arXiv subjects

C. Scannapieco

Publications and source records attributed to C. Scannapieco.

At least 19 recordsLinked to original sources

arXiv2026

Probing the kinematics of the Local Group with chemically enriched gas in the Hestia simulations

We present a study of the gas kinematics within the Hestia project, a state-of-the-art set of simulations of the Local Group, with a particular focus on the velocity patterns of different ions and the large-scale motion of gas and galaxies towards the Local Group barycentre. Using two high-resolution Hestia runs, we examine the distribution and velocities of H I, C IV, Si III, O VI, O VII, and O VIII and their imprints on sightlines observed from the Sun's location in different reference frames. To mimic observational strategies, we assess the contribution of rotating disc gas, assuming simple kinematic and geometrical considerations. Our results indicate that local absorption features in observed sightlines most likely trace material in the circumgalactic medium of the Milky Way. Some sightlines, however, show that intragroup material could be more easily observed towards the barycentre, which defines a preferred direction in the sky. In particular, H I, Si III, and C IV roughly trace cold gas inside the Milky Way and Andromeda haloes, as most of their mass flux occurs within the virial region of each galaxy, while oxygen high ions mostly trace hot halo and intragroup gas, with comparable mass fluxes in the Local Group outskirts and the circumgalactic medium of the two main galaxies. Additionally, we find that pressures traced by different ionic species outside the Milky Way halo show systematically higher values towards the barycentre direction in contrast to its antipode in the sky. Kinematic imprints of the global motion towards the barycentre can be seen at larger distances for all ionic species as the Milky Way rams into material in the direction of Andromeda, with gas towards the anti-barycentre lagging behind.

astro-ph.GA↗

arXiv2025

From atoms to stars: Modelling $\mathrm{H}_2$ formation and its impact on galactic evolution

We present a sub-grid model for star formation in galaxy simulations, incorporating molecular hydrogen ($\mathrm{H}_2$) production via dust grain condensation and its destruction through star formation and photodissociation. Implemented within the magnetohydrodynamical code AREPO, our model tracks the non-equilibrium mass fractions of molecular, ionised, and atomic hydrogen, as well as a stellar component, by solving a system of differential equations governing mass exchange between these phases. Star formation is treated with a variable rate dependent on the local $\mathrm{H}_2$ abundance, which itself varies in a complex way with key quantities such as gas density and metallicity. Testing the model in a cosmological simulation of a Milky Way-mass galaxy, we obtain a well-defined spiral structure at $z = 0$, including a gas disc twice the size of the stellar one, alongside a realistic star formation history. Our results show a broad range of star formation efficiencies per free-fall time, from as low as $0.001\%$ at high redshift to values between $0.1\%$ and $10\%$ for ages $\gtrsim 3-4 \, \mathrm{Gyr}$. These findings align well with observational estimates and simulations of a turbulent interstellar medium. Notably, our model reproduces a star formation rate versus molecular hydrogen surface densities relation akin to the molecular Kennicutt-Schmidt law. Furthermore, we find that the star formation efficiency varies with density and metallicity, providing an alternative to fixed-efficiency assumptions and enabling comparisons with more detailed star formation models. Comparing different star formation prescriptions, we find that in models that link star formation to $\mathrm{H}_2$, star formation onset is $\sim \! 500 \, \mathrm{Myr}$ later than those relying solely on total or cold gas density.

astro-ph.GA↗

arXiv2025

Kinematic patterns of the enriched gas phase in the Local Group {\sc Hestia} simulations

Observations of intergalactic absorbers in the Local Group suggest the existence of a velocity dipole in the general barycentre--antibarycentre direction which can be interpreted as evidence of a general flow of material towards the group's centre of mass. In this work, we study the kinematics of gas in the Local Group using one of the high-resolution realisations of the {\sc Hestia} simulations with a particular focus on the evidence left by different ionic species. Our simulation includes the correct cosmography for a region similar to the Local Group and a relative radial velocity between the candidate Milky Way and Andromeda galaxies consistent with the observed one. We examine the distribution and kinematics of six ionic species (H\,{\sc i}, C\,{\sc iv}, Si\,{\sc iii}, O\,{\sc vi}, O\,{\sc vii} and O\,{\sc viii}) and their imprints on synthetic sky maps constructed from the reference frames commonly used by observers. Our results indicate the presence of such a dipole for gas outside the Milky Way halo, favouring a paradigm in which the Milky Way is moving against the gas in the direction of the barycentre, while moving away from it in the opposite direction. This pattern is clearer for the higher oxygen ions, which preferentially trace hot gas. On the other hand, we observe a slight asymmetry in the pressure profiles in both directions, indicating higher pressures in the inner regions of the Local Group.

