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SMA Observations of 321 GHz water maser emission in Cepheus A
Nimesh A. Patel
Harvard-Smithsonian Center for Astrophysics Submillimeter Array

Collaborators:
Salvador Curiel (UNAM) Qizhou Zhang (CfA) T. K. Sridharan (CfA) Paul T. P. Ho (CfA, ASIAA) Jose M. Torrelles (CSIC-IEEC)

Patel, Curiel, Zhang et al. (2007), ApJ 658,L55

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Neufeld and Melnick (1991) ApJ 368,215
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Discovery of submillimeter H2O masers:
321 GHz: K. Menten, G. Melnick & G. Phillips, 1990, ApJ, 350, L41

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Motivation:
To map the 321 GHz water maser emission with the SMA To use the 22/321 GHz line ratio to probe the physical conditions in regions of massive star-formation with high spatial resolution. To understand the physics of the excitation of submillimeter water maser transitions.

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Cepheus A massive star-forming region
contours: VLA 1.3cm radio continuum, + 22 GHz masers @ 0.1"resolution
Torrelles, Gomez, Garay et al. 1998, ApJ 509,262

725 AU

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Disk and jet in Cepheus A HW2

SMA (ext. array) 0.8" 330 GHz continuum CH3CN

VLA radio continuum 3.6 cm 1.3 cm
Brogan et al. (2005 PPV) Martin-Pintado et al. (2005, ApJ, 628,L61) Comito et al. (2005 IAU#231)

Patel, Curiel, Sridharan et al., 2005, Nature, 427,109
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See also: Posters on methanol masers VLBI observations by K. Torstensson & H. J. van Langevelde (JIVE) Sugiyama et al. (JVN)

Gallimore et al. (2003) ApJ 586, 306 MERLIN observations

200 AU

Vlemmings, Diamond, van Langevelde & Torrelles, 2006, A&A, 448,597
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Bipolar molecular outflow observed in HCO+

blueshifted

+
redshifted

0.07 pc

+

HW2

Gomez, Sargent, Torrelles et al. 1999, ApJ, 514, 287
CO outflow: Rodriguez, Ho & Moran, 1980, ApJ, 240, L149
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Observations: SMA
30 August 2004
extended configuration, 0.8''x0.7''

rms noise ~350 mJy/beam

VLA

12 October 2004
A-array 0.09''x0.07''

rms noise ~3 mJy/beam

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Cepheus-A 321 GHz masers in HW2 and HW3c

-19 -21 -11 -3.5 to +1 km/s

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Neufeld & Melnick 1990

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Modelling population inversion of submm. water maser transitions Yates, Field & Gray (1997) MNRAS, 285, 303

ALI
no LVG approximation

22 GHz line is inverted over a broad range of parameters. 200-2000K n=10^8 - 10^9 cm^-3

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time-variability of 22 GHz masers
Over time scales of months: highly luminous sources less variable brighter (>10 Jy) masers less variable proper motion studies with VLBA

Cepheus A maser monitoring:
Lekht et al. 1983, Sov. Astron. 26, 170

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Cepheus-A 321 GHz masers Conclusions

321 GHz masers detected in HW2 and HW3c in the Cepheus-A highmass star-forming region 3 out of 9 submillimeter masers are associated with 22 GHz masers submillimeter masers trace the outflow jet, presumably arising in hot gas (1000~2000 K) Multi-transition observations of H2O masers can be used to constrain theoretical models of excitation Submillimeter masers, along with cm masers can be used to probe physical conditions such as temperature in star-forming regions

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Future work

Other high-mass star-forming regions: W75N, W3(OH), NGC6334 Masers in 400 GHz band Simultaneous observations with VLA

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The SMA project is a collaboration between SAO and ASIAA, Taiwan. We thank the SMA staff for their help with observations. We thank Jim Moran, Gary Melnick, David Neufeld and Liz Humphreys for helpful discussions.

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