GUAPOS:

2020

• The GUAPOS project: G31.41+0.31 Unbiased ALMA sPectral Observational Survey - I. Isomers of C₂H₄O₂

  C. Mininni, M. T. Beltrán, V. M. Rivilla, A. Sánchez-Monge, F. Fontani, T. Möller, R. Cesaroni, P. Schilke, S. Viti, I. Jiménez-Serra, L. Colzi, A. Lorenzani, L. Testi

  published in A&A (A&A, 644, A84) pdf - arXiv:2009.13297 pdf

  Abstract

  Understanding the degree of chemical complexity that can be reached in star-forming regions, together with the identification of precursors of the building blocks of life in the interstellar medium, is one of the goals of astrochemistry. To answer these questions, unbiased spectral surveys with large bandwidth and high spectral resolution are needed, to resolve line blending in chemically rich sources and identify each molecule (especially for complex organic molecules). This kind of observations has been successfully carried out, mainly towards the Galactic Center, a region that shows peculiar environmental conditions.
  We present an unbiased spectral survey of one of the most chemically rich hot molecular cores located outside the Galactic Center, in the high-mass star-forming region G31.41+0.31. The aim of this 3mm spectral survey is to identify and characterize the physical parameters of the gas emitting in different molecular species, focusing on complex organic molecules. In this first paper, we present the survey and discuss the detection and relative abundances of the 3 isomers of C₂H₄O₂: methyl formate, glycolaldehyde and acetic acid.
  Observations were carried out with the interferometer ALMA and cover the entire Band 3 from 84 to 116 GHz (∼32 GHz bandwidth) with an angular resolution of 1.2″×1.2″ (∼4400 au × 4400 au) and a spectral resolution of ∼0.488 MHz (∼1.3 - 1.7 km s^-1 ). The transitions of the 3 molecules have been analyzed with the software XCLASS to determine the physical parameters of the emitting gas.
  All three isomers were detected with abundances of (2±0.6)×10^-7, (4.3 - 8)×10^-8 and (5.0±1.4)×10^-9 for methyl formate, acetic acid and glycolaldehyde, respectively. Methyl formate and acetic acid abundances are the highest detected up to now, if compared to sources in literature. The size of the emission varies among the three isomers with acetic acid showing the most compact emission while methyl formate exhibits the most extended emission. Different chemical pathways, involving both grain surface chemistry and cold or hot gas-phase reactions, have been proposed for the formation of these molecules, but the small number of detections, especially of acetic acid and glycolaldehyde, made it very difficult to confirm or discard the predictions of the models. The comparison with chemical models in literature suggests the necessity of grain-surface routes for the formation of methyl formate in G31, while for glycolaldehyde both scenarios could be feasible. Proposed grain-surface reaction for acetic acid is not able to reproduce the observed abundance in this work, while gas-phase scenario should be further tested due to large uncertainties.

2021

• The GUAPOS project II: A comprehensive study of peptide-like bond molecules

  L. Colzi, V. M. Rivilla, M. T. Beltrán, I. Jiménez-Serra, C. Mininni, M. Melosso, R. Cesaroni, F. Fontani, A. Lorenzani, A. Sánchez-Monge, S. Viti, P. Schilke, L. Testi, E. R. Alonso, L. Kolesniková

