arXiv subjects

Benedetta Casavecchia

Publications and source records attributed to Benedetta Casavecchia.

11 recordsLinked to original sources

arXiv2026

New constraints on stellar feedback through [O III] emission: interpreting ALMA and JWST observations with SPICE simulations

ALMA and JWST have recently detected emission lines from the interstellar medium of star-forming galaxies during the Epoch of Reionization, reaching redshifts up to z = 14. Among these, [OIII] lines provide a powerful diagnostic of metal enrichment, gas ionization, and the impact of stellar feedback in galaxies at z > 6. Modeling this emission in cosmological simulations is challenging due to the wide range of spatial scales and physical processes involved. To address this, we have developed a post-processing pipeline that implements a sub-grid model for [OIII] line emission within the SPICE radiation-hydrodynamical simulations. These simulations explore three supernova feedback prescriptions: bursty-sn, smooth-sn, and the hypernova-based hyper-sn. We investigate how these feedback models affect metal enrichment, the neutral gas fraction, and the size and morphology of ionized halos traced by [OIII] emission in both the optical and far-infrared. We find that [OIII] emission predominantly originates from gas that is both shock-heated and radiatively ionized. We also examine the mass-metallicity relation and the correlation between neutral gas fraction and [OIII] luminosity. Our results show that the bursty-sn model efficiently ionizes gas but enriches galaxies less effectively by z = 5, leading to fewer bright [OIII] emitters compared to the smooth-sn model. Both bursty-sn and hyper-sn produce suppressed luminosity functions. Spatially resolved [OIII] emission further indicates that smooth-sn tends to generate more compact galaxies and slightly higher V/σ values, although there is significant overlap between models. Overall, our findings demonstrate that [OIII] emission is a sensitive tracer of stellar feedback at high redshift and highlight the importance of observations probing fainter luminosities, where feedback effects are strongest.

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arXiv2026

Uncovering the absorbed atomic Universe with the [OI]63um line

We report the discovery of strongly absorbed [OI]63um in a sample of 12 DSFGs at 4.2 4. Using ALMA Bands 9 and 10, we obtain spatially and spectrally resolved observations that probe the interstellar medium on sub-kpc scales. Despite reaching sensitivities 10-100x deeper than most previous studies, we detect [OI]63um in emission in only 2 sources at low significance, with the remaining galaxies yielding stringent non-detections over the full velocity range covered by robust detections of other far-infrared lines, including [CII] and [NII]205um. We identify several compact (0.05-0.2") regions having [OI]63um absorption against the far-infrared dust continuum, some of which are possibly reaching below rest-frame CMB radiation level. We also detect narrow, spatially localised [OI]63um emission "escape channels" preferentially detected in regions with weak or absent dust continuum emission. We predict that similar absorption effects may appear in the [CII] line, particularly when concentrating on the regions with the densest foreground material along the line of sight. The [OI]63um line appears to be originate from a mix of compact, high optical depth [OI]63um emitting regions and sub-thermally excited, oxygen-rich molecular clouds dispersed throughout high-redshift starbursts that are capable of absorbing the ground-state line emission. Combined with a comparison to cosmological radiation hydrodynamical simulations, this supports the interpretation that regions with higher gas and dust column densities may lead to weakening an intrinsically strong [OI]63um line emission. We argue that the high [OI]63um optical depth is the dominant effect causing the strong absorption, limiting the diagnostic power of this line to trace regions of massive star formation in high-redshift DSFGs.

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arXiv2026

Chemodynamical properties of gas-rich galaxies: a comparison of observations and simulations

