| 1. |
- 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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| 2. |
- Bisbas, T. G., et al.
(författare)
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The inception of star cluster formation revealed by [C ii] emission around an Infrared Dark Cloud
- 2018
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Ingår i: Monthly Notices of the Royal Astronomical Society: Letters. - : Oxford University Press (OUP). - 1745-3925 .- 1745-3933. ; 478:1, s. L54-L59
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Tidskriftsartikel (refereegranskat)abstract
- We present SOFIA-upGREAT observations of [C ii] emission of Infrared Dark Cloud (IRDC) G035.39-00.33, designed to trace its atomic gas envelope and thus test models of the origins of such clouds. Several velocity components of [C ii] emission are detected, tracing structures that are at a wide range of distances in the Galactic plane. We find a main component that is likely associated with the IRDC and its immediate surroundings. This strongest emission component has a velocity similar to that of the 13CO(2-1) emission of the IRDC, but offset by ∼3 km s-1 and with a larger velocity width of ∼9 km s-1. The spatial distribution of the [C ii] emission of this component is also offset predominantly to one side of the dense filamentary structure of the IRDC. The C ii column density is estimated to be of the order of ∼1017-1018 cm-2. We compare these results to the [C ii] emission from numerical simulations of magnetized, dense gas filaments formed from giant molecular cloud (GMC) collisions, finding similar spatial and kinematic offsets. These observations and modellingof [C ii] add further to the evidence that IRDC G035.39-00.33 has been formed by a process of GMC-GMC collision, which may thus be an important mechanism for initiating star cluster formation.
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| 3. |
- Cheng, Yu, et al.
(författare)
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Gas Kinematics of the Massive Protocluster G286.21+0.17 Revealed by ALMA
- 2020
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 894:2
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Tidskriftsartikel (refereegranskat)abstract
- We study the gas kinematics and dynamics of the massive protocluster G286.21+0.17 with the Atacama Large Millimeter/submillimeter Array using spectral lines of {equation presented}(3-2), and DCN(3-2). On the parsec clump scale, C18O emission appears highly filamentary around the systemic velocity, N2D+ and DCO+ are more closely associated with the dust continuum, and DCN is strongly concentrated toward the protocluster center, where no or only weak detection is seen for N2D and DCO+, possibly due to this region being at a relatively evolved evolutionary stage. Spectra of 76 continuum-defined dense cores, typically a few 1000 au in size, are analyzed to measure their centroid velocities and internal velocity dispersions. There are no statistically significant velocity offsets of the cores among the different dense gas tracers. Furthermore, the majority (71%) of the dense cores have subthermal velocity offsets with respect to their surrounding, lower-density C18O-emitting gas. Within the uncertainties, the dense cores in G286 show internal kinematics that are consistent with being in virial equilibrium. On clump scales, the core-to-core velocity dispersion is also similar to that required for virial equilibrium in the protocluster potential. However, the distribution in velocity of the cores is largely composed of two spatially distinct groups, which indicates that the dense molecular gas has not yet relaxed to virial equilibrium, perhaps due to there being recent/continuous infall into the system.
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| 4. |
- Cheng, Yu, et al.
(författare)
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The Core Mass Function in the Massive Protocluster G286.21+0.17 Revealed by ALMA
- 2018
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 853:2
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Tidskriftsartikel (refereegranskat)abstract
- We study the core mass function (CMF) of the massive protocluster G286.21+0.17 with the Atacama Large Millimeter/submillimeter Array via 1.3 mm continuum emission at a resolution of 1.″0 (2500 au). We have mapped a field of 5.′3 × 5.′3 centered on the protocluster clump. We measure the CMF in the central region, exploring various core detection algorithms, which give source numbers ranging from 60 to 125, depending on parameter selection. We estimate completeness corrections due to imperfect flux recovery and core identification via artificial core insertion experiments. For masses M 1 M o , the fiducial dendrogram-identified CMF can be fit with a power law of the form dN/dlog M ∝ M -α with α ≃ 1.24 ± 0.17, slightly shallower than, but still consistent with, the index of the Salpeter stellar initial mass function of 1.35. Clumpfind-identified CMFs are significantly shallower with α ≃ 0.64 ± 0.13. While raw CMFs show a peak near 1 M o , completeness-corrected CMFs are consistent with a single power law extending down to ∼0.5 M o , with only a tentative indication of a shallowing of the slope around ∼1 M o . We discuss the implications of these results for star and star cluster formation theories.
