arXiv subjects

Marta De Simone

Publications and source records attributed to Marta De Simone.

At least 19 recordsLinked to original sources

arXiv2026

FAUST XXXII. Chemically layered structures and ionisation in the disk and envelope of NGC 1333 IRAS 4C

Recent molecular line observations with high spatial resolutions have revealed vertical chemical stratification in Class I/II disks (i.e. chemical composition changing with height in the vertical direction of the disk), as well as a radial variation of ionisation rates. However, such chemical layered structures in Class 0 disk and envelope systems have been investigated only for limited objects, such as L1527. In the context of the ALMA Large Program FAUST, we report the results of molecular line observations toward the disk and envelope around the low-mass Class 0 protostar NGC 1333 IRAS 4C in the Perseus Molecular Cloud. Previous observations have shown that the disk rotation axis of this object is largely tilted to the line of sight, making it suitable for studying the molecular abundance distribution as a function of disk height. We found that the molecules known as gas density tracers such as C18O and H2CO are distributed around the disk midplane. In addition, molecules known as tracers of photochemical reactions such as CCH and c-C3H2 are distributed in the low-density upper layers of the disk, unlike the distribution in L1527. Moreover, the column density ratio of HCO+/CO derived from the H13CO+ and C18O line emission suggests that the ionisation degree and the ionisation rate vary with the disk radius and they are larger in the outer region of the disk and envelope.

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arXiv2026

Chemical Demographics of Star-forming Regions

Our understanding of complex organic chemistry during the formation of stars and planets is shaped by a handful of cherry-picked sources with bright molecular emission lines. This observational bias impedes our assessment of how universal chemical complexity is during star formation. The lack of systematic wideband spectral surveys for statistically significant samples of protostars and cores is a major roadblock to properly probing how COM inventories and abundances depend on the vast range of physical conditions, local cloud and global galactic environments, and evolutionary timescales of low- and high-mass star formation. In turn, this limits our ability to constrain and test physicochemical models, which depend critically on these parameters. The next-generation ALMA2040, with a 10x improvement in line sensitivity, is required to observe COMs, that we perceive as common today, in a fraction of the observing time that is needed today with ALMA. Such capabilities will propel us into the era of chemical demographics, whereby wideband (>100 GHz) spectral surveys at high sensitivity (routinely probing COM abundances down to 0.01% relative to CH3OH) will be executed towards >1000-10000 prestellar and protostellar sources. With robust chemical inventories towards large source sample sizes, we will be able to probe for dependencies of chemical complexity on mass regime, feedback processes in a cluster, Galactic position, metallicity, and time-variable accretion. Only with statistically significant samples at high sensitivity will we be able to assess the ubiquity and homogeneity of COM chemistry across the protostellar mass spectrum and natal cores. Constraining the diversity and availability of such species is critical for our understanding of the chemical reservoir available for planet formation, which eventually shapes (exo)planetary atmosphere compositions.

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arXiv2026

From local chemistry to galactic evolution: unlocking the power of interstellar isotopes with ALMA2040

Molecular isotopic ratios provide a unique window into the chemical evolution of the interstellar medium, linking stellar nucleosynthesis and Galactic chemical evolution to the physical and chemical processes shaping molecular clouds, star-forming regions, and planetary systems. However, molecular isotopic ratios do not necessarily trace the underlying elemental composition, as chemical isotopic fractionation, isotope-selective photodissociation, grain chemistry, and radiative-transfer effects can significantly alter the observed values. Disentangling these effects requires simultaneous observations of multiple transitions, isotope systems and molecular families, including rare, doubly, and multiply substituted isotopologues involving D, $^{13}$C, $^{15}$N, $^{17,18}$O, $^{29,30}$Si, and $^{33,34,36}$S (e.g., $^{13}$C$^{15}$N, $^{13}$C$^{34}$S, and $^{13}$C$^{18}$O). ALMA2040, with an order-of-magnitude improvement in sensitivity and at least 512 GHz of instantaneous bandwidth, will make these species accessible across statistically significant samples of Galactic and nearby extragalactic sources. By enabling systematic isotopic inventories from molecular clouds and prestellar cores to protoplanetary systems, across the Milky Way and in external galaxies, ALMA2040 will establish molecular isotopes as quantitative probes of chemical inheritance, stellar nucleosynthesis, and galaxy evolution, disentangling local chemical processing from the large-scale evolution of matter from stars to new planetary systems.