astro-ph.GA↗

arXiv2023

The temporal evolution of gas accretion onto the discs of simulated Milky Way-mass galaxies

In the standard model of structure formation, galaxies form in the centre of dark matter haloes that develop as a result of inhomogeneities in the primordial mass distribution of the Universe. Afterwards, galaxies grow by means of continuous accretion of gaseous material stemming from the intergalactic medium, both in diffuse form and through collisions with other systems. After an initial period of violent growth, the gas settles into a rotationally-supported structure where stars are born, giving birth to the stellar disc. The accretion of gaseous material onto the disc plays a fundamental role in its evolution as it can change its dynamical and morphological properties, generating gas flows within the disc. In this work, we use 30 galaxies from the Auriga Project, a set of cosmological magnetohydrodynamical simulations of disc galaxies, to study the temporal dependence of the gas accretion rates, focusing on the inflowing and outflowing fluxes.

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arXiv2021

Gas accretion onto the disc of a simulated Milky Way-mass galaxy

In the standard paradigm of galaxy formation and evolution, the baryonic component of galaxies forms from the collapse and condensation of gas within dark matter haloes, and later grows from continuous accretion of gaseous mass, both in diffuse form and in mergers with other systems. After a first period of rapid and violent halo growth, the gas settles into a rotationally-supported structure, eventually giving rise to the formation of a stellar disc. Stars evolve and return chemically-processed gas and energy to the interstellar medium, mainly through Type II supernova explosions. In the disc region, the cosmological accretion of gas combines with the outflows resulting from supernovae, affecting the hydrodynamical and structural properties of the disc and producing gas flows in the vertical and radial directions. In this work, we use a simulation of the Auriga Project, a suite of magneto-hydrodynamical, zoom-in cosmological simulations of Milky Way-like galaxies, to study the temporal and radial dependencies of gas accretion onto the disc. We also investigate the disc evolution, focusing on the inside-out disc formation scenario, which is one of the fundamental hypotheses of chemical evolution models of the Galaxy.

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arXiv2021

Chemical abundance patterns in Local Group galaxies within cosmological simulations

In the context of the concordance cosmology, structure formation in the Universe is the result of the amplification, by gravitational effects, of small perturbations in the primeval density field. This results in the formation of structures known as dark matter haloes, where gas collapses and forms stars, giving birth to galaxies. Numerical simulations are an important tool in the theoretical study of galaxy formation and evolution. In the present work, we describe the implementation of a chemical enrichment model in a state-of-the-art cosmological simulation of the Local Group. The simulation includes sub-grid models for the most relevant physical processes. We analyze the chemical and morphological evolution of two galaxies with virial masses similar to that of our Milky Way. For each of the stellar components (disc, bulge and halo), we establish links between their formation history and their chemical evolution. We find that $α$-element (O, Mg, Si) enrichment happens at early stages of evolution, as their main producers are short-lived stars which end their lives as type II supernova explosions. There is also a gradual contamination with the rest of the elements as type Ia supernovae and winds of stars in the asymptotic giant branch occur.

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arXiv2019

Yule-Simpson's paradox in Galactic Archaeology

Simpson's paradox, or Yule-Simpson effect, arises when a trend appears in different subsets of data but disappears or reverses when these subsets are combined. We describe here seven cases of this phenomenon for chemo-kinematical relations believed to constrain the Milky Way disk formation and evolution. We show that interpreting trends in relations, such as the radial and vertical chemical abundance gradients, the age-metallicity relation, and the metallicity-rotational velocity relation (MVR), can lead to conflicting conclusions about the Galaxy past if analyses marginalize over stellar age and/or birth radius. It is demonstrated that the MVR in RAVE giants is consistent with being always strongly negative, when narrow bins of [Mg/Fe] are considered. This is directly related to the negative radial metallicity gradients of stars grouped by common age (mono-age populations) due to the inside out disk formation. The effect of the asymmetric drift can then give rise to a positive MVR trend in high-[alpha/Fe] stars, with a slope dependent on a given survey's selection function and observational uncertainties. We also study the variation of lithium abundance, A(Li), with [Fe/H] of AMBRE:HARPS dwarfs. A strong reversal in the positive A(Li)-[Fe/H] trend of the total sample is found for mono-age populations, flattening for younger groups of stars. Dissecting by birth radius shows strengthening in the positive A(Li)-[Fe/H] trend, shifting to higher [Fe/H] with decreasing birth radius; these observational results suggest new constraints on chemical evolution models. This work highlights the necessity for precise age estimates for large stellar samples covering wide spatial regions.