We perform a comprehensive analysis of the chemical and dynamical properties of quasar-damped Lyman-α (DLA) galaxies and compare these to the GEAR chemodynamical simulations. Specifically, we aim to constrain the behavior of α-element enhancements with metallicity, the dependence of [α/Fe] on the specific star formation rate (sSFR), and the absorption-line velocity widths (Δv90) vs. stellar mass, Δv90 vs. metallicity, and mass-metallicity relations. For the comparison, we select five galaxies simulated with the chemodynamical Tree-SPH code GEAR with stellar masses in the range of log(M*/Msol) between 6.1 and 10.8, and at six different redshifts between 0.33 and 4.12. We find that the abundance ratios [α/Fe] and [M/H] observed in the interstellar medium (ISM) of DLA galaxies overlap with the abundance trends in gas of the simulated galaxies. Our findings corroborate a picture in which DLAs with Δv90 below and above 100 km/s trace galaxies with masses in the ranges of log M* 6 - 8 and 8 - 11 solar masses, respectively. We suggest that observations should be used with caution when constraining the theoretical [α/Fe] vs. sSFR relations because of systematics (if abundances are obtained from emission lines) or differences in the gas properties as probed by a DLA and its counterpart. So far, only the observations in absorption of inner gas of the LMC and SMC are in agreement with the simulated data. We confirm that DLAs detected at large impact parameters most likely probe the gas of satellite or other halo galaxies which are adjacent to the central galaxy. We further find that the velocity widths vs. stellar masses and mass-metallicity relations agree well with observations, while GEAR should be calibrated more carefully to reproduce the Δv90 vs. metallicity relation.

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arXiv2026

MUSE-ALMA Haloes XIII. Molecular gas in $z \sim 0.5$ HI-selected galaxies

We present new results from the MUSE-ALMA Haloes survey, covering 79 galaxies associated with strong HI absorption at redshift about 0.5. Our ALMA Cycle 10 observations add 39 systems to the initial 21, bringing the total to 60 galaxies. CO emission is detected in 9 new galaxies, and in 12 of 60 total, doubling the number of CO-emitting HI-selected galaxies and probing 1.2 dex deeper in molecular gas mass than previous studies. These galaxies span a wide range of stellar masses and metallicities. By comparing CO(2-1) and CO(3-2) properties with star formation rates and gas-phase metallicities from VLT/MUSE and HST, we find a dual behaviour in star formation efficiency: low-mass systems follow main-sequence scaling relations, while high-mass systems show suppressed star formation. This diversity indicates that HI absorbers trace both evolved and younger galaxies, providing a key step toward completing the baryon census at redshift about 0.5.

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arXiv2024

Atomic and molecular gas as traced by [C II] emission

The latest ALMA and JWST observations provide new information on the birth and evolution of galaxies in the early Universe, at the epoch of reionization. Of particular importance are measurements at redshift $ z > 5$ of their cold-gas budget, which is known to be the main fuel for star formation. A powerful tool for probing the physics characterising galaxies at high redshift is the \CII\ $158\,\rm μm$ emission line. Due to its low excitation potential, \CII\ emission can be produced in photodissociation regions, neutral atomic gas and molecular clouds. To properly capture the cold-gas processes taking place in such environments (molecule formation, self-shielding, dust grain catalysis, photoelectric and cosmic-ray heating), we make use of a new set of state-of-the-art hydrodynamic simulations (\coldsim) including time-dependent non-equilibrium chemistry, star formation, stellar evolution, metal spreading and feedback mechanisms. We are able to accurately track the evolution of \HI, \HII\ and H$_2$ in a cosmological context and predict the contribution of each gas phase to \CII\ luminosity. We provide formulas that can be used to estimate the mass of molecular and atomic gas from \CII\ detections. Furthermore, we analyse how conversion factors evolve with galactic properties, such as stellar metallicity, star formation rate and stellar mass. We demonstrate that \CII\ emission is dominated by \HI\ gas and most of the \CII\ luminosity is generated in warm, dense star-forming regions. Importantly, we conclude that, despite \CII\ tracing predominantly atomic rather than molecular gas, the \CII\ luminosity remains a robust indicator of the H$_2$ mass.