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arXiv2026

Chemistry on solar system scales

The initial chemical composition of planets, primitive bodies in our solar system, and exoplanets is ultimately set by their nascent protoplanetary disks. Yet observing key carbon-, oxygen-, and nitrogen-bearing molecules (as well as rarer but important sulphur- and phosphorus-bearing species) in the inner (exo)planet-forming zone ($\lesssim 10$~au) remains extremely challenging with current facilities. Therefore, to construct a complete picture of the chemistry of planet formation and understand how (exo)planetary composition is set by physical and chemical processes within the protoplanetary disk, a more powerful observing facility, i.e., ALMA2040, is needed. Compared to current ALMA (the Atacama Large Millimeter/submillimeter Array) this new facility must provide >~ a factor of 10 in line sensitivity at a spatial resolution of <~ 5 au at 140 pc, i.e., a factor of 3 - 4 better resolution to low surface brightness emission than currently possible. This distance includes many star-forming regions such as Taurus and Lupus that are host to populations of Sun-like stars. ALMA2040 will enable mapping of disk chemical composition on terrestrial planet-forming scales (within the water snowline) and detect molecules that are the feedstock for potentially habitable worlds.

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arXiv2026

An ALMA view on molecular complexity: water, methanol, and methyl formate in the HD 100546 and IRS 48 disks

Water and methanol are the fundamental constituents of interstellar and cometary ices: understanding their abundances in disks is therefore of high importance to reveal how this ice reservoir evolves across the timeline of star and planet formation. We present ALMA band 5 line emission observations of water and methanol in the warm Herbig disks of HD 100546 and IRS 48. While the IRS 48 disk is methanol-rich, water vapor is not detected, implying a high methanol-to-water column density ratio >0.2, possibly reflecting a distinct ice composition. Methanol and water are both detected in the HD 100546 disk, leading to a CH3OH/H2O ratio of ~0.02, consistent with the median of the cometary distribution and with the lower edge of the distribution of Young Stellar Objects. We suggest that the gas-phase methanol-to-water ratio in the HD 100546 disk directly reveals the ice reservoir subsequently sublimated in the warm disk stage. Moreover, we report a methyl formate-to-methanol ratio in the IRS 48 disk of ~0.2, consistent with the upper edge of the distribution of Young Stellar Objects. The methyl formate-to-methanol ratio in the HD 100546 disk is ~2, much higher than in younger and older sources, possibly reflecting a chemical enhancement of gas-phase methyl formate. We additionally constrain non-LTE conditions, optical depths, and emitting regions of the methanol lines in both disks. These results offer a new opportunity to probe the chemical trail of molecular complexity in the intermediate disk stage, bridging early and late phases of the star and planet formation history.

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arXiv2026

Interstellar disparity: N- vs O-bearing molecules: A multidisciplinary perspective across interstellar environments

Observations of O- and N-bearing molecules reveal systematic chemical differentiation across a wide range of interstellar environments. This pattern is peculiar and its origin likely reflects a combination of physical conditions, chemical pathways, and observational effects rather than a single mechanism. In this paper, we provide a comprehensive overview of the current understanding of the N-bearing and O-bearing species and their relative behaviour in the interstellar medium, integrating results from observations, laboratory experiments, chemical modelling, and theoretical studies. While inspired by discussions at the Lorentz Center workshop held in Leiden in August 2025, this work goes beyond a summary of the meeting and instead synthesizes the state of the field, highlights key open questions, and outlines future directions. We identify several key observational, experimental, and theoretical challenges that must be addressed to determine the origin of this chemical differentiation.

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arXiv2026

SKAO-ALMA Synergies in Star Formation Science

We highlight the potential for synergies between the SKA telescopes and ALMA, which will begin to be significant already with SKA Early Science. Broadly within star formation science, we focus on 1) (simultaneous) time domain and variability studies (e.g., of (proto-)stars), which is systematically opening a new observing window that will enable us to better constrain the physics of extreme stellar flares and their interplay with mass accretion in young stars, 2) possibilities for complementary coverage of different transitions of molecules as tracers of the ISM (e.g., H2CO to trace density and temperature), and 3) radio recombination lines to trace ionised gas at different densities. Furthermore, we address synergies in terms of the spatial resolution of both observatories and new capabilities not only on the SKAO side but extending to the ALMA2030 wideband sensitivity upgrade.

