Astron. Astrophys. 364, L47-L53 (2000)

Letter to the Editor

Stellar dynamics observations of a double nucleus in M 83

N. Thatte, M. Tecza and R. Genzel

Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse, 85748 Garching, Germany (thatte@mpe.mpg.de)

Received 17 August 2000 / Accepted 4 September 2000

Abstract

We report on the discovery of a double nucleus in M 83, based on measurements of the line of sight velocity distribution of stars observed at near infrared wavelengths with the VLT ISAAC spectrograph. We observe two peaks separated by in the velocity dispersion profile of light from late-type stars measured along a slit wide, centered on the peak of K band emission and with P.A. 51.7^o. The first peak coincides with the peak of the K band light distribution, widely assumed to be the galaxy nucleus. The second peak, of almost equal strength, almost coincides with the center of symmetry of the outer isophotes of the galaxy. The secondary peak location has little K band emission, and appears to be significantly extincted, even at near infrared wavelengths. It also lies along a mid-infrared bar, previously identified by Gallais et al. (1991) and shows strong hydrogen recombination emission at 1.875µm. If we interpret the observed stellar velocity dispersion as coming from a virialized system, the two nuclei would each contain an enclosed mass of 13.2 10⁶ within a radius of 5.4 pc. These could either be massive star clusters, or supermassive dark objects.

Key words: galaxies: kinematics and dynamics galaxies: nuclei galaxies: individual: M 83 galaxies: spiral galaxies: starburst galaxies: stellar content galaxies: structure

Send offprint requests to: N. Thatte

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Contents

• 1. Introduction
• 2. Observations and data reduction
  • 2.1. NTT SOFI imaging
  • 2.2. VLT ISAAC spectroscopy
  • 2.3. Archival HST NICMOS images
• 3. Analysis and results
  • 3.1. Isophote fits: the location of the photometric centroid
  • 3.2. Recession velocity and velocity dispersion: discovery of a hidden nucleus
  • 3.3. Stellar population analysis: extinction and luminous mass estimates
    • 3.3.1. Magnitudes and colors
    • 3.3.2. Equivalent width, age and luminosity
• 4. The nature of the second nucleus
• 5. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: December 15, 2000
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