arXiv subjects

S. Zeng

Publications and source records attributed to S. Zeng.

At least 19 recordsLinked to original sources

arXiv2026

The Galactic Centre G+0.633-0.0604 Molecular Cloud: A New Gold Mine for Astrochemistry

Astrochemistry is living a golden age, with more than a quarter of the ~350 molecules in the current interstellar census having been detected over the last three years. One of the sources driving this progress is the G+0.693-0.027 cloud, located in the northern part of the Galactic Centre Sgr B2 complex. In this contribution, we present the astrochemical characterisation of G+0.633-0.0604, a newly discovered chemically rich molecular cloud at the southern edge of Sgr B2. With an inventory of >120 species, G+0.633 provides robust second detections of several prebiotic molecules only reported towards G+0.693, establishing it as the first confirmed astrochemical twin of G+0.693 while demonstrating that the extraordinary chemistry of this cloud is not unique. Furthermore, G+0.633 offers an observational advantage over G+0.693 since it displays half narrower linewidths. Together, G+0.633 and G+0.693 form a unique benchmark pair for unveiling molecular complexity and prebiotic chemistry in the interstellar medium.

astro-ph.GA↗

arXiv2026

Chemical modelling of interstellar MgS

The detection of magnesium sulphide (MgS) and sodium sulphide (NaS) towards the Galactic Center molecular cloud G+0.693 constitutes the first detection of metal sulphides in the interstellar medium (ISM). However, there is scarce information about the key reactions (either in the gas phase or on grains) involved in their formation. In this paper, we model the chemistry of MgS simulating the passage of a low-velocity shock to recover the abundances recently measured towards G+0.693. Through this chemical modelling, we analyse the dominant reactions involved in the formation and destruction of this molecule, their associated chemical time-scales, and the depletion factor needed to recover the observed abundances. We build the initial chemical network of MgS by using SiS as a proxy for this metal sulphide, and we investigate the exothermicity of these and additional, uniquely proposed reactions through quantum chemical computations. We run a three-phase model (initial translucent cloud, cloud collapse phase and shock interaction stage) that mimics the evolution and physical conditions of G+0.693. Our results show that a depletion factor of 1000 is required for elemental Mg to recover the observed abundances of MgS. This implies that potentially more than 99.9% of Mg is locked in dust grains. The dominant reaction leading to the formation of MgS is the neutral-neutral reaction between MgH and S in the gas phase. This work represents the first analysis of the chemistry of the metal-sulphide MgS and suggests that Mg is largely incorporated into dust grains, most likely in the form of silicates. However, additional laboratory and/or theoretical studies of the key MgS formation reactions are essential to obtain more reliable constraints. Future missions, such as PRIMA, will provide insights into the amount of metal-sulphides locked into interstellar dust grains.

astro-ph.GA↗

arXiv2026

High $^{12}$C/$^{13}$C isotopic ratios toward G+0.693-0.027: evidence for gas inflow to the Central Molecular Zone

Isotopic ratios are key tracers of Galactic chemical evolution because different isotopes are synthesized through distinct stellar nucleosynthesis processes. While the $^{12}$C/$^{13}$C ratio increases with galactocentric distance across the Galactic disc, measurements in the Central Molecular Zone (CMZ) have historically yielded low values ($\sim$3-30), often affected by high optical depths. We aim to determine the initial $^{12}$C/$^{13}$C ratio of the parent material of the CMZ molecular cloud G+0.693$-$0.027 using optically thin molecular tracers and correcting for isotopic fractionation. We analyzed an ultra-high-sensitivity spectral survey obtained with the IRAM 30m and Yebes 40m telescopes, detecting single and double $^{13}$C isotopologues of HC$_3$N and HC$_5$N. Column densities and isotopic ratios were derived and compared with astrochemical models including $^{13}$C- and $^{15}$N-isotopologues to quantify isotopic fractionation. We derive $^{12}$C/$^{13}$C ratios of $36.7\pm1.0$ for HC$_3$N (using double $^{13}$C isotopologues) and $38.8\pm1.5$ for HC$_5$N, significantly higher than previous CMZ estimates based on simpler molecules. The models indicate low to intermediate isotopic fractionation at early times ($<3\times10^4$ yr), implying an initial $^{12}$C/$^{13}$C ratio of $\sim$48 for the gas from which present-day CMZ molecular clouds formed. The inferred range (37-48) is consistent with values observed at Galactocentric distances of 3-5 kpc, supporting a scenario in which the CMZ is replenished by gas inflows from the Galactic disc driven by the Galactic bar, with a possible contribution from less chemically processed material accreted from external systems such as dwarf galaxies.