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arXiv2026

Chemical Complexity in the Early Stages of Star Formation in the SKAO Era

About 350 molecules have been identified in the interstellar medium (ISM), including complex molecules relevant to prebiotic chemistry. A remarkable level of molecular diversity has been observed from the earliest stages of star formation, providing the initial chemical inventory inherited by planetary systems. Radio observations have played a pivotal role in these discoveries, starting with the identification of the first polyatomic molecule, $\text{NH}_3$ (Cheung et al. 1968). (Sub-)millimeter observations have revealed complex organic molecules of prebiotic relevance, including formamide ($\text{NH}_2\text{CHO}$), glycolaldehyde ($\text{CH}_2\text{OHCHO}$), and even urea ($(\text{NH}_2)_2\text{CO}$), and hydroxylamine ($\text{NH}_2\text{OH}$), which are possible precursors of RNA nucleotides (Ceccarelli et al. 2023; Jiménez-Serra et al. 2020). However, in dense protostellar regions, dust opacity hampers the detection of molecular emission. Additionally, large molecules and those containing heavy atoms, which have rotational transitions at lower frequencies, often remain inaccessible to current instruments. The Square Kilometre Array Observatory (SKAO) will provide an unprecedented combination of sensitivity and angular resolution at radio wavelengths. This will allow for the detection of prebiotic species and offer new insights into the chemical pathways that shape emerging planetary systems (Jiménez-Serra et al. 2022). This chapter details the scientific questions and advancements that the SKAO, and more specifically, SKA-Mid equipped with the Band 5 receivers, will pursue in the field of astrochemistry, focusing on the chemical complexity in both high-mass and solar-type star-forming regions.

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arXiv2026

Unveiling Complex Chemistry in Planet-forming Disks with the SKAO

The chemical composition of planets is inherited from that of the natal protoplanetary disk at the time of planet formation. In recent years, we have made huge progress in characterizing disk chemistry. (Sub-)millimeter interferometers, such as ALMA, allowed us to detect emission lines from simple to complex organic molecules and to probe their radial and vertical distribution in disks. On the other hand, JWST has started to unveil the composition of disk ices, and line emission from the innermost disk regions. The advent of SKA will open new domains in the field, by observing emission lines from heavier molecules including heavy carbon chains and rings, and prebiotic molecules with peak emission in the cm range. Moreover, SKA will probe molecular emission from regions which are obscured by dust opacity at mm wavelengths, hence from the disk midplane, and often from the inner 30 au region. These observations will constrain the initial conditions for disk evolution and planet formation, allowing us to predict the chemical composition of the forming planets and their atmospheres. Comparison with forthcoming results on exoplanet atmospheres and on the chemistry of pristine bodies in the Solar System will provide new hints on the origin and evolution of planetary systems including our own.

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arXiv2026

Jets and Outflows in Young Stellar Objects with the SKAO

Jets and outflows are ubiquitous phenomena associated with the formation of young stellar objects (YSOs). They play a crucial role in removing angular momentum from the accreting system and in regulating star-formation efficiency. Theoretical studies and observations with ALMA and VLA have shown that jets and winds may have a crucial role in promoting dust growth in the envelope-disc system and in shaping the physical and chemical properties of the surrounding environment. Despite these significant advances, many fundamental questions remain unanswered regarding the acceleration, collimation, and chemical impact of jets and outflows from YSOs. The SKA-project will overcome the limitations of current mm/cm-facilities by enabling high-angular resolution and high-sensitivity cm-observations, crucial for probing jets/outflows near YSOs. Radio recombination lines, combined with proper motions, offer a unique opportunity to study the 3D-kinematics of jets. Non-thermal linearly polarised synchrotron emission will allow measuring magnetic field strength and morphology at unprecedented scales of a few au. Observations of dust emission in outflow cavities will allow studying how dust grows and is eventually transported from the disc to the envelope and back. Finally, the SKA-project will allow exploring the dust composition and chemical enrichment in shocks, where sputtering/shattering of grains cause the release of their mantles and refractory cores in the gas-phase. Complementary to ALMA's detection of simple and complex organic molecules, the SKAO will probe, for the first time, long carbon chains/rings, several Cl-, Al-, Mg-, and other metal-bearing species (missed by current sub-mm facilities).

