ALMA Survey of Orion Planck Galactic Cold Clumps (ALMASOP). II. Survey Overview: A First Look at 1.3 mm Continuum Maps and Molecular Outflows (original) (raw)
Related papers
Occurrence Frequency of CO Outflows in Massive Protostellar Candidates
The Astrophysical Journal, 2006
We mapped 12 massive protostellar candidates in the CO J=2−1 line, which in combination with Zhang et al. (2005) completes an unbiased survey of outflows for all 48 sources with l>50 • in a sample of 101 massive protostellar candidates. We detected outflows in 10 sources, implying 88% occurrence frequency of outflows for the 48 sources. This supports the conclusion of previous studies that bipolar outflows are an integral component in the formation process of massive stars. The vast majority of the observed outflows are much more massive (>10 M ⊙) and energetic (>100 M ⊙ km s −1) than outflows from low-mass protostars. They also have large mass outflow rates (>2×10 −4 M ⊙ yr −1), suggesting large (∼1×10 −4 M ⊙ yr −1) accretion rates sufficient to overcome radiation pressure of the central massive protostars. We compared the frequency distribution of collimation factors of 40 massive outflows including those of this study with that of 36 low-mass outflows from the literature, and found no significant difference between the two. All these results are consistent with the suggestion that massive stars form through accretion as do low-mass stars but with much higher accretion rates.
The Astrophysical Journal, 2023
We present Atacama Large Millimeter/submillimeter Array observations of the ∼10 kAU environment surrounding 21 protostars in the Orion A molecular cloud tracing outflows. Our sample is composed of Class 0 to flat-spectrum protostars, spanning the full ∼1 Myr lifetime. We derive the angular distribution of outflow momentum and energy profiles and obtain the first two-dimensional instantaneous mass, momentum, and energy ejection rate maps using our new approach: the Pixel Flux-tracing Technique (PFT). Our results indicate that by the end of the protostellar phase, outflows will remove ∼2 to 4 M from the surrounding ∼1 M low-mass core. These high values indicate that outflows remove a significant amount of gas from their parent cores and continuous core accretion from larger scales is needed to replenish core material for star formation. This poses serious challenges to the concept of "cores as well-defined mass reservoir", and hence to the simplified core to star conversion prescriptions. Furthermore, we show that cavity opening angles, and momentum and energy distributions all increase with protostar evolutionary stage. This is clear evidence that even garden-variety protostellar outflows: (a) effectively inject energy and momentum into their environments on 10 kAU scales, and (b) significantly disrupt their natal cores, ejecting a large fraction of the mass that would have otherwise fed the nascent star. Our results support the conclusion that protostellar outflows have a direct impact on how stars get their mass, and that the natal sites of individual low-mass star formation are far more dynamic than commonly accepted theoretical paradigms.
On the nature of outflows in intermediate-mass protostars: a case study of IRAS 20050+2720
Astronomy & Astrophysics, 2008
Context. This is the third in a series of papers devoted to studying intermediate-mass molecular outflows and their powering sources in detail and with high-angular resolution. Aims. This paper studies the intermediate-mass YSO IRAS 20050+2720 and its molecular outflow and puts the results of this and the previous studied sources in the context of intermediate-mass star formation. Methods. We carried out VLA observations of the 7 mm continuum emission and OVRO observations of the 2.7 mm continuum emission, CO (J = 1 → 0), C 18 O (J = 1 → 0), and HC 3 N (J = 12 → 11) to map the core towards IRAS 20050+2720. The highangular resolution of the observations allowed us to derive the properties of the dust emission, the molecular outflow, and the dense protostellar envelope. By adding this source to the sample of intermediate-mass protostars with outflows, we compared their properties and evolution with those of lower mass counterparts. Results. The 2.7 mm continuum emission has been resolved into three sources, labeled OVRO 1, OVRO 2, and OVRO 3. Two of them, OVRO 1 and OVRO 2, have also been detected at 7 mm. OVRO 3, which is located close to the C 18 O emission peak, could be associated with IRAS 20050+2720. The mass of the sources, estimated from the dust continuum emission, is 6.5 M for OVRO 1, 1.8 M for OVRO 2, and 1.3 M for OVRO 3. The CO (J = 1 → 0) emission traces two bipolar outflows within the OVRO field of view, a roughly east-west bipolar outflow, labeled A, driven by the intermediate-mass source OVRO 1, and a northeast-southwest bipolar outflow, labeled B, probably powered by a YSO engulfed in the circumstellar envelope surrounding OVRO 1. Conclusions. The multiplicity of sources observed towards IRAS 20050+2720 appears to be typical of intermediate-mass protostars, which form in dense clustered environments. In some cases, as for example IRAS 20050+2720, intermediate-mass protostars would start forming after a first generation of low-mass stars has completed their main accretion phase. The properties of intermediate-mass protostars and their outflows are not significantly different from those of low-mass stars. Although intermediate-mass outflows are intrinsically more energetic than those driven by low-mass YSOs, they do not show intrinsically more complex morphologies when observed at high angular resolution. Known intermediate-mass protostars do not form a homogeneous group. Some objects are likely in an earlier evolutionary stage as suggested by the infrared emission and the outflow properties.