astro-ph.GA↗

arXiv2026

The Galactic Centre G+0.633-0.0604 molecular cloud: a new astrochemical gold mine. I. Gas physical properties

In the Central Molecular Zone (CMZ), shocks play a key role in triggering star formation and driving chemical enrichment. The Sgr B2 complex is a prime template, hosting massive protoclusters (N, M, S) and the northern G+0.693 cloud, which exhibits shock-induced prestellar signatures. We report on G+0.633-0.0604, a newly identified shock-dominated and chemically rich cloud at the southern edge of Sgr B2, where the next star formation episodes are proposed. We characterise its physical properties and the shocks shaping it. We present analyses on CH$_3$CCH, CH$_3$CN, HC$_3$N, HNCO and several isotopologues of CO to infer the gas $T_{\rm kin}$ and density, using high-sensitivity spectral surveys from the Yebes 40m, IRAM 30m and APEX radio telescopes that covered ~100 GHz across the 31-275 GHz range. We also used 3 mm IRAM 30m mosaics (13'$\times$13') of Sgr B2 in HC$_3$N, HNCO and C$_2$H$_5$OH to probe G+0.633 environment. We identify three velocity components: a narrow main one (C1, $v_{\rm LSR}$~48.5 km/s; FWHM~10 km/s), and two broader, fainter components at higher velocities, C2 (~61 km/s; ~13 km/s) and C3 (~89 km/s; ~18 km/s), all showing similar properties ($T_{\rm kin}$~55-90 K, $N_{\rm H_2}$~(3-7)$\times$10$^{22}$ cm$^{-2}$, $n_{\rm H_2}$~(0.5-2.5)$\times$10$^{4}$ cm$^{-3}$) and extended distributions. C1 delineates G+0.633 physically and coincides with a peak in HNCO, supporting a shock-driven origin likely rooted in the cloud-cloud collision shaping Sgr B2 and also traced by C2, which extends north to G+0.693. C3 is kinematically unlinked and related to large-scale CMZ dynamics. Of the three, C1 may represent a very early protocluster phase, yet to be confirmed. G+0.633 thus emerges as a new shock-dominated CMZ cloud resembling G+0.693, providing another unique laboratory to investigate how shocks drive molecular complexity and regulate the onset of cluster formation in the CMZ.

astro-ph.GA↗

arXiv2026

Aromatic rings in the Central Molecular Zone: Benzonitrile

In recent years, several aromatic molecules (benzene-based rings) have been detected in the cold molecular cloud TMC-1, with its CN-derivative, benzonitrile (c-C$_6$H$_5$CN), also identified in other nearby cold sources. However, observed abundances differ significantly from chemical model predictions, indicating an incomplete understanding of its chemistry and motivating searches in distinct environments. We report new detections of benzonitrile in two warmer molecular clouds of the Central Molecular Zone (CMZ): G+0.693-0.027 and G+0.633-0.0604. Using Yebes 40m ultra-deep surveys in the 31--50 GHz range, we performed LTE and non-LTE analyses to derive the physical parameters of the emission. We obtain column densities of $N$=(7.4$\pm$0.5)$\times10^{12}$ and (2.60$\pm$0.13)$\times10^{12}$ cm$^{-2}$, corresponding to abundances relative to H$_2$ of (6$\pm$1)$\times10^{-11}$ and (4.3$\pm$0.9)$\times10^{-11}$, consistent with values in cold Galactic clouds. The HC$_7$N/benzonitrile ratio is lower (2.15-2.4) than in colder sources (4.5-30), suggesting environmental effects and a relative enhancement of aromatic chemistry in the CMZ. These results confirm that benzonitrile is widespread and can survive in harsher environments (e.g., high temperatures, shocks, enhanced cosmic-ray ionization) than those in Galactic cold clouds. This suggests that aromatics are stable and abundant species that can significantly contribute to the total budget of interstellar carbon in molecular clouds. A top-down formation scenario, involving fragmentation of larger carbonaceous species, is consistent with the nearly constant abundances observed with molecular size.

