| 1. |
- Fomalont, E. B., et al.
(författare)
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THE 2014 ALMA LONG BASELINE CAMPAIGN: AN OVERVIEW
- 2015
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 808:1
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Tidskriftsartikel (refereegranskat)abstract
- A major goal of the Atacama Large Millimeter/submillimeter Array (ALMA) is to make accurate images with resolutions of tens of milliarcseconds, which at submillimeter (submm) wavelengths requires baselines up to similar to 15 km. To develop and test this capability, a Long Baseline Campaign (LBC) was carried out from 2014 September to late November, culminating in end-to-end observations, calibrations, and imaging of selected Science Verification (SV) targets. This paper presents an overview of the campaign and its main results, including an investigation of the short-term coherence properties and systematic phase errors over the long baselines at the ALMA site, a summary of the SV targets and observations, and recommendations for science observing strategies at long baselines. Deep ALMA images of the quasar 3C 138 at 97 and 241 GHz are also compared to VLA 43 GHz results, demonstrating an agreement at a level of a few percent. As a result of the extensive program of LBC testing, the highly successful SV imaging at long baselines achieved angular resolutions as fine as 19 mas at similar to 350 GHz. Observing with ALMA on baselines of up to 15 km is now possible, and opens up new parameter space for submm astronomy.
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| 2. |
- Taquet, V, et al.
(författare)
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Seeds of Life in Space (SOLIS) VI. Chemical evolution of sulfuretted species along the outflows driven by the low-mass protostellar binary NGC1333-IRAS4A
- 2020
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 637
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Tidskriftsartikel (refereegranskat)abstract
- Context. Low-mass protostars drive powerful molecular outflows that can be observed with millimetre and submillimetre telescopes. Various sulfuretted species are known to be bright in shocks and could be used to infer the physical and chemical conditions throughout the observed outflows. Aims. The evolution of sulfur chemistry is studied along the outflows driven by the NGC1333-IRAS4A protobinary system located in the Perseus cloud to constrain the physical and chemical processes at work in shocks. Methods. We observed various transitions from OCS, CS, SO, and SO2 towards NGC1333-IRAS4A in the 1.3, 2, and 3mm bands using the IRAM NOrthern Extended Millimeter Array and we interpreted the observations through the use of the Paris-Durham shock model. Results. The targeted species clearly show different spatial emission along the two outflows driven by IRAS4A. OCS is brighter on small and large scales along the south outflow driven by IRAS4A1, whereas SO2 is detected rather along the outflow driven by IRAS4A2 that is extended along the north east-south west direction. SO is detected at extremely high radial velocity up to +25 km s 1 relative to the source velocity, clearly allowing us to distinguish the two outflows on small scales. Column density ratio maps estimated from a rotational diagram analysis allowed us to confirm a clear gradient of the OCS/SO2 column density ratio between the IRAS4A1 and IRAS4A2 outflows. Analysis assuming non Local Thermodynamic Equilibrium of four SO2 transitions towards several SiO emission peaks suggests that the observed gas should be associated with densities higher than 105 cm 3 and relatively warm (T > 100 K) temperatures in most cases. Conclusions. The observed chemical differentiation between the two outflows of the IRAS4A system could be explained by a different chemical history. The outflow driven by IRAS4A1 is likely younger and more enriched in species initially formed in interstellar ices, such as OCS, and recently sputtered into the shock gas. In contrast, the longer and likely older outflow triggered by IRAS4A2 is more enriched in species that have a gas phase origin, such as SO2.
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| 3. |
- Cosentino, Giuliana, 1990, et al.
(författare)
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Negative and positive feedback from a supernova remnant with SHREC. a detailed study of the shocked gas in IC443
- 2022
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 511:1, s. 953-963
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Tidskriftsartikel (refereegranskat)abstract
- 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 (HCO+)-C-13 (1-0) maps obtained by SHREC together with SiO(1-0) observations obtained with the 40-m 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 towards 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 per cent 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.
