Examinando por Autor "Rivilla, V. M."

Mostrando 1 - 9 de 9

Acceso Abierto
Cloud–cloud collision as drivers of the chemical complexity in Galactic Centre molecular clouds.
(Oxford Academics: Blackwell Publishing, 2020-07-29) Zeng, S.; Zhang, Q.; Jiménez Serra, I.; Tercero, B.; Lu, X.; Martín Pintado, J.; De Vicente, P.; Rivilla, V. M.; Li, S.; European Research Council (ERC); Agencia Estatal de Investigación (AEI); European Commission (EC); Japan Society for the Promotion of Science (KAKENHI); De Vicente, P. [0000-0002-5902-5005]; Rivilla, V. M. [0000-0002-2887-5859]; Li, S. [0000-0003-1275-5251]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
G+0.693-0.03 is a quiescent molecular cloud located within the Sagittarius B2 (Sgr B2) star-forming complex. Recent spectral surveys have shown that it represents one of the most prolific repositories of complex organic species in the Galaxy. The origin of such chemical complexity, along with the small-scale physical structure and properties of G+0.693-0.03, remains a mystery. In this paper, we report the study of multiple molecules with interferometric observations in combination with single-dish data in G+0.693-0.03. Despite the lack of detection of continuum source, we find small-scale (0.2 pc) structures within this cloud. The analysis of the molecular emission of typical shock tracers such as SiO, HNCO, and CH3OH unveiled two molecular components, peaking at velocities of 57 and 75 km s(-1). They are found to be interconnected in both space and velocity. The position-velocity diagrams show features that match with the observational signatures of a cloud-cloud collision. Additionally, we detect three series of class I methanol masers known to appear in shocked gas, supporting the cloud-cloud collision scenario. From the maser emission we provide constraints on the gas kinetic temperatures (similar to 30-150 K) and H-2 densities (10(4)-10(5) cm(-2)). These properties are similar to those found for the starburst galaxy NGC 253 also using class I methanol masers, suggested to be associated with a cloud-cloud collision. We conclude that shocks driven by the possible cloud-cloud collision is likely the most important mechanism responsible for the high level of chemical complexity observed in G+0.693-0.03.
Acceso Abierto
Fragmentation in the massive G31.41+0.31 protocluster
(EDP Sciences, 2021-04-20) Beltrán, M. T.; Rivilla, V. M.; Cesaroni, R.; Maud, L. T.; Galli, D.; Moscadelli, L.; Lorenzani, A.; Ahmadi, A.; Beuther, H.; Csengeri, T.; Etoka, S.; Goddi, C.; Klaassen, P. D.; Kuiper, R.; Kumar, M. S. N.; Peters, T.; Sánchez Monge, Á.; Schilke, P.; Van der Tak, F.; Vig, S.; Zinnecker, H.; Comunidad de Madrid; Deutsche Forschungsgemeinschaft (DFG); European Research Council (ERC); Fundacao para a Ciencia e a Tecnologia (FCT)
Context. ALMA observations at 1.4 mm and ~0.′′2 (~750 au) angular resolution of the Main core in the high-mass star-forming region G31.41+0.31 have revealed a puzzling scenario. On the one hand, the continuum emission looks very homogeneous and the core appears to undergo solid-body rotation, suggesting a monolithic core stabilized by the magnetic field; on the other hand, rotation and infall speed up toward the core center, where two massive embedded free-free continuum sources have been detected, pointing to an unstable core having undergone fragmentation. Aims. To establish whether the Main core is indeed monolithic or if its homogeneous appearance is due to a combination of large dust opacity and low angular resolution, we carried out millimeter observations at higher angular resolution and different wavelengths. Methods. We carried out ALMA observations at 1.4 mm and 3.5 mm that achieved angular resolutions of ~0.′′1 (~375 au) and ~0.′′075 (~280 au), respectively. VLA observations at 7 mm and 1.3 cm at even higher angular resolution, ~0.