astro-ph.GA↗

arXiv2026

Expanding the C$_3$H$_6$O$_2$ Isomeric Interstellar Inventory: Discovery of Lactaldehyde and Methoxyacetaldehyde in G+0.693-0.027

The tentative detection of 3-hydroxypropanal (HO(CH$_2$)$_2$C(O)H) toward the Galactic center molecular cloud G+0.693-0.027 prompts a systematic survey in this source aimed at detecting all C$_3$H$_6$O$_2$ isomers with available spectroscopy. We use an ultra-deep broadband spectral survey of G+0.693-0.027, carried out with the Yebes 40 m and IRAM 30 m telescopes, to conduct the astronomical search. We report the first interstellar detection of lactaldehyde (CH$_3$CH(OH)C(O)H) and methoxyacetaldehyde (CH$_3$OCH$_2$C(O)H), together with the second detections (i.e., confirmation) of methyl acetate (CH$_3$C(O)OCH$_3$) and hydroxyacetone (CH$_3$C(O)CH$_2$OH), and new detections in this source of both $anti$- and $gauche$- conformers of ethyl formate (CH$_3$CH$_2$OC(O)H), the latter tentatively. In contrast, neither propionic acid, CH$_3$CH$_2$C(O)OH, nor glycidol, c-CH$_2$OCHCH$_2$OH (i.e., the most and the least stable species within the C$_3$H$_6$O$_2$ family, respectively) were detected, and we provide upper limits on their fractional abundances of $\leq$1.5 $\times$ 10$^{-10}$ and $\leq$3.7 $\times$ 10$^{-11}$. Interestingly, all C$_3$H$_6$O$_2$ isomers can be synthesized through radical-radical reactions on the surface of dust grains, ultimately tracing back to CO as the parent molecule. We suggest that formation of the detected isomers is mainly driven by successive hydrogenation of CO, producing CH$_3$OH and CH$_3$CH$_2$OH as the primary parent species. Conversely, propionic acid is thought to originate from the oxygenation of CO via the HOCO intermediate, which help us rationalize its non-detection. Overall, our findings notably expand the known chemical inventory of the interstellar medium and provide direct observational evidence that increasingly complex chemistry involving O-bearing species occurs in space.

astro-ph.GA↗

arXiv2025

High-energy interstellar isomers: cis-N-methylformamide in the G+0.693-0.027 molecular cloud

Isomerism in complex organic molecules provides key insights into the formation mechanisms and physical conditions of the interstellar medium (ISM). Among the C$_2$H$_5$NO isomers, only acetamide and trans-N-methylformamide (trans-NMF) have been detected in space. The recent detection of higher-energy isomers in other chemical families raises questions about the formation and abundance of less stable isomers. We used ultra-sensitive wide-band spectral surveys obtained with the Yebes 40 m and IRAM 30 m telescopes to search for cis-NMF towards the Galactic Centre molecular cloud G+0.693-0.027. We present the first detection of cis-NMF in the ISM, with 55 unblended or slightly blended transitions, 44 of which were new transitions identified based on extrapolated spectroscopic data. Due to the lack of collisional rate coefficients, a quasi-non-LTE analysis, which separated the transitions into different K$_a$ ladders, was used to determine the excitation conditions. The resulting trans/cis-NMF isomeric ratio of 2.9$\pm$0.6 deviates significantly from thermodynamic expectations, suggesting that kinetic non-equilibrium processes and stereospecific chemical pathways are responsible for the formation of cis-NMF in this environment. The detection of cis-NMF expands the known inventory of interstellar C$_2$H$_5$NO isomers and challenges the assumption that isomer abundances strictly correlate with thermodynamic stability. Laboratory and theoretical studies propose formation via CH$_3$NCO hydrogenation or spin-forbidden reactions involving CH$_2$ and NH$_2$CHO, though these may not reflect typical ISM conditions. This finding highlights the need for further investigation into isomerisation mechanisms and constrains astrochemical models of complex organic molecules.

astro-ph.GA↗

arXiv2024

Interaction between the Supernova Remnant W44 and the Infrared Dark Cloud G034.77-00.55: shock induced star formation?

