arXiv subjects

Viviana Casasola

Publications and source records attributed to Viviana Casasola.

At least 19 recordsLinked to original sources

arXiv2026

Molecular atlas of nearby galaxies through sensitive high-resolution multi-band molecular line surveys

Star formation and associated feedback processes play a key role in galaxy evolution. Astrochemistry is a powerful tool for characterising the physical conditions of dense star-forming gas and understanding the reciprocal relation between stellar feedback and the interstellar medium (ISM): from the way feedback influences the ISM to how the ISM conditions regulate the formation of new stars. The advent of large spectral surveys of a few individual galaxy centres have demonstrated the potential of molecular gas inventories to reveal the physical conditions of star-forming gas in great detail. A next-generation (sub)mm facility in the 2040s would extend this science to the local star-forming galaxy population, providing for the first time a comprehensive view of the physical and chemical conditions of the molecular ISM in the local universe.

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arXiv2026

From Scaling Relations to Physical Laws: Constraining the Physics of Star Formation Across Local Galaxies

The conversion of cold dense gas, traced by molecular line emission, into stars remains one of the fundamental unsolved problems in galaxy evolution. Observations over the past decades have established empirical relations between gas and star formation, yet their physical origin remains uncertain. Gravity, turbulence, and stellar feedback as main drivers provide fundamentally different pictures of how star formation is regulated, while reproducing remarkably similar galaxy-scale scaling relations. To disentangle the individual importance of each process, not only its mass and distribution, but also its temperature, density, excitation, and chemistry must be probed. However, current or planned (sub)millimetre facilities cannot combine statistical breadth, cloud-scale resolution, and multi-line diagnostics across large galaxy samples. A new, flagship interferometer with increased line sensitivity and bandwidth enables obtaining multi-transition, multi-isotopologue observations of molecular gas at GMC-resolved scales across nearby galaxies, enabling millions of independent measurements of its physical state across a wide range of extragalactic environments. This will transform molecular gas from an empirical tracer into a quantitative probe of the physical processes governing the relation between the dense gas and star formation. With the 2040s landscape of optical and radio facilities, ALMA2040 will facilitate a predictive theory of the conversion of gas into stars.

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arXiv2026

Resolved Dust-Gas-Metallicity relations in nearby spiral galaxies

Context: Understanding the interstellar medium (ISM) requires high-resolution, multi-component mapping to capture its complex physical structure. Nearby spiral galaxies, with their abundant and diverse ISM, provide an ideal laboratory for such a comprehensive analysis at sub-galactic scales. Aims: We investigate dust-to-gas (DGR) and dust-to-metal (DMR) ratios as a functions of gas-phase metallicity (Z), on spatial scales ranging from 0.6 to 2.3 kpc, in a sample of 10 nearby spiral galaxies, spanning more than an order of magnitude in stellar mass (9.7 \le \log(M_*/M_\odot) \leq 11.0), star formation rate (SFR, \sim 0.3--3 \, M_\odot \, \rm yr^{-1}) and metallicity ranging from 8.3 \lesssim 12 + \log( O/H) \lesssim 8.8. We explore how the DGR-Z and DMR-Z relations are shaped by the assumptions behind the CO-to-H_2 conversion factor (α_{CO}). Methods: We homogeneously combine maps of dust, atomic gas, molecular gas, and metallicity. Motivated by the diversity in L_{CO(1-0)}/SFR ratios and metallicity across our sample, we introduce a hybrid α_{CO} prescription to distinguish between CO-bright and CO-dark regimes. The derived DGR-Z and DMR-Z relations are compared with other global and resolved observational results, and with the predictions of dust and chemical evolution models. Results: Both DGR-Z and DMR-Z relations are dependent on the adopted α_{CO} prescription, and no single α_{CO} can reproduce the properties of the entire sample, motivating the use of a hybrid approach. The DGR increases with metallicity, spanning \sim 1 dex across the sampled range; while the DMR remains approximately constant at \log(\mathrm{DMR}) = -0.53 \pm 0.13, implying that \sim 30 \% of metals are locked into dust grains. This flat behavior indicates an evolved dust phase where efficient ISM grain growth drives a saturation regime balancing dust formation and destruction.