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| 5. |
- Entekhabi, N., et al.
(författare)
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Astrochemical modelling of infrared dark clouds
- 2022
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 662
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Tidskriftsartikel (refereegranskat)abstract
- Context. Infrared dark clouds (IRDCs) are cold, dense regions of the interstellar medium (ISM) that are likely to represent the initial conditions for massive star and star cluster formation. It is thus important to study the physical and chemical conditions of IRDCs to provide constraints and inputs for theoretical models of these processes. Aims. We aim to determine the astrochemical conditions, especially the cosmic ray ionisation rate (CRIR) and chemical age, in different regions of the massive IRDC G28.37+00.07 by comparing observed abundances of multiple molecules and molecular ions with the predictions of astrochemical models. Methods. We have computed a series of single-zone, time-dependent, astrochemical models with a gas-grain network that systematically explores the parameter space of the density, temperature, CRIR, and visual extinction. We have also investigated the effects of choices of CO ice binding energy and temperatures achieved in the transient heating of grains when struck by cosmic rays. We selected ten positions across the IRDC that are known to have a variety of star formation activity. We utilised mid-infrared extinction maps and sub-millimetre (sub-mm) emission maps to measure the mass surface densities of these regions needed for abundance and volume density estimates. The sub-mm emission maps were also used to measure temperatures. We then used Instituto de Radioas-tromía Milimétrica (IRAM) 30 m observations of various tracers, especially C18O(1-0), H13CO+(1-0), HC18O+(1-0), and N2H+(1-0), to estimate column densities and thus abundances. Finally, we investigated the range of astrochemical conditions that are consistent with the observed abundances. Results. The typical physical conditions of the IRDC regions are nH ∼ 3 ×-104 to 105 cm-3 and T ∼ 10 to 15 K. Strong emission of H13CO+(1-0) and N2H+(1-0) is detected towards all the positions and these species are used to define relatively narrow velocity ranges of the IRDC regions, which are used for estimates of CO abundances, via C18O(1-0). We would like to note that CO depletion factors are estimated to be in the range fD ∼ 3 to 10. Using estimates of the abundances of CO, HCO+, and N2H+, we find consistency with astrochemical models that have relatively low CRIRs of ζ ∼ 10-18 to ∼10-17 s-1, with no evidence for systematic variation with the level of star formation activity. Astrochemical ages, which are defined with a reference to an initial condition of all H in H2, all C in CO, and all other species in atomic form, are found to be <1 Myr. We also explore the effects of using other detected species, that is HCN, HNC, HNCO, CH3OH, and H2CO, to constrain the models. These generally lead to implied conditions with higher levels of CRIRs and older chemical ages. Considering the observed fD versus nH relation of the ten positions, which we find to have relatively little scatter, we discuss potential ways in which the astrochemical models can match such a relation as a quasi-equilibrium limit valid at ages of at least a few free-fall times, that is 3;0.3 Myr, including the effect of CO envelope contamination, small variations in temperature history near 15 K, CO-ice binding energy uncertainties, and CR-induced desorption. We find general consistency with the data of ∼0.5 Myr-old models that have ζ ∼ 2-5-10-18 s-1 and CO abundances set by a balance of freeze-out with CR-induced desorption. Conclusions. We have constrained the astrochemical conditions in ten regions in a massive IRDC, finding evidence for relatively low values of CRIR compared to diffuse ISM levels. We have not seen clear evidence for variation in the CRIR with the level of star formation activity. We favour models that involve relatively low CRIRs (≲ 10-17 s-1) and relatively old chemical ages (≳ 3;0.3 Myr, i.e. 3;3tff). We discuss potential sources of systematic uncertainties in these results and the overall implications for IRDC evolutionary history and astrochemical models.
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| 6. |
- Law, Chi Yan, 1990, et al.