How Supernova Remnant (SNR) shocks impact nearby molecular clouds is still poorly observationally constrained. It is unclear if SNRs can positively or negatively affect clouds star formation potential. We have studied the dense gas morphology and kinematics toward the Infrared Dark Cloud (IRDC) G034.77-00.55, shock-interacting with the SNR W44, to identify evidence of early stage star formation induced by the shock. We have used high-angular resolution N2H+(1-0) images across G034.77-00.55, obtained with ALMA. N2H+ is a well known tracer of dense and cold material, optimal to identify gas with the highest potential to harbour star formation. The N2H+ emission is distributed into two elongated structures, one toward the dense ridge at the edge of the source and one toward the inner cloud. Both elongations are spatially associated with well-defined mass-surface density features. The velocities of the gas in the two structures i.e., 38-41 km s-1 and 41-43 km s-1 are consistent with the lowest velocities of the J- and C-type parts of the SNR-driven shock, respectively. A third velocity component is present at 43-45.5 km s-1. The dense gas shows a fragmented morphology with core-like fragments of scales consistent with the Jeans lengths, masses $\sim$1-20 M$_{\odot}$, densities (n(H$_2$)$\geq$10$^5$ cm$^{-3}$) sufficient to host star formation in free-fall time scales (few 10$^4$ yr) and with virial parameters that hint toward possible collapse. The W44 driven shock may have swept up the encountered material which is now seen as a dense ridge, almost detached from the main cloud, and an elongation within the inner cloud, well constrained in both N2H+ emission and mass surface density. This shock compressed material may have then fragmented into cores that are either in a starless or pre-stellar stage. Additional observations are needed to confirm this scenario and the nature of the cores.

astro-ph.GA↗

arXiv2024

Excitation and spatial study of a prestellar cluster towards G+0.693-0.027 in the Galactic centre

Star formation in the central molecular zone (CMZ) is suppressed with respect to that of the Galactic disk, and this is likely related to its high turbulent environment. This turbulence impedes the potential detection of prestellar cores. We present the temperature, density, and spatial structure of the CMZ molecular cloud G+0.693-0.027, which has been proposed to host a prestellar cluster in the Sgr B2 region. We analysed multiple HC$_{3}$N rotational transitions that were observed with the IRAM 30m, APEX, Yebes 40m, and GBT radio telescopes, together with SMA+APEX spatially resolved maps. The spectral shape of HC$_{3}$N lines shows three velocity components: a broad component with a line width of 23 km s$^{-1}$ (C1), and two narrow components with line widths of 7.2 and 8.8 km s$^{-1}$ (C2 and C3). This suggests that a fraction of the molecular gas in this cloud is undergoing turbulence dissipation. From a non-local thermodynamic equilibrium analysis we have found H$_{2}$ densities of 2$\times$10$^{4}$ cm$^{-3}$, 5$\times$10$^{4}$ cm$^{-3}$, and 4$\times$10$^{5}$ cm$^{-3}$ and kinetic temperatures of 140 K, 30 K, and 80 K for C1, C2, and C3, respectively. The spatially resolved maps confirm that the colder and high-density condensations C2 and C3, which peak in the 70-85 km s$^{-1}$ velocity range, are embedded in a more diffuse and warmer gas (C1). The larger-scale structure of the Sgr B2 region shows a hole at 40-50 km s$^{-1}$ that is likely due to a small cloud that shocked the Sgr B2 region and is spatially related with a massive cloud at 60-80 km s$^{-1}$. We propose that the impacting small cloud sequentially triggered the formation of Sgr B2(M), (N), and (S) and the condensations in G+0.693-0.027 during its passage. Based on the analysis of the masses of the two condensations and on the virial parameters, C2 might expand, while C3 might further fragment or collapse.

astro-ph.GA↗

arXiv2024

The factors that influence protostellar multiplicity I: Gas temperature, density, and mass in Perseus with Nobeyama

