Showing 1–50 of 85 results for author: Marchetti, A

Emergence of information interference in stochastic systems with non-diagonal noise and switching environments

Authors: Andrea Marchetti, Daniel Maria Busiello, Giorgio Nicoletti

Abstract: Stochastic forces in natural systems are rarely isotropic. From hydrodynamically coupled colloids to chemical reaction networks, noise contributions are inherently correlated. Together with internal interactions and changing environments, they shape the dependencies between the degrees of freedom of real-world systems, as quantified by their mutual information. In this work, we focus on linearized… ▽ More Stochastic forces in natural systems are rarely isotropic. From hydrodynamically coupled colloids to chemical reaction networks, noise contributions are inherently correlated. Together with internal interactions and changing environments, they shape the dependencies between the degrees of freedom of real-world systems, as quantified by their mutual information. In this work, we focus on linearized stochastic systems with both non-diagonal noise matrices and stochastically switching environments. We study how their presence leads to the emergence of information interference, so that the total mutual information cannot be decomposed as the sum of the contributions from deterministic interactions, noise anisotropy, and environmental switching alone. We identify two distinct sources of information interference: a static term, arising from the simultaneous presence of deterministic coupling and noise anisotropy; and a dynamic term, emerging from the interplay between internal processes and environmental switches. We then apply this framework to different physical systems. In the presence of switching temperatures, the mutual information disentangles exactly into internal and environmental contributions. When the noise anisotropy arises instead from hydrodynamic interactions, we find that the presence of a shared fluid can either mask or enhance the information stemming from a non-conservative force depending on its degree of non-reciprocity. Finally, in a fuel-driven chemical reaction network, we show that information interference is controlled by the non-equilibrium driving. These results establish a general information-theoretic perspective on how anisotropic noise and environmental variability shape statistical dependencies in stochastic systems. △ Less

Submitted 13 May, 2026; originally announced May 2026.

Chasing Gamma-Ray Signals from Binary Neutron Star Coalescences with the Cherenkov Telescope Array: Prospects and Observing Strategies

Authors: S. Abe, J. Abhir, A. Abhishek, F. Acero, A. Acharyya, R. Adam, A. Aguasca-Cabot, I. Agudo, I. Albanese, J. Alfaro, C. Alispach, R. Alves Batista, E. Amato, G. Ambrosi, D. Ambrosino, F. Ambrosino, L. Angel, C. Aramo, A. Arbet-Engels, C. Arcaro, C. Arena, T. T. H. Arnesen, K. Asano, H. Ashkar, C. Bakshi , et al. (435 additional authors not shown)

Abstract: The detection of gravitational waves (GWs) from a binary neutron star (BNS) merger by Advanced LIGO and Advanced Virgo (GW170817), together with its electromagnetic counterpart, the short gamma-ray burst GRB~170817A, heralded the birth of multi-messenger astronomy. The detection of TeV emission from GRBs motivates follow-up observations with the Cherenkov Telescope Array Observatory (CTAO), ideal… ▽ More The detection of gravitational waves (GWs) from a binary neutron star (BNS) merger by Advanced LIGO and Advanced Virgo (GW170817), together with its electromagnetic counterpart, the short gamma-ray burst GRB~170817A, heralded the birth of multi-messenger astronomy. The detection of TeV emission from GRBs motivates follow-up observations with the Cherenkov Telescope Array Observatory (CTAO), ideal for detecting such signals due to its unprecedented sensitivity, rapid response, and wide-field survey capabilities. The aim of this work is to evaluate GeV--TeV GW follow-up strategies for CTAO using a multi-step simulation pipeline and to estimate the expected rate of joint GW-GRB detections during observing run O5. Using a simulated sample of BNS systems with corresponding GW detections, gamma-ray emission is simulated through phenomenological prescriptions based on the observed population of short GRBs, including off-axis jet scenarios. CTAO observations are simulated to account for instrument response, sky tiling strategies, integration times, and varying observing conditions. Strategies with variable and constant integration times are investigated. We find that, via an optimized follow-up strategy, about 5% of simulated GW-associated short GRBs produce GeV--TeV radiation detectable by CTAO. Detectability is strongly influenced by the jet opening angle and viewing angle, suggesting that even rough estimates of the viewing angle in GW alerts could enhance targeting. This framework motivates future follow-ups of GW-detectable events, including neutron star-black hole mergers, and further supports the development of advanced strategies incorporating galaxy distributions and synergies with future detectors such as the Einstein Telescope. △ Less

Submitted 9 April, 2026; originally announced April 2026.

Rate-Dependent Reversibility and Lithium Losses in Hybrid Anode-Collector Metal Electrodes

Authors: Arturo Galindo, Jesus Diaz-Sanchez, Sunil Kumar, Bouthayna Alrifai, Andrea Marchetti, Gaston Garcia, Celia Polop, Enrique Vasco

Abstract: Understanding how practical lithium storage capacity varies with charge-discharge rate is crucial for designing durable anode free lithium batteries. We examine the lithiation behavior of single element metal electrodes-Al (alloying), Mg (solid solution intercalation), Ag (solid solution then alloying), and Cu (surface Li plating)-to determine how their mechanisms influence reversibility, measured… ▽ More Understanding how practical lithium storage capacity varies with charge-discharge rate is crucial for designing durable anode free lithium batteries. We examine the lithiation behavior of single element metal electrodes-Al (alloying), Mg (solid solution intercalation), Ag (solid solution then alloying), and Cu (surface Li plating)-to determine how their mechanisms influence reversibility, measured by coulombic efficiency. Using electrochemistry combined with depth resolved ion beam profiling, we map local coulombic efficiency across current densities and identify dominant lithium loss pathways. Ag uniquely sustains fast kinetics and high reversibility at elevated rates due to rapid formation of gamma brass-type alloy phases. In contrast, Mg and Al show increasing irreversibility from kinetically or structurally driven Li trapping, while Cu exhibits the largest losses through porous, highly reactive plated lithium. These results reveal fundamental limits of anode free systems that depend on reversible Li plating without excess lithium and underscore the importance of metal selection for stable, high rate performance. △ Less

Submitted 13 March, 2026; originally announced March 2026.

Prospects for dark matter observations in dwarf spheroidal galaxies with the Cherenkov Telescope Array Observatory

Authors: K. Abe, S. Abe, J. Abhir, A. Abhishek, F. Acero, A. Acharyya, R. Adam, A. Aguasca-Cabot, I. Agudo, A. Aguirre-Santaella, J. Alfaro, R. Alfaro, C. Alispach, R. Alves Batista, J. -P. Amans, E. Amato, G. Ambrosi, D. Ambrosino, F. Ambrosino, L. Angel, L. A. Antonelli, C. Aramo, C. Arcaro, K. Asano, Y. Ascasibar , et al. (469 additional authors not shown)

Abstract: The dwarf spheroidal galaxies (dSphs) orbiting the Milky Way are widely regarded as systems supported by velocity dispersion against self-gravity, and as prime targets for the search for indirect dark matter (DM) signatures in the GeV-to-TeV $γ$-ray range owing to their lack of astrophysical $γ$-ray background. We present forecasts of the sensitivity of the forthcoming Cherenkov Telescope Array Ob… ▽ More The dwarf spheroidal galaxies (dSphs) orbiting the Milky Way are widely regarded as systems supported by velocity dispersion against self-gravity, and as prime targets for the search for indirect dark matter (DM) signatures in the GeV-to-TeV $γ$-ray range owing to their lack of astrophysical $γ$-ray background. We present forecasts of the sensitivity of the forthcoming Cherenkov Telescope Array Observatory (CTAO) to annihilating or decaying DM signals in these targets. An original selection of candidates is performed from the current catalogue of known objects, including both classical and ultra-faint dSphs. For each, the expected DM content is derived using the most comprehensive photometric and spectroscopic data available, within a consistent framework of analysis. This approach enables the derivation of novel astrophysical factor profiles for indirect DM searches, which are compared with results from the literature. From an initial sample of 64 dSphs, eight promising targets are identified -- Draco I, Coma Berenices, Ursa Major II, Ursa Minor and Willman 1 in the North, Reticulum II, Sculptor and Sagittarius II in the South -- for which different DM density models yield consistent expectations, leading to robust predictions. CTAO is expected to provide the strongest limits above $\sim$10 TeV, reaching velocity-averaged annihilation cross sections of $\sim$5$\times$10$^{-25}$ cm$^3$ s$^{-1}$ and decay lifetimes up to $\sim$10$^{26}$ s for combined limits. The dominant uncertainties arise from the imprecise determination of the DM content, particularly for ultra-faint dSphs. Observation strategies are proposed that optimise either deep exposures of the best candidates or diversified target selections. △ Less

Submitted 13 October, 2025; v1 submitted 26 August, 2025; originally announced August 2025.

Comments: 40 pages, 19 figures, 10 tables, accepted for publication on MNRAS

Journal ref: Mon Not R Astron Soc (2025) 2946-2986

Interpolation-Based Gradient-Error Bounds for Use in Derivative-Free Optimization of Noisy Functions

Authors: Alejandro G. Marchetti, Dominique Bonvin

Abstract: In this paper, we analyze the accuracy of gradient estimates obtained by linear interpolation when the underlying function is subject to bounded measurement noise. The total gradient error is decomposed into a deterministic component arising from the interpolation (finite-difference) approximation, and a stochastic component due to noise. Various upper bounds for both error components are derived… ▽ More In this paper, we analyze the accuracy of gradient estimates obtained by linear interpolation when the underlying function is subject to bounded measurement noise. The total gradient error is decomposed into a deterministic component arising from the interpolation (finite-difference) approximation, and a stochastic component due to noise. Various upper bounds for both error components are derived and compared through several illustrative examples. Our comparative study reveals that strict deterministic bounds, including those commonly used in derivative-free optimization (DFO), tend to be overly conservative. To address this, we propose approximate gradient error bounds that aim to upper bound the gradient error norm more realistically, without the excessive conservatism of classical bounds. Finally, drawing inspiration from dual real-time optimization strategies, we present a DFO scheme based on sequential programming, where the approximate gradient error bounds are enforced as constraints within the optimization problem. △ Less

Submitted 25 July, 2025; originally announced July 2025.

Comments: 40 pages, 13 figures

Directionality measures in evolutionary ecological networks: Insights from the Tangled Nature model

Authors: Andrea Marchetti, Henrik Jeldtoft Jensen

Abstract: The myriad microscopic interactions among the individual organisms that constitute an ecological system collectively give rise, at the macroscopic scale, to evolutionary trends. The ability to detect the directionality of such trends is crucial for understanding and managing the dynamics of natural systems. Nevertheless, identifying the key observable quantities that capture such directional behav… ▽ More The myriad microscopic interactions among the individual organisms that constitute an ecological system collectively give rise, at the macroscopic scale, to evolutionary trends. The ability to detect the directionality of such trends is crucial for understanding and managing the dynamics of natural systems. Nevertheless, identifying the key observable quantities that capture such directional behaviour poses a major challenge. In this study, we propose that translating ecological data into a network framework is a valuable strategy to measure system stability and evolution. We examine the Tangled Nature model as a test case, evaluating network entropy, species diversity, and the clustering coefficient as metrics of network stability and directionality. △ Less

Submitted 18 July, 2025; originally announced July 2025.

Comments: Two Supplementary Information files provided

How Generative AI Adoption Alters the Demand for Cognitive and Social Skills Within Roles: A Skill-Centric Analysis

Authors: Piyush Gulati, Arianna Marchetti, Victoria Sevcenko, Phanish Puranam

Abstract: A common view holds that generative AI (GenAI) automates cognitive tasks, reshaping roles to emphasize social skills over cognitive ones. Drawing on the framework we develop in this paper, we argue that other outcomes are theoretically possible. We analyze seven million job postings from 595 U.S. public firms that adopted GenAI in 2022-2024, estimating difference-in-differences models comparing Ge… ▽ More A common view holds that generative AI (GenAI) automates cognitive tasks, reshaping roles to emphasize social skills over cognitive ones. Drawing on the framework we develop in this paper, we argue that other outcomes are theoretically possible. We analyze seven million job postings from 595 U.S. public firms that adopted GenAI in 2022-2024, estimating difference-in-differences models comparing GenAI-adopting and non-adopting roles around ChatGPT's launch. We find no evidence of greater emphasis on social skills in GenAI-adopting roles; instead, their relative demand for social skills declined by 3.4%, while demand for cognitive skills held steady. This decline reflects the addition of functional administrative skills to roles outside those functions. Concentrated in non-managerial roles, this pattern points toward GenAI-enabled self-service rather than intensified cross-functional coordination. △ Less

Submitted 18 August, 2026; v1 submitted 12 March, 2025; originally announced March 2025.

