arXiv subjects

Francesca Perrotta

Publications and source records attributed to Francesca Perrotta.

At least 19 recordsLinked to original sources

arXiv2026

The ViSta method for optimized stacking of broadband interferometric data in the Fourier domain

We present the optimized version of ViSta, a visibility-domain stacking method that combines interferometric observations in the Fourier domain from radio to sub-millimeter wavelengths. By stacking visibilities directly and transforming them into the rest frame, ViSta enhances the signal, suppresses noise, and improves image reconstruction through extended uv-coverage. ViSta outperforms image stacking when individual sources are too faint to detect, achieving higher SNR in the low-signal and extended regime. This new optimized version features a C++/OpenMP kernel which replaces CASA demanding functions, enabling GPU acceleration while minimising memory usage and intermediate data products. The method is highly flexible, allowing stacking regardless of array configuration, spectral setup, or telescope. In the SKA era, where visibilities will not be routinely preserved, ViSta helps in assessing the information lost in the image-plane transition and in exploiting the vast amount of data still stored in interferometric archives.

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arXiv2025

The ViSta method for stacking in the Fourier domain and its application to the dusty star-forming galaxies in the ALMA Science Archive

We present ViSta, a Visibility Stacking method to combine interferometric observations in the Fourier domain at radio to sub-millimeter wavelengths for galaxies. The goal of our method is to maximize the exploitation of available archival interferometric data. By stacking visibilities of galaxies with secure spectroscopic redshifts directly in the Fourier domain and transforming them into the rest-frame, we can enhance the stacked signal, suppress noise, and improve image reconstruction thanks to an extended coverage of the visibility domain. The ViSta method is highly flexible, allowing stacking of visibilities regardless of the array configuration or spectral setup. It is effective for both targeted sources and spurious detections offset from the phase center, whether unresolved or extended, within the field of view of the telescope. We validated the method using simulated interferometric datasets. For point-like sources, we can reconstruct the true emission with approximately 90% accuracy, obtaining similar results to classical image-plane stacking. In contrast, for faint and extended sources below the noise level, our method can provide a more accurate estimate of the signal compared to traditional image-based approaches. Finally, we applied ViSta to a sample of dusty star-forming galaxies (DSFGs) observed with the Atacama Large Millimeter/sub-millimeter Array (ALMA) to detect the CO(3-2) emission line. As for the simulated case, we demonstrated that our tool performs better than image-plane stacking when the signal from individual sources is no longer easily detectable, achieving higher SNR. Finally, we outline potential future applications of this stacking approach.

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arXiv2025

SHORES: Serendipitous H-ATLAS-fields Observations of Radio Extragalactic Sources with the ATCA. I: catalog generation and analysis

We introduce the Serendipitous H-ATLAS-fields Observations of Radio Extragalactic Sources (SHORES) multiple pencil beam survey that observed at 2.1 GHz with the Australia Telescope Compact Array (ATCA) 29 fields in total intensity and polarization within the Herschel-ATLAS Southern Galactic Field. This paper presents the observations, calibration and analysis of the 27 shallow fields that cover an overall area of $\sim 26$ square degree with increasing sensitivity towards the phase centers of each pointing according to the ATCA 22 m dish response function, down to $\sigma\lesssim 33\, \mu$Jy. Two additional (deep) fields have been observed to even higher sensitivity. All the SHORES observations have been calibrated to account also for linear polarization. Polarization and deeper field analysis will be presented in future papers. The SHORES shallow-field sample considered in the present paper counts $2294$ sources detected with BLOBCAT to signal-to-noise ratio $SNR\gtrsim 4.5$. Simulations determined that our procedure and final catalog is 95% reliable above $497.5\, \mu$Jy and $95\%$ complete to the $SNR\gtrsim 4.5$ significance level. By exploiting ATCA E-W 6 km configuration we reached resolutions of $3.2\times 7.2$ arcsec, to which level $81\%$ of our sources are unresolved. We determined source counts down to the $150\, \mu$Jy level. For the sources with a counterpart in H-ATLAS, the FIR-radio correlation is calculated and discussed.