′′05 (~190 au) and ~0.′′07 (~260 au), respectively, were also carried out to better study the nature of the free-free continuum sources detected in the core. Results. The millimeter continuum emission of the Main core has been clearly resolved into at least four sources, A, B, C, and D, within 1″, indicating that the core is not monolithic. The deconvolved radii of the dust emission of the sources, estimated at 3.5 mm, are ~400–500 au; their masses range from ~15 to ~26 M⊙; and their number densities are several 109 cm−3. Sources A and B, located closer to the center of the core and separated by ~750 au, are clearly associated with two free-free continuum sources, likely thermal radio jets, and are brightest in the core. The spectral energy distribution of these two sources and their masses and sizes are similar and suggest a common origin. Source C has not been detected at centimeter wavelengths, while source D has been clearly detected at 1.3 cm. Source D is likely the driving source of an E–W SiO outflow previously detected in the region, which suggests that the free-free emission might be coming from a radio jet. Conclusions. The observations have confirmed that the Main core in G31 is collapsing, that it has undergone fragmentation, and that its homogeneous appearance previously observed at short wavelengths is a consequence of both high dust opacity and insufficient angular resolution. The low level of fragmentation together with the fact that the core is moderately magnetically supercritical, suggests that G31 could have undergone a phase of magnetically regulated evolution characterized by a reduced fragmentation efficiency, eventually leading to the formation of a small number of relatively massive dense cores.
Acceso Abierto
On the Effects of UV Photons/X-Rays on the Chemistry of the Sgr B2 Cloud
(The Institute of Physics (IOP), 2020-05-26) Armijos Abendaño, J.; Martín Pintado, J.; López, E.; Llerena, M.; Harada, N.; Requeña Torres, M. A.; Martín, S.; Rivilla, V. M.; Riquelme, D.; Aldas, F.; Comisión Nacional de Investigación Científica y Tecnológica (CONICYT); European Research Council (ERC); Armijos Abendaño, J. [0000-0003-3341-6144]; Llerena, M. [0000-0003-1354-4296]; Martín, S. [0000-0001-9281-2919]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
The lines of HOC+, HCO, and CO+ are considered good tracers of photon-dominated regions (PDRs) and X-ray-dominated regions. We study these tracers toward regions of the Sgr B2 cloud selected to be affected by different heating mechanisms. We find the lowest values of the column density ratios of HCO+ versus HOC+, HCO, and CO+ in dense H ii gas, where UV photons dominate the heating and chemistry of the gas. The HOC+, HCO, and CO+ abundances and the above ratios are compared with those of chemical modeling, finding that high-temperature chemistry, a cosmic-ray ionization rate of 10(-16) s(-1), and timescales >10(5.0) yr explain well the HOC+ abundances in quiescent Sgr B2 regions, while shocks are also needed to explain the highest HCO abundances derived for these regions. The CO+ is mainly formed in PDRs, since the highest CO+ abundances of similar to(6-10) x 10(-10) are found in H ii regions with electron densities >540 cm(-3) and CO+ emission is undetected in quiescent gas. Among the ratios, the HCO+/HCO ratio is sensitive to the electron density, as it shows different values in dense and diffuse H ii regions. We compare SiO J = 2-1 emission maps of Sgr B2 with X-ray maps from 2004 and 2012. One known spot shown on the 2012 X-ray map is likely associated with molecular gas at velocities of 15-25 km s(-1). We also derive the X-ray ionization rate of similar to 10(-19) s(-1) for Sgr B2 regions pervaded by X-rays in 2004, which is quite low to affect the chemistry of the molecular gas.