  published in A&A (A&A, 653, A129) pdf - arXiv:2107-11258 pdf

  Abstract

  Peptide-like molecules, which can take part to the formation of proteins in a primitive Earth environment, have been detected up to now only towards a few hot cores and hot corinos.
  We present a study of HNCO, HC(O)NH₂, CH₃NCO, CH₃C(O)NH₂, CH₃NHCHO, CH₃CH₂NCO, NH₂C(O)NH₂, NH₂C(O)CN, and HOCH₂C(O)NH₂ towards the hot core G31.41+0.31. The aim of this work is to study these species together to allow a consistent study among them.
  We have used the spectrum obtained from the ALMA 3mm spectral survey GUAPOS, with a spectral resolution of ∼0.488 MHz (∼1.3–1.7 km s ) and an angular resolution of 1.2″×1.2″ (∼4500 au), to derive column densities of all the molecular species presented in this work, together with 0.2″×0.2″ (∼750 au) ALMA observations from another project to study the morphology of HNCO, HC(O)NH₂ and CH₃C(O)NH₂.
  We have detected HNCO, HC(O)NH₂, CH₃NCO, CH₃C(O)NH₂, and CH₃NHCHO, but no CH₃CH₂NCO, NH₂C(O)NH₂, NH₂C(O)CN, and HOCH₂C(O)NH₂. This is the first time that these molecules have been detected all together outside the Galactic center. We have obtained molecular fractional abundances with respect to H₂ from 10⁻⁷ down to a few 10⁻⁹ and abundances with respect to CH₃OH from 10⁻³ to ∼4×10⁻², and their emission is found to be compact (∼2″, i.e. ∼7500 au). From the comparison with other sources, we find that regions in an earlier stage of evolution, such as pre-stellar cores, show abundances at least two orders of magnitude lower than those in hot cores, hot corinos or shocked regions. Moreover, molecular abundance ratios towards different sources are found to be consistent between them within ∼1 order of magnitude, regardless of the physical properties (e.g. different masses and luminosities), or the source position throughout the Galaxy. Correlations have also been found between HNCO and HC(O)NH₂, and CH₃NCO and HNCO abundances, and for the first time between CH₃NCO and HC(O)NH₂, CH₃C(O)NH₂ and HNCO, and CH₃C(O)NH₂ and HC(O)NH₂ abundances. These results suggest that all these species are formed on grain surfaces in early evolutionary stages of molecular clouds, and that they are subsequently released back to the gas-phase through thermal desorption or shock-triggered desorption.

2022

• The trans/cis ratio of formic, HCOOH, and thioformic, HC(O)SH, acids in the Interstellar Medium

  J. García de la Concepción, L. Colzi, I. Jiménez-Serra, G. Molpeceres, J. C. Corchado, V. M. Rivilla, J. Martín-Pintado, M. T. Beltrán, C. Mininni

  published in A&A (A&A, 658, A150) pdf - arXiv:2111-10842 pdf

  Abstract

  Observations of the different isomers of molecules in the interstellar medium (ISM), have revealed that both low- and high- energy isomers can be present in space despite the low temperature conditions. It has been shown that the presence of these isomers may be due to tunneling effects.
  We studied theoretically the cis-trans isomerization reactions of two astrophysically relevant acids, formic acid (HCOOH) and thioformic acid (HC(O)SH), where the latter has recently been discovered in space. We also searched for these molecules towards the hot core G31.41+0.31 to compare with the theoretical isomerization results.
  High-level Ab Initio calculations have been employed to study the reaction rates constants of the isomerization reactions. We used the canonical variational transition state theory (CVT) with the multidimensional small curvature tunneling approximation (SCT) in the temperature range 10-400 K. Moreover, we have used the spectrum obtained from the ALMA 3mm spectral survey GUAPOS, with a spectral resolution of ∼0.488 MHz and an angular resolution of 1.2″×1.2″ (∼4500 au), to derive column densities of HCOOH and HC(O)SH towards G31.
  Our results demonstrate that these isomerizations are viable in the conditions of the ISM due to ground-state tunneling effects, which allows the system to reach the thermodynamic equilibrium at moderately low temperatures. At very low temperatures (Tkin ∼10 K), the reaction rate constants for the cis to trans isomerizations are very small, which implies that the cis isomers should be non-existent under cold ISM conditions. This is in disagreement with observations of the cis/trans isomers of formic acid in cold cores where the cis isomer is found to be ∼5-6% the trans isomer. At high temperatures (∼150-300 K), our theoretical data not only match the observed behaviour of the trans/cis abundance ratios for formic acid (the cis form is undetected), but they support our tentative detection of the trans and, for the first time in the insterstellar medium, of the cis isomers of thioformic acid towards the hot molecular core G31 (with a measured trans/cis abundance ratio of ∼3.7).
  The trans/cis ratio for these acids in the ISM depend on the relative stability of the isomers, except for those cases where the isomerization cannot occur and the ratio depends on competitive chemical processes (as for e.g. formic acid in cold molecular sources).