Comments: 55 pages

Psychomatics -- A Multidisciplinary Framework for Understanding Artificial Minds

Authors: Giuseppe Riva, Fabrizia Mantovani, Brenda K. Wiederhold, Antonella Marchetti, Andrea Gaggioli

Abstract: Although LLMs and other artificial intelligence systems demonstrate cognitive skills similar to humans, like concept learning and language acquisition, the way they process information fundamentally differs from biological cognition. To better understand these differences this paper introduces Psychomatics, a multidisciplinary framework bridging cognitive science, linguistics, and computer science… ▽ More Although LLMs and other artificial intelligence systems demonstrate cognitive skills similar to humans, like concept learning and language acquisition, the way they process information fundamentally differs from biological cognition. To better understand these differences this paper introduces Psychomatics, a multidisciplinary framework bridging cognitive science, linguistics, and computer science. It aims to better understand the high-level functioning of LLMs, focusing specifically on how LLMs acquire, learn, remember, and use information to produce their outputs. To achieve this goal, Psychomatics will rely on a comparative methodology, starting from a theory-driven research question - is the process of language development and use different in humans and LLMs? - drawing parallels between LLMs and biological systems. Our analysis shows how LLMs can map and manipulate complex linguistic patterns in their training data. Moreover, LLMs can follow Grice's Cooperative Principle to provide relevant and informative responses. However, human cognition draws from multiple sources of meaning, including experiential, emotional, and imaginative facets, which transcend mere language processing and are rooted in our social and developmental trajectories. Moreover, current LLMs lack physical embodiment, reducing their ability to make sense of the intricate interplay between perception, action, and cognition that shapes human understanding and expression. Ultimately, Psychomatics holds the potential to yield transformative insights into the nature of language, cognition, and intelligence, both artificial and biological. Moreover, by drawing parallels between LLMs and human cognitive processes, Psychomatics can inform the development of more robust and human-like AI systems. △ Less

Submitted 23 July, 2024; originally announced July 2024.

Comments: 15 pages, 4 tables, 2 figures

The Electrochemical Transistor: a device based on the Electrochemical control of a polymer Polaronic state. The PCPDT-BT as a case study

Authors: Andrea Stefani, Agnese Giacomino, Sara Morandi, Andrea Marchetti, Claudio Fontanesi

Abstract: This work presents an original concept directed to implement an unconventional methodology where a device is produced by integrating a solid-state circuitry concept and an electrochemistry cell. In our experimental system an organic semiconductor, (PCPDT-BT), serves both as the gate and working electrode. Gating is obtained via electrochemical polarization exploiting a conventional three electrode… ▽ More This work presents an original concept directed to implement an unconventional methodology where a device is produced by integrating a solid-state circuitry concept and an electrochemistry cell. In our experimental system an organic semiconductor, (PCPDT-BT), serves both as the gate and working electrode. Gating is obtained via electrochemical polarization exploiting a conventional three electrodes electrochemical cell placed on top of a traditional source/drain/gate solid-state device configuration. Source/drain conduction is probed via impedance measurement (electrochemical impedance spectroscopy, EIS) performed as a function of time at constant frequency, under constant potential control. The conductivity of the PCPDT-BT is due to the polaronic state induced via application of a suitable electrochemical potential (in the oxidation regime), as it is proved by infrared (IR) spectra recorded in-situ/in-operando (in attenuated under total reflection, ATR, mode) upon both electrochemical and chemical ionization/doping of the PCPDT-BT. △ Less

Submitted 28 February, 2024; originally announced February 2024.

Comments: Main ms., 15 pages, 4 figures Supp Info, 9 pages, 10 figures, 3 equations

Increasing biases can be more efficient than increasing weights

Authors: Carlo Metta, Marco Fantozzi, Andrea Papini, Gianluca Amato, Matteo Bergamaschi, Silvia Giulia Galfrè, Alessandro Marchetti, Michelangelo Vegliò, Maurizio Parton, Francesco Morandin

Abstract: We introduce a novel computational unit for neural networks that features multiple biases, challenging the traditional perceptron structure. This unit emphasizes the importance of preserving uncorrupted information as it is passed from one unit to the next, applying activation functions later in the process with specialized biases for each unit. Through both empirical and theoretical analyses, we… ▽ More We introduce a novel computational unit for neural networks that features multiple biases, challenging the traditional perceptron structure. This unit emphasizes the importance of preserving uncorrupted information as it is passed from one unit to the next, applying activation functions later in the process with specialized biases for each unit. Through both empirical and theoretical analyses, we show that by focusing on increasing biases rather than weights, there is potential for significant enhancement in a neural network model's performance. This approach offers an alternative perspective on optimizing information flow within neural networks. See source code at https://github.com/CuriosAI/dac-dev. △ Less

Submitted 18 January, 2024; v1 submitted 2 January, 2023; originally announced January 2023.

Comments: Major rewriting. Supersedes v1 and v2. Focusing on the fact that not all parameters are born equal: biases can be more important than weights. Accordingly, new title and new abstract, and many more experiments on fully connected architectures. This is the extended version of the paper published at WACV 2024

ACM Class: I.2.6

Score vs. Winrate in Score-Based Games: which Reward for Reinforcement Learning?

Authors: Luca Pasqualini, Gianluca Amato, Marco Fantozzi, Rosa Gini, Alessandro Marchetti, Carlo Metta, Francesco Morandin, Maurizio Parton

Abstract: In the last years, the DeepMind algorithm AlphaZero has become the state of the art to efficiently tackle perfect information two-player zero-sum games with a win/lose outcome. However, when the win/lose outcome is decided by a final score difference, AlphaZero may play score-suboptimal moves because all winning final positions are equivalent from the win/lose outcome perspective. This can be an i… ▽ More In the last years, the DeepMind algorithm AlphaZero has become the state of the art to efficiently tackle perfect information two-player zero-sum games with a win/lose outcome. However, when the win/lose outcome is decided by a final score difference, AlphaZero may play score-suboptimal moves because all winning final positions are equivalent from the win/lose outcome perspective. This can be an issue, for instance when used for teaching, or when trying to understand whether there is a better move. Moreover, there is the theoretical quest for the perfect game. A naive approach would be training an AlphaZero-like agent to predict score differences instead of win/lose outcomes. Since the game of Go is deterministic, this should as well produce an outcome-optimal play. However, it is a folklore belief that "this does not work". In this paper, we first provide empirical evidence for this belief. We then give a theoretical interpretation of this suboptimality in general perfect information two-player zero-sum game where the complexity of a game like Go is replaced by the randomness of the environment. We show that an outcome-optimal policy has a different preference for uncertainty when it is winning or losing. In particular, when in a losing state, an outcome-optimal agent chooses actions leading to a higher score variance. We then posit that when approximation is involved, a deterministic game behaves like a nondeterministic game, where the score variance is modeled by how uncertain the position is. We validate this hypothesis in AlphaZero-like software with a human expert. △ Less

Submitted 9 January, 2023; v1 submitted 31 January, 2022; originally announced January 2022.

Comments: Published at 2022 21st IEEE International Conference on Machine Learning and Applications (ICMLA). This version (v2) is a major revision and superseeds version v1

ACM Class: I.2.6

Charge carriers with fractional exclusion statistics in cuprates

Authors: P. A. Marchetti, F. Ye, Z. B. Su, L. Yu

Abstract: We show that in the SU(2)XU(1) spin-charge gauge approach we developed earlier one can attribute consistently an exclusion statistics with parameter 1/2 to the spinless charge carriers of the t-J model in two dimensions(2D), as it occurs in one dimension (1D). Like the 1D case, the no-double occupation constraint is at the origin of this fractional exclusion statistics. With this statistics we rec… ▽ More We show that in the SU(2)XU(1) spin-charge gauge approach we developed earlier one can attribute consistently an exclusion statistics with parameter 1/2 to the spinless charge carriers of the t-J model in two dimensions(2D), as it occurs in one dimension (1D). Like the 1D case, the no-double occupation constraint is at the origin of this fractional exclusion statistics. With this statistics we recover a "large" Fermi volume of holes at high dopings, close to that of the tight binding approximation. Furthermore, the composite nature of the hole, made of charge and spin carriers only weakly bounded, can provide a natural explanation of many unusual experimental features of the hole-doped cuprates. △ Less

Submitted 11 July, 2019; originally announced July 2019.

Journal ref: Phys. Rev. B 100, 035103 (2019)

Chemical abundances and radial velocities in the extremely metal-poor galaxy DDO 68

Authors: F. Annibali, V. La Torre, M. Tosi, C. Nipoti, F. Cusano, A. Aloisi, M. Bellazzini, L. Ciotti, A. Marchetti, M. Mignoli, D. Romano, E. Sacchi

Abstract: We present chemical abundances and radial velocities of six HII regions in the extremely metal-poor star-forming dwarf galaxy DDO 68. They are derived from deep spectra in the wavelength range 3500 - 10,000 Å, acquired with the Multi Object Double Spectrograph (MODS) at the Large Binocular Telescope (LBT). In the three regions where the [O III]$λ$4363 Å line was detected, we inferred the abundance… ▽ More We present chemical abundances and radial velocities of six HII regions in the extremely metal-poor star-forming dwarf galaxy DDO 68. They are derived from deep spectra in the wavelength range 3500 - 10,000 Å, acquired with the Multi Object Double Spectrograph (MODS) at the Large Binocular Telescope (LBT). In the three regions where the [O III]$λ$4363 Å line was detected, we inferred the abundance of He, N, O, Ne, Ar, and S through the "direct" method. We also derived the oxygen abundances of all the six regions adopting indirect method calibrations. We confirm that DDO 68 is an extremely metal-poor galaxy, and a strong outlier in the luminosity - metallicity relation defined by star-forming galaxies. With the direct-method we find indeed an oxygen abundance of 12+log(O/H)=7.14$\pm$0.07 in the northernmost region of the galaxy and, although with large uncertainties, an even lower 12+log(O/H)=6.96$\pm$0.09 in the "tail". This is, at face value, the most metal-poor direct abundance detection of any galaxy known. We derive a radial oxygen gradient of -0.06$\pm$0.03 dex/kpc (or -0.30 dex $R_{25}^{-1}$) with the direct method, and a steeper gradient of -0.12$\pm$0.03 dex/kpc (or -0.59 dex $R_{25}^{-1}$) from the indirect method. For the $α$-element to oxygen ratios we obtain values in agreement with those found in other metal-poor star-forming dwarfs. For nitrogen, instead, we infer much higher values, leading to log(N/O)$\sim-1.4$, at variance with the suggested existence of a tight plateau at $-1.6$ in extremely metal poor dwarfs. The derived helium mass fraction ranges from Y=0.240$\pm$0.005 to Y=0.25$\pm$0.02, compatible with standard big bang nucleosynthesis. Finally, we measured HII region radial velocities in the range 479$-$522 km/s from the tail to the head of the "comet", consistent with the rotation derived in the HI. △ Less

Submitted 5 October, 2018; originally announced October 2018.