The Evolution of Outflow‐Envelope Interactions in Low‐Mass Protostars
The Astrophysical Journal, 2006
We present multiline and continuum observations of the circumstellar environment within 10 4 AU of a sample of protostars to investigate how the effects of outflows on their immediate environment change over time. 12 CO (1Y0) emission probes the high-velocity molecular outflows near the protostars and demonstrates that the outflow opening angle widens as the nascent star evolves. Maps of the 13 CO (1Y0) and HCO + (1Y0) outflow emission show that protostellar winds erode the circumstellar envelope through the entrainment of the outer envelope gas. The spatial and velocity distribution of the dense circumstellar envelope, as well as its mass, is traced by the C 18 O (1Y0) emission and also displays evolutionary changes. We show that outflows are largely responsible for these changes and propose an empirical model for the evolution of outflow-envelope interactions. In addition, some of the outflows in our sample appear to affect the chemical composition of the surrounding environment, enhancing the HCO + abundance. Overall, our results confirm that outflows play a major role in the star formation process through their strong physical and chemical impacts on the environments of the young protostars.
Episodic molecular outflow in the very young protostellar cluster Serpens South
Nature, 2015
ACCEPTED FOR PUBLICATION IN NATURE. The loss of mass from protostars, in the form of a jet or outflow, is a necessary counterpart to protostellar mass accretion. 1,2 Outflow ejection events probably vary in their velocity and/or in the rate of mass loss. Such 'episodic' ejection events 3 have been observed during the Class 0 protostellar phase (the early accretion stage), 4-10 and continue during the subsequent class I phase that marks the first one million years of star formation. 11-14 Previously observed episodic-ejection sources were relatively isolated; however, the most common sites of star formation are clusters. 15 Outflows link protostars with their environment and provide a viable source of turbulence that is necessary for regulating star formation in clusters, 3 but it is not known how an accretion-driven jet or outflow in a clustered environment manifests itself in its earliest stage. This early stage is important in establishing the initial conditions for momentum and energy transfer to the environment as the protostar and cluster evolve. Here we report that an outflow from a very young class 0 protostar, at the hub of the very active and filamentary Serpens South protostellar cluster, 16-18 shows unambiguous episodic events. The 12 C 16 O (J = 2 − 1) emission from the protostar reveals 22 distinct features of outflow ejecta, the most recent having the highest velocity. The outflow forms bipolar lobes-one of the first detectable signs of star formation-which originate from the peak of 1-mm continuum emission. Emission from the surrounding C 18 O envelope shows kinematics consistent with rotation and an infall of material onto the protostar. The data suggest that episodic accretion-driven outflow begins in the earliest phase of protostellar evolution, and that the outflow remains intact in a very clustered environment, probably providing efficient momentum transfer for driving turbulence.
ALMA Observations of Massive Clouds in the Central Molecular Zone: Ubiquitous Protostellar Outflows
The Astrophysical Journal, 2021
We observe 1.3 mm spectral lines at 2000 AU resolution toward four massive molecular clouds in the Central Molecular Zone of the Galaxy to investigate their star formation activities. We focus on several potential shock tracers that are usually abundant in protostellar outflows, including SiO, SO, CH 3 OH, H 2 CO, HC 3 N, and HNCO. We identify 43 protostellar outflows, including 37 highly likely ones and 6 candidates. The outflows are found toward both known high-mass star forming cores and less massive, seemingly quiescent cores, while 791 out of the 834 cores identified based on the continuum do not have detected outflows. The outflow masses range from less than 1 M to a few tens of M , with typical uncertainties of a factor of 70. We do not find evidence of disagreement between relative molecular abundances in these outflows and in nearby analogs such as the well-studied L1157 and NGC7538S outflows. The results suggest that i) protostellar accretion disks driving outflows ubiquitously exist in the CMZ environment, ii) the large fraction of candidate starless cores is expected if these clouds are at very early evolutionary phases, with a caveat on the potential incompleteness of the outflows, iii) high-mass and low-mass star formation is ongoing simultaneously in these clouds, and iv) current data do not show evidence of difference between the shock chemistry in the outflows that determines the molecular abundances in the CMZ environment and in nearby clouds.
