VLBI observations of the 6.7 GHz methanol masers toward W3(OH)

Menten, K. M.; Reid, M. J.; Pratap, Preethi; Moran, J. M.; Wilson, T. L.

doi:10.1086/186665

Cited by 102 publications

(119 citation statements)

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“…Some are observed in the vicinity of UC H ii regions (e.g. the W3(OH) source, Menten et al 1992). Other methanol masers originate in the direction of (sub)-millimeter condensations containing luminous very red mid-or far-IR sources (Spitzer-GLIMPSE sources: Ellingsen 2006; 24 μm sources: Xu et al 2009;, and references therein).…”

Section: Other Signposts Of Massive-star Formationmentioning

confidence: 99%

A gallery of bubbles

Deharveng

Schüller

Anderson

et al. 2010

A&A

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364

584

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Context. This study deals with infrared bubbles, the H ii regions they enclose, and triggered massive-star formation on their borders.Aims. We attempt to determine the nature of the bubbles observed by Spitzer in the Galactic plane, mainly to establish if possible their association with massive stars. We take advantage of the very simple morphology of these objects to search for star formation triggered by H ii regions, and to estimate the importance of this mode of star formation.Methods. We consider a sample of 102 bubbles detected by Spitzer-GLIMPSE, and catalogued by Churchwell et al. (2006; hereafter CH06). We use mid-infrared and radio-continuum public data (respectively the Spitzer-GLIMPSE and -MIPSGAL surveys and the MAGPIS and VGPS surveys) to discuss their nature. We use the ATLASGAL survey at 870 μm to search for dense neutral material collected on their borders. The 870 μm data traces the distribution of cold dust, thus of the dense neutral material where stars may form. Results. We find that 86% of the bubbles contain ionized gas detected by means of its radio-continuum emission at 20-cm. Thus, most of the bubbles observed at 8.0 μm enclose H ii regions ionized by O-B2 stars. This finding differs from the earlier CH06 results (∼25% of the bubbles enclosing H ii regions). Ninety-eight percent of the bubbles exhibit 24 μm emission in their central regions. The ionized regions at the center of the 8.0 μm bubbles seem to be devoid of PAHs but contain hot dust. PAH emission at 8.0 μm is observed in the direction of the photodissociation regions surrounding the ionized gas. Among the 65 regions for which the angular resolution of the observations is high enough to resolve the spatial distribution of cold dust at 870 μm, we find that 40% are surrounded by cold dust, and that another 28% contain interacting condensations. The former are good candidates for the collect and collapse process, as they display an accumulation of dense material at their borders. The latter are good candidates for the compression of pre-existing condensations by the ionized gas. Thirteen bubbles exhibit associated ultracompact H ii regions in the direction of dust condensations adjacent to their ionization fronts. Another five show methanol masers in similar condensations. Conclusions. Our results suggest that more than a quarter of the bubbles may have triggered the formation of massive objects.Therefore, star formation triggered by H ii regions may be an important process, especially for massive-star formation.

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Section: Other Signposts Of Massive-star Formationmentioning

confidence: 99%

A gallery of bubbles

Deharveng

Schüller

Anderson

et al. 2010

A&A

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584

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“…Since then, observations have shown that many OH and CH 3 OH masers are coincident (see Fig. 33; Menten et al, 1992) and theoretical considerations indicate that methanol is not readily formed and should not have high equilibrium abundance in photodissociated gas. In a slight twist on these models, these masers are currently thought to reflect the evaporation of icy grain mantles in the photodissociation region (Hartquist et al, 1995).…”

Section: G Oh and Ch 3 Oh Maser Regionsmentioning

confidence: 99%

“…Many ultracompact HII regions show associated OH and CH 3 OH maser emission outside the ionized gas (Moran et al, 1968;Reid et al, 1980;Menten et al, 1988Menten et al, , 1992. The earliest model located the OH maser emission in the dense compressed shell created by the expanding HII region.…”

Section: G Oh and Ch 3 Oh Maser Regionsmentioning

confidence: 99%

Photodissociation regions in the interstellar medium of galaxies

Hollenbach

Tielens²

1999

Rev. Mod. Phys.