Comments: Accepted for publication in MNRAS

The attraction between antiferromagnetic quantum vortices as origin of superconductivity in cuprates

Authors: P. A. Marchetti

Abstract: We propose as key of superconductivity in (hole-doped) cuprates a novel excitation of magnetic origin, characteristic of two-dimensions and of purely quantum nature: the antiferromagnetic spin vortices. In this formalism the charge pairing arises from a Kosterlitz-Thouless-like attraction between such vortices centered on opposite Néel sublattices. This charge pairing induces also the spin pairing… ▽ More We propose as key of superconductivity in (hole-doped) cuprates a novel excitation of magnetic origin, characteristic of two-dimensions and of purely quantum nature: the antiferromagnetic spin vortices. In this formalism the charge pairing arises from a Kosterlitz-Thouless-like attraction between such vortices centered on opposite Néel sublattices. This charge pairing induces also the spin pairing through the action of a gauge force generated by the no-double occupation constraint imposed in the t-J model of the CuO planes of the cuprates. Superconductivity arises from coherence of pairs of excitations describing Zhang-Rice singlets and it is not of standard BCS type. We show that many experimental features of the cuprates can find a natural explanation in this formalism. △ Less

Submitted 1 June, 2018; originally announced June 2018.

Comments: Based on a talk given at the "Workshop on Topological Phase Transitions and New Developments" Nanyang Technological University, Singapore 5-8 July 2017; to appear in the Proceedings

MSC Class: 82D55

LBT/MODS spectroscopy of globular clusters in the irregular galaxy NGC 4449

Authors: F. Annibali, E. Morandi, L. L. Watkins, M. Tosi, A. Aloisi, A. Buzzoni, F. Cusano, M. Fumana, A. Marchetti, M. Mignoli, A. Mucciarelli, D. Romano, R. P. van der Marel, .

Abstract: We present intermediate-resolution (R$\sim$1000) spectra in the $\sim$3500-10,000 A range of 14 globular clusters in the magellanic irregular galaxy NGC 4449 acquired with the Multi Object Double Spectrograph on the Large Binocular Telescope. We derived Lick indices in the optical and the CaII-triplet index in the near-infrared in order to infer the clusters' stellar population properties. The inf… ▽ More We present intermediate-resolution (R$\sim$1000) spectra in the $\sim$3500-10,000 A range of 14 globular clusters in the magellanic irregular galaxy NGC 4449 acquired with the Multi Object Double Spectrograph on the Large Binocular Telescope. We derived Lick indices in the optical and the CaII-triplet index in the near-infrared in order to infer the clusters' stellar population properties. The inferred cluster ages are typically older than $\sim$9 Gyr, although ages are derived with large uncertainties. The clusters exhibit intermediate metallicities, in the range $-1.2\lesssim$[Fe/H]$\lesssim-0.7$, and typically sub-solar [$α/Fe$] ratios, with a peak at $\sim-0.4$. These properties suggest that i) during the first few Gyrs NGC 4449 formed stars slowly and inefficiently, with galactic winds having possibly contributed to the expulsion of the $α$-elements, and ii) globular clusters in NGC 4449 formed relatively "late", from a medium already enriched in the products of type Ia supernovae. The majority of clusters appear also under-abundant in CN compared to Milky Way halo globular clusters, perhaps because of the lack of a conspicuous N-enriched, second-generation of stars like that observed in Galactic globular clusters. Using the cluster velocities, we infer the dynamical mass of NGC 4449 inside 2.88 kpc to be M($<$2.88 kpc)=$3.15^{+3.16}_{-0.75} \times 10^9~M_\odot$. We also report the serendipitous discovery of a planetary nebula within one of the targeted clusters, a rather rare event. △ Less

Submitted 8 February, 2018; v1 submitted 7 February, 2018; originally announced February 2018.

Comments: Accepted for publication in MNRAS; corrected typo in author list

The contribution of faint AGNs to the ionizing background at z~4

Authors: A. Grazian, E. Giallongo, K. Boutsia, S. Cristiani, E. Vanzella, C. Scarlata, P. Santini, L. Pentericci, E. Merlin, N. Menci, F. Fontanot, A. Fontana, F. Fiore, F. Civano, M. Castellano, M. Brusa, A. Bonchi, R. Carini, F. Cusano, M. Faccini, B. Garilli, A. Marchetti, A. Rossi, R. Speziali

Abstract: Finding the sources responsible for the hydrogen reionization is one of the most pressing issues in cosmology. Bright QSOs are known to ionize their surrounding neighborhood, but they are too few to ensure the required HI ionizing background. A significant contribution by faint AGNs, however, could solve the problem, as recently advocated on the basis of a relatively large space density of faint a… ▽ More Finding the sources responsible for the hydrogen reionization is one of the most pressing issues in cosmology. Bright QSOs are known to ionize their surrounding neighborhood, but they are too few to ensure the required HI ionizing background. A significant contribution by faint AGNs, however, could solve the problem, as recently advocated on the basis of a relatively large space density of faint active nuclei at z>4. We have carried out an exploratory spectroscopic program to measure the HI ionizing emission of 16 faint AGNs spanning a broad U-I color interval, with I~21-23 and 3.6<z<4.2. These AGNs are three magnitudes fainter than the typical SDSS QSOs (M1450<~-26) which are known to ionize their surrounding IGM at z>~4. The LyC escape fraction has been detected with S/N ratio of ~10-120 and is between 44 and 100% for all the observed faint AGNs, with a mean value of 74% at 3.6<z<4.2 and -25.1<M1450<-23.3, in agreement with the value found in the literature for much brighter QSOs (M1450<~-26) at the same redshifts. The LyC escape fraction of our faint AGNs does not show any dependence on the absolute luminosities or on the observed U-I colors. Assuming that the LyC escape fraction remains close to ~75% down to M1450~-18, we find that the AGN population can provide between 16 and 73% (depending on the adopted luminosity function) of the whole ionizing UV background at z~4, measured through the Lyman forest. This contribution increases to 25-100% if other determinations of the ionizing UV background are adopted. Extrapolating these results to z~5-7, there are possible indications that bright QSOs and faint AGNs can provide a significant contribution to the reionization of the Universe, if their space density is high at M1450~-23. △ Less

Submitted 6 February, 2018; originally announced February 2018.

Comments: Accepted for publication on A&A, 16 pages, 22 figures

Journal ref: A&A 613, A44 (2018)

Skin Lesion Analysis Toward Melanoma Detection: A Challenge at the 2017 International Symposium on Biomedical Imaging (ISBI), Hosted by the International Skin Imaging Collaboration (ISIC)

Authors: Noel C. F. Codella, David Gutman, M. Emre Celebi, Brian Helba, Michael A. Marchetti, Stephen W. Dusza, Aadi Kalloo, Konstantinos Liopyris, Nabin Mishra, Harald Kittler, Allan Halpern

Abstract: This article describes the design, implementation, and results of the latest installment of the dermoscopic image analysis benchmark challenge. The goal is to support research and development of algorithms for automated diagnosis of melanoma, the most lethal skin cancer. The challenge was divided into 3 tasks: lesion segmentation, feature detection, and disease classification. Participation involv… ▽ More This article describes the design, implementation, and results of the latest installment of the dermoscopic image analysis benchmark challenge. The goal is to support research and development of algorithms for automated diagnosis of melanoma, the most lethal skin cancer. The challenge was divided into 3 tasks: lesion segmentation, feature detection, and disease classification. Participation involved 593 registrations, 81 pre-submissions, 46 finalized submissions (including a 4-page manuscript), and approximately 50 attendees, making this the largest standardized and comparative study in this field to date. While the official challenge duration and ranking of participants has concluded, the dataset snapshots remain available for further research and development. △ Less

Submitted 8 January, 2018; v1 submitted 13 October, 2017; originally announced October 2017.

Fractional exclusion and braid statistics in one dimension: a study via dimensional reduction of Chern-Simons theory

Authors: Fei Ye, P. A. Marchetti, Z. B. Su, L. Yu

Abstract: The relation between braid and exclusion statistics is examined in one-dimensional systems, within the framework of Chern-Simons statistical transmutation in gauge invariant form with an appropriate dimensional reduction. If the matter action is anomalous, as for chiral fermions, a relation between braid and exclusion statistics can be established explicitly for both mutual and nonmutual cases. Ho… ▽ More The relation between braid and exclusion statistics is examined in one-dimensional systems, within the framework of Chern-Simons statistical transmutation in gauge invariant form with an appropriate dimensional reduction. If the matter action is anomalous, as for chiral fermions, a relation between braid and exclusion statistics can be established explicitly for both mutual and nonmutual cases. However, if it is not anomalous, the exclusion statistics of emergent low energy excitations is not necessarily connected to the braid statistics of the physical charged fields of the system. Finally, we also discuss the bosonization of one-dimensional anyonic systems through T-duality. △ Less

Submitted 12 September, 2017; v1 submitted 9 August, 2017; originally announced August 2017.

Comments: 19 pages, fix typos

Journal ref: J. Phys. A: Math. Theor. 50 (2017) 395401

PNe and H II regions in the starburst irregular galaxy NGC 4449 from LBT MODS data

Authors: F. Annibali, M. Tosi, D. Romano, A. Buzzoni, F. Cusano, M. Fumana, A. Marchetti, M. Mignoli, A. Pasquali, A. Aloisi

Abstract: We present deep 3500$-$10000 $Å$ spectra of H II regions and planetary nebulae (PNe) in the starburst irregular galaxy NGC 4449, acquired with the Multi Object Double Spectrograph at the Large Binocular Telescope. Using the "direct" method, we derived the abundance of He, N, O, Ne, Ar, and S in six H II regions and in four PNe in NGC 4449. This is the first case of PNe studied in a starburst irreg… ▽ More We present deep 3500$-$10000 $Å$ spectra of H II regions and planetary nebulae (PNe) in the starburst irregular galaxy NGC 4449, acquired with the Multi Object Double Spectrograph at the Large Binocular Telescope. Using the "direct" method, we derived the abundance of He, N, O, Ne, Ar, and S in six H II regions and in four PNe in NGC 4449. This is the first case of PNe studied in a starburst irregular outside the Local Group. Our H II region and PN sample extends over a galacto-centric distance range of $\approx$2 kpc and spans $\approx$0.2 dex in oxygen abundance, with average values of $12+\log(O/H)=8.37 \pm 0.05$ and $8.3 \pm 0.1$ for H II regions and PNe, respectively. PNe and H II regions exhibit similar oxygen abundances in the galacto-centric distance range of overlap, while PNe appear more than $\sim$1 dex enhanced in nitrogen with respect to H II regions. The latter result is the natural consequence of N being mostly synthesized in intermediate-mass stars and brought to the stellar surface during dredge-up episodes. On the other hand, the similarity in O abundance between H II regions and PNe suggests that NGC 4449' s interstellar medium has been poorly enriched in $α$ elements since the progenitors of the PNe were formed. Finally, our data reveal the presence of a negative oxygen gradient for both H II regions and PNe, whilst nitrogen does not exhibit any significant radial trend. We ascribe the (unexpected) nitrogen behaviour as due to local N enrichment by the conspicuous Wolf-Rayet population in NGC 4449. △ Less

Submitted 7 June, 2017; originally announced June 2017.

Comments: Accepted for publication on ApJ

The 2015-2016 outburst of the classical EXor V1118 Ori

Authors: T. Giannini, S. Antoniucci, D. Lorenzetti, U. Munari, G. Li Causi, C. F. Manara, B. Nisini, A. A. Arkharov, S. Dallaporta, A. Di Paola, A. Giunta, A. Harutyunyan, S. A. Klimanov, A. Marchetti, G. L. Righetti, A. Rossi, F. Strafella, V. Testa

Abstract: After a quiescence period of about 10 years, the classical EXor source V1118 Ori has undergone an accretion outburst in 2015 September. The maximum brightness (DV > 4 mag) was reached in 2015 December and was maintained for several months. Since 2016 September, the source is in a declining phase. Photometry and low/ high-resolution spectroscopy were obtained with MODS and LUCI2 at the {\it Large B… ▽ More After a quiescence period of about 10 years, the classical EXor source V1118 Ori has undergone an accretion outburst in 2015 September. The maximum brightness (DV > 4 mag) was reached in 2015 December and was maintained for several months. Since 2016 September, the source is in a declining phase. Photometry and low/ high-resolution spectroscopy were obtained with MODS and LUCI2 at the {\it Large Binocular Telescope}, with the facilities at the Asiago 1.22 and 1.82 m telescopes, and with GIANO at the {\it Telescopio Nazionale Galileo}. The spectra are dominated by emission lines of \hi\ and neutral metallic species. From line and continuum analysis we derive the mass accretion rate and its evolution during the outburst. Considering that extinction may vary between 1.5 and 2.9 mag, we obtain m_acc= 0.3$-$2.0 10$^{-8}$ m_sun/yr, in quiescence and m_acc= 0.2$-$1.9 10$^{-6}$ m_sun/yr, at the outburst peak. The Balmer decrement shape has been interpreted by means of line excitation models, finding that from quiescence to outburst peak, the electron density has increased from $\sim$ 2 10$^9$ cm$^{-3}$ to $\sim$ 4 10$^{11}$ cm$^{-3}$. The profiles of the metallic lines are symmetric and narrower than 100 km s$^{-1}$, while \hi\, and \hei\,\,lines show prominent wings extending up to $\pm$ 500 km s$^{-1}$. The metallic lines likely originate at the base of the accretion columns, where neutrals are efficiently shielded against the ionizing photons, while faster ionized gas is closer to the star. Outflowing activity is testified by the detection of a variable P Cyg-like profile of the H$α$ and \hei\, 1.08\,$μ$m lines. △ Less

Submitted 19 April, 2017; originally announced April 2017.

