Triggered massive-star formation on the borders of Galactic H II regions

Deharveng, L.; Zavagno, A.; Caplan, J.

doi:10.1051/0004-6361:20041946

Cited by 226 publications

(249 citation statements)

References 67 publications

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“…It is also evident that the molecular gas encompasses the circle, showing the velocity structure of the molecular shell related to G45L. As Deharveng et al (2005) propose, the presence of a molecular shell surrounding the ionized gas of an HII region, or the presence of massive fragments regularly spaced along the ionization front, suggest The grayscale is displayed at the top of the figure and is in K km s −1 , the contour levels are 5, 9.5 and 11 K km s −1 . Note that the molecular gas encompasses the circle, which highlights the position and size of G45L as suggested by the north and south PDRs (see Fig.…”

Section: Fig 2 Two Color Imagesmentioning

confidence: 96%

The environs of the ultracompact HII region G45.45+0.06

Paron¹,

Cichowolski²,

Ortega³

2009

A&A

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Aims. G45.45+0.06 is an ultra-compact HII (UCHII) region that has been extensively studied. It is known that G45.45+0.06 is embedded in a complex of UCHII regions, but to date, the surrounding ISM on a larger spatial scale has not been analyzed. Methods. Using data from large-scale surveys, the Two Micron All Sky Survey, GLIMPSE, MIPSGAL, MAGPIS and GRS, we performed a multiwavelength study of a region of about 7 × 7 in the vicinity of G45.45+0.06. Results. We found that the UCHII complex lies on the border of a larger (diameter of ∼3 ) and fainter HII region, which is located at the same distance as G45.45+0.06, ∼8 kpc. In this work, this larger HII region is called G45L. A good morphological correlation is observed between the PDRs and the molecular gas mapped in the 13 CO J = 1−0 and CS J = 2−1 lines, suggesting that G45L may be collecting molecular material. From a near-and mid-IR photometric study, we found three sources, likely O-type stars, that are possibly responsible for the creation of G45L. Additionally, we found several YSO candidates lying preferentially in the molecular shell that surrounds G45L. Our results confirm that the region southeast of the UCHII complex where G45.45+0.06 is embedded and east of G45L is undergoing active star formation. We suggest that G45L has been expanding for about 2 × 10 6 yr and could have triggered the formation of the zero-age main sequence stars that ionize the UCHII region G45.45+0.06. However we cannot discard that both HII regions are coeval.

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Section: Fig 2 Two Color Imagesmentioning

confidence: 96%

The environs of the ultracompact HII region G45.45+0.06

Paron¹,

Cichowolski²,

Ortega³

2009

A&A

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“…Finally, between 54 and 59 km s −1 , several molecular clumps appear distributed over the borders of G35.6 and the southern PDR, which may indicate that the collect and collapse process could be taking place in this region. As Deharveng et al (2005) point out, the presence of a dense molecular shell surrounding the ionized gas of an HII region, or massive fragments regularly spaced along the ionization front, may be indicative of the collect and collapse mechanism. Figure 4 shows the 13 CO J = 1-0 emission integrated between 53 and 61 km s −1 (in green) over the 8 μm emission (in red).…”

Section: Molecular Analysismentioning

confidence: 99%

The HII region G35.673-00.847: another case of triggered star formation?

Paron

Petriella

Ortega

2010

A&A

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Aims. As part of a systematic study that we are performing to increase the observational evidence of triggered star formation in the surroundings of HII regions, we analyze the ISM around the HII region G35.673-00.847, a poorly studied source. Methods. Using data from the large-scale surveys Two Micron All Sky Survey, Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE), MIPSGAL, Galactic Ring Survey (GRS), VLA Galactic Plane Survey (VGPS), and NRAO VLA Sky Survey (NVSS), we performed a multiwavelength study of G35.673-00.847 and its surroundings. Results. The mid-IR emission shows that G35.673-00.847 has an almost semi-ring like shape with a cut towards the galactic west. The radius of this semi-ring is about 1. 5 (∼1.6 pc, at the distance of ∼3.7 kpc). The distance was estimated from an HI absorption study and the analysis of the molecular gas. We find a molecular shell composed of several clumps distributed around the HII region, suggesting that its expansion is collecting the surrounding material. We identify several YSO candidates across the molecular shell. Finally, comparing the HII region dynamical age and the fragmentation time of the molecular shell, we discard the so-called collect and collapse as being the mechanism responsible for the YSO formation, suggesting that other processes such as radiative-driven implosion and/or small-scale Jeans gravitational instabilities operate.

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“…Another topic that can be addressed with these data is the importance of triggered star formation, which can be assessed by identifying the second generation stars at the edges of H ii regions (e.g., Deharveng et al 2005) and supernova remnants. In the context of high-mass star formation in particular, the importance of triggering compared to spontaneous star formation remains an open question.…”

Section: Evolutionary Stages Of High-mass Star-formationmentioning

confidence: 99%

ATLASGAL – The APEX telescope large area survey of the galaxy at 870 $\mathsf{\mu}$m

Schüller¹,

Menten²,

Contreras

et al. 2009

A&A

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927

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Context. Thanks to its excellent 5100 m high site in Chajnantor, the Atacama Pathfinder Experiment (APEX) systematically explores the southern sky at submillimeter wavelengths, in both continuum and spectral line emission. Studying continuum emission from interstellar dust is essential to locating the highest density regions in the interstellar medium, and deriving their masses, column densities, density structures, and large-scale morphologies. In particular, the early stages of (massive) star formation remain poorly understood, mainly because only small samples of high-mass proto-stellar or young stellar objects have been studied in detail so far. Aims. Our goal is to produce a large-scale, systematic database of massive pre-and proto-stellar clumps in the Galaxy, to understand how and under what conditions star formation takes place. Only a systematic survey of the Galactic Plane can provide the statistical basis for unbiased studies. A well characterized sample of Galactic star-forming sites will deliver an evolutionary sequence and a mass function of high-mass, star-forming clumps. This systematic survey at submillimeter wavelengths also represents a preparatory work for Herschel and ALMA. Methods. The APEX telescope is ideally located to observe the inner Milky Way. The Large APEX Bolometer Camera (LABOCA) is a 295-element bolometer array observing at 870 μm, with a beam size of 19. 2. Taking advantage of its large field of view (11. 4) and excellent sensitivity, we started an unbiased survey of the entire Galactic Plane accessible to APEX, with a typical noise level of 50−70 mJy/beam: the APEX Telescope Large Area Survey of the Galaxy (ATLASGAL). Results. As a first step, we covered ∼95 deg 2 of the Galactic Plane. These data reveal ∼6000 compact sources brighter than 0.25 Jy, or 63 sources per square degree, as well as extended structures, many of them filamentary. About two thirds of the compact sources have no bright infrared counterpart, and some of them are likely to correspond to the precursors of (high-mass) proto-stars or protoclusters. Other compact sources harbor hot cores, compact H ii regions, or young embedded clusters, thus tracing more evolved stages after massive stars have formed. Assuming a typical distance of 5 kpc, most sources are clumps smaller than 1 pc with masses from a few 10 to a few 100 M . In this first introductory paper, we show preliminary results from these ongoing observations, and discuss the mid-and long-term perspectives of the survey.

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Triggered massive-star formation on the borders of Galactic H II regions

Cited by 226 publications

References 67 publications

The environs of the ultracompact HII region G45.45+0.06

The environs of the ultracompact HII region G45.45+0.06

The HII region G35.673-00.847: another case of triggered star formation?

ATLASGAL – The APEX telescope large area survey of the galaxy at 870 $\mathsf{\mu}$m

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