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arXiv2026

High-resolution mid-IR spectroscopy of SVS 13-A with EXES/SOFIA: The surprisingly high CH$_3$OH/H$_2$O ratio in the planet-forming zone of a solar mass protostar

Water and methanol are key components of interstellar ices and gas in star- and planet-forming regions, but direct observations of water in low-mass protostars are challenging due to atmospheric absorption. We present high-resolution (R = 70,500) mid-infrared spectroscopy of the Class I protostar SVS13-A with EXES on board SOFIA at 26 $μ$m, targeting both H$_2$O and CH$_3$OH absorption lines. Several lines of each species are detected, tracing warm gas with rotational temperatures of $\sim$140--170 K. Remarkably, the methanol column density is a factor of $\sim$4 higher than that of water, well above typical interstellar ice ratios ($<$10\%). Comparison with previous millimeter observations indicates that absorption and emission probe distinct regions, with the mid-IR lines likely tracing cooler gas along the line of sight. The surprising observed CH$_3$OH/H$_2$O ratio may reflect selective sublimation due to the distribution of binding energies or ice stratification in the inner envelope. These observations probe the inner regions of the protostar, where planets are expected to form and inherit the chemical composition of their natal environment, providing a direct link between ice sublimation and gas-phase chemistry. Our results represent the first high-spectral-resolution mid-infrared view of both water and methanol toward a low-mass protostar, offering a unique window into the chemical composition of the innermost envelope and planet-forming region, and highlighting the diagnostic power of high-resolution mid-infrared spectroscopy to uncover hidden chemical layers and the ice-to-gas transition in embedded protostars.

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arXiv2026

Carbon chain diversity in L1544 and IRAS 16293-2422: an astrochemical pathfinder study for the SKAO

Astrochemical observations have revealed a surprisingly high level of chemical complexity, including long carbon chains, in the earliest stages of Sun-like star formation. The origin of these species and whether they undergo further growth, possibly contributing to the molecular complexity of planetary systems, remain open questions. We present recent observations performed using the 100-m Green Bank Telescope of the prestellar core L1544 and the protostellar system IRAS 16293-2422. In L1544, we detected several complex carbon-bearing species, including $\mathrm{C_2S}$, $\mathrm{C_3S}$, $\mathrm{C_3N}$, $\mathrm{c\text{-}C_3H}$, $\mathrm{C_4H}$, and $\mathrm{C_6H}$, complementing previously reported emission of cyanopolyynes. In IRAS 16293-2422, we detected $\mathrm{c\text{-}C_3H}$ and, for the first time, $\mathrm{HC_7N}$. Thanks to the high spectral resolution, we refine the rest frequencies of several $\mathrm{c\text{-}C_3H}$ and $\mathrm{C_6H}$ transitions. We perform radiative transfer analysis, highlighting a chemical difference between the two sources: IRAS 16293-2422 shows column densities 10-100 times lower than L1544. We perform astrochemical modeling, employing an up-to-date chemical network with revised reaction rates. The models reproduce the general trends, with cyanopolyyne and polyynyl radical abundances decreasing as molecular size increases, but they underestimate the abundances of cyanopolyynes longer than $\mathrm{HC_5N}$ by up to two orders of magnitude. Current models, which include the dominant neutral-neutral formation routes, cannot account for this discrepancy, suggesting that the chemical network is incomplete. We propose that additional ion-molecule reactions are crucial for the formation of these species. Developing a more comprehensive chemical network for long carbon chains is essential for accurately interpreting present and future observations.

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arXiv2025

FAUST XXIX. OCS line emission: a new method for measuring the luminosity of embedded protostars in binary systems

The luminosity of embedded protostars is commonly measured via observations of the dust continuum spectral energy distribution from millimetre to infrared wavelengths. However, this method cannot be applied to embedded protostars in binary or multiple systems, where their components are usually unresolved over this extended wavelength range. We propose a new method, based on the idea that a molecule formed (mainly) on the grain surfaces only emits lines in the region where it thermally sublimates from the grain mantles, heated by the photons emitted by the embedded source. In this respect, carbonyl sulfide (OCS) is an optimal molecule, because of its low binding energy and rotational lines in the millimetre. We apply the method to the protobinary system NGC1333 IRAS4A, using ALMA high-spatial resolution ($\sim$50 au) observations of the OCS(19-18) line as part of the ALMA Large Program FAUST. We also present new quantum mechanics calculations of the OCS binding energy distribution, essential for the application of the method. We found that the two binary components, A1 and A2, have a comparable luminosity within the error bars, 7.5$\pm$2.5 and 7$\pm$1 L$_\odot$, respectively. We discuss the reliability of the estimated luminosities and the potential of this new method for measuring the luminosity of embedded protostars in binary and multiple systems.