Comments: Accepted by ApJ

Redshift, metallicity and size of two extended dwarf Irregular galaxies. A link between dwarf Irregulars and Ultra Diffuse Galaxies?

Authors: M. Bellazzini, V. Belokurov, L. Magrini, F. Fraternali, V. Testa, G. Beccari, A. Marchetti, R. Carini

Abstract: We present the results of the spectroscopic and photometric follow-up of two field galaxies that were selected as possible stellar counterparts of local high velocity clouds. Our analysis shows that the two systems are distant (D>20 Mpc) dwarf irregular galaxies unrelated to the local HI clouds. However, the newly derived distance and structural parameters reveal that the two galaxies have luminos… ▽ More We present the results of the spectroscopic and photometric follow-up of two field galaxies that were selected as possible stellar counterparts of local high velocity clouds. Our analysis shows that the two systems are distant (D>20 Mpc) dwarf irregular galaxies unrelated to the local HI clouds. However, the newly derived distance and structural parameters reveal that the two galaxies have luminosities and effective radii very similar to the recently identified Ultra Diffuse Galaxies (UDGs). At odds with classical UDGs, they are remarkably isolated, having no known giant galaxy within ~2.0 Mpc. Moreover, one of them has a very high gas content compared to galaxies of similar stellar mass, with a HI to stellar mass ratio M_HI/M_* ~90, typical of almost-dark dwarfs. Expanding on this finding, we show that extended dwarf irregulars overlap the distribution of UDGs in the M_V vs. log(r_e) plane and that the sequence including dwarf spheroidals, dwarf irregulars and UDGs appears as continuously populated in this plane. △ Less

Submitted 26 January, 2017; originally announced January 2017.

Comments: Accepted for publication by MNRAS. PDFLatex. 8 pages, 4 figures, 2 tables

The VIMOS Public Extragalactic Redshift Survey (VIPERS): PCA-based automatic cleaning and reconstruction of survey spectra

Authors: A. Marchetti, B. Garilli, B. R. Granett, L. Guzzo, A. Iovino, M. Scodeggio, M. Bolzonella, S. de la Torre, U. Abbas, C. Adami, D. Bottini, A. Cappi, O. Cucciati, I. Davidzon, P. Franzetti, A. Fritz, J. Krywult, V. Le Brun, O. Le Fèvre, D. Maccagni, K. Małek, F. Marulli, M. Polletta, A. Pollo, L. A. M. Tasca , et al. (12 additional authors not shown)

Abstract: Identifying spurious reduction artefacts in galaxy spectra is a challenge for large surveys. We present an algorithm for identifying and repairing residual spurious features in sky-subtracted galaxy spectra with application to the VIPERS survey. The algorithm uses principal component analysis (PCA) applied to the galaxy spectra in the observed frame to identify sky line residuals imprinted at char… ▽ More Identifying spurious reduction artefacts in galaxy spectra is a challenge for large surveys. We present an algorithm for identifying and repairing residual spurious features in sky-subtracted galaxy spectra with application to the VIPERS survey. The algorithm uses principal component analysis (PCA) applied to the galaxy spectra in the observed frame to identify sky line residuals imprinted at characteristic wavelengths. We further model the galaxy spectra in the rest-frame using PCA to estimate the most probable continuum in the corrupted spectral regions, which are then repaired. We apply the method to 90,000 spectra from the VIPERS survey and compare the results with a subset where careful editing was performed by hand. We find that the automatic technique does an extremely good job in reproducing the time-consuming manual cleaning and does it in a uniform and objective manner across a large data sample. The mask data products produced in this work are released together with the VIPERS second public data release (PDR-2). △ Less

Submitted 6 December, 2016; originally announced December 2016.

Comments: Find the VIPERS data release at http://vipers.inaf.it

Journal ref: A&A 600, A54 (2017)

The VIMOS Public Extragalactic Redshift Survey (VIPERS). Full spectroscopic data and auxiliary information release (PDR-2)

Authors: M. Scodeggio, L. Guzzo, B. Garilli, B. R. Granett, M. Bolzonella, S. de la Torre, U. Abbas, C. Adami, S. Arnouts, D. Bottini, A. Cappi, J. Coupon, O. Cucciati, I. Davidzon, P. Franzetti, A. Fritz, A. Iovino, J. Krywult, V. Le Brun, O. Le Févre, D. Maccagni, K. Malek, A. Marchetti, F. Marulli, M. Polletta , et al. (20 additional authors not shown)

Abstract: We present the full public data release (PDR-2) of the VIMOS Public Extragalactic Redshift Survey (VIPERS), performed at the ESO VLT. We release redshifts, spectra, CFHTLS magnitudes and ancillary information (as masks and weights) for a complete sample of 86,775 galaxies (plus 4,732 other objects, including stars and serendipitous galaxies); we also include their full photometrically-selected par… ▽ More We present the full public data release (PDR-2) of the VIMOS Public Extragalactic Redshift Survey (VIPERS), performed at the ESO VLT. We release redshifts, spectra, CFHTLS magnitudes and ancillary information (as masks and weights) for a complete sample of 86,775 galaxies (plus 4,732 other objects, including stars and serendipitous galaxies); we also include their full photometrically-selected parent catalogue. The sample is magnitude limited to i_AB < 22.5, with an additional colour-colour pre-selection devised as to exclude galaxies at z<0.5. This practically doubles the effective sampling of the VIMOS spectrograph over the range 0.5<z<1.2 (reaching 47% on average), yielding a final median local galaxy density close to 5 10^{-3} h^3 Mpc}^{-3}. The total area spanned by the final data set is ~ 23.5 deg^2, corresponding to 288 VIMOS fields with marginal overlaps, split over two regions within the CFHTLS-Wide W1 and W4 equatorial fields (at R.A. ~2 and ~22 hours, respectively). Spectra were observed at a resolution R=220, covering a wavelength range 5500-9500 Angstrom. Data reduction and redshift measurements were performed through a fully automated pipeline; all redshift determinations were then visually validated and assigned a quality flag. Measurements with a quality flag >= 2 are shown to have a confidence level of 96% or larger and make up 88% of all measured galaxy redshifts (76,552 out of 86,775), constituting the VIPERS prime catalogue for statistical investigations. For this sample the rms redshift error, estimated using repeated measurements of about 3,000 galaxies, is found to be sigma_z = 0.00054(1+z). All data are available at http://vipers.inaf.it and on the ESO Archive. △ Less

Submitted 21 November, 2016; originally announced November 2016.

Comments: Submitted to Astronomy and Astrophysics; 14 pages, 14 figures. High resolution version of Fig. 14 available at http://vipers.inaf.it

Journal ref: A&A 609, A84 (2018)

Superfluid density in cuprates: hints on gauge compositeness of the holes

Authors: P. A. Marchetti, G. Bighin

Abstract: We show that several features (the three-dimensional XY universality for moderate underdoping, the almost-BCS behaviour for moderate overdoping and the critical exponent) of the superfluid density in hole-doped cuprates hint at a composite structure of the holes. This idea can be implemented in a spin-charge gauge approach to the $t - t' - J$ model and provides indeed good agreement with available… ▽ More We show that several features (the three-dimensional XY universality for moderate underdoping, the almost-BCS behaviour for moderate overdoping and the critical exponent) of the superfluid density in hole-doped cuprates hint at a composite structure of the holes. This idea can be implemented in a spin-charge gauge approach to the $t - t' - J$ model and provides indeed good agreement with available experimental data. △ Less

Submitted 13 July, 2016; originally announced July 2016.

Comments: 5 pages, 1 figure, to be published in the proceedings of the International Conference in Superconductivty and Magnetism ICSM2016

The VIMOS Public Extragalactic Redshift Survey (VIPERS). Star formation history of passive galaxies

Authors: M. Siudek, K. Małek, M. Scodeggio, B. Garilli, A. Pollo, C. P. Haines, A. Fritz, M. Bolzonella, S. de la Torre, B. R. Granett, L. Guzzo, U. Abbas, C. Adami, D. Bottini, A. Cappi, O. Cucciati, G. De Lucia, I. Davidzon, P. Franzetti, A. Iovino, J. Krywult, V. Le Brun, O. Le Fèvre, D. Maccagni, A. Marchetti , et al. (14 additional authors not shown)

Abstract: We trace the evolution and the star formation history of passive galaxies, using a subset of the VIMOS Public Extragalactic Redshift Survey (VIPERS). We extracted from the VIPERS survey a sample of passive galaxies in the redshift range 0.4<z<1.0 and stellar mass range 10<$log(M_{star}/M_{\odot})$<12. The sample was selected using an evolving cut in the rest-frame U-V color distribution and additi… ▽ More We trace the evolution and the star formation history of passive galaxies, using a subset of the VIMOS Public Extragalactic Redshift Survey (VIPERS). We extracted from the VIPERS survey a sample of passive galaxies in the redshift range 0.4<z<1.0 and stellar mass range 10<$log(M_{star}/M_{\odot})$<12. The sample was selected using an evolving cut in the rest-frame U-V color distribution and additional quality-ensuring cuts. We use the stacked spectra to measure the 4000$Å$ break (D4000) and the $Hδ$ Lick index ($Hδ_{A}$) with high precision. We compare the results with a grid of synthetic spectra to constrain the star formation epochs of these galaxies. We characterize the formation redshift-stellar mass relation for intermediate-redshift passive galaxies. We find that at $z\sim1$ stellar populations in low-mass passive galaxies are younger than in high-mass passive galaxies, similarly to what is observed at the present epoch. Over the full analyzed redshift and stellar mass range, the $D4000$ index increases with redshift, while $Hδ_{A}$ gets lower. This implies that the stellar populations are getting older with increasing stellar mass. Comparison to the spectra of passive galaxies in the SDSS survey shows that the shape of the relations of $D4000$, and $Hδ_{A}$ with stellar mass has not changed significantly with redshift. Assuming a single burst formation, this implies that high-mass passive galaxies formed their stars at $z_{form}\sim2$, while low-mass galaxies formed their main stellar population more recently, at $z_{form}\sim1$. The consistency of these results, obtained using two independent estimator of the formation redshift ($D4000$ and $Hδ_{A}$), further strengthens a scenario in which star formation proceeds from higher- to lower-mass systems as time passes, i.e. what has become known as the 'downsizing' picture. △ Less

Submitted 17 November, 2016; v1 submitted 18 May, 2016; originally announced May 2016.