astro-ph.GA↗

arXiv2016

On the nature of diffuse ionized gas in galaxies -- I The contribution of dust scattering to diffuse line emission

In this work, we investigate the contribution of dust scattering to the diffuse H-alpha emission observed in nearby galaxies. As initial conditions for the spatial distribution of HII regions, gas, and dust, we take three Milky Way-like galaxies from state-of-the-art cosmological hydrodynamical simulations that implement different prescriptions for star formation, feedback, and chemical enrichment. Radiative transfer has been solved a posteriori, using the publicly-available Monte Carlo code Sunrise to take into account dust absorption and scattering of the H-alpha photons, originating exclusively from the HII regions. No contribution from recombinations in the diffuse ionized gas (DIG) component is explicitly or implicitly included in our model. Our main result is that the flux arising from scattered light is of the order of 1-2 per cent of the H-alpha flux coming directly from the HII regions. Building upon previous studies, we conclude that the DIG contributes lass than 50 per cent of the total H-alpha emission.

astro-ph.GA↗

arXiv2015

On the Formation of Galactic Thick Disks

Recent spectroscopic observations in the Milky Way suggest that the chemically defined thick disk (stars with high [alpha/Fe] ratios and thus old) has a significantly smaller scale-length than the thin disk. This is in apparent contradiction with observations of external edge-on galaxies, where the thin and thick components have comparable scale-lengths. Moreover, while observed disks do not flare (scale-height does not increase with radius), numerical simulations suggest that disk flaring is unavoidable, resulting from both environmental effects and secular evolution. Here we address these problems by studying two different suites of simulated galactic disks formed in the cosmological context. We show that the scale-heights of coeval populations always increase with radius. However, the total population can be decomposed morphologically into thin and thick disks, which do not flare. We relate this to the disk inside-out formation, where younger populations have increasingly larger scale-lengths and flare at progressively larger radii. In this new picture, thick disks are composed of the imbedded flares of mono-age stellar populations. Assuming that disks form inside out, we predict that morphologically defined thick disks must show a decrease in age (or [alpha/Fe] ratios) with radius and that coeval populations should always flare. This also explains the observed inversion in the metallicity and [alpha/Fe] gradients for stars away from the disk midplane in the Milky Way. The results of this work are directly linked to, and can be seen as evidence of, inside-out disk growth.

astro-ph.GA↗

arXiv2014

Stellar haloes in Milky-Way mass galaxies: From the inner to the outer haloes

We present a comprehensive study of the chemical properties of the stellar haloes of Milky-Way mass galaxies, analysing the transition between the inner to the outer haloes. We find the transition radius between the relative dominance of the inner-halo and outer-halo stellar populations to be ~15-20 kpc for most of our haloes, similar to that inferred for the Milky Way from recent observations. While the number density of stars in the simulated inner-halo populations decreases rapidly with distance, the outer-halo populations contribute about 20-40 per cent in the fiducial solar neighborhood, in particular at the lowest metallicities. We have determined [Fe/H] profiles for our simulated haloes; they exhibit flat or mild gradients, in the range [-0.002, -0.01 ] dex/kpc. The metallicity distribution functions exhibit different features, reflecting the different assembly history of the individual stellar haloes. We find that stellar haloes formed with larger contributions from massive subgalactic systems have steeper metallicity gradients. Very metal-poor stars are mainly contributed to the halo systems by lower-mass satellites. There is a clear trend among the predicted metallicity distribution functions that a higher fraction of low-metallicity stars are found with increasing radius. These properties are consistent with the range of behaviours observed for stellar haloes of nearby galaxies.

astro-ph.CO↗

arXiv2013

A new stellar chemo-kinematic relation reveals the merger history of the Milky Way disc

The velocity dispersions of stars near the Sun are known to increase with stellar age, but age can be difficult to determine so a proxy like the abundance of alpha elements (e.g., Mg) with respect to iron, [alpha/Fe], is used. Here we report an unexpected behavior found in the velocity dispersion of a sample of giant stars from the RAdial Velocity Experiment (RAVE) survey with high quality chemical and kinematical information, in that it decreases strongly for stars with [Mg/Fe] > 0.4 dex (i.e., those that formed in the first Gyr of the Galaxy's life). These findings can be explained by perturbations from massive mergers in the early Universe, which have affected more strongly the outer parts of the disc, and the subsequent radial migration of stars with cooler kinematics from the inner disc. Similar reversed trends in velocity dispersion are also found for different metallicity subpopulations. Our results suggest that the Milky Way disc merger history can be recovered by relating the observed chemo-kinematic relations to the properties of past merger events.