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arXiv2024

ColdSIM predictions of [C II] emission in primordial galaxies

A powerful tool to probe the gas content at high redshift is the [C II] 158 $μ$m sub-millimeter emission line, which, due to its low excitation potential and luminous emission, is considered a possible direct tracer of star forming gas. In this work we investigate the origin, evolution and environmental dependencies of [C II] 158 $μ$m emission line, as well as its expected correlation with stellar mass and star formation activity of the high-redshift galaxies observed by JWST. We use a set of state-of-the-art cold-gas hydrodynamic simulations (ColdSIM) with fully coupled time-dependent atomic and molecular non-equilibrium chemistry and self-consistent [C II] emission from metal enriched gas. We accurately track the evolution of H I, H II and $H_2$ in a cosmological context and predict both global and galaxy-based [C II] properties. For the first time, we predict the cosmic mass density evolution of [C II] and find that it is in good agreement with new measurements at redshift z = 6 from high-resolution optical quasar spectroscopy. We find a correlation between [C II] luminosity, $L_{[C II]}$, and stellar mass, consistent with results from ALMA high-redshift large programs. We predict a redshift evolution in the relation between $L_{[C II]}$ and the star formation rate, SFR, and provide a fit to relate $L_{[C II]}$ to SFR which can be adopted as a more accurate alternative to the currently used linear relation. Our findings provide physical grounds to interpret high-redshift detections in contemporary and future observations, such as the ones performed by ALMA and JWST, and to advance our knowledge on structure formation at early times.

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arXiv2024

The imprint of magnetic fields on absorption spectra from circumgalactic wind-cloud systems

Galactic winds probe how stellar feedback regulates the mass and metallicity of galaxies. Observations show that galactic winds are multiphase and magnetised. In the local Universe, the dense phase is traced by emission and absorption lines, which reveal the presence of fast-moving clouds embedded in hot streams. Simulations tell us that magnetic fields can shield such clouds and delay their disruption, but there is little discussed on their observational effects. Using 3D MHD simulations, we study the influence of two orientations of the magnetic field (aligned and transverse) on the cloud morphology, temperature and density structure, mixing fraction, ion kinematics, column densities, and absorption spectra. We study supersonic wind-cloud systems with radiative processes, and develop a framework to extract ion column density maps and synthetic absorption spectra. The framework relies on studying ion populations and creating down-the-barrel spectra via an interface that links our PLUTO simulations to TRIDENT using YT, CLOUDY, and STARBURST99. We find that the transverse magnetic field makes the cloud asymmetric, shields and protects dense cold gas, and reduces mixing fractions compared to the aligned case. Ions can reach higher velocities in the transverse field case. The imprints of the initial orientation of the field on the synthetic spectra are: in the cold phase we find no signature of C ii and Si ii when the field is aligned, in the intermediate phase traced by C iv and Si iv we find broader lines in the transverse case, and in the warm phase we find deeper lines for O vi and N v in the aligned case, but they are less sensitive to the field orientation. Magnetic fields significantly affect the absorption spectra of cold clouds. Intermediate ions are the most sensitive to the magnetic field orientation and can potentially yield information about magnetic field topology.

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arXiv2023

The physical origins of gas in the circumgalactic medium using observationally-motivated TNG50 mocks

Absorbers in the spectrum of background objects probe the circumgalactic medium (CGM) surrounding galaxies, but its physical properties remain unconstrained. We use the cosmological hydrodynamical simulation TNG50 to statistically trace the origins of HI Ly-$α$ absorbers around galaxies at $z = 0.5$ with stellar masses ranging from 10$^8$ to 10$^{11}$ M$_\odot$. We emulate observational CGM studies by considering all gas within a line of sight velocity range of $\pm 500$ km s$^{-1}$ from the central, to quantitatively assess the impact of other galaxy haloes and overdense gas in the IGM that intersect sightlines. The impact of satellites to the total absorber fraction is most significant at impact parameters $0.5 R_{\rm vir} < b < R_{\rm vir}$ and satellites with masses below typical detection limits ($M_* < 10^8$ M$_\odot$) account for 10 (40) per cent of absorbers that intersect any satellite bound to $10^{10}$ and $10^{11}$ $(10^9)$ M$_\odot$ centrals. After confirming outflows are more dominant along the minor axis, we additionally show that at least 20 per cent of absorbers exhibit no significant radial movement, indicating that absorbers can also trace quasi-static gas. The metallicity of absorbers also depends on the azimuthal angle, but this signal is largely driven by enriched inflowing and quasi-static gas. Our work shows that determining the stellar mass of galaxies at $z_{\rm abs}$ is essential to constrain the physical origin of the gas traced in absorption, which in turn is key to characterising the kinematics and distribution of gas and metals in the CGM.