Comments: 17 pages, 12 figures, 1 table, accepted to A&A

Journal ref: A&A 597, A107 (2017)

Spotting the diffusion of New Psychoactive Substances over the Internet

Authors: Fabio Del Vigna, Marco Avvenuti, Clara Bacciu, Paolo Deluca, Andrea Marchetti, Marinella Petrocchi, Maurizio Tesconi

Abstract: Online availability and diffusion of New Psychoactive Substances (NPS) represent an emerging threat to healthcare systems. In this work, we analyse drugs forums, online shops, and Twitter. By mining the data from these sources, it is possible to understand the dynamics of drugs diffusion and their endorsement, as well as timely detecting new substances. We propose a set of visual analytics tools t… ▽ More Online availability and diffusion of New Psychoactive Substances (NPS) represent an emerging threat to healthcare systems. In this work, we analyse drugs forums, online shops, and Twitter. By mining the data from these sources, it is possible to understand the dynamics of drugs diffusion and their endorsement, as well as timely detecting new substances. We propose a set of visual analytics tools to support analysts in tackling NPS spreading and provide a better insight about drugs market and analysis. △ Less

Submitted 11 July, 2016; v1 submitted 12 May, 2016; originally announced May 2016.

Universality in cuprates: a gauge approach

Authors: P. A. Marchetti, G. Bighin

Abstract: In high-$T_c$ cuprates many quantities exhibit a non-Fermi liquid universality hinting at a very peculiar structure of the underlying pairing mechanism for superconductivity: in this work we focus on the universality for the in-plane resistivity and for the superfluid density. We outline the previously developed spin-charge gauge approach to superconductivity in hole-doped cuprates: we decompose… ▽ More In high-$T_c$ cuprates many quantities exhibit a non-Fermi liquid universality hinting at a very peculiar structure of the underlying pairing mechanism for superconductivity: in this work we focus on the universality for the in-plane resistivity and for the superfluid density. We outline the previously developed spin-charge gauge approach to superconductivity in hole-doped cuprates: we decompose the hole of the $t-t'-J$ model for the $\mathrm{Cu}\mathrm{O}_2$ planes as the product of a spinful, chargeless gapped spinon and of a spinless, charged holon with Fermi surface. Each one of these particle excitations is bound to a statistical gauge flux, allowing one to optimize their statistics. We show that this model allows for a natural interpretation of the universality: within this approach, under suitable conditions, the spinonic and holonic contributions to a response function sum up according to a Ioffe-Larkin rule. We argue that, if the spinonic contribution dominates, then one should expect strongly non-Fermi-liquid-like universality, due to the insensitivity of spinons to Fermi surface details. The in-plane resistivity and superfluid density are indeed dominated by the spinons in the underdoped region. We theoretically derive these quantities, discussing their universal behaviours and comparing them with experimental data. △ Less

Submitted 4 May, 2016; v1 submitted 29 February, 2016; originally announced February 2016.

Comments: 16 pages, 3 figures, to be published in a Festschrift issue of Journal of Low Temperature Physics in honor of Prof. Flavio Toigo on the occasion of his 70th birthday

On the 2015 outburst of the EXor variable star V1118 Ori

Authors: T. Giannini, D. Lorenzetti, S. Antoniucci, A. A. Arkharov, V. M. Larionov, A. Di Paola, S. Bisogni, A. Marchetti

Abstract: After a long-lasting period of quiescence of about a decade, the source V1118 Ori, one of the most representative members of the EXor variables, is now outbursting. Since the initial increase of the near-infrared flux of about 1 mag (JHK bands) registered on 2015 September 22, the source brightness has remained fairly stable. We estimate DeltaV about 3 mag with respect to the quiescence phase. An… ▽ More After a long-lasting period of quiescence of about a decade, the source V1118 Ori, one of the most representative members of the EXor variables, is now outbursting. Since the initial increase of the near-infrared flux of about 1 mag (JHK bands) registered on 2015 September 22, the source brightness has remained fairly stable. We estimate DeltaV about 3 mag with respect to the quiescence phase. An optical/near-IR low-resolution spectrum has been obtained with the Large Binocular Telescope instruments MODS and LUCI2, and compared with a spectrum of similar spectral resolution and sensitivity level taken during quiescence. Together with the enhancement of the continuum, the outburst spectrum presents a definitely higher number of emission lines, in particular HI recombination lines of the Balmer, Paschen, and Brackett series, along with bright permitted lines of several species, forbidden atomic lines, and CO ro-vibrational lines. Both mass accretion and mass loss rates have significantly increased (by to about an order of magnitude, mass accretion rate = 1.2-4.8 10^-8 M_sun/yr, mass loss rate = 0.8-2 10^-9 M_sun/yr) with respect to the quiescence phase. If compared with previous outbursts, the present one appears less energetic. Alternatively, it could already be in the fading phase (with the maximum brightness level reached when the source was not visible), or, viceversa, still in the rising phase. △ Less

Submitted 19 February, 2016; v1 submitted 4 February, 2016; originally announced February 2016.

Comments: Accepted ApJ Letters

Fractional excitations in one-dimensional fermionic superfluids

Authors: Fei Ye, P. A. Marchetti

Abstract: We study the soliton modes carrying fractional quantum numbers in one-dimensional superfluids. In the $s$-wave pairing superfluid with the phase of the order parameter twisted by opposite angles $\pm \varphi/2$ at the two ends there is an emergent complex $Z_2$ soliton mode carrying fractional spin number $\varphi /(2π)$ if there is only one pairing branch. We demonstrate that in finite systems of… ▽ More We study the soliton modes carrying fractional quantum numbers in one-dimensional superfluids. In the $s$-wave pairing superfluid with the phase of the order parameter twisted by opposite angles $\pm \varphi/2$ at the two ends there is an emergent complex $Z_2$ soliton mode carrying fractional spin number $\varphi /(2π)$ if there is only one pairing branch. We demonstrate that in finite systems of length $L$, the spin density for one pairing branch in the presence of a single soliton mode consists of two terms, a localized spin density profile carrying fractional quantum number $\varphi/(2π)$, and a uniform background $-\varphi /(2πL)$. The latter one vanishes in the thermodynamic limit leaving a single soliton mode carrying fractional excitation, however it is essential to keep the total quantum number conserved in finite systems. This analysis is also applicable to other systems with fractional quantum numbers, thus provides a mechanism to understand the compatibility of the emergence of fractional charges with the integral quantization of charges in a finite system. For the $p$-wave pairing superfluid with the chemical potential interpolating between the strong and weak pairing phases, the $Z_2$ soliton is associated with a Majorana zero mode. By introducing the dimension density, we argue that the Majorana zero mode may be understood as an object with 1/2 dimension of the single particle Hilbert space. We conjecture a connection of the dimension density of one-dimensional solitons with the quantum dimension of topological excitations. △ Less

Submitted 1 December, 2017; v1 submitted 20 December, 2015; originally announced December 2015.

Comments: Adding the discussion on the majorana zero mode

Hall effect, edge states and Haldane exclusion statistics in two-dimensional space

Authors: F. Ye, P. A. Marchetti, Z. B. Su, L. Yu

Abstract: We clarify the relation between two kinds of statistics for particle excitations in planar systems: the braid statistics of anyons and the Haldane exclusion statistics(HES). It is shown non-perturbatively that the HES exists for incompressible anyon liquid in the presence of a Hall response. We also study the statistical properties of a specific quantum anomalous Hall model with Chern-Simons term… ▽ More We clarify the relation between two kinds of statistics for particle excitations in planar systems: the braid statistics of anyons and the Haldane exclusion statistics(HES). It is shown non-perturbatively that the HES exists for incompressible anyon liquid in the presence of a Hall response. We also study the statistical properties of a specific quantum anomalous Hall model with Chern-Simons term by perturbation in both compressible and incompressible regimes, where the crucial role of edge states to the HES is shown. △ Less

Submitted 6 December, 2015; originally announced December 2015.

Journal ref: Physical Review B 92, 235151 (2015)

Beliaev damping of the Goldstone mode in atomic Fermi superfluids

Authors: G. Bighin, L. Salasnich, P. A. Marchetti, F. Toigo

Abstract: Beliaev damping in a superfluid is the decay of a collective excitation into two lower frequency collective excitations; it represents the only decay mode for a bosonic collective excitation in a superfluid at T = 0. The standard treatment for this decay assumes a linear spectrum, which in turn implies that the final state momenta must be collinear to the initial state. We extend this treatment, s… ▽ More Beliaev damping in a superfluid is the decay of a collective excitation into two lower frequency collective excitations; it represents the only decay mode for a bosonic collective excitation in a superfluid at T = 0. The standard treatment for this decay assumes a linear spectrum, which in turn implies that the final state momenta must be collinear to the initial state. We extend this treatment, showing that the inclusion of a gradient term in the Hamiltonian yields a realistic spectrum for the bosonic excitations; we then derive a formula for the decay rate of such excitations, and show that even moderate nonlinearities in the spectrum can yield substantial deviations from the standard result. We apply our result to an attractive Fermi gas in the BCS-BEC crossover: here the low-energy bosonic collective excitations are density oscillations driven by the phase of the pairing order field. These collective excitations, which are gapless modes as a consequence of the Goldstone mechanism, have a spectrum which is well established both theoretically and experimentally, and whose linewidth, we show, is determined at low temperatures by the Beliaev decay mechanism. △ Less

Submitted 30 July, 2015; originally announced July 2015.

Comments: 8 pages, 3 figures

Journal ref: Phys. Rev. A 92, 023638 (2015)

The VIMOS Public Extragalactic Redshift Survey (VIPERS): Reconstruction of the redshift-space galaxy density field

Authors: B. R. Granett, E. Branchini, L. Guzzo, U. Abbas, C. Adami, S. Arnouts, J. Bel, M. Bolzonella, D. Bottini, A. Cappi, J. Coupon, O. Cucciati, I. Davidzon, G. De Lucia, S. de la Torre, A. Fritz, P. Franzetti, M. Fumana, B. Garilli, O. Ilbert, A. Iovino, J. Krywult, V. Le Brun, O. Le Fèvre, D. Maccagni , et al. (21 additional authors not shown)

Abstract: Aims. Using the VIMOS Public Extragalactic Redshift Survey (VIPERS) we aim to jointly estimate the key parameters that describe the galaxy density field and its spatial correlations in redshift space. Methods. We use the Bayesian formalism to jointly reconstruct the redshift-space galaxy density field, power spectrum, galaxy bias and galaxy luminosity function given the observations and survey sel… ▽ More Aims. Using the VIMOS Public Extragalactic Redshift Survey (VIPERS) we aim to jointly estimate the key parameters that describe the galaxy density field and its spatial correlations in redshift space. Methods. We use the Bayesian formalism to jointly reconstruct the redshift-space galaxy density field, power spectrum, galaxy bias and galaxy luminosity function given the observations and survey selection function. The high-dimensional posterior distribution is explored using the Wiener filter within a Gibbs sampler. We validate the analysis using simulated catalogues and apply it to VIPERS data taking into consideration the inhomogeneous selection function. Results. We present joint constraints on the anisotropic power spectrum as well as the bias and number density of red and blue galaxy classes in luminosity and redshift bins as well as the measurement covariances of these quantities. We find that the inferred galaxy bias and number density parameters are strongly correlated although these are only weakly correlated with the galaxy power spectrum. The power spectrum and redshift-space distortion parameters are in agreement with previous VIPERS results with the value of the growth rate $fσ_8 = 0.38$ with 18% uncertainty at redshift 0.7. △ Less

Submitted 23 May, 2015; originally announced May 2015.

Comments: Submitted to Astronomy & Astrophysics

Journal ref: A&A 583, A61 (2015)

A high-dimensional look at VIPERS galaxies

Authors: B. R. Granett, U. Abbas, C. Adami, S. Arnouts, J. Bel, M. Bolzonella, D. Bottini, E. Branchini, A. Burden, A. Cappi, J. Coupon, O. Cucciati, I. Davidzon, G. De Lucia, S. de la Torre, C. Di Porto, P. Franzetti, A. Fritz, M. Fumana, B. Garilli, L. Guzzo, P. Hudelot, O. Ilbert, A. Iovino, J. Krywult , et al. (22 additional authors not shown)

Abstract: We investigate how galaxies in VIPERS (the VIMOS Public Extragalactic Redshift Survey) inhabit the cosmological density field by examining the correlations across the observable parameter space of galaxy properties and clustering strength. The high-dimensional analysis is made manageable by the use of group-finding and regression tools. We find that the major trends in galaxy properties can be exp… ▽ More We investigate how galaxies in VIPERS (the VIMOS Public Extragalactic Redshift Survey) inhabit the cosmological density field by examining the correlations across the observable parameter space of galaxy properties and clustering strength. The high-dimensional analysis is made manageable by the use of group-finding and regression tools. We find that the major trends in galaxy properties can be explained by a single parameter related to stellar mass. After subtracting this trend, residual correlations remain between galaxy properties and the local environment pointing to complex formation dependencies. As a specific application of this work we build subsamples of galaxies with specific clustering properties for use in cosmological tests. △ Less

Submitted 23 May, 2015; originally announced May 2015.