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arXiv2025

FAUST XXVII: The circumbinary disk and the outflow of the L 1551 IRS 5 binary system

Using continuum and $\text{C}^{18}\text{O}\:(2-1)$ line data obtained from the large ALMA program FAUST, we studied the structure of the protostellar binary system L1551 IRS5 at scales between 30 and 3,000 au to constrain its properties, from the circumstellar and circumbinary disks up to the envelope and outflow scales, which exhibits complex and entangled structures at the scales of its inner and outer envelopes, presumably caused by the influence of the central binary. Assuming a dust-to-gas ratio of 100, we calculated the dust+gas mass for the circumbinary disk and each circumstellar disk of the binary, obtaining 0.018 M$_{\odot}$, for the circumbinary disk, 0.004 M$_{\odot}$, and 0.002 M$_{\odot}$, for the northern and southern circumstellar disk respectively. From the line emission, we retrieved the gas masses for each structure component. With the $\text{C}^{18}\text{O}\:(2-1)$ PV diagram along the circumbinary disk, we were able to constrain the centrifugal barrier, $r_{CB}=55$ au, update the specific angular momentum, $j\sim270$~au~km~s$^{-1}$. We built an analytical model that can be used to predict the influence of the morphology of the outflow and a few dynamic features that can reproduce the system emission, allowing us to explain and discern the outflow contribution from the complex emission due to the binary. Additionally, we inferred the density power law index, $α=1.7$, and the envelope rotation velocity, $v_{c}=2$~km~s$^{-1}$. Finally, the observations gave us the physical constraints to obtain a coherent outflow model for L1551 IRS5.

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arXiv2024

FAUST XIX. D$_2$CO in the outflow cavities of NGC\,1333 IRAS\,4A: recovering the physical structure of its original prestellar core

Molecular deuteration is a powerful diagnostic tool for probing the physical conditions and chemical processes in astrophysical environments. In this work, we focus on formaldehyde deuteration in the protobinary system NGC\,1333 IRAS\,4A, located in the Perseus molecular cloud. Using high-resolution ($\sim$\,100\,au) ALMA observations, we investigate the [D$_2$CO]/[HDCO] ratio along the cavity walls of the outflows emanating from IRAS\,4A1. Our analysis reveals a consistent decrease in the deuteration ratio (from $\sim$\,60-20\% to $\sim$\,10\%) with increasing distance from the protostar (from $\sim$\,2000\,au to $\sim$\,4000\,au). Given the large measured [D$_2$CO]/[HDCO], both HDCO and D$_2$CO are likely injected by the shocks along the cavity walls into the gas-phase from the dust mantles, formed in the previous prestellar phase. We propose that the observed [D$_2$CO]/[HDCO] decrease is due to the density profile of the prestellar core from which NGC\,1333 IRAS\,4A was born. When considering the chemical processes at the base of formaldehyde deuteration, the IRAS\,4A's prestellar precursor had a predominantly flat density profile within 3000\,au and a decrease of density beyond this radius.

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arXiv2024

Multiple chemical tracers finally unveil the intricate NGC\,1333 IRAS\,4A outflow system. FAUST XVI