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arXiv2026

Tracing the Cosmic web across Cosmic time through SKA observations of radio galaxies

The Square Kilometre Array will transform studies of the cosmic web by tracing radio galaxies (RGs) and star-forming systems across cosmic time with unprecedented sensitivity, angular resolution, frequency coverage, and survey speed. Powered by accreting supermassive black holes, RGs are not only signposts of AGN feedback but also incisive probes of their environments, from dense clusters to the low-density intergalactic medium. Their lobes, magnetic fields, and energy outflows encode the thermal and non-thermal histories of the surrounding gas, offering diagnostics of IGM pressure, particle ageing, and magnetisation over megaparsec scales. With its broad frequency coverage (50 MHz-15 GHz), microJy to sub-microJy continuum sensitivity, and wide field of view, the SKA will detect vast radio-source populations across broad ranges of redshift and environment. Measurements of source size, morphology, spectral ageing, radio power, polarisation, and Faraday rotation will reveal how the environment regulates jet propagation and lobe evolution, how radio plasma heats and magnetises the intracluster and intergalactic media, and how early AGN activity influences galaxy growth and star formation in protoclusters. Combined with host identifications, spectroscopic redshifts, and optical, infrared, X-ray, Sunyaev--Zel'dovich, and cosmic-web catalogues, SKA observations will place RGs within their three-dimensional large-scale environments. This chapter presents a framework for using RGs to trace and probe the cosmic web, from nearby filaments and clusters to high-redshift protoclusters, and to test how environment, magnetic fields, feedback, and gas dynamics shape radio-galaxy evolution, protocluster assembly, and star formation across cosmic time.

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arXiv2026

Advancing Astrophysics with the SKA II

Advancing Astrophysics with the SKA II (AASKAII), written by our science community, outlines the transformative scientific advances that will be enabled by the SKA telescopes. In the decade since the publication of the previous edition, telescope designs have matured, construction has commenced, and the SKA Organisation has evolved into the SKA Observatory (SKAO). At the same time, observations from SKA precursor and pathfinder telescopes have provided new insights into longstanding scientific challenges while revealing entirely new phenomena. Published in advance of the first science verification campaign for the SKA Observatory, this volume looks ahead to the coming decades of discovery and innovation in radio astronomy. AASKAII spans the broad range of scientific research enabled by the SKA telescopes, SKA-Mid and SKA-Low. The contributions are organised into six thematic categories according to their scientific focus. The opening section presents overview chapters from the SKA Science Working Groups, around which our community is organised. Each overview provides the broader context that connects the contributions in this volume to the key scientific questions being pursued by their respective communities.

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arXiv2026

Advancing extragalactic spectral line studies with the Square Kilometre Array Observatory

We present an overview of the Square Kilometre Array Observatory (SKAO) science potential in the area of extragalactic spectral lines besides 21-cm neutral hydrogen. It highlights the main points from the SKAO Science Book chapters on individual topics, but is augmented by additional prospects. The SKAO will push studies and use of masers, kilomasers, megamasers, molecular and radio-recombination-line emission and absorption to a wider variety of environments, including to very high redshift where it may detect the first molecule (HeH$^+$). It will open the door to measurements of hydrogen and helium isotopes, probing the conditions for star formation and Big Bang nucleosynthesis. While the planned SKAO of the 2030s (AA*) is destined to forge major progress, an SKAO as initially envisaged (AA4) will truly transform the landscape, and an extension towards higher frequencies (up to 24 GHz) would enable water maser and ammonia surveys in nearby galaxies and systematic molecular gas inventories at redshift 5.