The Envelope-Disk-Outflow System in Massive Protostellar Source G339.88-1.26
arXiv (Cornell University), 2018
We report molecular line observations of the massive protostellar source G339.88-1.26 with the Atacama Large Millimeter/Submillimeter Array. The observations reveal a highly collimated SiO jet extending from the 1.3 mm continuum source, which connects to a slightly wider but still highly collimated CO outflow. Rotational features perpendicular to the outflow axis are detected in various molecular emissions, including SiO, SO$_2$, H$_2$S, CH$_3$OH, and H$_2$CO emissions. Based on their spatial distributions and kinematics, we find that they trace different parts of the envelope-disk system. The SiO traces the disk and inner envelope in addition to the jet, the CH$_3$OH and H$_2$CO trace the infalling-rotating envelope outside of the disk, and the SO$_2$ and H$_2$S appear enhanced around the transition region between envelope and disk, i.e., the centrifugal barrier, as well as the outer part of the disk. Envelope kinematics are consistent with rotating-infalling motion, while those of the disk are consistent with Keplerian rotation. The radius and velocity of the centrifugal barrier are estimated to be about 530 au and 6 km s$^{-1}$, leading to a central mass of about 11M˜odot11~M_\odot11M˜odot, consistent with estimates based on spectral energy distribution fitting. These results indicate that an ordered transition from an infalling-rotating envelope to a Keplerian disk through a centrifugal barrier, accompanied by change of chemical composition, is a valid description of this massive protostellar source. This implies that at least some massive stars form in a similar way as low-mass stars via Core Accretion.
Predictions for Observing Protostellar Outflows with Alma
The Astrophysical Journal, 2015
Protostellar outflows provide a means to probe the accretion process of forming stars and their ability to inject energy into their surroundings. However, conclusions based on outflow observations depend upon the degree of accuracy with which their properties can be estimated. We examine the quality of ALMA observations of protostellar outflows by producing synthetic 12 CO(1-0) and 13 CO(1-0) observations of numerical simulations. We use various ALMA configurations, observational parameters, and outflow inclinations to assess how accurately different assumptions and setups can recover underlying properties. We find that more compact arrays and longer observing times can improve the mass and momentum recovery by a factor of two. During the first ∼0.3 Myr of evolution, 12 CO(1-0) is optically thick, even for velocities |v| ≥ 1km s −1 , and outflow mass is severely underestimated without an optical depth correction. Likewise, 13 CO(1-0) is optically thick during the first 0.1 Myr. However, underestimation due to shorter observing time, missing flux, and optical depth are partially offset by the assumption of LTE and higher excitation temperatures. Overall, we expect that full ALMA 13 CO(1-0) observations of protostellar sources within 500 pc with observing times 1 hrs and assumed excitation temperatures of T < 20K will reliably measure mass and line-of-sight momentum to within 20%.
Massive young stellar objects with molecular outflows
Astronomy and Astrophysics
We studied three members of the sample of 31 cold and luminous southern IRAS sources, which was compiled by Osterloh et al. (1997). These young stellar objects are characterized by extremely red IRAS colours [Snu (100 mu m) > Snu (60 mu m) > Snu (25 mu m) > 20xSnu (12 mu m)]. Based on their strong CO line wings found in previous observations, the three objects IRAS 12091-6129, IRAS 12405-6238, and IRAS 16019-4903 were selected in order to investigate their nature and the outflow structure in more detail. The mapping in the CO J = 2->1 line as well as the lambda 1.3 mm continuum dust emission show that all three sources are deeply embedded in dense cloud cores. Strong CO line wings and their mapping indicate the presence of bipolar gas outflows in all three cases. N- and Q-band imaging resolve some substructures inside the lambda 1.3 mm maps and give evidence for deeply embedded young stellar objects which seem to drive the observed outflows. The comparison of the FIR ima...
2014
We present a survey of 28 molecular outflows driven by low-mass protostars, all of which are sufficiently isolated spatially and/or kinematically to fully separate into individual outflows. Using a combination of new and archival data from several single-dish telescopes, 17 outflows are mapped in CO (2-1) and 17 are mapped in CO (3-2), with 6 mapped in both transitions. For each outflow, we calculate and tabulate the mass, momentum, kinetic energy, mechanical luminosity, and force assuming optically thin emission in LTE at an excitation temperature of 50 K. We show that all of the calculated properties are underestimated when calculated under these assumptions. Taken together, the effects of opacity, outflow emission at low velocities confused with ambient cloud emission, and emission below the sensitivities of the observations increase outflow masses and dynamical properties by an order of magnitude, on average, and factors of 50-90 in the most extreme cases. Different (and non-uni...