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A&A Supplement series, Vol. 127, February I 1998, 397-408

Received October 14, 1996; accepted May 22, 1997

An HI line search for optically identified dwarf galaxy candidates in the M 81 group

W. van Drieltex2html_wrap1530, R.C. Kraan-Kortewegtex2html_wrap1532, B. Binggelitex2html_wrap1534, - W.K. Huchtmeiertex2html_wrap1536

Send offprint request: W. van Driel, e-mail:

tex2html_wrap1538  Nançay Radio Observatory, USN, Observatoire de Paris, 5 Place Jules Janssen, F-92195 Meudon Cedex, France
tex2html_wrap1540  DAEC, Observatoire de Paris, 5 Place Jules Janssen, F-92195 Meudon Cedex, France
tex2html_wrap1542  Astronomical Institute, University of Basel, Venusstrasse 7, CH-4102 Binningen, Switzerland
tex2html_wrap1544  Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany


Sensitive 21cm HI line observations were performed for 23 dwarf members and possible members of the nearby M 81 group of galaxies, including five objects of a clustering of extremely low-surface brightness objects of unknown nature. With the Nançay decimetric radio telescope the radial velocity range of -529 to 1826 tex2html_wrap_inline1496 was searched to an rms noise of tex2html_wrap_inline1498. Only three objects were detected. However, their high radial velocities (between 600 and 1150 tex2html_wrap_inline1496) show them to lie behind the M 81 group. These three objects, classified as dS0: (UGC 4998) and Im (Kar 1N and UGC 5658), have HI masses of 0.4, 1.6 and tex2html_wrap_inline1502tex2html_wrap_inline1504, for the assumed distance of 4 Mpc, and HI mass-to-blue light ratios of 0.04, 0.73 and 0.18 tex2html_wrap_inline1506, respectively.

Considering that half of the observed objects are classified as irregular dwarfs, hence expected to be relatively gas-rich, the resulting detection rate of about 1/3 is quite low. However, the mean redshift and velocity dispersion of the M 81 group (<V> = 101 tex2html_wrap_inline1496, tex2html_wrap_inline1514 tex2html_wrap_inline1496) suggest that the HI emission of low velocity HI-rich members of the M 81 group may still remain hidden within the strong Galactic HI emission (typically tex2html_wrap_inline1518 115 tex2html_wrap_inline1496) or, for the 6 dwarf candidates in the immediate vicinity of M 81, overshadowed by the very extended HI envelope encompassing M 81, M 82, NGC 3077, and NGC 2976 (tex2html_wrap_inline1522 tex2html_wrap_inline1496).

keywords: galaxies: distances and redshifts -- galaxies: irregular -- galaxies: ISM -- radio lines: galaxies -- galaxies: clusters of: M 81 group

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