The association between masers and outflows in massive star forming regions

We report the results of a single-dish survey of molecular outflows towards a homogeneous sample of 136 ultracompact H ii regions for which we had previously obtained observations in the methanol 6.7 GHz and water 22.2 GHz maser lines. The line profiles of the 13 CO $J = 1{-}0$ and 2–1 transitions have been compared to those of the corresponding lines of the C 18 O isotopomer to reveal the occurrence of line wings and hence of molecular outflows. We found 53 outflows resulting in an overall detection rate of ~39%. The probability to have an outflow increases to about 50% in regions with maser emission, whereas it is about 25% in those without masers. If we consider just the outflow sources, the chance to find a maser is very high: 74%, without a significant difference between H 2 O and CH 3 OH. These results strongly confirm from a statistical point of view that both types of masers are closely associated with the evolutionary phase when outflows occur.
The temperatures and optical depths of the molecular cloud hosting the ultracompact H ii regions and the comparison between the detection rates suggest a tentative evolutionary scheme for massive star forming regions: the earliest phase is associated with maser emission and with an outflow not yet developed enough to be detected with single-dish observations; then maser emission disappears while the outflow is still present; and finally, only the ultracompact Hii  region without masers or outflows is present.

[1]  Michael G. Burton,et al.  Observations of warm dust near methanol masers , 2003 .

[2]  C. Watson,et al.  Resolution of Distance Ambiguities of Inner Galaxy Massive Star Formation Regions. I. , 2003 .

[3]  K. Menten,et al.  CH3OH and H2O masers in high-mass star-forming regions , 2002, astro-ph/0205348.

[4]  E. Churchwell,et al.  Arecibo Observations of Formaldehyde and Radio Recombination Lines toward Ultracompact H II Regions , 2001 .

[5]  G. Garay,et al.  Discovery of Linear “Building Blocks” of Water Masers Shaping Linear/Arcuate Microstructures in Cepheus A , 2001 .

[6]  K. Menten,et al.  Massive molecular outflows , 2001, astro-ph/0112508.

[7]  K. Menten,et al.  High-Mass Protostellar Candidates. I. The Sample and Initial Results , 2001, astro-ph/0110363.

[8]  Todd R. Hunter,et al.  Search for CO Outflows toward a Sample of 69 High-Mass Protostellar Candidates: Frequency of Occurrence , 2001 .

[9]  D. Benford,et al.  350 Micron Images of Massive Star Formation Regions , 2000 .

[10]  A. Kus,et al.  A survey of the 6.7 GHz methanol maser emission from IRAS sources - I. Data , 2000 .

[11]  Garry Robinson,et al.  Studies of ultracompact H ii regions — II. High-resolution radio continuum and methanol maser survey , 1998 .

[12]  R. Norris,et al.  Methanol Masers as Tracers of Circumstellar Disks , 1998, astro-ph/9806284.

[13]  P. Ho,et al.  A Radio Jet-H2O Maser System in W75N(B) at a 200 Au Scale: Exploring the Evolutionary Stages of Young Stellar Objects , 1997 .

[14]  E. Churchwell,et al.  Bipolar Molecular Outflows in Massive Star Formation Regions , 1996 .

[15]  R. Bachiller.  BIPOLAR MOLECULAR OUTFLOWS FROM YOUNG STARS AND PROTOSTARS , 1996 .

[16]  R. Norris,et al.  Continuum Emission Associated with 6.7-GHz Methanol Masers , 1995, astro-ph/9509068.

[17]  T. Wilson,et al.  Abundances in the interstellar medium , 1992 .

[18]  R. Becker,et al.  The infrared properties of compact galactic radio sources - The young and the restless , 1991 .

[19]  Robert H. Becker,et al.  A catalog of small-diameter radio sources in the Galactic plane , 1990 .

[20]  E. Churchwell,et al.  Massive stars embedded in molecular clouds - Their population and distribution in the galaxy , 1989 .

[21]  E. Churchwell,et al.  The morphologies and physical properties of ultracompact H II regions , 1989 .

[22]  A. R. Rivolo,et al.  Mass, luminosity, and line width relations of Galactic molecular clouds , 1987 .

[23]  V. Slysh,et al.  The Medicina survey of methanol masers at 6.7 GHz , 1999 .

[24]  E. Churchwell,et al.  High-Velocity Molecular Gas from High-Mass Star Formation Regions , 1996 .

[25]  Ray P. Norris,et al.  Galactic methanol masers at 6.6 GHz , 1995 .