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| 4. |
- Barnes, A. T., et al.
(författare)
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ALMA-IRDC: dense gas mass distribution from cloud to core scales
- 2021
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 503:3, s. 4601-4626
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Tidskriftsartikel (refereegranskat)abstract
- Infrared dark clouds (IRDCs) are potential hosts of the elusive early phases of high mass star formation (HMSF). Here, we conduct an in-depth analysis of the fragmentation properties of a sample of 10 IRDCs, which have been highlighted as some of the best candidates to study HMSF within the Milky Way. To do so, we have obtained a set of large mosaics covering these IRDCs with Atacama Large Millimeter/submillimeter Array (ALMA) at Band 3 (or 3 mm). These observations have a high angular resolution (similar to 3 arcsec; similar to 0.05 pc), and high continuum and spectral line sensitivity (similar to 0.15 mJy beam(-1) and similar to 0.2 K per 0.1 km s(-1) channel at the N2H+ (1 - 0) transition). From the dust continuum emission, we identify 96 cores ranging from low to high mass (M = 3.4-50.9M(circle dot)) that are gravitationally bound (alpha(vir) = 0.3-1.3) and which would require magnetic field strengths of B = 0.3-1.0 mG to be in virial equilibrium. We combine these results with a homogenized catalogue of literature cores to recover the hierarchical structure within these clouds over four orders of magnitude in spatial scale (0.01-10 pc). Using supplementary observations at an even higher angular resolution, we find that the smallest fragments (<0.02 pc) within this hierarchy do not currently have the mass and/or the density required to form high-mass stars. None the less, the new ALMA observations presented in this paper have facilitated the identification of 19 (6 quiescent and 13 star-forming) cores that retain >16M(circle dot) without further fragmentation. These high-mass cores contain trans-sonic non-thermal motions, are kinematically sub-virial, and require moderate magnetic field strengths for support against collapse. The identification of these potential sites of HMSF represents a key step in allowing us to test the predictions from high-mass star and cluster formation theories.
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| 5. |
- Barnes, Ashley T., et al.
(författare)
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Mother of dragons: A massive, quiescent core in the dragon cloud (IRDC G028.37+00.07)
- 2023
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 675
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Tidskriftsartikel (refereegranskat)abstract
- Context. Core accretion models of massive star formation require the existence of massive, starless cores within molecular clouds. Yet, only a small number of candidates for such truly massive, monolithic cores are currently known. Aims. Here we analyse a massive core in the well-studied infrared-dark cloud (IRDC) called the dragon clouda'(also known as G028.37+00.07 or Cloud Ca). This core (C2c1) sits at the end of a chain of a roughly equally spaced actively star-forming cores near the center of the IRDC. Methods. We present new high-angular-resolution 1 mm ALMA dust continuum and molecular line observations of the massive core. Results. The high-angular-resolution observations show that this region fragments into two cores, C2c1a and C2c1b, which retain significant background-subtracted masses of 23 M· and 2 M· (31 M· and 6 M· without background subtraction), respectively. The cores do not appear to fragment further on the scales of our highest-angular-resolution images (0.2 , 0.005 pc ∼ 1000 AU). We find that these cores are very dense (nH2 > 106 cm-3) and have only trans-sonic non-thermal motions ( 3s ∼ 1). Together the mass, density, and internal motions imply a virial parameter of
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| 6. |
- Calcutt, Hannah, 1988, et al.