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arXiv2024

Semi-empirical Estimates of the Cosmic Planet Formation Rate

We devise and exploit a data-driven, semi-empirical framework of galaxy formation and evolution, coupling it to recipes for planet formation from stellar and planetary science, to compute the cosmic planet formation rate, and the properties of the planets' preferred host stellar and galactic environments. We also discuss how the rates and formation sites of planets are affected when considering their habitability, and when including possible threatening sources related to star formation and nuclear activity. Overall, we conservatively estimate a cumulative number of some $10^{20}$ Earth-like planets and around $10^{18}$ habitable Earths in our past lightcone. Finally, we find that a few $10^{17}$ are older than our own Earth, an occurrence which places a loose lower limit a few $10^{-18}$ to the odds for a habitable world to ever hosting a civilization in the observable Universe.

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arXiv2024

Astrochemistry of the molecular gas in Dusty Star-Forming Galaxies at the Cosmic Noon

FIR and submm observations have established the fundamental role of dust-obscured star formation in the assembly of stellar mass over the past 12 billion years. At z between 2 and 4, the bulk of star formation is enshrouded in dust, and dusty star forming galaxies (DSFGs) contain about half of the total stellar mass density. Star formation develops in dense molecular clouds, and is regulated by a complex interplay between all the ISM components that contribute to the energy budget of a galaxy: gas, dust, cosmic rays, interstellar electromagnetic fields, gravitational field, dark matter. Molecular gas is the actual link between star forming gas and its complex environment, providing by far the richest amount of information about the star formation process. However, molecular lines interpretation requires complex modeling of astrochemical networks, which regulate the molecular formation and establishes molecular abundances in a cloud, and a modeling of the physical conditions of the gas in which molecular energy levels become populated. This paper critically reviews the main astrochemical parameters needed to get predictions about molecular signals in DSFGs. We review the current knowledge and the open questions about the interstellar medium of DSFGs, outlying the key role of molecular gas as a tracer and shaper of the star formation process.

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arXiv2024

GalaPy, the highly optimised C++/Python spectral modelling tool for galaxies -- I. Library presentation and photometric fitting

Fostered by upcoming data from new generation observational campaigns, we are about to enter a new era for the study of how galaxies form and evolve. The unprecedented quantity of data that will be collected, from distances only marginally grasped up to now, will require analysis tools designed to target the specific physical peculiarities of the observed sources and handle extremely large datasets. One powerful method to investigate the complex astrophysical processes that govern the properties of galaxies is to model their observed spectral energy distribution (SED) at different stages of evolution and times throughout the history of the Universe. To address these challenges, we have developed GalaPy, a new library for modelling and fitting SEDs of galaxies from the X-ray to the radio band, as well as the evolution of their components and dust attenuation/reradiation. GalaPy incorporates both empirical and physically-motivated star formation histories, state-of-the-art single stellar population synthesis libraries, a two-component dust model for attenuation, an age-dependent energy conservation algorithm to compute dust reradiation, and additional sources of stellar continuum such as synchrotron, nebular/free-free emission and X-ray radiation from low and high mass binary stars. GalaPy has a hybrid implementation that combines the high performance of compiled C++ with the flexibility of Python, and exploits an object-oriented design. It generates models on the fly without relying on templates, and exploits fully Bayesian parameter space sampling. In this first work, we introduce the project and showcase the photometric SED fitting tools already available to users. The library is available on the Python Package Index (PyPI) and comes with extensive online documentation and tutorials.