Acceso Abierto
Prebiotic Precursors of the Primordial RNA World in Space: Detection of NH2OH
(The Institute of Physics (IOP), 2020-08-19) Rivilla, V. M.; Martín Pintado, J.; Jiménez Serra, I.; Martín, S.; Rodríguez Almeida, L. F.; Requeña Torres, M. A.; Rico Villas, F.; Zeng, S.; Briones, C.; European Research Council (ERC); Agencia Estatal de Investigación (AEI); Comunidad de Madrid; Briones, C. [0000-0003-2213-8353]; Martín Ruiz, S. [0000-0001-9281-2919]; Rico Villas, F. [0000-0002-5351-3497]; Rivilla, V. M. [0000-0002-2887-5859]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
One of the proposed scenarios for the origin of life is the primordial RNA world, which considers that RNA molecules were likely responsible for the storage of genetic information and the catalysis of biochemical reactions in primitive cells, before the advent of proteins and DNA. In the last decade, experiments in the field of prebiotic chemistry have shown that RNA nucleotides can be synthesized from relatively simple molecular precursors, most of which have been found in space. An important exception is hydroxylamine, NH2OH, which, despite several observational attempts, it has not been detected in space yet. Here we present the first detection of NH2OH in the interstellar medium toward the quiescent molecular cloud G+0.693-0.027 located in the Galactic Center. We have targeted the three groups of transitions from the J = 2−1, 3−2, and 4−3 rotational lines, detecting five transitions that are unblended or only slightly blended. The derived molecular abundance of NH2OH is (2.1 ± 0.9) × 10−10. From the comparison of the derived abundance of NH2OH and chemically related species, with those predicted by chemical models and measured in laboratory experiments, we favor the formation of NH2OH in the interstellar medium via hydrogenation of NO on dust grain surfaces, with possibly a contribution of ice-mantle NH3 oxidation processes. Further laboratory studies and quantum chemical calculations are needed to completely rule out the formation of NH2OH in the gas phase.
Acceso Abierto
Propargylimine in the laboratory and in space: millimetre-wave spectroscopy and its first detection in the ISM
(EDP Sciences, 2020-08-20) Bizzocchi, L.; Prudenzano, D.; Rivilla, V. M.; Pietropolli Charmet, A.; Giuliano, B. M.; Caselli, P.; Martín Pintado, J.; Jiménez Serra, I.; Martín, S.; Requena Torres, M. A.; Rico Villas, F.; Guillemin, J. C.; Centre National D'Etudes Spatiales (CNES); European Research Council (ERC); Agencia Estatal de Investigación (AEI); Rico Villas, F. [0000-0002-5351-3497]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
Context. Small imines containing up to three carbon atoms are present in the interstellar medium (ISM). As alkynyl compounds are abundant in this medium, propargylimine (2-propyn-1-imine, HC ≡C−CH =NH) thus represents a promising candidate for a new interstellar detection. Aims. The goal of the present work is to perform a comprehensive laboratory investigation of the rotational spectrum of propargylimine in its ground vibrational state in order to obtain a highly precise set of rest frequencies and to search for it in space. Methods. The rotational spectra of E and Z geometrical isomers of propargylimine have been recorded in the laboratory in the 83–500 GHz frequency interval. The measurements have been performed using a source-modulation millimetre-wave spectrometer equipped with a pyrolysis system for the production of unstable species. High-level ab initio calculations were performed to assist the analysis and to obtain reliable estimates for an extended set of spectroscopic quantities. We searched for propargylimine at 3 mm and 2 mm in the spectral survey of the quiescent giant molecular cloud G+0.693-0.027 located in the central molecular zone, close to the Galactic centre. Results. About 1000 rotational transitions have been recorded for the E- and Z-propargylimine, in the laboratory. These new data have enabled the determination of a very accurate set of spectroscopic parameters including rotational, quartic, and sextic centrifugal distortion constants. The improved spectral data allowed us to perform a successful search for this new imine in the G+0.693-0.027 molecular cloud. Eighteen lines of Z-propargylimine were detected at level >2.5σ, resulting in a column-density estimate of N = (0.24 ± 0.02) × 1014 cm−2. An upper limit was retrieved for the higher energy E isomer, which was not detected in the data. The fractional abundance (with respect to H2) derived for Z-propargylimine is 1.8 × 10−10. We discuss the possible formation routes by comparing the derived abundance with those measured in the source for possible chemical precursors.