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arXiv2026

Survival of very small carbonaceous dust grains in the inner-CGM of NGC 891 from JWST/MIRI MRS

We present new spectroscopic observations of the inner circumgalactic medium (CGM) of NGC 891 taken with the Mid-Infrared Imager/Medium Resolution Spectroscopy instrument onboard JWST, in four positions: two near the bulge and two at galactocentric radii (r) of ~ 1.5, 4.7 kpc. Each pair of pointings has one position along the minor axis (h) at ~ 0.5 kpc and one at ~ 1 kpc away from the mid-plane. We analyse both 1D spectra and 3D cubes using the dust emission model PAHFIT to extract properties of typical mid-IR features. These spectra reveal that the earlier reported mid-IR emission out to 4 kpc is dominated by the emission of polycyclic aromatic hydrocarbons (PAHs), and not hot dust continuum, providing direct evidence of the survival of PAHs in the inner CGM of NGC 891. Comparing PAH band ratios with other environments (Orion, M51), it is obvious that the 11.2 $μ$m PAH feature -- and not the usual 7.7 $μ$m -- dominates in NGC 891, which seems to imply the presence of more neutral, large PAHs in the CGM. Overall, PAH-to-continuum ratios show little variations with scale-height and radius in NGC 891, which suggests little PAH processing. However, we do see a decrease in the PAH feature strengths with the [Ne III]/[Ne II] ratio, pointing at elevated dust processing with increased radiation field hardness. We also confirm a tight correlation between H2 and PAH features, suggesting that both tracers must be co-spatial and, hence, implying that PAH emission predominantly arises from cool dense parts of cloudlets entrained in galactic outflows. Finally, we report the clear detection of a previously unidentified PAH feature at 16.72 $μ$m.

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arXiv2026

DustPedia and Local Volume Legacy samples as benchmarks for dust evolution in galaxies

DustPedia and LVL are two samples representative of the local galaxy population, including in total 1011 unique objects of all morphological types, with a wide range of stellar masses ($M_*$) and star-formation activity, and a spectral coverage from the FUV to the FIR. The purpose of this work is to show that these samples cover two complementary ranges in $M_*$ and morphology, making them an ideal set for constraining the dominant processes in the evolution of the galactic dust content. Using the multiwavelength data provided by the two surveys, we fitted the galaxies' spectral energy distribution and estimated their physical properties, in particular the $M_*$, $sM_\mathrm{dust}=M_\mathrm{dust}/M_*$, and sSFR = SFR$/M_*$. By combining DustPedia and LVL, we highlight that the $\log_{10}(sM_{\rm dust})$-$\log_{10}(M_*)$ trend is not monotonic. Thanks to a large number of objects across a wide range of $M_*$, we have been able to fit two smoothly-joined linear correlations: a positive for $\log_{10}(M_{*}/$M$_\odot)\lesssim9.5$ (mainly LVL late spirals and irregulars), and a negative one for larger-mass, mainly DustPedia spirals (early types are distinct and more dispersed in the same mass regime). For $\log_{10}(M_{*}/$M$_\odot)>9.5$, we confirm a strong sM_{\rm dust}-sSFR correlation; dwarf galaxies, instead, lie below this trend, with a large scatter of $sM_{\rm dust}$, for -10.5<$\log_{10}$(sSFR/yr$^{-1}$)<-9.0. By using chemical evolution models we find that the observed $\log_{10}(sM_{\rm dust})$-$\log_{10}(M_{*})$ and $\log_{10}(sM_{\rm dust})$-$\log_{10}$(sSFR) trends can be interpreted mainly by variations in the initial gas mass budget and the galaxy ages, respectively. Low-mass Sm-Irr galaxies with low $sM_{\rm dust}$ and high sSFR can only be reproduced by the models by assuming high photofragmentation rate of large grains, and/or low grain-growth in clouds.

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arXiv2025

ALMACAL. XV. Band 3 ALMA Survey and Number Counts

The ALMACAL project leverages ALMA maps of calibrator-centered fields to conduct deep mm/sub-mm surveys, enabling the detection of extragalactic sources with flux densities orders of magnitude fainter than achievable with other instruments. These faint sources are critical for refining evolutionary models, as their number counts provide key constraints. In this study, we analyzed band-3 ALMACAL maps from 606 calibrator fields, employing a novel machine learning approach to mitigate the often-overlooked bias introduced by the calibrator itself. Supported by extensive simulations, we extended 100 GHz radio AGN counts by approximately 1.5 orders of magnitude in flux density and refined constraints on dusty star-forming galaxies, reaching sensitivities as low as $\sim$180 $μ$Jy. We have improved the sampling, compared to previous results, in the region of the dominant population transition (between dusty star-forming galaxies and radio AGN). Our results are in good agreement with model predictions.