astro-ph.GA↗

arXiv2013

The RAVE survey: the Galactic escape speed and the mass of the Milky Way

We construct new estimates on the Galactic escape speed at various Galactocentric radii using the latest data release of the Radial Velocity Experiment (RAVE DR4). Compared to previous studies we have a database larger by a factor of 10 as well as reliable distance estimates for almost all stars. Our analysis is based on the statistical analysis of a rigorously selected sample of 90 high-velocity halo stars from RAVE and a previously published data set. We calibrate and extensively test our method using a suite of cosmological simulations of the formation of Milky Way-sized galaxies. Our best estimate of the local Galactic escape speed, which we define as the minimum speed required to reach three virial radii $R_{340}$, is $533^{+54}_{-41}$ km/s (90% confidence) with an additional 5% systematic uncertainty, where $R_{340}$ is the Galactocentric radius encompassing a mean over-density of 340 times the critical density for closure in the Universe. From the escape speed we further derive estimates of the mass of the Galaxy using a simple mass model with two options for the mass profile of the dark matter halo: an unaltered and an adiabatically contracted Navarro, Frenk & White (NFW) sphere. If we fix the local circular velocity the latter profile yields a significantly higher mass than the un-contracted halo, but if we instead use the statistics on halo concentration parameters in large cosmological simulations as a constraint we find very similar masses for both models. Our best estimate for $M_{340}$, the mass interior to $R_{340}$ (dark matter and baryons), is $1.3^{+0.4}_{-0.3} \times 10^{12}$ M$_\odot$ (corresponding to $M_{200} = 1.6^{+0.5}_{-0.4} \times 10^{12}$ M$_\odot$). This estimate is in good agreement with recently published independent mass estimates based on the kinematics of more distant halo stars and the satellite galaxy Leo I.

astro-ph.GA↗

arXiv2013

Stellar haloes of simulated Milky Way-like galaxies: Chemical and kinematic properties

We investigate the chemical and kinematic properties of the diffuse stellar haloes of six simulated Milky Way-like galaxies from the Aquarius Project. Binding energy criteria are adopted to defined two dynamically distinct stellar populations: the diffuse inner and outer haloes, which comprise different stellar sub-populations with particular chemical and kinematic characteristics. Our simulated inner- and outer-halo stellar populations have received contributions from debris stars (formed in sub-galactic systems while they were outside the virial radius of the main progenitor galaxies) and endo-debris stars (those formed in gas-rich sub-galactic systems inside the dark matter haloes). The inner haloes possess an additional contribution from disc-heated stars in the range $\sim 3 - 30 %$, with a mean of $\sim 20% $. Disc-heated stars might exhibit signatures of kinematical support, in particular among the youngest ones. Endo-debris plus disc-heated stars define the so-called \insitu stellar populations. In both the inner- and outer-halo stellar populations, we detect contributions from stars with moderate to low [$α$/Fe] ratios, mainly associated with the endo-debris or disc-heated sub-populations. The observed abundance gradients in the inner-halo regions are influenced by both the level of chemical enrichment and the relative contributions from each stellar sub-population. Steeper abundance gradients in the inner-halo regions are related to contributions from the disc-heated and endo-debris stars, which tend to be found at lower binding energies than debris stars. (Abridged).

astro-ph.GA↗

arXiv2012

The Aquila comparison Project: The Effects of Feedback and Numerical Methods on Simulations of Galaxy Formation

We compare the results of thirteen cosmological gasdynamical codes used to simulate the formation of a galaxy in the LCDM structure formation paradigm. The various runs differ in their hydrodynamical treatment (SPH, moving-mesh and AMR) but share the same initial conditions and adopt their latest published model of cooling, star formation and feedback. Despite the common halo assembly history, we find large code-to-code variations in the stellar mass, size, morphology and gas content of the galaxy at z=0, due mainly to the different implementations of feedback. Compared with observation, most codes tend to produce an overly massive galaxy, smaller and less gas-rich than typical spirals, with a massive bulge and a declining rotation curve. A stellar disk is discernible in most simulations, though its prominence varies widely from code to code. There is a well-defined trend between the effects of feedback and the severity of the disagreement with observation. Models that are more effective at limiting the baryonic mass of the galaxy come closer to matching observed galaxy scaling laws, but often to the detriment of the disk component. Our conclusions hold at two different numerical resolutions. Some differences can also be traced to the numerical techniques: more gas seems able to cool and become available for star formation in grid-based codes than in SPH. However, this effect is small compared to the variations induced by different feedback prescriptions. We conclude that state-of-the-art simulations cannot yet uniquely predict the properties of the baryonic component of a galaxy, even when the assembly history of its host halo is fully specified. Developing feedback algorithms that can effectively regulate the mass of a galaxy without hindering the formation of high-angular momentum stellar disks remains a challenge.

