arXiv subjects

Andrea Socci

Publications and source records attributed to Andrea Socci.

4 recordsLinked to original sources

arXiv2026

Emergence of high-mass stars in complex fiber networks (EMERGE) VII. Multi-Tracer Column Density Synthesis

Obtaining accurate estimates of the gas column density $\mathrm{N(H_2)}$ is crucial to determine the physical conditions of the molecular gas in the Interstellar Medium. This paper introduces the "Multi-Tracer Column Density Synthesis" (MT-CDS) technique, a new empirical approach to derive high dynamic-range column density maps with interferometers such as ALMA. We have compared the integrated intensity maps of two density selective tracers, namely HNC (1-0) and $\mathrm{N_2H^+}$ (1-0), obtained with IRAM-30m with ancillary Herschel column density estimates in seven star-forming regions in Orion and derived individual temperature-corrected conversion factors for each of these tracers. We applied these conversion factors obtained at low-resolution into similar high sensitivity ALMA observations to derive independent column density maps describing both the low $N_\mathrm{HNC}\mathrm{(H_2)}$ and high $N_\mathrm{N_2H^+}\mathrm{(H_2)}$ column density components at high spatial resolution (4.5"). We also combined these independent maps into estimates for the total gas column density gas $N_\mathrm{tot}\mathrm{(H_2)}$ sampling more than two orders of magnitude in column density between $\sim 10^{21.5}-10^{23.5}$ cm$^{-2}$. A comparison with independent ArTeMiS column density maps at intermediate resolution (8") shows typical deviations of $\lesssim$0.2 dex from our MT-CDS gas column density estimates. We obtained individual column density maps in five of our targets at $\sim$2000 au resolution in which ALMA observations were available, that is a factor of $\sim$5 better than originally calibrated. These results demonstrate the potential of this MT-CDS technique to retrieve accurate, high dynamic range $N\mathrm{(H_2)}$ total gas column density estimates at interferometric resolution combining multiple molecular line tracers.

astro-ph.GA↗

arXiv2026

Low cosmic-ray ionisation at parsec scales in G035.39-00.33

Cosmic rays (CRs) regulate the chemical evolution of the gas and its coupling to the magnetic field in the densest and coldest regions of the interstellar medium (ISM). However, the CR ionisation rate of H$_2$ ($ζ_2$) is one of the most debated parameters characterising molecular clouds due to the uncertainties in its estimation. We developed a new analytical framework based on the chemistry of N$_2$H$^+$, N$_2$D$^+$ and DCO$^+$ to overcome observational limitations in current estimates of $ζ_2$ and to probe the latter and the electron fraction, $x(e)$, in the gas across multiple density regimes. We applied this method towards the parsec-scale filament of the infrared dark cloud (IRDC) G035.39-00.33 with new observations from the NOrthern Extended Array (NOEMA) at a resolution of $3''$ (or $\sim9000$ au). Ancillary observations of C$^{18}$O complete this survey to measure $x(e)$ and $ζ_2$ in G035.39-00.33. CO depletion is widespread in G035.39-00.33 with factors, $f_\mathrm{D}$, positively correlated with column and number densities of H$_2$ in the cloud. The deuterium fractions ($R_\mathrm{D}$) are enhanced towards these same sites in which the corresponding electron fraction values cluster below $\lesssim10^{-8}$. $ζ_2$ varies by three orders of magnitude in G035.39-00.33 ($\sim10^{-18}-10^{-15}$ s$^{-1}$) with a median of $\sim2.3\times10^{-18}$ s$^{-1}$, consistent with those reported for other IRDCs and giant filaments, but on average lower than the typical $ζ_2$ for the ISM. $ζ_2$ shows a functional dependence on $N(\mathrm{H_2})$, but with absolute values lower compared to those predicted by theoretical models. This behaviour suggests the presence of an overall attenuation of the CR flux taking place in G035.39-00.33. The CR flux appears to be reduced by the change in magnetic field strength and morphology previously reported in the region.

astro-ph.GA↗

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.

astro-ph.SR↗

arXiv2025

Kinematics of young stellar objects in NGC 2024 based on infrared proper motions

The most recently formed young stellar objects (YSOs) in active star forming regions are excellent tracers of their parent cloud motion. Their positions and dynamics provide insight into cluster formation and constrain kinematic decoupling timescales between stars and gas. However, because of their strong extinction and young age, embedded YSOs are mainly visible at infrared wavelengths and thus absent from astrometric surveys such as Gaia. We measured the proper motions of 6,769 sources toward the NGC 2024 cluster in the Flame Nebula using multi-epoch near-infrared observations from three ESO public surveys: VISIONS, VHS, and the VISTA/VIRCAM science verification program. Cross-validation of our results with Gaia using optically visible stars shows excellent agreement, with uncertainties on the same order of magnitude. For 362 YSO candidates identified from the literature, we derived proper motions on the order of <5 mas/yr with mean measurement uncertainties of ~0.22 mas/yr. This is the first homogeneous proper motion measurement of this quality for more than half of these stars. For Class I and flat-spectrum sources, our results provide a >13-fold increase in available proper motion measurements. We analyzed the positional and kinematic differences between YSO classes and confirmed a previously reported inside-out age segregation from younger to older stars, likely driven by an outward movement of older stars. No evidence of prolonged hierarchical assembly was found. Instead, the results support a rapid (<1 Myr) cluster collapse. This scenario also accounts for the observed slightly higher 1D velocity dispersion of Class I sources relative to Class flat objects. YSO radial velocities generally align with the gas velocities measured from 12CO(3-2), HNC(1-0), HCN(1-0), and show a weaker correlation with N_2H+(1-0). Some Class II and III objects appear to be already decoupling.

astro-ph.GA↗