Temperature and Density Distribution in the Molecular Gas Toward Westerlund 2: Further Evidence for Physical Association

Ohama, Akio; Dawson, J. R.; Furukawa, N.; Kawamura, Akiko; Moribe, N.; Yamamoto, Hiroaki; Okuda, Takeshi; Mizuno, N.; Onishi, Toshikazu; Maezawa, Hiroyuki; Minamidani, Tetsuhiro; Mizuno, Akira; Fukui, Y.

doi:10.1088/0004-637x/709/2/975

Cited by 113 publications

(131 citation statements)

References 29 publications

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“…Dame (2007) observed Westerlund 2 with the CfA 1.2 m telescope using 12 CO(J = 1-0) survey data and found a possible association with a giant molecular cloud (GMC) on the far side of the Carina spiral arm, at a distance of 5.0 kpc. Observations at a higher resolution (90 ) on the J = 2-1 transition of 12 CO performed by the Nanten 2 4-m sub-millimeter telescope Ohama et al 2010) confirm the Dame (2007) results but also suggest another possible association. A significant clump of molecular gas, consisting of a foreground component at 0 km s −1 is found, with a mass of (9.1 ± 4.1) × 10 4 M , and a background component at 16 km s −1 , with a mass of (8.1 ± 3.7) × 10 4 M , both of which are claimed to be connected with RCW 49, at a distance of 5.4 +1.1 −1.4 kpc.…”

Section: Introductionmentioning

confidence: 56%

Revisiting the Westerlund 2 field with the HESS telescope array

Abramowski¹,

Acero²,

Aharonian³

et al. 2010

A&A

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Aims. Previous observations with the HESS telescope array revealed the existence of extended very-high-energy (VHE; E > 100 GeV) γ-ray emission, HESS J1023-575, coincident with the young stellar cluster Westerlund 2. At the time of discovery, the origin of the observed emission was not unambiguously identified, and follow-up observations have been performed to further investigate the nature of this γ-ray source. Methods. The Carina region towards the open cluster Westerlund 2 has been re-observed, increasing the total exposure to 45.9 h. The combined dataset includes 33 h of new data and now permits a search for energy-dependent morphology and detailed spectroscopy. Results. A new, hard spectrum VHE γ-ray source, HESS J1026-582, was discovered with a statistical significance of 7σ. It is positionally coincident with the Fermi LAT pulsar PSR J1028-5819. The positional coincidence and radio/γ-ray characteristics of the LAT pulsar favors a scenario where the TeV emission originates from a pulsar wind nebula. The nature of HESS J1023-575 is discussed in light of the deep HESS observations and recent multi-wavelength discoveries, including the Fermi LAT pulsar PSR J1022-5746 and giant molecular clouds in the region. Despite the improved VHE dataset, a clear identification of the object responsible for the VHE emission from HESS J1023-575 is not yet possible, and contribution from the nearby high-energy pulsar and/or the open cluster remains a possibility.

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Section: Introductionmentioning

confidence: 56%

Revisiting the Westerlund 2 field with the HESS telescope array

Abramowski¹,

Acero²,

Aharonian³

et al. 2010

A&A

Self Cite

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“…Due to the size difference between the two clouds, the shock front becomes oblique as the clouds merge, pressing down on the shocked disk to form a crescent structure that is commonly observed in observations of suspected cloud-cloud collision events (Ohama et al 2010;Furukawa et al 2009). …”

Section: Discussionmentioning

confidence: 96%

“…Their formation has historically perplexed researchers due to the problem of creating such a high-mass cluster if the star formation efficiency inside the GMC is low. The first cluster to be identified as a possible collision object was Westerland 2, which was observed by Furukawa et al (2009) and Ohama et al (2010) and found to have two associated clouds with relative velocity of 20 km s −1 . The authors propose that the resulting shock between the clouds compressed the gas to produce the massive star cluster.…”

Section: Observational Evidence For Cloud-cloud Collisionsmentioning

confidence: 99%

Do Cloud-Cloud Collisions Trigger High-Mass Star Formation? I. Small Cloud Collisions

Takahira

Tasker

Habe

2014

ApJ

183

230

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We performed sub-parsec (∼0.06 pc) scale simulations of two idealized molecular clouds with different masses undergoing a collision. Gas clumps with densities greater than 10 −20 g cm −3 (0.3 × 10 4 cm −3 ) were identified as pre-stellar cores and tracked throughout the simulation. The colliding system showed a partial gas arc morphology with core formation in the oblique shock front at the collision interface. These characteristics support NANTEN observations of objects suspected to be colliding giant molecular clouds (GMCs). We investigated the effect of turbulence and collision speed on the resulting core population and compared the cumulative mass distribution to cores in observed GMCs. Our results suggest that a faster relative velocity increases the number of cores formed but that cores grow via accretion predominately while in the shock front, leading to a slower shock being more important for core growth. The core masses obey a power-law relation with index γ = −1.6, in good agreement with observations. This suggests that core production through collisions should follow a similar mass distribution as quiescent formation, albeit at a higher mass range. If cores can be supported against collapse during their growth, then the estimated ram pressure from gas infall is of the right order to counter the radiation pressure and form a star of 100 M .

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“…The studies of the molecular hydrogen by Dame (2007), Furukawa et al (2009) and Ohama et al (2010) show a complex environment around Westerlund 2. Two molecular clouds in the velocity ranges of [-11 : 9] km/s and [11: 21] km/s physically coincide with Westerlund 2 and and the large H ii region RCW 49.…”

Section: Gas Around Westerlundmentioning

confidence: 99%

Diffuse γ-ray emission in the vicinity of young star cluster Westerlund 2

Yang

Wilhelmi

Aharonian

2018

A&A

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We report the results of our analysis of the publicly available data obtained by the Large Area Telescope (LAT) on board of the Fermi satellite towards the direction of the young massive star cluster Westerlund 2. We found significant extended γ-ray emission in the vicinity of Westerlund 2 with a hard power-law energy spectrum extending from 1 GeV to 250 GeV with a photon index of 2.0 ± 0.1. We argue that amongst several alternatives, the luminous stars in Westerlund 2 are likely sites of acceleration of particles responsible for the diffuse γ-ray emission of the surrounding interstellar medium. In particular, the young star cluster Westerlund 2 can provide sufficient non-thermal energy to account for the gamma-ray emission. In this scenario, since the γ-ray production region is significantly larger than the area occupied by the star cluster, we conclude that the γ-ray production is caused by hadronic interactions of the accelerated protons and nuclei with the ambient gas. In that case, the total energy budget in relativistic particles is estimated of the order of 10 50 erg.

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Temperature and Density Distribution in the Molecular Gas Toward Westerlund 2: Further Evidence for Physical Association

Cited by 113 publications

References 29 publications

Revisiting the Westerlund 2 field with the HESS telescope array

Revisiting the Westerlund 2 field with the HESS telescope array

Do Cloud-Cloud Collisions Trigger High-Mass Star Formation? I. Small Cloud Collisions

Diffuse γ-ray emission in the vicinity of young star cluster Westerlund 2

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