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arXiv2025

PRIMA survey of the Virgo cluster

Clusters of galaxies are unique laboratories for investigating the dependence of galaxy evolution on their environment. The Herschel Virgo Cluster Survey (HeViCS) mapped the central 84 square degrees region of the Virgo Cluster in five bands between 100 and 500 micron, which resulted in the first detailed view of cold dust in cluster galaxies. Major limitations of the HeViCS survey were the lack of data, or its limited availability, in the 20 to 80 micron range, and the quite low sensitivity of the Photodetector Array Camera and Spectrometer instrument, resulting in poor constraints on the warmer dust component. The PRIMAger instrument onboard PRIMA offers the capability to map a large portion of the Virgo Cluster -- including regions beyond its virial radius -- in hyperspectral and polarimetric bands from 25 to 265 micron, enabling a direct comparison with the area previously covered by HeViCS. By combining PRIMA and Herschel data with existing multi-wavelength photometry, it becomes possible to explore the connection between stellar and dust properties in a complete sample of cluster galaxies, to investigate environmental effects on the warm dust component within the Virgo Cluster, to map the magnetic field structure of the cold interstellar medium (ISM), to search for dust emission from the intra-cluster medium, and to study the ISM in background galaxies projected behind the cluster.

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arXiv2025

The radial variation of the silicate-to-carbon ratio in M31 probed by PRIMA

The properties of interstellar dust grains are being scrutinized more than ever before, with the advent of large facilities. Infrared emission from dust grains is a powerful asset than can help constrain their physical and chemical properties. Among these, the relative ratio of carbon-rich to silicate-rich grains remains one that has not yet been investigated thoroughly, due to the lack of dedicated instruments and modeling limitations. In this paper, we quantify the modeling degeneracies inherent to constraining the far-infrared (far-IR) slope of the dust emission spectral energy distribution. Used as a proxy for the silicate-to-carbon ratio, we find that recovering the far-IR slope is affected by the estimate of the local radiation field, and the input abundances of different grain species. We show that PRIMA's Hyperspectral Imaging will lead to better constrained local radiation fields which will aid -- together with PRIMA's polarization capabilities -- to better constrain the silicate-to-carbon ratio in M31, and how it spatially varies within the galaxy.

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arXiv2025

The PRIMA promise of deciphering interstellar dust evolution with observations of the nearby Universe

This paper develops a few science cases, using the PRIMA far-IR probe, aimed at achieving several breakthroughs in our understanding of the dust properties and their evolution. We argue that the specific observational capabilities of PRIMA, namely its unprecedented sensitivity over the whole far-IR range and the possibility to obtain continuous spectra between wavelengths 24 and 235 microns, are essential to progress in our understanding of the physics of the interstellar medium and galaxy evolution. Our science cases revolve around observations of nearby galaxies. We discuss the importance of detecting the IR emission of the diffuse interstellar medium of these galaxies, including very low-metallicity systems. We also discuss the opportunity of detecting various solid-state features to understand the mineralogy of interstellar grains. Finally, we stress the unique opportunity brought by the possible simultaneous measures of both the dust continuum and the far-IR fine-structure gas lines. These science cases could be distributed in a few large programs.