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arXiv2015

Predictions for Ultra-Deep Radio Counts of Star-Forming Galaxies

We have worked out predictions for the radio counts of star-forming galaxies down to nJy levels, along with redshift distributions down to the detection limits of the phase 1 Square Kilometer Array MID telescope (SKA1-MID) and of its precursors. Such predictions were obtained by coupling epoch dependent star formation rate (SFR) functions with relations between SFR and radio (synchrotron and free-free) emission. The SFR functions were derived taking into account both the dust obscured and the unobscured star-formation, by combining far-infrared (FIR), ultra-violet (UV) and H_alpha luminosity functions up to high redshifts. We have also revisited the South Pole Telescope (SPT) counts of dusty galaxies at 95\,GHz performing a detailed analysis of the Spectral Energy Distributions (SEDs). Our results show that the deepest SKA1-MID surveys will detect high-z galaxies with SFRs two orders of magnitude lower compared to Herschel surveys. The highest redshift tails of the distributions at the detection limits of planned SKA1-MID surveys comprise a substantial fraction of strongly lensed galaxies. We predict that a survey down to 0.25 microJy at 1.4 GHz will detect about 1200 strongly lensed galaxies per square degree, at redshifts of up to 10. For about 30% of them the SKA1-MID will detect at least 2 images. The SKA1-MID will thus provide a comprehensive view of the star formation history throughout the re-ionization epoch, unaffected by dust extinction. We have also provided specific predictions for the EMU/ASKAP and MIGHTEE/MeerKAT surveys.

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arXiv2015

SKA synergy with Microwave Background studies

The extremely high sensitivity and resolution of the Square Kilometre Array (SKA) will be useful for addressing a wide set of themes relevant for cosmology, in synergy with current and future cosmic microwave background (CMB) projects. Many of these themes also have a link with future optical-IR and X-ray observations. We discuss the scientific perspectives for these goals, the instrumental requirements and the observational and data analysis approaches, and identify several topics that are important for cosmology and astrophysics at different cosmic epochs.

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arXiv2013

PRISM (Polarized Radiation Imaging and Spectroscopy Mission): A White Paper on the Ultimate Polarimetric Spectro-Imaging of the Microwave and Far-Infrared Sky

PRISM (Polarized Radiation Imaging and Spectroscopy Mission) was proposed to ESA in response to the Call for White Papers for the definition of the L2 and L3 Missions in the ESA Science Programme. PRISM would have two instruments: (1) an imager with a 3.5m mirror (cooled to 4K for high performance in the far-infrared---that is, in the Wien part of the CMB blackbody spectrum), and (2) an Fourier Transform Spectrometer (FTS) somewhat like the COBE FIRAS instrument but over three orders of magnitude more sensitive. Highlights of the new science (beyond the obvious target of B-modes from gravity waves generated during inflation) made possible by these two instruments working in tandem include: (1) the ultimate galaxy cluster survey gathering 10e6 clusters extending to large redshift and measuring their peculiar velocities and temperatures (through the kSZ effect and relativistic corrections to the classic y-distortion spectrum, respectively) (2) a detailed investigation into the nature of the cosmic infrared background (CIB) consisting of at present unresolved dusty high-z galaxies, where most of the star formation in the universe took place, (3) searching for distortions from the perfect CMB blackbody spectrum, which will probe a large number of otherwise inaccessible effects (e.g., energy release through decaying dark matter, the primordial power spectrum on very small scales where measurements today are impossible due to erasure from Silk damping and contamination from non-linear cascading of power from larger length scales). These are but a few of the highlights of the new science that will be made possible with PRISM.

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arXiv2005

Scaling solutions in scalar-tensor cosmologies

The possibility of a connection between dark energy and gravity through a direct coupling in the Lagrangian of the underlying theory has acquired an increasing interest due to the recently discovered capability of the extended quintessence model to encompass the fine-tuning problem of the cosmological constant. The gravity induced "R-boost" mechanism is indeed responsible for an early, enhanced scalar field dynamics, by virtue of which the residual imprint of a wide set of initial field values is cancelled out. The initial conditions problem is particularly relevant, as the most recent observations indicate that the dark energy equation of state approaches, at the present time, the cosmological constant value, wDE = -1; if confirmed, such observational evidence would cancel the advantage of a standard, minimally coupled scalar field as a Dark Energy candidate instead of the cosmological constant, because of the huge fine tuning it would require. We give here a general classification of the scalar-tensor gravity theories admitting R-boost solutions scaling as a power of the cosmological redshift, outlining those behaving as an attractor for the quintessence field. In particular, we show that all the R-boost solutions with the dark energy density scaling as the relativistic matter or shallower represent attractors. This analysis is exhaustive as for the classification of the couplings which admit R-boost and the subsequent enlargement of the basin of attraction enclosing the initial scalar field values.

