N.; Paolillo, M.; Pignata, Giuliano; Ragost, F.
    The VLT Survey Telescope (VST) Optical Imaging of the CDFS and ES1 Fields Survey, in synergy with the SUDARE survey, is a deep optical ugri imaging of the CDFS and ES1 fields using the VST. The observations for the CDFS field comprise about 4.38 deg2 down to r ∼ 26 mag. The total on-sky time spans over 4 yr in this field, distributed over four adjacent sub-fields. In this paper, we use the multiepoch r-band imaging data to measure the variability of the detected objects and search for transients. We perform careful astrometric and photometric calibrations and point spread function modelling. A new method, referring to as differential running-average photometry, is proposed to measure the light curves of the detected objects. With the method, the difference of PSFs between different epochs can be reduced, and the background fluctuations are also suppressed. Detailed uncertainty analysis and detrending corrections on the light curves are performed. We visually inspect the light curves to select variable objects, and present some objects with interesting light curves. Further investigation of these objects in combination with multiband data will be presented in our forthcoming paper.
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    X-Ray Unveiling Events in a z ≈ 1.6 Active Galactic Nucleus in the 7 Ms Chandra Deep Field-South
    (2023) Yu, Li-Ming; Luo, Bin; Brandt, W. N.; Bauer, Franz E.; De Cicco, D.; Fabian, A.; Gilli, R.; Koekemoer, A.; Paolillo, M.; Schneider, D. P.; Shemmer, O.; Tozzi, P.; Trump, Jonathan R.; Vignali, C.; Vito, F.; Wang, J. -x.; Xue, Y. Q.
    We investigate the extreme X-ray variability of a z = 1.608 active galactic nucleus in the 7 Ms Chandra Deep Field-South (XID 403), which showed two significant X-ray brightening events. In the first event, XID 403 brightened by a factor of >2.5 in less than or similar to 6.1 rest-frame days in the observed-frame 0.5-5 keV band. The event lasted for approximate to 5.0-7.3 days, and then XID 403 dimmed by a factor of >6.0 in less than or similar to 6.1 days. After approximate to 1.1-2.5 yr in the rest frame (including long observational gaps), it brightened again, with the 0.5-5 keV flux increasing by a factor of >12.6. The second event lasted over 251 days, and the source remained bright until the end of the 7 Ms exposure. The spectrum is a steep power law (photon index Gamma = 2.8 +/- 0.3) without obscuration during the second outburst, and the rest-frame 2-10 keV luminosity reaches 1.5(-0.5)(+0.8) x 10(43) erg s(-1); there is no significant spectral evolution within this epoch. The infrared-to-UV spectral energy distribution of XID 403 is dominated by the host galaxy. There is no significant optical/UV variability and R-band (rest-frame approximate to 2500 angstrom) brightening contemporaneous with the X-ray brightening. The extreme X-ray variability is likely due to two X-ray unveiling events, where the line of sight to the corona is no longer shielded by high-density gas clumps in a small-scale dust-free absorber. XID 403 is probably a high-redshift analog of local narrow-line Seyfert 1 galaxies, and the X-ray absorber is a powerful accretion disk wind. On the other hand, we cannot exclude the possibility that XID 403 is an unusual candidate for tidal disruption events.