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arXiv2023

The BarYon CYCLE Project (ByCycle): Identifying and Localizing MgII Metal Absorbers with Machine Learning

The upcoming ByCycle project on the VISTA/4MOST multi-object spectrograph will offer new prospects of using a massive sample of $\sim 1$ million high spectral resolution ($R$ = 20,000) background quasars to map the circumgalactic metal content of foreground galaxies (observed at $R$ = 4000 - 7000), as traced by metal absorption. Such large surveys require specialized analysis methodologies. In the absence of early data, we instead produce synthetic 4MOST high-resolution fibre quasar spectra. To do so, we use the TNG50 cosmological magnetohydrodynamical simulation, combining photo-ionization post-processing and ray tracing, to capture MgII ($\lambda2796$, $\lambda2803$) absorbers. We then use this sample to train a Convolutional Neural Network (CNN) which searches for, and estimates the redshift of, MgII absorbers within these spectra. For a test sample of quasar spectra with uniformly distributed properties ($λ_{\rm{MgII,2796}}$, $\rm{EW}_{\rm{MgII,2796}}^{\rm{rest}} = 0.05 - 5.15$ Å, $\rm{SNR} = 3 - 50$), the algorithm has a robust classification accuracy of 98.6 per cent and a mean wavelength accuracy of 6.9 Å. For high signal-to-noise spectra ($\rm{SNR > 20}$), the algorithm robustly detects and localizes MgII absorbers down to equivalent widths of $\rm{EW}_{\rm{MgII,2796}}^{\rm{rest}} = 0.05$ Å. For the lowest SNR spectra ($\rm{SNR=3}$), the CNN reliably recovers and localizes EW$_{\rm{MgII,2796}}^{\rm{rest}}$ $\geq$ 0.75 Å\, absorbers. This is more than sufficient for subsequent Voigt profile fitting to characterize the detected MgII absorbers. We make the code publicly available through GitHub. Our work provides a proof-of-concept for future analyses of quasar spectra datasets numbering in the millions, soon to be delivered by the next generation of surveys.

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arXiv2023

MUSE-ALMA Halos XI: Gas flows in the circumgalactic medium

The flow of gas into and out of galaxies leaves traces in the circumgalactic medium which can then be studied using absorption lines towards background quasars. We analyse 27 log(N_HI) > 18.0 HI absorbers at z = 0.2 to 1.4 from the MUSE-ALMA Halos survey with at least one galaxy counterpart within a line of sight velocity of +/-500 km s^{-1}. We perform 3D kinematic forward modelling of these associated galaxies to examine the flow of dense, neutral gas in the circumgalactic medium. From the VLT/MUSE, HST broadband imaging and VLT/UVES and Keck/HIRES high-resolution UV quasar spectroscopy observations, we compare the impact parameters, star-formation rates and stellar masses of the associated galaxies with the absorber properties. We find marginal evidence for a bimodal distribution in azimuthal angles for strong HI absorbers, similar to previous studies of the MgII and OVI absorption lines. There is no clear metallicity dependence on azimuthal angle and we suggest a larger sample of absorbers are required to fully test the relationship predicted by cosmological hydrodynamical simulations. A case-by-case study of the absorbers reveals that ten per cent of absorbers are consistent with gas accretion, up to 30 per cent trace outflows while the remainder trace gas in the galaxy disk, the intragroup medium and low-mass galaxies below the MUSE detection limit. Our results highlight that the baryon cycle directly affects the dense neutral gas required for star-formation and plays a critical role in galaxy evolution.

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arXiv2022

Absorption spectra from galactic wind models: a framework to link PLUTO simulations to TRIDENT

Galactic winds probe how feedback regulates the mass and metallicity of galaxies. Galactic winds have cold gas, which is mainly observable with absorption and emission lines. Theoretically studying how absorption lines are produced requires numerical simulations and realistic starburst UV backgrounds. We use outputs from a suite of 3D PLUTO simulations of wind-cloud interactions to first estimate column densities and temperatures. Then, to create synthetic spectra, we developed a python interface to link our PLUTO simulations to TRIDENT via the YT-package infrastructure. First we produce UV backgrounds accounting for the star formation rate of starbursts. For this purpose, we use fluxes generated by STARBURST99, which are then processed through CLOUDY to create customised ion tables. Such tables are subsequently read into TRIDENT to generate absorption spectra. We explain how the various packages and tools communicate with each other to create ion spectra consistent with spectral energy distributions of starburst systems.

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