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arXiv2025

The role of young and evolved stars in the heating of dust in local galaxies

Context. Dust is a fundamental component of the interstellar medium (ISM) and plays a critical role in galaxy evolution. Dust grains influence the ISM by cooling the gas, altering its chemistry, and absorbing stellar radiation, re-emitting it at longer wavelengths in the far-infrared (FIR) and sub-millimeter regimes. The cold dust component, which dominates the dust mass, is primarily heated by stellar radiation, including both young, massive stars and the diffuse emission from older stars. Understanding dust heating is essential to trace the connection between stellar populations and their environments. Aims. We aim to identify the dominant heating mechanisms of the cold dust in typical nearby spiral galaxies and explore the contributions of young and evolved stars to dust heating. Methods. Using 18 large, face-on spiral galaxies from the DustPedia project, we apply two complementary approaches: (1) correlation analysis between dust temperature (T_dust), SFR surface density (Sigma_SFR), and stellar mass surface density (Sigma_Mstar); and (2) study of the relationship between T_dust and dust mass surface density (Sigma_dust). Results. T_dust peaks at ~24 K in galaxy centers and drops to ~15 K at large radii. Galaxies with and without AGNs show similar T_dust profiles. For ~72% of the sample, both methods agree on the dominant heating source. Overall, we find that both young and evolved stars contribute to dust heating, with their relative roles varying between galaxies.

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arXiv2025

Metal-THINGS: gas metallicity gradients in nearby galaxies

This paper explores the gas metallicity gradients in a sample of 25 nearby galaxies using new Integral Field Spectroscopy observations from the Metal-THINGS survey. We derive and study the resolved diffuse ionised gas content, Baldwin, Phillips and Terlevich diagrams and gas metallicities for our entire sample, at spatial resolutions of 40-300 pc. Gas metallicity gradients are studied as a function of the galaxy's stellar mass, H I gas fraction, diffuse ionised gas content, and using different parametric length scales for normalisation. The metallicity gradients are analysed using Bayesian statistics based on data from the Metal-THINGS survey. Bayesian MCMC models are developed to explore how metallicity gradients vary with a galaxy's mass and how they correlate with properties such as the stellar mass or the atomic gas fraction. For our sample, we find that the metallicity typically decreases with galactic radius, consistent with inside-out galaxy growth. We find a trend dependent on the stellar mass, with a break at log(M_star/M_sun)=9.5, and another between the metallicity gradients and the atomic gas fraction (f_g,HI) of a galaxy at fg,HI=0.75, indicating relatively shallower gradients for lower gas fractions. We find that normalisation using NUV-band effective radii are preferable for galaxies with a higher atomic gas content and lower stellar masses, while r-band radii are better suited for those with lower atomic gas fractions and more massive ones. Our results highlight a strong connection between gas content, stellar mass, and metallicity gradients. The breaks at log(M_star/M_sun)=9.5 and fg,HI=0.75 mark shifts in chemical enrichment behaviour, with low-mass galaxies showing greater sensitivity to gas processes. Overall, this points to gas accretion and removal as key drivers of chemical evolution in low-mass systems.

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arXiv2024

JWST MIRI and NIRCam observations of NGC 891 and its circumgalactic medium

We present new JWST observations of the nearby, prototypical edge-on, spiral galaxy NGC 891. The northern half of the disk was observed with NIRCam in its F150W and F277W filters. Absorption is clearly visible in the mid-plane of the F150W image, along with vertical dusty plumes that closely resemble the ones seen in the optical. A $\sim 10 \times 3~{\rm kpc}^2$ area of the lower circumgalactic medium (CGM) was mapped with MIRI F770W at 12 pc scales. Thanks to the sensitivity and resolution of JWST, we detect dust emission out to $\sim 4$ kpc from the disk, in the form of filaments, arcs, and super-bubbles. Some of these filaments can be traced back to regions with recent star formation activity, suggesting that feedback-driven galactic winds play an important role in regulating baryonic cycling. The presence of dust at these altitudes raises questions about the transport mechanisms at play and suggests that small dust grains are able to survive for several tens of million years after having been ejected by galactic winds in the disk-halo interface. We lay out several scenarios that could explain this emission: dust grains may be shielded in the outer layers of cool dense clouds expelled from the galaxy disk, and/or the emission comes from the mixing layers around these cool clumps where material from the hot gas is able to cool down and mix with these cool cloudlets. This first set of data and upcoming spectroscopy will be very helpful to understand the survival of dust grains in energetic environments, and their contribution to recycling baryonic material in the mid-plane of galaxies.