751

712

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The interstellar medium of galaxies is the reservoir out of which stars are born and into which stars inject newly created elements as they age. The physical properties of the interstellar medium are governed in part by the radiation emitted by these stars. Far-ultraviolet (6 eVϽh Ͻ13.6 eV) photons from massive stars dominate the heating and influence the chemistry of the neutral atomic gas and much of the molecular gas in galaxies. Predominantly neutral regions of the interstellar medium in which the heating and chemistry are regulated by far ultraviolet photons are termed PhotoDissociation Regions (PDRs). These regions are the origin of most of the non-stellar infrared (IR) and the millimeter and submillimeter CO emission from galaxies. The importance of PDRs has become increasingly apparent with advances in IR and submillimeter astronomy. The IR emission from PDRs includes fine structure lines of C, C ϩ , and O; rovibrational lines of H 2 ; rotational lines of CO; broad mid-IR features of polycyclic aromatic hydrocarbons; and a luminous underlying IR continuum from interstellar dust. The transition of H to H 2 and C ϩ to CO occurs within PDRs. Comparison of observations with theoretical models of PDRs enables one to determine the density and temperature structure, the elemental abundances, the level of ionization, and the radiation field. PDR models have been applied to interstellar clouds near massive stars, planetary nebulae, red giant outflows, photoevaporating planetary disks around newly formed stars, diffuse clouds, the neutral intercloud medium, and molecular clouds in the interstellar radiation field-in summary, much of the interstellar medium in galaxies. Theoretical PDR models explain the observed correlations of the [CII] 158 m with the CO Jϭ1 -0 emission, the CO Jϭ1 -0 luminosity with the interstellar molecular mass, and the [CII] 158 m plus [OI] 63 m luminosity with the IR continuum luminosity. On a more global scale, PDR models predict the existence of two stable neutral phases of the interstellar medium, elucidate the formation and destruction of star-forming molecular clouds, and suggest radiation-induced feedback mechanisms that may regulate star formation rates and the column density of gas through giant molecular clouds. [S0034-6861(99)01001-6] CONTENTS

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“…It is well established that the 6.7-GHz methanol masers are associated with high-mass stars (e.g., W3(OH); see Menten et al 1992), which are able to pump the masers by heating a sufficient amount of surrounding dust to temperatures higher than 100 K, or producing hypercompact HII regions with extremely high emission measures . No 6.7-GHz methanol masers have been found to be associated with low-mass young stellar objects (Minier et al 2003;Bourke et al 2005).…”

Section: Association With Star Formation Tracersmentioning

confidence: 99%

“…The 2 0 −3 −1 E transition at 12.2-GHz is the second brightest methanol maser transition and the locations of the 6.7-GHz and 12.2-GHz methanol maser spots largely overlap, with several features showing a one-to-one correspondence within milliarcseconds and the spectra of the two transitions typically covering similar velocity ranges (Menten et al 1992;Norris et al 1993;Minier et al 2000). Since 6.7 GHz masers are almost always stronger, i.e., much stronger than their 12.2-GHz counterparts, they are also expected to be a useful for probing distances to massive star-forming regions in the Galaxy.…”

Section: Introductionmentioning

confidence: 97%

Absolute positions of 6.7-GHz methanol masers

Voronkov

Pandian

et al. 2009

A&A

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The ATCA, MERLIN and VLA interferometers were used to measure the absolute positions of 35 6.7-GHz methanol masers to subarcsecond or higher accuracy. Our measurements represent essential preparatory data for Very Long Baseline Interferometry, which can provide accurate parallax and proper motion determinations of the star-forming regions harboring the masers. Our data also allow associations to be established with infrared sources at different wavelengths. Our findings support the view that the 6.7 GHz masers are associated with the earliest phases of high-mass star formation.

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VLBI observations of the 6.7 GHz methanol masers toward W3(OH)

Cited by 102 publications

References 0 publications

A gallery of bubbles

A gallery of bubbles

Photodissociation regions in the interstellar medium of galaxies

Absolute positions of 6.7-GHz methanol masers

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