(författare)
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Polarized Light from Massive Protoclusters (POLIMAP). I. Dissecting the Role of Magnetic Fields in the Massive Infrared Dark Cloud G28.37+0.07
- 2024
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Ingår i: Astrophysical Journal. - 1538-4357 .- 0004-637X. ; 967:2
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic fields may play a crucial role in setting the initial conditions of massive star and star cluster formation. To investigate this, we report SOFIA-HAWC+ 214 μm observations of polarized thermal dust emission and high-resolution GBT-Argus C18O(1-0) observations toward the massive Infrared Dark Cloud (IRDC) G28.37+0.07. Considering the local dispersion of B-field orientations, we produce a map of the B-field strength of the IRDC, which exhibits values between ∼0.03 and 1 mG based on a refined Davis-Chandrasekhar-Fermi method proposed by Skalidis & Tassis. Comparing to a map of inferred density, the IRDC exhibits a B-n relation with a power-law index of 0.51 ± 0.02, which is consistent with a scenario of magnetically regulated anisotropic collapse. Consideration of the mass-to-flux ratio map indicates that magnetic fields are dynamically important in most regions of the IRDC. A virial analysis of a sample of massive, dense cores in the IRDC, including evaluation of magnetic and kinetic internal and surface terms, indicates consistency with virial equilibrium, sub-Alfvénic conditions, and a dominant role for B-fields in regulating collapse. A clear alignment of magnetic field morphology with the direction of the steepest column density gradient is also detected. However, there is no preferred orientation of protostellar outflow directions with the B-field. Overall, these results indicate that magnetic fields play a crucial role in regulating massive star and star cluster formation, and therefore they need to be accounted for in theoretical models of these processes.
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| 7. |
- Lim, Wanggi, et al.
(författare)
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Star cluster formation in Orion A
- 2021
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Ingår i: Publication of the Astronomical Society of Japan. - : Oxford University Press (OUP). - 2053-051X .- 0004-6264. ; 73, s. S239-S255
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Tidskriftsartikel (refereegranskat)abstract
- We introduce new analysis methods for studying the star cluster formation processes in Orion A, especially examining the scenario of a cloud-cloud collision. We utilize the CARMA-NRO Orion survey (CO)-C-13 (1-0) data to compare molecular gas to the properties of young stellar objects from the SDSS III IN-SYNC survey. We show that the increase of v(13CO) - v(YSO) and Sigma scatter of older YSOs can be signals of cloud-cloud collision. SOFIA-upGREAT 158 mu m [C II] archival data toward the northern part of Orion A are also compared to the (CO)-C-13 data to test whether the position and velocity offsets between the emission from these two transitions resemble those predicted by a cloud-cloud collision model. We find that the northern part of Orion A, including regions ONC-OMC-1, OMC-2, OMC-3, and OMC-4, shows qualitative agreements with the cloud-cloud collision scenario, while in one of the southern regions, NGC 1999, there is no indication of such a process in causing the birth of new stars. On the other hand, another southern cluster, L 1641 N, shows slight tendencies of cloud-cloud collision. Overall, our results support the cloud-cloud collision process as being an important mechanism for star cluster formation in Orion A.
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| 8. |
- Moser, Emily, et al.
(författare)
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The High-mass Protostellar Population of a Massive Infrared Dark Cloud
- 2020
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 897:2
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Tidskriftsartikel (refereegranskat)abstract
- We conduct a census of the high-mass protostellar population of the similar to 70,000Minfrared dark cloud (IRDC) G028.37+00.07, identifying 35 sources based on their 70 mu m emission, as reported in the Herschel Hi-GAL catalog of Molinari et al. We perform aperture photometry to construct spectral energy distributions, which are then fit with the massive protostar models of Zhang & Tan. We find that the sources span a range of isotropic luminosities from similar to 20 to 4500L. The most luminous sources are predicted to have current protostellar masses ofm(*) similar to 10Mforming from cores of massM(c) similar to 40 to 400M. The least luminous sources in our sample are predicted to be protostars with masses as low as similar to 0.5Mforming from cores withM(c) similar to 10M, which are the minimum values explored in the protostellar model grid. The detected protostellar population has a total estimated protostellar mass ofM(*) similar to 100M. Allowing for completeness corrections, which are constrained by comparison with an ALMA study in part of the cloud, we estimate a star formation efficiency per freefall time of similar to 3% in the IRDC. Finally, analyzing the spatial distribution of the sources, we find relatively low degrees of central concentration of the protostars. The protostars, including the most massive ones, do not appear to be especially centrally concentrated in the protocluster as defined by the IRDC boundary.
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