astro-ph.GA↗

arXiv2007

The host galaxies of long-duration GRBs in a cosmological hierarchical scenario

We developed a Monte Carlo code to generate long-duration gamma ray burst (LGRB) events within cosmological hydrodynamical simulations consistent with the concordance model. As structure is assembled, LGRBs are generated in the substructure that formed galaxies today. We adopted the collapsar model so that LGRBs are produced by single, massive stars at the final stage of their evolution. We found that the observed properties of the LGRB host galaxies (HGs) are reproduced if LGRBs are also required to be generated by low metallicity stars. The low metallicity condition imposed on the progenitor stars of LGRBs selects a sample of HGs with mean gas abundances of 12 + log O/H \~ 8.6. For z<1 the simulated HGs of low metallicity LGRB progenitors tend to be faint, slow rotators with high star formation efficiency, compared with the general galaxy population, in agreement with observations. At higher redshift, our results suggest that larger systems with high star formation activity could also contribute to the generation of LGRBs from low metallicity progenitors since the fraction of low metallicity gas available for star formation increases for all systems with look-back time. Under the hypothesis of our LGRB model, our results support the claim that LGRBs could be unbiased tracers of star formation at high redshifts.

astro-ph↗

arXiv2006

Feedback and metal enrichment in cosmological SPH simulations I. A model for chemical enrichment

We discuss a model for treating chemical enrichment by SNII and SNIa explosions in simulations of cosmological structure formation. Our model includes metal-dependent radiative cooling and star formation in dense collapsed gas clumps. Metals are returned into the diffuse interstellar medium by star particles using a local SPH smoothing kernel. A variety of chemical abundance patterns in enriched gas arise in our treatment owing to the different yields and lifetimes of SNII and SNIa progenitor stars. In the case of SNII chemical production, we adopt metal-dependent yields. Because of the sensitive dependence of cooling rates on metallicity, enrichment of galactic haloes with metals can in principle significantly alter subsequent gas infall and the build up of the stellar components. Indeed, in simulations of isolated galaxies we find that a consistent treatment of metal-dependent cooling produces 25% more stars outside the central region than simulations with a primordial cooling function. In the highly-enriched central regions, the evolution of baryons is however not affected by metal cooling, because here the gas is always dense enough to cool. A similar situation is found in cosmological simulations because we include no strong feedback processes which could spread metals over large distances and mix them into unenriched diffuse gas. We demonstrate this explicitly with test simulations which adopt super-solar cooling functions leading to large changes both in the stellar mass and in the metal distributions. We also find that the impact of metallicity on the star formation histories of galaxies may depend on their particular evolutionary history. Our results hence emphasise the importance of feedback processes for interpreting the cosmic metal enrichment.

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arXiv2006

Study of the relationship between the gamma ray bursts and their host galaxies

Gamma ray bursts (GRBs) belong to the most energetic events in the Universe. Recently, the extragalactic nature of these sources has been confirmed with the discovery of several host galaxies (HGs) and the measurement of their redshifts. To explain the origin of GRBs various models have been proposed, among which the coalescence of compact objects and the "collapsar" scenarios are the most representative, being the collapsar model one of the most accepted to explain the long duration GRBs. A natural consequence of this model is that the GRBs would trace the star formation rate (SFR) of their HGs. In this contributed paper we present preliminary results of the development of a Montecarlo-based code for collapsar event formation which is coupled to chemical-cosmological simulations aiming at studying the properties of HGs in a hierarchical scenario.

astro-ph↗

arXiv2006

Galaxy Formation and SN Feedback

We present a Supernova (SN) feedback model that succeeds at describing the chemical and energetic effects of SN explosions in galaxy formation simulations. This new SN model has been coupled to GADGET-2 and works within a new multiphase scheme which allows the description of a co-spatial mixture of cold and hot interstellar medium phases. No ad hoc scale-dependent parameters are associated to these SN and multiphase models making them particularly suited to studies of galaxy formation in a cosmological framework. Our SN model succeeds not only in setting a self-regulated star formation activity in galaxies but in triggering collimated chemical-enriched galactic winds. The effects of winds vary with the virial mass of the systems so that the smaller the galaxy, the larger the fraction of swept away gas and the stronger the decrease in its star formation activity. The fact that the fraction of ejected metals exceeds 60 per cent regardless of mass, suggests that SN feedback can be the responsible mechanism of the enrichment of the intergalactic medium to the observed levels.

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