The exploration of outflows in protobinary systems presents a challenging yet crucial endeavour, offering valuable insights into the dynamic interplay between protostars and their evolution. In this study, we examine the morphology and dynamics of jets and outflows within the IRAS\,4A protobinary system. This analysis is based on ALMA observations of SiO(5--4), H$_2$CO(3$_{0,3}$--2$_{0,3}$), and HDCO(4$_{1,4}$--3$_{1,3}$) with a spatial resolution of $\sim$150\,au. Leveraging an astrochemical approach involving the use of diverse tracers beyond traditional ones has enabled the identification of novel features and a comprehensive understanding of the broader outflow dynamics. Our analysis reveals the presence of two jets in the redshifted emission, emanating from IRAS\,4A1 and IRAS\,4A2, respectively. Furthermore, we identify four distinct outflows in the region for the first time, with each protostar, 4A1 and 4A2, contributing to two of them. We characterise the morphology and orientation of each outflow, challenging previous suggestions of bends in their trajectories. The outflow cavities of IRAS\,4A1 exhibit extensions of 10$''$ and 13$''$ with position angles (PA) of 0$^{\circ}$ and -12$^{\circ}$, respectively, while those of IRAS\,4A2 are more extended, spanning 18$''$ and 25$''$ with PAs of 29$^{\circ}$ and 26$^{\circ}$. We propose that the misalignment of the cavities is due to a jet precession in each protostar, a notion supported by the observation that the more extended cavities of the same source exhibit lower velocities, indicating they may stem from older ejection events.

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arXiv2023

FAUST VII. Detection of A Hot Corino in the Prototypical Warm Carbon-Chain Chemistry Source IRAS 15398-3359

We have observed the low-mass protostellar source, IRAS 15398$-$3359, at a resolution of 0.$''$2-0.$''$3, as part of the Atacama Large Millimeter/Submillimeter Array Large Program FAUST, to examine the presence of a hot corino in the vicinity of the protostar. We detect nine CH$_3$OH lines including the high excitation lines with upper state energies up to 500 K. The CH$_3$OH rotational temperature and the column density are derived to be 119$^{+20}_{-26}$ K and 3.2$^{+2.5}_{-1.0}\times$10$^{18}$ cm$^{-2}$, respectively. The beam filling factor is derived to be 0.018$^{+0.005}_{-0.003}$, indicating that the emitting region of CH$_3$OH is much smaller than the synthesized beam size and is not resolved. The emitting region of three high excitation lines, 18$_{3,15}-18_{2,16}$, A ($E_u=$447 K), 19$_{3,16}-19_{2,17}$, A ($E_u=$491 K), and 20$_{3,17}-20_{2,18}$, A ($E_u=$537 K), is located within the 50 au area around the protostar, and seems to have a slight extension toward the northwest. Toward the continuum peak, we also detect one emission line from CH$_2$DOH and two features of multiple CH$_3$OCHO lines. These results, in combination with previous reports, indicate that IRAS 15398$-$3359 is a source with hybrid properties showing both hot corino chemistry rich in complex organic molecules on small scales $\sim$10 au) and warm carbon-chain chemistry (WCCC) rich in carbon-chain species on large scales ($\sim$100-1000 au). A possible implication of the small emitting region is further discussed in relation to the origin of the hot corino activity.

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arXiv2022

Tracking the ice mantle history in the Solar-type Protostars of NGC 1333 IRAS 4

To understand the origin of the diversity observed in exoplanetary systems, it is crucial to characterize the early stages of their formation, represented by Solar-type protostars. Likely, the gaseous chemical content of these objects directly depends on the composition of the dust grain mantles formed before the collapse. Directly retrieving the ice mantle composition is challenging, but it can be done indirectly by observing the major components, such as NH3 and CH3OH at cm wavelengths, once they are released into the gas-phase during the warm protostellar stage. We observed several CH3OH and NH3 lines toward three Class 0 protostars in NGC1333 (IRAS 4A1, IRAS 4A2, and IRAS 4B), at high angular resolution (1"; ~300 au) with the VLA interferometer at 24-26 GHz. Using a non-LTE LVG analysis, we derived a similar NH3/CH3OH abundance ratio in the three protostars (<0.5, 0.015-0.5, and 0.003-0.3 for IRAS 4A1, 4A2, and 4B, respectively). Hence, we infer they were born from pre-collapse material with similar physical conditions. Comparing the observed abundance ratios with astrochemical model predictions, we constrained the dust temperature at the time of the mantle formation to be ~17 K, which coincides with the average temperature of the southern NGC 1333 diffuse cloud. We suggest that a brutal event started the collapse that eventually formed IRAS 4A1, 4A2 and 4B, which,therefore, did not experience the usual pre-stellar core phase. This event could be the clash of a bubble with NGC 1333 south, that has previously been evoked in the literature.

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