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arXiv2005

Cosmic microwave background constraints on dark energy dynamics: analysis beyond the power spectrum

We consider the distribution of the non-Gaussian signal induced by weak lensing on the primary total intensity cosmic microwave background (CMB) anisotropies. Our study focuses on the three point statistics exploiting an harmonic analysis based on the CMB bispectrum. By considering the three multipoles as independent variables, we reveal a complex structure of peaks and valleys determined by the re-projection of the primordial acoustic oscillations through the lensing mechanism. We study the dependence of this system on the expansion rate at the epoch in which the weak lensing power injection is relevant, probing the dark energy equation of state at redshift corresponding to the equivalence with matter or higher ($w_\infty$). We evaluate the impact of the bispectrum observable on the CMB capability of constraining the dark energy dynamics. We perform a maximum likelihood analysis by varying the dark energy abundance, the present equation of state $w_0$ and $w_\infty$. We show that the projection degeneracy affecting a pure power spectrum analysis in total intensity is broken if the bispectrum is taken into account. For a Planck-like experiment, assuming nominal performance, no foregrounds or systematics, and fixing all the parameters except $w_0$, $w_\infty$ and the dark energy abundance, a percent and ten percent precision measure of $w_0$ and $w_\infty$ is achievable from CMB data only. These results indicate that the detection of the weak lensing signal by the forthcoming CMB probes may be relevant to gain insight into the dark energy dynamics at the onset of cosmic acceleration.

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arXiv2005

Structure formation constraints on the Jordan-Brans-Dicke theory

We use cosmic microwave background data from WMAP, ACBAR, VSA and CBI, and galaxy power spectrum data from 2dF, to constrain flat cosmologies based on the Jordan-Brans-Dicke theory, using a Markov Chain Monte Carlo approach. Using a parametrization based on ξ=1/4ω, and performing an exploration in the range \lnξ\in [-9,3], we obtain a 95% marginalized probability bound of \lnξ< -6.2, corresponding to a 95% marginalized probability lower bound on the Brans-Dicke parameter ω>120.

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arXiv2004

Weak lensing and gravity theories

We present the theory of weak gravitational lensing in cosmologies with generalized gravity, described in the Lagrangian by a generic function depending on the Ricci scalar and a non-minimally coupled scalar field. We work out the generalized Poisson equations relating the dynamics of the fluctuating components to the two gauge invariant scalar gravitational potentials, fixing the new contributions from the modified background expansion and fluctuations. We show how the lensing observables are affected by the cosmic expansion as well as by the presence of the anisotropic stress, which is non-null at the linear level both in scalar-tensor gravity and in theories where the gravitational Lagrangian term features a non-minimal dependence on the Ricci scalar. We derive the generalized expressions for the convergence power spectrum, and illustrate phenomenologically the new effects in Extended Quintessence scenarios, where the scalar field coupled to gravity plays the role of the dark energy.

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arXiv2004

Approaching Lambda without fine-tuning

We address the fine-tuning problem of dark energy cosmologies which arises when the dark energy density needs to initially lie in a narrow range in order for its present value to be consistent with observations. As recently noticed, this problem becomes particularly severe in canonical Quintessence scenarios, when trying to reproduce the behavior of a cosmological constant, i.e. when the dark energy equation of state w_Q approaches -1: these models may be reconciled with a large basin of attraction only by requiring a rapid evolution of w_Q at low reshifts, which is in conflict with the most recent estimates from type Ia Supernovae discovered by Hubble Space Telescope. Next, we focus on scalar-tensor theories of gravity, discussing the implications of a coupling between the Quintessence scalar field and the Ricci scalar (``Extended Quintessence''). We show that, even if the equation of state today is very close to -1, by virtue of the scalar-tensor coupling the quintessence trajectories still possess the attractive feature which allows to reach the present level of cosmic acceleration starting by a set of initial conditions which covers tens of orders of magnitude; this effect, entirely of gravitational origin, represents a new important consequence of the possible coupling between dark energy and gravity.