Comments: 3 pages. To appear in Statistical Challenges in 21st Century Cosmology, Proceedings IAU Symposium No. 306, A. H. Heavens & J.-L. Starck, eds

The VIMOS Public Extragalactic Redshift Survey (VIPERS). Hierarchical scaling and biasing

Authors: A. Cappi, F. Marulli, J. Bel, O. Cucciati, E. Branchini, S. de la Torre, L. Moscardini, M. Bolzonella, L. Guzzo, U. Abbas, C. Adami, S. Arnouts, D. Bottini, J. Coupon, I. Davidzon, G. De Lucia, A. Fritz, P. Franzetti, M. Fumana, B. Garilli, B. R. Granett, O. Ilbert, A. Iovino, J. Krywult, V. Le Brun , et al. (25 additional authors not shown)

Abstract: We investigate the higher-order correlation properties of the VIMOS Public Extragalactic Redshift Survey (VIPERS) to test the hierarchical scaling hypothesis at z~1 and the dependence on galaxy luminosity, stellar mass, and redshift. We also aim to assess deviations from the linearity of galaxy bias independently from a previously performed analysis of our survey (Di Porto et al. 2014). We have me… ▽ More We investigate the higher-order correlation properties of the VIMOS Public Extragalactic Redshift Survey (VIPERS) to test the hierarchical scaling hypothesis at z~1 and the dependence on galaxy luminosity, stellar mass, and redshift. We also aim to assess deviations from the linearity of galaxy bias independently from a previously performed analysis of our survey (Di Porto et al. 2014). We have measured the count probability distribution function in cells of radii 3 < R < 10 Mpc/h, deriving $σ_{8g}$, the volume-averaged two-,three-,and four-point correlation functions and the normalized skewness $S_{3g}$ and kurtosis $S_{4g}$ for volume-limited subsamples covering the ranges $-19.5 \le M_B(z=1.1)-5log(h) \le -21.0$, $9.0 < log(M*/M_{\odot} h^{-2}) \le 11.0$, $0.5 \le z < 1.1$. We have thus performed the first measurement of high-order correlations at z~1 in a spectroscopic redshift survey. Our main results are the following. 1) The hierarchical scaling holds throughout the whole range of scale and z. 2) We do not find a significant dependence of $S_{3g}$ on luminosity (below z=0.9 $S_{3g}$ decreases with luminosity but only at 1σ-level). 3) We do not detect a significant dependence of $S_{3g}$ and $S_{4g}$ on scale, except beyond z~0.9, where the dependence can be explained as a consequence of sample variance. 4) We do not detect an evolution of $S_{3g}$ and $S_{4g}$ with z. 5) The linear bias factor $b=σ_{8g}/σ_{8m}$ increases with z, in agreement with previous results. 6) We quantify deviations from the linear bias by means of the Taylor expansion parameter $b_2$. Our results are compatible with a null non-linear bias term, but taking into account other available data we argue that there is evidence for a small non-linear bias term. △ Less

Submitted 20 May, 2015; originally announced May 2015.

Comments: 20 pages, 14 figures, accepted for publication in Astronomy and Astrophysics

Journal ref: A&A 579, A70 (2015)

The VIMOS Public Extragalactic Redshift Survey (VIPERS): On the correct recovery of the count-in-cell probability distribution function

Authors: J. Bel, E. Branchini, C. Di Porto, O. Cucciati, B. R. Granett, A. Iovino, S. de la Torre, C. Marinoni, L. Guzzo, L. Moscardini, A. Cappi, U. Abbas, C. Adami, S. Arnouts, M. Bolzonella, D. Bottini, J. Coupon, I. Davidzon, G. De Lucia, A. Fritz, P. Franzetti, M. Fumana, B. Garilli, O. Ilbert, J. Krywult , et al. (23 additional authors not shown)

Abstract: We compare three methods to measure the count-in-cell probability density function of galaxies in a spectroscopic redshift survey. From this comparison we found that when the sampling is low (the average number of object per cell is around unity) it is necessary to use a parametric method to model the galaxy distribution. We used a set of mock catalogues of VIPERS, in order to verify if we were ab… ▽ More We compare three methods to measure the count-in-cell probability density function of galaxies in a spectroscopic redshift survey. From this comparison we found that when the sampling is low (the average number of object per cell is around unity) it is necessary to use a parametric method to model the galaxy distribution. We used a set of mock catalogues of VIPERS, in order to verify if we were able to reconstruct the cell-count probability distribution once the observational strategy is applied. We find that in the simulated catalogues, the probability distribution of galaxies is better represented by a Gamma expansion than a Skewed Log-Normal. Finally, we correct the cell-count probability distribution function from the angular selection effect of the VIMOS instrument and study the redshift and absolute magnitude dependency of the underlying galaxy density function in VIPERS from redshift $0.5$ to $1.1$. We found very weak evolution of the probability density distribution function and that it is well approximated, independently from the chosen tracers, by a Gamma distribution. △ Less

Submitted 3 May, 2015; originally announced May 2015.

Comments: 14 pages, 11 figures, 2 tables

HII regions within a compact high velocity cloud. A nearly star-less dwarf galaxy?

Authors: M. Bellazzini, L. Magrini, A. Mucciarelli, G. Beccari, R. Ibata, G. Battaglia, N. Martin, V. Testa, M. Fumana, A. Marchetti, M. Correnti, F. Fraternali

Abstract: Within the SECCO survey we identified a candidate stellar counterpart to the Ultra Compact High Velocity Cloud (UCHVC) HVC274.68+74.70-123, that was suggested by Adams et al. (2013) as a possible mini-halo within the Local Group of galaxies. The spectroscopic follow-up of the brightest sources within the candidate reveals the presence of two HII regions whose radial velocity is compatible with phy… ▽ More Within the SECCO survey we identified a candidate stellar counterpart to the Ultra Compact High Velocity Cloud (UCHVC) HVC274.68+74.70-123, that was suggested by Adams et al. (2013) as a possible mini-halo within the Local Group of galaxies. The spectroscopic follow-up of the brightest sources within the candidate reveals the presence of two HII regions whose radial velocity is compatible with physical association with the UVHVC. The available data does not allow us to give a definite answer on the nature of the newly identified system. A few alternative hypotheses are discussed. However, the most likely possibility is that we have found a new faint dwarf galaxy residing in the Virgo cluster of galaxies, which we name SECCO-1. Independently of its actual distance, SECCO-1 displays a ratio of neutral hydrogen mass to V luminosity of M_{HI}/L_V>= 20, by far the largest among local dwarfs. Hence, it appears as a nearly star-less galaxy and it may be an example of the missing links between normal dwarfs and the dark mini halos that are predicted to exist in large numbers according to the currently accepted cosmological model. △ Less

Submitted 26 January, 2015; originally announced January 2015.

Comments: Accepted for publication in ApJ Letters. Pdflatex, emulateapj.cls. 6 pages, 3 figures, 2 tables

Gauge approach to superfluid density in underdoped cuprates

Authors: P. A. Marchetti, G. Bighin

Abstract: We prove that a gauge approach based on a composite structure of the hole in hole-doped cuprates is able to capture analytically many features of the experimental data on superfluid density in the moderate-underdoping to nearly-optimal doping region, including critical exponent, the Uemura relation and near universality of the normalized superfluid density. We prove that a gauge approach based on a composite structure of the hole in hole-doped cuprates is able to capture analytically many features of the experimental data on superfluid density in the moderate-underdoping to nearly-optimal doping region, including critical exponent, the Uemura relation and near universality of the normalized superfluid density. △ Less

Submitted 11 May, 2015; v1 submitted 14 January, 2015; originally announced January 2015.

Comments: 13 pages, 2 figures, accepted for publication in EPL

Journal ref: Europhys. Lett. 110, 37001 (2015)

Spectroscopy of the Type Ia supernova 2011fe past 1000 days

Authors: S. Taubenberger, N. Elias-Rosa, W. E. Kerzendorf, S. Hachinger, J. Spyromilio, C. Fransson, M. Kromer, A. J. Ruiter, I. R. Seitenzahl, S. Benetti, E. Cappellaro, A. Pastorello, M. Turatto, A. Marchetti

Abstract: In this letter we present an optical spectrum of SN 2011fe taken 1034 d after the explosion, several hundred days later than any other spectrum of a Type Ia supernova (disregarding light-echo spectra and local-group remnants). The spectrum is still dominated by broad emission features, with no trace of a light echo or interaction of the supernova ejecta with surrounding interstellar material. Comp… ▽ More In this letter we present an optical spectrum of SN 2011fe taken 1034 d after the explosion, several hundred days later than any other spectrum of a Type Ia supernova (disregarding light-echo spectra and local-group remnants). The spectrum is still dominated by broad emission features, with no trace of a light echo or interaction of the supernova ejecta with surrounding interstellar material. Comparing this extremely late spectrum to an earlier one taken 331 d after the explosion, we find that the most prominent feature at 331 d - [Fe III] emission around 4700 A - has entirely faded away, suggesting a significant change in the ionisation state. Instead, [Fe II] lines are probably responsible for most of the emission at 1034 d. An emission feature at 6300-6400 A has newly developed at 1034 d, which we tentatively identify with Fe I λ6359, [Fe I] λλ6231, 6394 or [O I] λλ6300, 6364. Interestingly, the features in the 1034-d spectrum seem to be collectively redshifted, a phenomenon that we currently have no convincing explanation for. We discuss the implications of our findings for explosion models, but conclude that sophisticated spectral modelling is required for any firm statement. △ Less

Submitted 15 December, 2014; v1 submitted 27 November, 2014; originally announced November 2014.

Comments: 6 pages, 3 figures, MNRAS Letters accepted

Interplay of superconductivity and magnetism in a t-t'-J approach to high Tc cuprates

Authors: P. A. Marchetti

Abstract: We review a recently proposed mechanism for superconductivity in hole-doped cuprates exhibiting a strong interplay between pairing and antiferromagnetism. Starting from the t-t'-J model for the CuO planes, we show that this interplay can explain in a unified framework the pseudogap phenomenology of the spectral weight of the hole, the hourglass-like structure of the magnetic excitation, the critic… ▽ More We review a recently proposed mechanism for superconductivity in hole-doped cuprates exhibiting a strong interplay between pairing and antiferromagnetism. Starting from the t-t'-J model for the CuO planes, we show that this interplay can explain in a unified framework the pseudogap phenomenology of the spectral weight of the hole, the hourglass-like structure of the magnetic excitation, the critical exponent of the superfluid density, the relation between the scale of the magnetic resonance and Tc. △ Less

Submitted 7 November, 2014; originally announced November 2014.

Comments: 2 figures, talk given at the International Conference in Superconductivty and Magnetism ICSM2014-Antalya

The VIMOS Public Extragalactic Survey (VIPERS): First Release of spectra

Authors: P. Franzetti, B. Garilli, L. Guzzo, A. Marchetti, M. Scodeggio

Abstract: We release the spectra for the more than 57000 objects presented in the First VIPERS Data Release. For each object we distribute the observed, wavelength and flux calibrated spectrum, as well as cleaned spectra, where artifacts due to fringing are removed. We also provide the sky and noise spectrum and the 2D spectrum. Data can be downloaded from http://vipers.inaf.it. We release the spectra for the more than 57000 objects presented in the First VIPERS Data Release. For each object we distribute the observed, wavelength and flux calibrated spectrum, as well as cleaned spectra, where artifacts due to fringing are removed. We also provide the sky and noise spectrum and the 2D spectrum. Data can be downloaded from http://vipers.inaf.it. △ Less

Submitted 2 October, 2014; originally announced October 2014.

