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Astron. Astrophys. 355, 1115-1121 (2000)
NH3(1,1) survey toward southern hemisphere HII regions. I
J.W.S. Vilas-Boas 1 and
Z. Abraham 2
1 Centro de Radio Astronomia e Aplicações Espaciais (CRAAE-INPE), CRAAM, Inst. Presbiteriano Mackenzie, R. Consolação 89, CEP 01302-000 São Paulo, SP, Brazil
2 Instituto Astronômico e Geofísico, Universidade de São Paulo, Av. M. Stefano 4200, CEP 04301-904 São Paulo, SP, Brazil
Received 19 July 1999 / Accepted 20 January 2000
Abstract
The (J,K) = (1,1) metastable ammonia line was searched for in the
direction of more than one hundred southern HII regions located
between ![[FORMULA]](img1.gif)
and
![[FORMULA]](img2.gif)
in galactic longitude, resulting in
new detections toward 21 of them. Ammonia detection rate was about
30 % towards all directions except in the longitude interval
![[FORMULA]](img3.gif)
-![[FORMULA]](img4.gif)
where no ammonia lines were found in the 15 selected HII regions. A
high detection rate ![[FORMULA]](img5.gif)
was observed
toward positions where IRAS point sources with color indices of
ultra-compact HII regions were in the beam of the telescope. An
anticorrelation between the number of detected NH3 sources
and the distance to the Galactic Center was found, compatible with the
observed gradient in N abundance. From the value of this gradient and
the detection rate of ammonia lines toward HII regions, it is inferred
that the number of ammonia sources must be proportional to the inverse
of the column density of the molecular cloud.
Key words: ISM:
abundances 
ISM: clouds
ISM: molecules
radio lines: ISM
Contents
- 1. Introduction
- 2. Instrument and observing technique
- 3. Data reduction and observational results
- 4. Discussion
- 5. Summary and conclusion
- Acknowledgements
- References
© European Southern Observatory (ESO) 2000
Online publication: March 21, 2000
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