Acceso Abierto
Spectral Line Identification and Modelling (SLIM) in the MAdrid Data CUBe Analysis (MADCUBA) package Interactive software for data cube analysis
(EDP Sciences, 2019-11-13) Martín, S.; Martín Pintado, J.; Blanco Sánchez, C.; Rivilla, V. M.; Rodríguez Franco, A.; Rico Villas, F.; Agencia Estatal de Investigación (AEI); Ministerio de Economía y Competitividad (MINECO); European Research Council (ERC); Rivilla, V. M. [0000-0002-2887-5859]; Martín Ruiz, S. [0000-0001-9281-2919]; Rico Villas, F. [0000-0002-5351-3497]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
Context. The increase in bandwidth and sensitivity of state-of-the-art radio observatories is providing a wealth of molecular data from nearby star-forming regions up to high-z galaxies. Analysing large data sets of spectral cubes requires efficient and user-friendly tools optimised for astronomers with a wide range of backgrounds. Aims. In this paper we present the detailed formalism at the core of Spectral Line Identification and Modelling (SLIM) within the MAdrid Data CUBe Analysis (MADCUBA) package and their main data-handling functionalities. These tools have been developed to visualise, analyse, and model large spectroscopic data cubes. Methods. We present the highly interactive on-the-fly visualisation and modelling tools of MADCUBA and SLIM, which includes a stand-alone spectroscopic database. The parameters stored therein are used to solve the full radiative transfer equation under local thermodynamic equilibrium (LTE). The SLIM package provides tools to generate synthetic LTE model spectra based on input physical parameters of column density, excitation temperature, velocity, line width, and source size. It also provides an automatic fitting algorithm to obtain the physical parameters (with their associated errors) better fitting the observations. Synthetic spectra can be overlayed in the data cubes/spectra to ease the task of multi-molecular line identification and modelling. Results. We present the Java-based MADCUBA and its internal module SLIM packages which provide all the necessary tools for manipulation and analysis of spectroscopic data cubes. We describe in detail the spectroscopic fitting equations and make use of this tool to explore the breaking conditions and implicit errors of commonly used approximations in the literature. Conclusions. Easy-to-use tools like MADCUBA allow users to derive physical information from spectroscopic data without the need for simple approximations. The SLIM tool allows the full radiative transfer equation to be used, and to interactively explore the space of physical parameters and associated uncertainties from observational data.
Acceso Abierto
The ionized heart of a molecular disk ALMA observations of the hyper-compact HII region G24.78+0.08 A1
(EDP Sciences, 2021-06-21) Moscadelli, L.; Cesaroni, R.; Beltrán, M. T.; Rivilla, V. M.
Context. Hyper-compact (HC) or ultra-compact H II regions are the first manifestations of the radiation feedback from a newly born massive star. Therefore, their study is fundamental to understanding the process of massive (≥8 M⊙) star formation. Aims. We employed Atacama Large Millimeter/submillimeter Array (ALMA) 1.4 mm Cycle 6 observations to investigate at high angular resolution (≈0.′′050, corresponding to 330 au) the HC H II region inside molecular core A1 of the high-mass star-forming cluster G24.78+0.08. Methods. We used the H30α emission and different molecular lines of CH3CN and 13CH3CN to study the kinematics of the ionized and molecular gas, respectively. Results. At the center of the HC H II region, at radii ≲500 au, we observe two mutually perpendicular velocity gradients, which are directed along the axes at PA = 39° and PA = 133°, respectively. The velocity gradient directed along the axis at PA = 39° has an amplitude of 22 km s−1 mpc−1, which is much larger than the other’s, 3 km s−1 mpc−1. We interpret these velocity gradients as rotation around, and expansion along, the axis at PA = 39°. We propose a scenario where the H30α line traces the ionized heart of a disk-jet system that drives the formation of the massive star (≈20 M⊙) responsible for the HC H II region. Such a scenario is also supported by the position-velocity plots of the CH3CN and 13CH3CN lines along the axis at PA = 133°, which are consistent with Keplerian rotation around a 20 M⊙ star. Conclusions. Toward the HC H II region in G24.78+0.08, the coexistence of mass infall (at radii of ~5000 au), an outer molecular disk (from ≲4000 au to ≳500 au), and an inner ionized disk (≲500 au) indicates that the massive ionizing star is still actively accreting from its parental molecular core. To our knowledge, this is the first example of a molecular disk around a high-mass forming star that, while becoming internally ionized after the onset of the H II region, continues to accrete mass onto the ionizing star.