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arXiv2004

Weak lensing in generalized gravity theories

We extend the theory of weak gravitational lensing to cosmologies with generalized gravity, described in the Lagrangian by a generic function depending on the Ricci scalar and a non-minimal coupled scalar field. We work out the generalized Poisson equations relating the dynamics of the fluctuating components to the two gauge invariant scalar gravitational potentials, fixing the new contributions from the modified background expansion and fluctuations. We show how the lensing equation gets modified by the cosmic expansion as well as by the presence of the anisotropic stress, which is non-null at the linear level both in scalar-tensor gravity and in theories where the gravitational Lagrangian term features a non-minimal dependence on the Ricci scalar. Starting from the geodesic deviation, we derive the generalized expressions for the shear tensor and projected lensing potential, encoding the spacetime variation of the effective gravitational constant and isolating the contribution of the anisotropic stress, which introduces a correction due to the spatial correlation between the gravitational potentials. Finally, we work out the expressions of the lensing convergence power spectrum as well as the correlation between the lensing potential and the Integrated Sachs-Wolfe effect affecting Cosmic Microwave Background total intensity and polarization anisotropies. To illustrate phenomenologically the new effects, we work out approximate expressions for the quantities above in Extended Quintessence scenarios where the scalar field coupled to gravity plays the role of the dark energy.

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arXiv2004

Strong lensing by cluster-sized haloes in dark-energy cosmologies

We study the efficiency of numerically simulated galaxy clusters for producing strong gravitational lensing events in different dark-energy cosmologies with constant and time-variable equation of state and we compare it with ``standard'' $Λ$CDM and OCDM models. Our main results are that: (1) the expected abundance of gravitational arcs with large length-to-width ratio depends on the equation of state of dark energy at the epoch of formation of the halo; (2) as found in previous studies, the strong lensing cross section of galaxy clusters is very sensitive to dynamical processes like mergers, whose impact however is different for different cosmologies, being stronger for models in which halos are less concentrated. As expected, the largest differences in the lensing optical depth occur at moderate and high redshift.

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arXiv2003

Numerical study of halo concentrations in dark-energy cosmologies

We study the concentration parameters, their mass dependence and redshift evolution, of dark-matter halos in different dark-energy cosmologies with constant and time-variable equation of state, and compare them with "standard'' Lambda-CDM and OCDM models. We find that previously proposed algorithms for predicting halo concentrations can be well adapted to dark-energy models. When centred on the analytically expected values, halo concentrations show a log-normal distribution with a uniform standard deviation of ~0.2. The dependence of averaged halo concentrations on mass and redshift permits a simple fit of the form (1+z) c=c0 (M/M0)^a, with a~-0.1 throughout. We find that the cluster concentration depends on the dark energy equation of state at the cluster formation redshift z_{coll} through the linear growth factor D_+(z_{coll}). As a simple correction accounting for dark-energy cosmologies, we propose scaling c0 from Lambda-CDM with the ratio of linear growth factors, c0 -> c0 D_+(z_{coll})/D_{+,Lambda-CDM}(z_{coll}).

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arXiv2003

Weak lensing, structure formation and dark energy

We study how CMB bispectrum, produced by weak gravitational lensing and structure formation, can constrain the redshift evolution of the dark energy equation of state independently on its present value. Analyzing the line of sight contribution to the angular CMB bispectrum, we find that the relevant redshift at which the structure formation contributes to the signal is $0.1 \lsim z \lsim 2$ for multipoles $1000 \gsim l \gsim 100$: just the epoch when the dark energy starts to dominate the cosmological expansion rate. For scenarios having the same equation of state at the present, this turns out to be a new observable capable to discriminate between models of dark energy with different time evolution of equation of state. We assess the strength of this effetc within the framework of tracking Quintessence trajectories obeying SUGRA and Ratra-Peebles potentials.

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