2023

• The GUAPOS project III: Characterization of the O- and N-bearing complex organic molecules content and search for chemical differentiation

  C. Mininni, M. T. Beltrán, L. Colzi, V. M. Rivilla, F. Fontani, A. Lorenzani, Á. López-Gallifa, S. Viti, A. Sánchez-Monge, P. Schilke, L. Testi

  published in A&A (A&A, 677, A15) pdf - arXiv:2306.13563 pdf

  Abstract

  The G31.41+0.31 Unbiased ALMA sPectral Observational Survey (GUAPOS) project targets the hot molecular core (HMC) G31.41+0.31 (G31), to unveil the complex chemistry of one of the most chemically rich high-mass star-forming regions outside the Galactic Center (GC). In the third paper of the project we present a study of nine O-bearing (CH₃OH, ¹³CH₃OH, CH₃¹⁸OH, CH₃CHO, CH₃OCH₃, CH₃COCH₃, C₂H₅OH, aGg'-(CH₂OH)₂, and gGg'-(CH₂OH)₂) and six N-bearing (CH₃CN, ¹³CH₃CN, CH₃¹³CN, C₂H₃CN, C₂H₅CN, and C₂H₅¹³CN) complex organic molecules toward G31. The aim of this work is to characterize the abundances in %one of the most chemically-rich hot molecular cores outside the GC, and to compare the values found in G31 and to compare them with the values estimated in other sources. Moreover, we search for a possible chemical segregation between O-bearing and N-bearing species in G31, which hosts four compact sources as seen with higher angular resolution data. In the discussion we also include the three isomers of C₂H₄O₂ and the O- and N-bearing molecular species NH₂CHO, CH₃NCO, CH₃C(O)CH₂, and CH3NHCHO, analyzed in previous GUAPOS papers.
  Observations were carried out with the interferometer ALMA and cover the entire Band 3 from 84 to 116 GHz (∼32 GHz bandwidth) with an angular resolution of 1.2″ (∼4400 au) and a spectral resolution of ∼0.488 MHz (∼1.3-1.7 km s^-1). The transitions of the fourteen molecular species have been analyzed with the tool SLIM of MADCUBA to determine the physical parameters of the emitting gas. Moreover, we have analyzed the morphology of the emission of the molecular species.
  The values of abundances w.r.t H₂ in G31 range from 10^-6 to 10^-10 for the different species. We have compared the abundances w.r.t methanol of O-bearing, N-bearing, and O- and N-bearing COMs in G31 with other twenty-seven sources, including other hot molecular cores inside and outside the Galactic Center, hot corinos, shocked regions, envelopes around young stellar objects, and quiescent molecular clouds, and with chemical models.
  From the comparison with other sources there is not a unique template for the abundances in hot molecular cores, pointing towards the importance of the thermal history for the chemistry of the various sources. The abundances derived from the chemical models are well in agreement, within a factor ten, with those of G31. From the analysis of the maps we derived the peak positions of all the molecular species toward G31. Different species peak at slightly different positions, and this, together with the different central velocities of the lines obtained from the spectral fitting, point to chemical differentiation of selected O-bearing species.