Protostellar multiplicity is common at all stages and mass ranges. However, the factors that determine the multiplicity of protostellar systems have not been systematically characterized through their molecular gas. Nobeyama 45m Radio Observatory OTF maps of HCN, HNC, HCO$^+$, and N$_2$H$^+$ (J = 1--0) toward five subregions in Perseus, complemented with single pointing APEX observations of HNC (J = 4--3) are used to derive physical parameters of the dense gas. Both observations have angular resolutions of $\sim$18", equivalent to $\sim$5000 AU scales at the distance of Perseus. Kinetic gas temperature is derived from the $I$(HCN)/$I$(HNC) J = 1--0 ratio, and H$_2$ density is obtained from the HNC J=4--3/J=1--0 ratio. These parameters are used to obtain the N$_2$H$^+$ and HCO$^+$ gas masses. The inferred and derived parameters are compared to source parameters. Inferred mean kinetic gas temperature ($I$(HCN)/$I$(HNC) J=1--0 ratio; ranging between 15 and 26 K), and H$_2$ volumetric density (HNC J=4--3/J=1--0; 10$^5$ -- 10$^6$ cm$^{-3}$) do not show correlations with multiplicity in Perseus. The derived gas and dust masses, 1.3 to 16 $\times~10^{-9}$ M$_{\odot}$ for the N$_2$H$^+$ gas mass, 0.1 to 25 M$_{\odot}$ for envelope dust masses (850 $\mu$m), and 0.8 to 10 $\times~10^{-10}$ M$_{\odot}$ for the HCO$^+$ gas mass, are correlated to multiplicity and number of protostellar components. The warm gas masses are a factor of 16 lower than the cold gas masses. This work shows that gas and dust mass is correlated to multiplicity at $\sim$5000 AU scales in Perseus. Higher order multiples tend to have higher gas and dust masses in general, while close binaries (separations $\leq$7") and single protostars have similar gas and dust mass distributions. On the other hand, H$_2$ density and kinetic gas temperature do not show any correlation with multiplicity.

astro-ph.GA↗

arXiv2024

Discovery of MgS and NaS in the Interstellar Medium and tentative detection of CaO

We report the first detection of the metal-bearing molecules sodium sulfide (NaS) and magnesium sulfide (MgS) and the tentative detection of calcium monoxide (CaO) in the interstellar medium (ISM) towards the Galactic Center molecular cloud G+0.693-0.027. The derived column densities are (5.0+-1.1) x 10$^{10}$ cm$^{-2}$, (6.0+-0.6) x $^{10}$ cm$^{-2}$, and (2.0+-0.5) x $^{10}$ cm$^{-2}$, respectively. This translates into fractional abundances with respect to H$_2$ of (3.7+-1.0) x $10^{-13}$, (4.4+-0.8) x $10^{-13}$, and (1.5+-0.4) x $10^{-13}$, respectively. We have also searched for other Na-, Mg- and Ca-bearing species towards this source but none of them have been detected and thus we provide upper limits for their abundances. We discuss the possible chemical routes involved in the formation of these molecules containing metals under interstellar conditions. Finally, we compare the ratio between sulfur-bearing and oxygen-bearing molecules with and without metals, finding that metal-bearing sulfur molecules are much more abundant than metal-bearing oxygen ones, in contrast with the general trend found in the ratios between other non metal- oxygen- and sulfur-bearing molecules. This further strengthen the idea that sulfur may be little depleted in G+0.693-0.027 as a result of the low velocity shocks present in this source sputtering large amounts of material from dust grains.

astro-ph.GA↗

arXiv2023

The first detection of SiC$_2$ in the interstellar medium

We report the first detection of SiC$_2$ in the interstellar medium. The molecule was identified through six rotational transitions toward G\,+0.693$-$0.027, a molecular cloud located in the Galactic center. The detection is based on a line survey carried out with the GBT, the Yebes 40m, and the IRAM 30m telescopes covering a range of frequencies from 12 to 276 GHz. We fit the observed spectra assuming local thermodynamic equilibrium and derive a column density of ($1.02\pm0.04)\times10^{13}$ cm$^{-2}$, which gives a fractional abundance of $7.5\times10^{-11}$ with respect to H$_2$, and an excitation temperature of $5.9\pm0.2$ K. We conclude that SiC$_2$ can be formed in the shocked gas by a reaction between the sputtered atomic silicon and C$_2$H$_2$, or it can be released directly from the dust grains due to disruption. We also search for other Si-bearing molecules and detect eight rotational transitions of SiS and four transitions of Si$^{18}$O. The derived fractional abundances are $3.9\times10^{-10}$ and $2.1\times10^{-11}$, respectively. All Si-bearing species toward G\,+0.693$-$0.027 show fractional abundances well below what is typically found in late-type evolved stars.

astro-ph.GA↗

arXiv2023

Deuterium Fractionation across the Infrared Dark Cloud G034.77-00.55 interacting with the Supernova Remnant W44