Acceso Abierto
The Ionized Warped Disk and Disk Wind of the Massive Protostar Monoceros R2-IRS2 Seen with ALMA
(The Institute of Physics (IOP), 2020-07-13) Jiménez Serra, I.; Báez Rubio, A.; Martín Pintado, J.; Zhang, Q.; Rivilla, V. M.; Agencia Estatal de Investigación (AEI); European Research Council (ERC); Jiménez Serra, I. [0000-0003-4493-8714]; Zhang, Q. [0000-0003-2384-6589]; Rivilla, V. M. [0000-0002-2887-5859]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
Theories of massive star formation predict that massive protostars accrete gas through circumstellar disks. Although several cases have been found already thanks to high angular-resolution interferometry, the internal physical structure of these disks remains unknown, in particular whether they present warps or internal holes, as observed in low-mass protoplanetary disks. Here, we report very high angular-resolution observations of the H21 alpha radio recombination line carried out in Band 9 with the Atacama Large Millimeter/submillimeter Array (beam of 80 mas x 60 mas, or 70 au x 50 au) toward the IRS2 massive young stellar object in the Monoceros R2 star-forming cluster. The H21 alpha line shows maser amplification, which allows us to study the kinematics and physical structure of the ionized gas around the massive protostar down to spatial scales of similar to 1-2 au. Our ALMA images and 3D radiative transfer modeling reveal that the ionized gas around IRS2 is distributed in a Keplerian circumstellar disk and an expanding wind. The H21 alpha emission centroids at velocities between -10 and 20 km s(-1)deviate from the disk plane, suggesting a warping for the disk. This could be explained by the presence of a secondary object (a stellar companion or a massive planet) within the system. The ionized wind seems to be launched from the disk surface at distances similar to 11 au from the central star, consistent with magnetically-regulated disk wind models. This suggests a similar wind-launching mechanism to that recently found for evolved massive stars such as MWC349A and MWC922.
Restringido
Vibrationally excited HC3N emission in NGC 1068: tracing the recent star formation in the starburst ring
(Oxford Academics: Oxford University Press, 2021-01-25) Rico Villas, F.; Martín Pintado, J.; González Alfonso, E.; Rivilla, V. M.; Martín, S.; García Burillo, S.; Jiménez Serra, I.; Sánchez García, M.; Agencia Estatal de Investigación (AEI); European Research Council (ERC); Rivilla, V. M. [0000-0002-2887-5859]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
Using the ALMA data, we have studied the HC3N and continuum emission in the starburst pseudo-ring (SB pseudo-ring) and the circumnuclear disc (CND) of the SB/active galactic nucleus (AGN) composite galaxy NGC 1068. We have detected emission from vibrationally excited HC3N (HC3N*) only towards one star-forming region of the SB pseudo-ring. Remarkably, HC3N* was not detected towards the CND despite its large HC3N v = 0 column density. From local thermodynamic equilibrium (LTE) and non-LTE modelling of HC3N*, we obtained a dust temperature (Tdust) of ∼250 K and a density (nH2) of 6×105 cm−3 for this star-forming region. The estimated infrared (IR) luminosity of 5.8 × 108 L⊙ is typical of proto-superstar clusters (proto-SSCs) observed in the SB galaxy NGC 253. We use the continuum emissions at 147 and 350 GHz, along with CO and Pa α, to estimate the ages of other 14 SSCs in the SB pseudo-ring. We find the SSCs to be associated with the region connecting the nuclear bar with the SB pseudo-ring, supporting the inflow scenario. For the CND, our analysis yields Tdust ≤ 100 K and nH2∼(3−6)×105 cm−3. The very different dust temperatures found for the CND and the proto-SSC indicate that, while the dust in the proto-SSC is being efficiently heated from the inside by the radiation from massive protostars, the CND is being heated externally by the AGN, which in the IR optically thin case can only heat the dust to 56 K. We discuss the implications of the non-detection of HC3N* near the luminous AGN in NGC 1068 on the interpretation of the HC3N* emission observed in the SB/AGN composite galaxies NGC 4418 and Arp 220.