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arXiv2024

The impact of stellar bars on star-formation quenching: Insights from a spatially resolved analysis in the local Universe

Stellar bars are common morphological structures in the local Universe; according to optical and NIR surveys, they are present in about two-thirds of disc galaxies. These elongated structures are also believed to play a crucial role in secular evolutionary processes, because they are able to efficiently redistribute gas, stars, and angular momentum within their hosts, although it remains unclear as to whether they enhance or suppress star formation. A useful tool to investigate this ambiguity is the main sequence (MS) relation, which tightly links stellar mass ($M_{\star}$) and star formation rate (SFR). The main goal of this work is to explore star-formation processes in barred galaxies in order to assess the relevance of bars in star-formation quenching and whether or not they affect the typical log-linear trend of the resolved MS. To this purpose, we carried out a spatially resolved analysis on subkiloparsec (subkpc) scales for a sample of six nearby barred galaxies. We collected multi-wavelength photometric data from far-ultraviolet (FUV) to far-infrared (FIR) from the DustPedia database and applied a panchromatic spectral energy distribution (SED) fitting procedure on square apertures of fixed angular size (8" $\times$ 8") using the magphys code. For each galaxy, we obtain the distributions of stellar mass and SFR surface density and relate them in the $\log Σ_{\star}$ - $\log Σ_{\rm SFR}$ plane, deriving the spatially resolved MS relation. Although significant galaxy-to-galaxy variations are in place, we infer the presence of a common anti-correlation track in correspondence with the bar-hosting region, which shows systematically lower SFRs. This central quiescent signature can be interpreted as the result of a bar-driven depletion of gas reservoirs and a consequent halting of star formation. Our findings appear to support an inside-out quenching scenario.

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arXiv2024

Correlations between IR Luminosity, Star Formation Rate, and CO Luminosity in the Local Universe

We exploit the DustPedia sample of galaxies within approximately 40 Mpc, selecting 388 sources, to investigate the correlations between IR luminosity (L$_{\rm IR}$), the star formation rate (SFR), and the CO(1-0) luminosity (L$_{\rm CO}$) down to much lower luminosities than reached by previous analyses. We find a sub-linear dependence of the SFR on L$_{\rm IR}$. Below $\log(\hbox{L}_{\rm IR}/\hbox{L}_\odot)\simeq 10$ or $\hbox{SFR}\simeq 1\,\hbox{M}_\odot\,\hbox{yr}^{-1}$, the SFR/L$_{\rm IR}$ ratio substantially exceeds the standard ratio for dust-enshrouded star formation, and the difference increases with decreasing L$_{\rm IR}$ values. This implies that the effect of unobscured star formation overcomes that of dust heating by old stars, at variance with results based on the $\textit{Planck}$ ERCSC galaxy sample. We also find that the relations between the L$_{\rm CO}$ and L$_{\rm IR}$ or the SFR are consistent with those obtained at much higher luminosities.

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arXiv2024

The Wide-field Spectroscopic Telescope (WST) Science White Paper

The Wide-field Spectroscopic Telescope (WST) is proposed as a new facility dedicated to the efficient delivery of spectroscopic surveys. This white paper summarises the initial concept as well as the corresponding science cases. WST will feature simultaneous operation of a large field-of-view (3 sq. degree), a high multiplex (20,000) multi-object spectrograph (MOS) and a giant 3x3 sq. arcmin integral field spectrograph (IFS). In scientific capability these requirements place WST far ahead of existing and planned facilities. Given the current investment in deep imaging surveys and noting the diagnostic power of spectroscopy, WST will fill a crucial gap in astronomical capability and work synergistically with future ground and space-based facilities. This white paper shows that WST can address outstanding scientific questions in the areas of cosmology; galaxy assembly, evolution, and enrichment, including our own Milky Way; origin of stars and planets; time domain and multi-messenger astrophysics. WST's uniquely rich dataset will deliver unforeseen discoveries in many of these areas. The WST Science Team (already including more than 500 scientists worldwide) is open to the all astronomical community. To register in the WST Science Team please visit https://www.wstelescope.com/for-scientists/participate

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