Supernova remnants (SNRs) may regulate star formation in galaxies. For example, SNR-driven shocks may form new molecular gas or compress pre-existing clouds and trigger the formation of new stars. To test this scenario, we measure the deuteration of $N_2H^+$, $D_{frac}^{N_2H^+}$, a well-studied tracer of pre-stellar cores, across the Infrared Dark Cloud (IRDC) G034.77-00.55, known to be experiencing a shock interaction with the SNR W44. We use N$_2$H$^+$ and N$_2$D$^+$ J=1-0 single pointing observations obtained with the 30m antenna at the Instituto de Radioastronomia Millimetrica to infer $D_{frac}^{N_2H^+}$ toward five positions across the cloud, namely a massive core, different regions across the shock front, a dense clump and ambient gas. We find $D_{frac}^{N_2H^+}$ in the range 0.03-0.1, several orders of magnitude larger than the cosmic D/H ratio ($\sim$10$^{-5}$). Across the shock front, $D_{frac}^{N_2H^+}$ is enhanced by more than a factor of 2 ($D_{frac}^{N_2H^+}\sim$0.05-0.07) with respect to the ambient gas ($\leq$0.03) and similar to that measured generally in pre-stellar cores. Indeed, in the massive core and dense clump regions of this IRDC we measure $D_{frac}^{N_2H^+}$}$\sim$0.1. We find enhanced deuteration of $N_2H^+$ across the region of the shock, at a level that is enhanced with respect to regions of unperturbed gas. It is possible that this has been induced by shock compression, which would then be indirect evidence that the shock is triggering conditions for future star formation. However, since unperturbed dense regions also show elevated levels of deuteration, further, higher-resolution studies are needed to better understand the structure and kinematics of the deuterated material in the shock region, e.g., if it still in relatively diffuse form or already organised in a population of low-mass pre-stellar cores.

astro-ph.GA↗

arXiv2023

Amides inventory towards the G+0.693-0.027 molecular cloud

Interstellar amides have attracted significant attentions as they are potential precursors for a wide variety of organics essential to life. However, our current understanding of their formation in space is heavily based on observations in star-forming regions and hence the chemical networks lack the constraints on their early origin. In this work, unbiased sensitive spectral surveys with IRAM 30m and Yebes 40m telescopes are used to systematically study a number of amides towards a quiescent Galactic Centre molecular cloud, G+0.693-0.027. We report the first detection of acetamide (CH3C(O)NH2) and trans-N-methylformamide (CH3NHCHO) towards this cloud. In addition, with the wider frequency coverage of the survey, we revisited the detection of formamide (NH2CHO) and urea (carbamide; NH2C(O)NH2), which had been reported previously towards G+0.693-0.027. Our results are compared with those present in the literature including recent laboratory experiments and chemical models. We find constant abundance ratios independently of the evolutionary stages, suggesting that amides related chemistry is triggered in early evolutionary stages of molecular cloud and remain unaffected by the warm-up phase during the star formation process. Although a correlation between more complex amides and NH2CHO have been suggested, alternative formation routes involving other precursors such as acetaldehyde (CH3CHO), methyl isocyanate (CH3NCO) and methylamine (CH3NH2) may also contribute to the production of amides. Observations of amides together with these species towards a larger sample of sources can help to constrain the amide chemistry in the interstellar medium.

astro-ph.GA↗

arXiv2022

Deep underground laboratory measurement of $^{13}$C($\alpha$,$n$)$^{16}$O in the Gamow windows of the $s$- and $i$-processes

The $^{13}$C($\alpha$,$n$)$^{16}$O reaction is the main neutron source for the slow-neutron-capture (s-) process in Asymptotic Giant Branch stars and for the intermediate (i-) process. Direct measurements at astrophysical energies in above-ground laboratories are hindered by the extremely small cross sections and vast cosmic-ray induced background. We performed the first consistent direct measurement in the range of $E_{\rm c.m.}=$0.24 MeV to 1.9 MeV using the accelerators at the China Jinping Underground Laboratory (CJPL) and Sichuan University. Our measurement covers almost the entire i-process Gamow window in which the large uncertainty of the previous experiments has been reduced from 60\% down to 15\%, eliminates the large systematic uncertainty in the extrapolation arising from the inconsistency of existing data sets, and provides a more reliable reaction rate for the studies of the s- and i-processes along with the first direct determination of the alpha strength for the near-threshold state.