The VIMOS Public Extragalactic Redshift Survey - Searching for Cosmic Voids

Authors: D. Micheletti, A. Iovino, A. J. Hawken, B. R. Granett, M. Bolzonella, A. Cappi, L. Guzzo, U. Abbas, C. Adami, S. Arnouts, J. Bel, D. Bottini, E. Branchini, J. Coupon, O. Cucciati, I. Davidzon, G. De Lucia, S. de la Torre, A. Fritz, P. Franzetti, M. Fumana, B. Garilli, O. Ilbert, J. Krywult, V. Le Brun , et al. (24 additional authors not shown)

Abstract: The characterisation of cosmic voids gives unique information about the large-scale distribution of galaxies, their evolution and the cosmological model. We identify and characterise cosmic voids in the VIMOS Public Extragalactic Redshift Survey (VIPERS) at redshift 0.55 < z < 0.9. A new void search method is developed based upon the identification of empty spheres that fit between galaxies. The m… ▽ More The characterisation of cosmic voids gives unique information about the large-scale distribution of galaxies, their evolution and the cosmological model. We identify and characterise cosmic voids in the VIMOS Public Extragalactic Redshift Survey (VIPERS) at redshift 0.55 < z < 0.9. A new void search method is developed based upon the identification of empty spheres that fit between galaxies. The method can be used to characterise the cosmic voids despite the presence of complex survey boundaries and internal gaps. We investigate the impact of systematic observational effects and validate the method against mock catalogues. We measure the void size distribution and the void-galaxy correlation function. We construct a catalogue of voids in VIPERS. The distribution of voids is found to agree well with the distribution of voids found in mock catalogues. The void-galaxy correlation function shows indications of outflow velocity from the voids. △ Less

Submitted 12 September, 2014; v1 submitted 10 July, 2014; originally announced July 2014.

Journal ref: A&A 570, A106 (2014)

The VIMOS Public Extragalactic Redshift Survey (VIPERS). Measuring nonlinear galaxy bias at z~0.8

Authors: C. Di Porto, E. Branchini, J. Bel, F. Marulli, M. Bolzonella, O. Cucciati, S. de la Torre, B. R. Granett, L. Guzzo, C. Marinoni, L. Moscardini, U. Abbas, C. Adami, S. Arnouts, D. Bottini, A. Cappi, J. Coupon, I. Davidzon, G. De Lucia, A. Fritz, P. Franzetti, M. Fumana, B. Garilli, O. Ilbert, A. Iovino , et al. (24 additional authors not shown)

Abstract: We use the first release of the VImos Public Extragalactic Redshift Survey of galaxies (VIPERS) of ~50,000 objects to measure the biasing relation between galaxies and mass in the redshift range z=[0.5,1.1]. We estimate the 1-point distribution function [PDF] of VIPERS galaxies from counts in cells and, assuming a model for the mass PDF, we infer their mean bias relation. The reconstruction of the… ▽ More We use the first release of the VImos Public Extragalactic Redshift Survey of galaxies (VIPERS) of ~50,000 objects to measure the biasing relation between galaxies and mass in the redshift range z=[0.5,1.1]. We estimate the 1-point distribution function [PDF] of VIPERS galaxies from counts in cells and, assuming a model for the mass PDF, we infer their mean bias relation. The reconstruction of the bias relation from PDFs is performed through a novel method that accounts for Poisson noise, redshift distortions, inhomogeneous sky coverage and other selection effects. With this procedure we constrain galaxy bias and its deviations from linearity down to scales as small as 4 Mpc/h and out to z=1.1. We detect small (~3%) but significant deviations from linear bias. The mean biasing function is close to linear in regions above the mean density. The mean slope of the biasing relation is a proxy to the linear bias parameter. It increases both with luminosity, in agreement with results of previous analyses, and with redshift. However, we detect a strong bias evolution only for z>0.9 in agreement with some, but not all, previous studies. We also detected a significant increase of the bias with the scale, from 4 to 8 Mpc/h, now seen for the first time out to z=1. The amplitude of nonlinearity depends on redshift, luminosity and on scales but no clear trend is detected. Thanks to the large cosmic volume probed by VIPERS we find that the mismatch between the previous estimates of bias at z~1 from zCOSMOS and VVDS-Deep galaxy samples is fully accounted for by cosmic variance. The results of our work confirm the importance of going beyond the over-simplistic linear bias hypothesis showing that non-linearities can be accurately measured through the applications of the appropriate statistical tools to existing datasets like VIPERS. △ Less

Submitted 7 July, 2016; v1 submitted 25 June, 2014; originally announced June 2014.

Comments: 20 pages, 15 figures

Journal ref: A&A 594, A62 (2016)

The VIMOS Public Extragalactic Redshift Survey (VIPERS): A quiescent formation of massive red-sequence galaxies over the past 9 Gyr

Authors: A. Fritz, M. Scodeggio, O. Ilbert, M. Bolzonella, I. Davidzon, J. Coupon, B. Garilli, L. Guzzo, G. Zamorani, U. Abbas, C. Adami, S. Arnouts, J. Bel, D. Bottini, E. Branchini, A. Cappi, O. Cucciati, G. De Lucia, S. de la Torre, P. Franzetti, M. Fumana, B. R. Granett, A. Iovino, J. Krywult, V. Le Brun , et al. (24 additional authors not shown)

Abstract: We explore the evolution of the Colour-Magnitude Relation (CMR) and Luminosity Function (LF) at 0.4<z<1.3 from the VIMOS Public Extragalactic Redshift Survey (VIPERS) using ~45,000 galaxies with precise spectroscopic redshifts down to i'_AB<22.5 over ~10.32 deg^2 in two fields. From z=0.5 to z=1.3 the LF and CMR are well defined for different galaxy populations and M^*_B evolves by ~1.04(1.09)+/-0… ▽ More We explore the evolution of the Colour-Magnitude Relation (CMR) and Luminosity Function (LF) at 0.4<z<1.3 from the VIMOS Public Extragalactic Redshift Survey (VIPERS) using ~45,000 galaxies with precise spectroscopic redshifts down to i'_AB<22.5 over ~10.32 deg^2 in two fields. From z=0.5 to z=1.3 the LF and CMR are well defined for different galaxy populations and M^*_B evolves by ~1.04(1.09)+/-0.06(0.10) mag for the total (red) galaxy sample. We compare different criteria for selecting early-type galaxies (ETGs): (1) fixed cut in rest-frame (U-V) colours, (2) evolving cut in (U-V) colours, (3) rest-frame (NUV-r')-(r'-K) colour selection, and (4) SED classification. Regardless of the method we measure a consistent evolution of the red-sequence (RS). Between 0.4<z<1.3 we find a moderate evolution of the RS intercept of Delta(U-V)=0.28+/-0.14 mag, favouring exponentially declining star formation (SF) histories with SF truncation at 1.7<=z<=2.3. Together with the rise in the ETG number density by 0.64 dex since z=1, this suggests a rapid build-up of massive galaxies (M>10^11 M_sun) and expeditious RS formation over a short period of ~1.5 Gyr starting before z=1. This is supported by the detection of ongoing SF in ETGs at 0.9<z<1.0, in contrast with the quiescent red stellar populations of ETGs at 0.5<z<0.6. There is an increase in the observed CMR scatter with redshift, two times larger than in galaxy clusters and at variance with theoretical models. We discuss possible physical mechanisms that support the observed evolution of the red galaxy population. Our findings point out that massive galaxies have experienced a sharp SF quenching at z~1 with only limited additional merging. In contrast, less-massive galaxies experience a mix of SF truncation and minor mergers which build-up the low- and intermediate-mass end of the CMR. △ Less

Submitted 23 January, 2014; originally announced January 2014.

Comments: 27 pages, 21 figures, accepted for publication in A&A

The VIMOS Public Extragalactic Redshift Survey (VIPERS): $Ω_{\rm m_0}$ from the galaxy clustering ratio measured at $z \sim 1$

Authors: J. Bel, C. Marinoni, B. R. Granett, L. Guzzo, J. A. Peacock, E. Branchini, O. Cucciati, S. de la Torre, A. Iovino, W. J. Percival, H. Steigerwald, U. Abbas, C. Adami, S. Arnouts, M. Bolzonella, D. Bottini, A. Cappi, J. Coupon, I. Davidzon, G. De Lucia, A. Fritz, P. Franzetti, M. Fumana, B. Garilli, O. Ilbert , et al. (25 additional authors not shown)

Abstract: We use a sample of about 22,000 galaxies at $0.65<z<1.2$ from the VIPERS PDR-1 catalogue, to constrain the cosmological model through a measurement of the galaxy {\it clustering ratio} $η_{g,R}$. This statistic has favourable properties, being defined as the ratio of two quantities characterizing the smoothed density field in spheres of given radius $R$: the value of its correlation function on a… ▽ More We use a sample of about 22,000 galaxies at $0.65<z<1.2$ from the VIPERS PDR-1 catalogue, to constrain the cosmological model through a measurement of the galaxy {\it clustering ratio} $η_{g,R}$. This statistic has favourable properties, being defined as the ratio of two quantities characterizing the smoothed density field in spheres of given radius $R$: the value of its correlation function on a multiple of this scale, $ξ(nR)$, and its variance $σ^2(R)$. For sufficiently large values of $R$, this is a universal number, capturing 2-point clustering information independently of the linear bias and linear redshift-space distortions of the specific galaxy tracers. In this paper we discuss in detail how to extend the application of $η_{g,R}$ to quasi-linear scales and how to control and remove observational selection effects which are typical of redshift surveys as VIPERS. We verify the accuracy and efficiency of these procedures using mock catalogues that match the survey selection process. These results evidence the robustness of $η_{g,R}$ to non-linearities and observational effects, which is related to its very definition as a ratio of quantities that are similarly affected. We measure $Ω_{m,0}=0.270_{-0.025}^{+0.029}$. In addition to the great precision achieved on our estimation of $Ω_m$ using VIPERS PDR-1, this result is remarkable because it appears to be in good agreement with a recent estimate $z\simeq 0.3$, obtained applying the same technique to the SDSS-LRG catalogue. It, therefore, suports the robustness of the present analysis. Moreover, the combination of these two measurements at $z\sim 0.3$ and $z\sim 0.9$ provides us with a very precise estimate $Ω_{m,0}=0.274\pm0.017$ which highlights the great consistency between our estimation and other cosmological probes such as BAOs, CMB and Supernovae. △ Less

Submitted 12 December, 2013; v1 submitted 12 October, 2013; originally announced October 2013.

Comments: 18 pages, 17 figures, accepted for publication in A&A, references added

The VIMOS Public Extragalactic Survey (VIPERS): First Data Release of 57 204 spectroscopic measurements

Authors: B. Garilli, L. Guzzo, M. Scodeggio, M. Bolzonella, U. Abbas, C. Adami, S. Arnouts, J. Bel, D. Bottini, E. Branchini, A. Cappi, J. Coupon, O. Cucciati, I. Davidzon, G. De Lucia, S. de la Torre, P. Franzetti, A. Fritz, M. Fumana, B. R. Granett, O. Ilbert, A. Iovino, J. Krywult, V. Le Brun, O. Le Fèvre , et al. (24 additional authors not shown)

Abstract: We present the first Public Data Release (PDR-1) of the VIMOS Public Extragalactic Survey (VIPERS). It comprises 57 204 spectroscopic measurements together with all additional information necessary for optimal scientific exploitation of the data, in particular the associated photometric measurements and quantification of the photometric and survey completeness. VIPERS is an ESO Large Programme des… ▽ More We present the first Public Data Release (PDR-1) of the VIMOS Public Extragalactic Survey (VIPERS). It comprises 57 204 spectroscopic measurements together with all additional information necessary for optimal scientific exploitation of the data, in particular the associated photometric measurements and quantification of the photometric and survey completeness. VIPERS is an ESO Large Programme designed to build a spectroscopic sample of ' 100 000 galaxies with iAB < 22.5 and 0.5 < z < 1.5 with high sampling rate (~45%). The survey spectroscopic targets are selected from the CFHTLS-Wide five-band catalogues in the W1 and W4 fields. The final survey will cover a total area of nearly 24 deg2, for a total comoving volume between z = 0.5 and 1.2 of ~4x10^7 h^(-3)Mpc^3 and a median galaxy redshift of z~0.8. The release presented in this paper includes data from virtually the entire W4 field and nearly half of the W1 area, thus representing 64% of the final dataset. We provide a detailed description of sample selection, observations and data reduction procedures; we summarise the global properties of the spectroscopic catalogue and explain the associated data products and their use, and provide all the details for accessing the data through the survey database (http://vipers.inaf.it) where all information can be queried interactively. △ Less

Submitted 10 December, 2013; v1 submitted 3 October, 2013; originally announced October 2013.