(författare)
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A high-resolution study of complex organic molecules in hot cores
- 2014
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 443:4, s. 3157-3173
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Tidskriftsartikel (refereegranskat)abstract
- We present the results ofa line identification analysis using data from theIRAMPlateau de Bure Plateau de Bure Interferometer, focusing on six massive star-forming hot cores: G31.41+0.31, tify several transitions of vibrationally excited methyl formate (HCOOCH3) for the first time G29.96−0.02, G19.61−0.23, G10.62−0.38, G24.78+0.08A1 and G24.78+0.08A2.We iden- in these objects as well as transitions of other complex molecules, including ethyl cyanide (C2H5CN), and isocyanic acid (HNCO). We also postulate a detection of one transition of glycolaldehyde (CH2(OH)CHO) in two new hot cores. We find G29.96−0.02, G19.61−0.23, is chemically different: it manifests a larger chemical inventory and has significantly larger col- G24.78+0.08A1 and G24.78+0.08A2 to be chemically very similar. G31.41+0.31, however, umn densities. We suggest that it may represent a different evolutionary stage to the other hot cores in the sample, or it may surround a star with a higher mass. We derive column densities for methyl formate in G31.41+0.31, using the rotation diagram method, of 4 × 1017 cm−2 and methyl formate and methyl cyanide, all seem to trace the same material and peak at roughly a Trot of ∼170 K. For G29.96−0.02, G24.78+0.08A1 and G24.78+0.08A2, glycolaldehyde, the same position towards the dust emission peak. For G31.41+0.31, however, glycolaldehyde shows a different distribution to methyl formate and methyl cyanide and seems to trace the densest, most compact inner part of hot cores.
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| 7. |
- Cosentino, Giuliana, 1990, et al.
(författare)
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SiO emission as a probe of cloud-cloud collisions in infrared dark clouds
- 2020
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 499:2, s. 1666-1681
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Tidskriftsartikel (refereegranskat)abstract
- Infrared dark clouds (IRDCs) are very dense and highly extincted regions that host the initial conditions of star and stellar cluster formation. It is crucial to study the kinematics and molecular content of IRDCs to test their formation mechanism and ultimately characterize these initial conditions. We have obtained high-sensitivity Silicon Monoxide, SiO(2-1), emission maps towards the six IRDCs, G018.82-00.28, G019.27+00.07, G028.53-00.25, G028.67+00.13, G038.95-00.47, and G053.11+00.05 (cloud A, B, D, E, I, and J, respectively), using the 30-m antenna at the Instituto de Radioastronomia Millimetrica (IRAM30m). We have investigated the SiO spatial distribution and kinematic structure across the six clouds to look for signatures of cloud-cloud collision events that may have formed the IRDCs and triggered star formation within them. Towards clouds A, B, D, I, and J, we detect spatially compact SiO emission with broad-line profiles that are spatially coincident with massive cores. Towards the IRDCs A and I, we report an additional SiO component that shows narrow-line profiles and that is widespread across quiescent regions. Finally, we do not detect any significant SiO emission towards cloud E. We suggest that the broad and compact SiO emission detected towards the clouds is likely associated with ongoing star formation activity within the IRDCs. However, the additional narrow and widespread SiO emission detected towards cloud A and I may have originated from the collision between the IRDCs and flows of molecular gas pushed towards the clouds by nearby H II regions.
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| 8. |
- Fontani, F., et al.
(författare)
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ALMA-IRDC - II. First high-angular resolution measurements of the N-14/N-15 ratio in a large sample of infrared-dark cloud cores
- 2021
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 503:3, s. 4320-4335
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Tidskriftsartikel (refereegranskat)abstract
- The N-14/N-15 ratio in molecules exhibits a large variation in star-forming regions, especially when measured from N2H+ isotopologues. However, there are only a few studies performed at high-angular resolution. We present the first interferometric survey of the N-14/N-15 ratio in N2H+ obtained with Atacama Large Millimeter Array observations towards four infrared-dark clouds harbouring 3 mm continuum cores associated with different physical properties. We detect (NNH+)-N-15 (1-0) in of the cores, depending on the host cloud. The N-14/N-15 values measured towards the millimetre continuum cores range from a minimum of similar to 80 up to a maximum of similar to 400. The spread of values is narrower than that found in any previous single-dish survey of high-mass star-forming regions and than that obtained using the total power data only. This suggests that the N-14/N-15 ratio is on average higher in the diffuse gaseous envelope of the cores and stresses the need for high-angular resolution maps to measure correctly the N-14/N-15 ratio in dense cores embedded in IRDCs. The average N-14/N-15 ratio of similar to 210 is also lower than the interstellar value at the Galactocentric distance of the clouds (similar to 300-330), although the sensitivity of our observations does not allow us to unveil N-14/N-15 ratios higher than similar to 400. No clear trend is found between the N-14/N-15 ratio and the core physical properties. We find only a tentative positive trend between N-14/N-15 and H-2 column density. However, firmer conclusions can be drawn only with higher sensitivity measurements.