2024

• The GUAPOS project: G31.41+0.31 Unbiased ALMA sPectral Observational Survey. IV. Phosphorus-bearing molecules and their relation to shock tracers

  F. Fontani, C. Mininni, M. T. Beltrán, V. M. Rivilla, L. Colzi, I. Jiménez-Serra, Á. López-Gallifa, Á. Sánchez-Monge, S. Viti

  published in A&A (A&A, 682, A74) pdf - arXiv:2311.13367 pdf

  Abstract

  The astrochemistry of the important biogenic element phosphorus (P) is still poorly understood, but observational evidence indicates that P-bearing molecules are likely associated with shocks. We study P-bearing molecules and some shock tracers towards one of the chemically richest hot molecular cores, G31.41+0.31, in the framework of the project "G31.41+0.31 Unbiased ALMA sPectral Observational Survey" (GUAPOS), which is being carried out with the Atacama Large Millimeter Array (ALMA). Methods: We observed the molecules PN, PO, SO, SO₂, SiO, and SiS through their rotational lines in the spectral range 84.05- 115.91 GHz covered by the GUAPOS project. PN is clearly detected, while PO is tentatively detected. The PN emission arises from two regions southwest of the hot core peak, named regions 1 and 2 here, and is undetected or tentatively detected towards the hot core peak. The PN and SiO lines are very similar both in spatial emission morphology and spectral shape. Region 1 is partly overlapping with the hot core and is warmer than region 2, which is well separated from the hot core and located along the outflows identified in previous studies. The SO, SO₂, and SiS emissions are also detected towards the PN-emitting regions 1 and 2, but arise mostly from the hot core. Moreover, the column density ratio SiO/PN remains constant in regions 1 and 2, while SO/PN, SiS/PN, and SO₂/PN decrease by about an order of magnitude from region 1 to region 2, indicating that SiO and PN have a common origin even in regions with different physical conditions. The PO/PN ratio in region 2, where PO is tentatively detected, is ∼0.6-0.9, which is in line with the predictions of pure shock models. Our study provides robust confirmation of previous observational evidence that PN emission is tightly associated with SiO and is likely a product of shock chemistry, as the lack of a clear detection of PN towards the hot core allows us to rule out relevant formation pathways in hot gas. We propose the PN-emitting region 2 as a new astrophysical laboratory for shock-chemistry studies.

• The GUAPOS project. V: The chemical ingredients of a massive stellar protocluster in the making

  Á. López-Gallifa, V. M. Rivilla, M. T. Beltrán, L. Colzi, C. Mininni, Á. Sánchez-Monge, F. Fontani, S. Viti, I. Jiménez-Serra, L. Testi, R. Cesaroni, A. Lorenzani

  accepted for publication in MNRAS - arXiv:2403:02191 pdf

  Abstract

  Most stars, including the Sun, are born in rich stellar clusters containing massive stars. Therefore, the study of the chemical reservoir of massive star-forming regions is crucial to understand the basic chemical ingredients available at the dawn of planetary systems. We present a detailed study of the molecular inventory of the hot molecular core G31.41+0.31 from the project GUAPOS (G31.41+0.31 Unbiased ALMA sPectral Observational Survey). We analyze 34 species for the first time plus 20 species analyzed in previous GUAPOS works, including oxygen, nitrogen, sulfur, phosphorus, and chlorine species. We compare the abundances derived in G31.41+0.31 with those observed in other chemically-rich sources that represent the initial and last stages of the formation of stars and planets: the hot corino in the Solar-like protostar IRAS 16293–2422 B, and the comets 67P/Churyumov-Gerasimenko and 46P/Wirtanen. The comparative analysis reveals that the chemical feedstock of the two star-forming regions are similar. The abundances of oxygen- and nitrogen-bearing molecules exhibit a good correlation for all pair of sources, including the two comets, suggesting a chemical heritage of these species during the process of star formation, and hence an early phase formation of the molecules. However, sulfur- and phosphorus-bearing species present worse correlations, being more abundant in comets. This suggests that while sulfur- and phosphorus-bearing species are predominantly trapped on the surface of icy grains in the hot close surroundings of protostars, they could be more easily released into gas phase in comets, allowing their cosmic abundances to be almost recovered.