Astron. Astrophys. 361, L45-L48 (2000)

Letter to the Editor

Dense gas in nearby galaxies

XIV. Detection of hot ammonia in Maffei 2

C. Henkel ¹, R. Mauersberger ², A.B. Peck ¹, H. Falcke ¹ and Y. Hagiwara <sup>1

1</sup> Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
² Instituto de Radioastronomía Milimétrica, Avda. Divina Pastora, 7NC, 18012 Granada, Spain

Received 10 July 2000 / Accepted 7 September 2000

Abstract

The () = (1,1), (2,2), (3,3), and (4,4) inversion lines of ammonia (NH₃) have been detected toward the nuclear 40" sized bar of the nearby spiral galaxy Maffei 2. The relative intensities of the ammonia lines are characterized by a rotational temperature of 85 K. This is higher than rotational temperatures measured toward IC 342 and most Galactic Center clouds, implying kinetic temperatures 100 K. Since the kinetic temperature of the gas is larger than that of the dust, NH₃ is tracing a particularly dense warm gas component that is heated by young massive stars, cloud-cloud collisions, or ion-slip heating in the nuclear starburst. The gas north of the nucleus ( = -80 km s ^-1) is more highly excited than the gas further south (+6 km s ^-1). This asymmetry might be related to pronounced morphological distortions that are observed in the north-eastern part of the galaxy.

Key words: galaxies: individual: Maffei 2 galaxies: ISM radio lines: galaxies

Send offprint requests to: C. Henkel

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Contents

• 1. Introduction
• 2. Observations
• 3. Results
• 4. Determination of rotational temperatures
• 5. Discussion
  • 5.1. Interpretation of rotational temperatures
  • 5.2. A comparison with IC 342 and Galactic Center clouds
  • 5.3. The nuclear region of Maffei 2
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: October 10, 2000
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