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| 9. |
- Fontani, F., et al.
(författare)
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Fragmentation properties of massive protocluster gas clumps: an ALMA study
- 2018
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Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 1432-0746 .- 0004-6361. ; 615
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Tidskriftsartikel (refereegranskat)abstract
- Fragmentation of massive dense molecular clouds is the starting point in the formation of rich clusters and massive stars. Theory and numerical simulations indicate that the population of the fragments (number, mass, diameter, and separation) resulting from the gravitational collapse of such clumps is probably regulated by the balance between the magnetic field and the other competitors of self-gravity, in particular, turbulence and protostellar feedback. We have observed 11 massive, dense, and young star-forming clumps with the Atacama Large Millimeter Array (ALMA) in the thermal dust continuum emission at similar to 1 mm with an angular resolution of 0 ''.25 with the aim of determining their population of fragments. The targets have been selected from a sample of massive molecular clumps with limited or absent star formation activity and hence limited feedback. We find fragments on sub-arcsecond scales in 8 out of the 11 sources. The ALMA images indicate two different fragmentation modes: a dominant fragment surrounded by companions with much lower mass and smaller size, and many (>= 8) fragments with a gradual change in masses and sizes. The morphologies are very different, with three sources that show filament-like distributions of the fragments, while the others have irregular geometry. On average, the largest number of fragments is found towards the warmer and more massive clumps. The warmer clumps also tend to form fragments with higher mass and larger size. To understand the role of the different physical parameters in regulating the final population of the fragments, we simulated the collapse of a massive clump of 100 and 300 M-circle dot with different magnetic support. The 300 M-circle dot case was also run for different initial temperatures and Mach numbers M to evaluate the separate role of each of these parameters. The simulations indicate that (1) fragmentation is inhibited when the initial turbulence is low (M similar to 3), independent of the other physical parameters. This would indicate that the number of fragments in our clumps can be explained assuming a high (M similar to 6) initial turbulence, although an initial density profile different to that assumed can play a relevant role. (2) A filamentary distribution of the fragments is favoured in a highly magnetised clump. We conclude that the clumps that show many fragments distributed in a filament-like structure are likely characterised by a strong magnetic field, while the other morphologies are also possible in a weaker magnetic field.
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| 10. |
- Fontani, F., et al.
(författare)
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Magnetically regulated fragmentation of a massive, dense, and turbulent clump
- 2016
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 593
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Tidskriftsartikel (refereegranskat)abstract
- © ESO, 2016. Massive stars, multiple stellar systems, and clusters are born of the gravitational collapse of massive, dense, gaseous clumps, and the way these systems form strongly depends on how the parent clump fragments into cores during collapse. Numerical simulations show that magnetic fields may be the key ingredient in regulating fragmentation. Here we present ALMA observations at ∼ 0.25′′ resolution of the thermal dust continuum emission at ∼ 278 GHz towards a turbulent, dense, and massive clump, IRAS 16061-5048c1, in a very early evolutionary stage. The ALMA image shows that the clump has fragmented into many cores along a filamentary structure. We find that the number, the total mass, and the spatial distribution of the fragments are consistent with fragmentation dominated by a strong magnetic field. Our observations support the theoretical prediction that the magnetic field plays a dominant role in the fragmentation process of massive turbulent clumps.
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