Comments: Accepted for publication in A&A Added and/or replaced some figure, added section on DataBase interface, expaned Introduction

Superfluidity, Sound Velocity and Quasi Condensation in the 2D BCS-BEC Crossover

Authors: L. Salasnich, P. A. Marchetti, F. Toigo

Abstract: We study finite-temperature properties of a two-dimensional superfluid made of ultracold alkali-metal atoms in the BCS-BEC crossover. We investigate the region below the critical temperature $T_{BKT}$ of the Berezinskii-Kosterlitz-Thouless phase transition, where there is quasi-condensation, by analyzing the effects of phase and amplitude fluctuations of the order parameter. In particular, we calc… ▽ More We study finite-temperature properties of a two-dimensional superfluid made of ultracold alkali-metal atoms in the BCS-BEC crossover. We investigate the region below the critical temperature $T_{BKT}$ of the Berezinskii-Kosterlitz-Thouless phase transition, where there is quasi-condensation, by analyzing the effects of phase and amplitude fluctuations of the order parameter. In particular, we calculate the superfluid fraction, the sound velocity and the quasi-condensate fraction as a function of the temperature and of the binding energy of fermionic pairs. △ Less

Submitted 3 November, 2013; v1 submitted 28 September, 2013; originally announced September 2013.

Comments: 7 pages, 4 figures, improved version to be published in Phys. Rev. A

Journal ref: Phys. Rev. A 88, 053612 (2013)

VIPERS: An Unprecedented View of Galaxies and Large-Scale Structure Halfway Back in the Life of the Universe

Authors: L. Guzzo, U. Abbas, C. Adami, S. Arnouts, J. Bel, M. Bolzonella, D. Bottini, E. Branchini, A. Burden, A. Cappi, J. Coupon, O. Cucciati, I. Davidzon, S. de la Torre, G. De Lucia, C. Di Porto, P. Franzetti, A. Fritz, M. Fumana, B. Garilli, B. R. Granett, L. Guennou, O. Ilbert, A. Iovino, J. Krywult , et al. (26 additional authors not shown)

Abstract: The VIMOS Public Extragalactic Redshift Survey (VIPERS) is an ongoing ESO Large Programme to map in detail the large-scale distribution of galaxies at 0.5 < z <1.2. With a combination of volume and sampling density that is unique for these redshifts, it focuses on measuring galaxy clustering and related cosmological quantities as part of the grand challenge of understanding the origin of cosmic ac… ▽ More The VIMOS Public Extragalactic Redshift Survey (VIPERS) is an ongoing ESO Large Programme to map in detail the large-scale distribution of galaxies at 0.5 < z <1.2. With a combination of volume and sampling density that is unique for these redshifts, it focuses on measuring galaxy clustering and related cosmological quantities as part of the grand challenge of understanding the origin of cosmic acceleration. VIPERS has also been designed to guarantee a broader legacy, allowing detailed investigations of the properties and evolutionary trends of z~1 galaxies. The survey strategy exploits the specific advantages of the VIMOS spectrograph at the VLT, aiming at a final sample of nearly 100,000 galaxy redshifts to iAB = 22.5 mag, which represents the largest redshift survey ever performed with ESO telescopes. In this introductory article we describe the survey construction, together with early results based on a first sample of ~55,000 galaxies. △ Less

Submitted 15 March, 2013; originally announced March 2013.

Comments: 6 pages, 8 figures; introductory paper

Journal ref: The ESO Messenger, 2013, 151, 41

The VIMOS Public Extragalactic Redshift Survey (VIPERS). A precise measurement of the galaxy stellar mass function and the abundance of massive galaxies at redshifts 0.5<z<1.3

Authors: I. Davidzon, M. Bolzonella, J. Coupon, O. Ilbert, S. Arnouts, S. de la Torre, A. Fritz, G. De Lucia, A. Iovino, B. R. Granett, G. Zamorani, L. Guzzo, U. Abbas, C. Adami, J. Bel, D. Bottini, E. Branchini, A. Cappi, O. Cucciati, P. Franzetti, M. Fumana, B. Garilli, J. Krywult, V. Le Brun, O. Le Fevre , et al. (25 additional authors not shown)

Abstract: We measure the evolution of the galaxy stellar mass function from z=1.3 to z=0.5 using the first 53,608 redshifts of the ongoing VIMOS Public Extragalactic Survey (VIPERS). We estimate the galaxy stellar mass function at several epochs discussing in detail the amount of cosmic variance affecting our estimate. We find that Poisson noise and cosmic variance of the galaxy mass function in the VIPERS… ▽ More We measure the evolution of the galaxy stellar mass function from z=1.3 to z=0.5 using the first 53,608 redshifts of the ongoing VIMOS Public Extragalactic Survey (VIPERS). We estimate the galaxy stellar mass function at several epochs discussing in detail the amount of cosmic variance affecting our estimate. We find that Poisson noise and cosmic variance of the galaxy mass function in the VIPERS survey are comparable with the statistical uncertainties of large surveys in the local universe. VIPERS data allow us to determine with unprecedented accuracy the high-mass tail of the galaxy stellar mass function, which includes a significant number of galaxies that are usually too rare to detect with any of the past spectroscopic surveys. At the epochs sampled by VIPERS, massive galaxies had already assembled most of their stellar mass. We apply a photometric classification in the (U-V) rest-frame colour to compute the mass function of blue and red galaxies, finding evidence for the evolution of their contribution to the total number density budget: the transition mass above which red galaxies dominate is found to be about 10^10.4 M_sun at z=0.55 and evolves proportionally to (1+z)^3. We are able to trace separately the evolution of the number density of blue and red galaxies with masses above 10^11.4 M_sun, in a mass range barely studied in previous work. We find that for such large masses, red galaxies show a milder evolution with redshift, when compared to objects at lower masses. At the same time, we detect a population of similarly massive blue galaxies, which are no longer detectable below z=0.7. These results show the improved statistical power of VIPERS data, and give initial promising indications of mass-dependent quenching of galaxies at z~1. [Abridged] △ Less

Submitted 2 September, 2013; v1 submitted 15 March, 2013; originally announced March 2013.

Comments: 19 pages, 14 figures, 2 tables. A&A in press (accepted for publication on July 12th)

The VIMOS Public Extragalactic Redshift Survey (VIPERS). Luminosity and stellar mass dependence of galaxy clustering at 0.5<z<1.1

Authors: F. Marulli, M. Bolzonella, E. Branchini, I. Davidzon, S. de la Torre, B. R. Granett, L. Guzzo, A. Iovino, L. Moscardini, A. Pollo, U. Abbas, C. Adami, S. Arnouts, J. Bel, D. Bottini, A. Cappi, J. Coupon, O. Cucciati, G. De Lucia, A. Fritz, P. Franzetti, M. Fumana, B. Garilli, O. Ilbert, J. Krywult , et al. (24 additional authors not shown)

Abstract: We investigate the dependence of galaxy clustering on luminosity and stellar mass in the redshift range 0.5<z<1.1, using the first ~55000 redshifts from the VIMOS Public Extragalactic Redshift Survey (VIPERS). We measured the redshift-space two-point correlation functions (2PCF), and the projected correlation function, in samples covering different ranges of B-band absolute magnitudes and stellar… ▽ More We investigate the dependence of galaxy clustering on luminosity and stellar mass in the redshift range 0.5<z<1.1, using the first ~55000 redshifts from the VIMOS Public Extragalactic Redshift Survey (VIPERS). We measured the redshift-space two-point correlation functions (2PCF), and the projected correlation function, in samples covering different ranges of B-band absolute magnitudes and stellar masses. We considered both threshold and binned galaxy samples, with median B-band absolute magnitudes -21.6<MB-5log(h)<-19.5 and median stellar masses 9.8<log(M*[Msun/h^2])<10.7. We assessed the real-space clustering in the data from the projected correlation function, which we model as a power law in the range 0.2<r_p[Mpc/h]<20. Finally, we estimated the galaxy bias as a function of luminosity, stellar mass, and redshift, assuming a flat LCDM model to derive the dark matter 2PCF. We provide the best-fit parameters of the power-law model assumed for the real-space 2PCF -- the correlation length and the slope -- as well as the linear bias parameter, as a function of the B-band absolute magnitude, stellar mass, and redshift. We confirm and provide the tightest constraints on the dependence of clustering on luminosity at 0.5<z<1.1. We prove the complexity of comparing the clustering dependence on stellar mass from samples that are originally flux-limited and discuss the possible origin of the observed discrepancies. Overall, our measurements provide stronger constraints on galaxy formation models, which are now required to match, in addition to local observations, the clustering evolution measured by VIPERS galaxies between z=0.5 and z=1.1 for a broad range of luminosities and stellar masses. △ Less

Submitted 20 July, 2013; v1 submitted 11 March, 2013; originally announced March 2013.

Comments: 17 pages, 10 figures, 4 tables. Accepted for publication in A&A

The VIMOS Public Extragalactic Redshift Survey (VIPERS). An unprecedented view of galaxies and large-scale structure at 0.5<z<1.2

Authors: L. Guzzo, M. Scodeggio, B. Garilli, B. R. Granett, U. Abbas, C. Adami, S. Arnouts, J. Bel, M. Bolzonella, D. Bottini, E. Branchini, A. Cappi, J. Coupon, O. Cucciati, I. Davidzon, G. De Lucia, S. de la Torre, A. Fritz, P. Franzetti, M. Fumana, P. Hudelot, O. Ilbert, A. Iovino, J. Krywult, V. Le Brun , et al. (25 additional authors not shown)

Abstract: We describe the construction and general features of VIPERS, the VIMOS Public Extragalactic Redshift Survey. This `Large Programme' has been using the ESO VLT with the aim of building a spectroscopic sample of ~100,000 galaxies with i_{AB}<22.5 and 0.5<z<1.5. The survey covers a total area of ~24 deg^2 within the CFHTLS-Wide W1 and W4 fields. VIPERS is designed to address a broad range of problems… ▽ More We describe the construction and general features of VIPERS, the VIMOS Public Extragalactic Redshift Survey. This `Large Programme' has been using the ESO VLT with the aim of building a spectroscopic sample of ~100,000 galaxies with i_{AB}<22.5 and 0.5<z<1.5. The survey covers a total area of ~24 deg^2 within the CFHTLS-Wide W1 and W4 fields. VIPERS is designed to address a broad range of problems in large-scale structure and galaxy evolution, thanks to a unique combination of volume (~ 5 x 10^7 h^{-3} Mpc^3) and sampling rate (~ 40%), comparable to state-of-the-art surveys of the local Universe, together with extensive multi-band optical and near-infrared photometry. Here we present the survey design, the selection of the source catalogue and the development of the spectroscopic observations. We discuss in detail the overall selection function that results from the combination of the different constituents of the project. This includes the masks arising from the parent photometric sample and the spectroscopic instrumental footprint, together with the weights needed to account for the sampling and the success rates of the observations. Using the catalogue of 53,608 galaxy redshifts composing the forthcoming VIPERS Public Data Release 1 (PDR-1), we provide a first assessment of the quality of the spectroscopic data. Benefiting from the combination of size and detailed sampling of this dataset, we conclude by presenting a map showing in unprecedented detail the large-scale distribution of galaxies between 5 and 8 billion years ago. [abridged] △ Less

Submitted 13 March, 2013; v1 submitted 11 March, 2013; originally announced March 2013.

Comments: 20 pages, 19 figures, submitted to A&A. See http://www.vipers.inaf.it for version with higher resolution figures and movie