nucl-ex↗

arXiv2022

Deuterium fractionation as a multi-phase component tracer in the Galactic Centre

The Central Molecular Zone (CMZ) contains most of the mass of our Galaxy but its star formation rate is one order of magnitude lower than in the Galactic disc. This is likely related to the fact that the bulk of the gas in the CMZ is in a warm ($>$100 K) and turbulent phase with little material in the pre-stellar phase. We present in this Letter observations of deuterium fractionation (D/H ratios) of HCN, HNC, HCO$^{+}$, and N$_{2}$H$^{+}$ towards the CMZ molecular cloud G+0.693-0.027. These observations clearly show, for the first time, the presence of a colder, denser, and less turbulent narrow component, with a line width of $\sim$9 km s$^{-1}$, in addition to the warm, less dense and turbulent broad component with a line width of $\sim$20 km s$^{-1}$. The very low D/H ratio $\le$6$\times$10$^{-5}$ for HCO$^{+}$ and N$_{2}$H$^{+}$, close to the cosmic value ($\sim$2.5$\times$10$^{-5}$), and the high D/H ratios $>$4$\times$10$^{-4}$ for HCN and HNC derived for the broad component, confirm the presence of high-temperatures deuteration routes for nitriles. For the narrow component we have derived D/H ratios $>$10$^{-4}$ and excitation temperatures of $7$ K for all molecules, suggesting kinetic temperatures $\le$30 K and H$_2$ densities $\ge$5$\times$10$^{4}$ cm$^{-3}$, at least one order of magnitude larger than for the broad component. The method presented in this Letter allows to identify clouds on the verge of star formation, i.e. under pre-stellar conditions, towards the CMZ. This method can also be used for the identification of such clouds in external galaxies.

astro-ph.GA↗

arXiv2022

Negative and Positive Feedback from a Supernova Remnant with SHREC: A detailed Study of the Shocked Gas in IC443

Supernova remnants (SNRs) contribute to regulate the star formation efficiency and evolution of galaxies. As they expand into the interstellar medium (ISM), they transfer vast amounts of energy and momentum that displace, compress and heat the surrounding material. Despite the extensive work in galaxy evolution models, it remains to be observationally validated to what extent the molecular ISM is affected by the interaction with SNRs. We use the first results of the ESO-ARO Public Spectroscopic Survey SHREC, to investigate the shock interaction between the SNR IC443 and the nearby molecular clump G. We use high sensitivity SiO(2-1) and H$^{13}$CO$^+$(1-0) maps obtained by SHREC together with SiO(1-0) observations obtained with the 40m telescope at the Yebes Observatory. We find that the bulk of the SiO emission is arising from the ongoing shock interaction between IC443 and clump G. The shocked gas shows a well ordered kinematic structure, with velocities blue-shifted with respect to the central velocity of the SNR, similar to what observed toward other SNR-cloud interaction sites. The shock compression enhances the molecular gas density, n(H$_2$), up to $>$10$^5$ cm$^{-3}$, a factor of >10 higher than the ambient gas density and similar to values required to ignite star formation. Finally, we estimate that up to 50\% of the momentum injected by IC443 is transferred to the interacting molecular material. Therefore the molecular ISM may represent an important momentum carrier in sites of SNR-cloud interactions.

astro-ph.GA↗

arXiv2021

Charge and spin order dichotomy in NdNiO$_2$ driven by SrTiO$_3$ capping layer

Superconductivity in infinite-layer nickelates holds exciting analogies with that of cuprates, with similar structures and $3d$-electron count. Using resonant inelastic x-ray scattering (RIXS) we studied electronic and magnetic excitations and charge density correlations in Nd$_{1-x}$Sr$_{x}$NiO$_2$ thin films with and without an SrTiO$_3$ capping layer. We observe dispersing magnons only in the capped samples, progressively dampened at higher doping. In addition, we detect an elastic resonant scattering peak in the uncapped $x=0$ compound at wave vector (1/3,0), remindful of the charge order signal in hole doped cuprates. The peak weakens at $x=0.05$ and disappears in the superconducting $x=0.20$ film. The uncapped samples also present a higher degree of Ni$3d$-Nd$5d$ hybridization and a smaller anisotropy of the Ni$3d$ occupation with respect to the capped samples. The role of the capping on the possible hydrogen incorporation or on other mechanisms responsible for the electronic reconstruction far from the interface remains to be understood.

cond-mat.supr-con↗