Astron. Astrophys. Suppl. Ser.
Volume 127, Number 3, February I 1998
|Page(s)||397 - 408|
|Published online||15 February 1998|
An H i line search for optically identified dwarf galaxy candidates in the M 81 group
Nançay Radio Observatory, USN, Observatoire de Paris, 5 Place Jules Janssen, F-92195 Meudon Cedex, France
2 DAEC, Observatoire de Paris, 5 Place Jules Janssen, F-92195 Meudon Cedex, France
3 Astronomical Institute, University of Basel, Venusstrasse 7, CH-4102 Binningen, Switzerland
4 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany
Send offprint request to: W. van Driel
Accepted: 22 May 1997
Sensitive 21 cm H I 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 was searched to an rms noise of . Only three objects were detected. However, their high radial velocities (between 600 and 1150 ) 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 H I masses of 0.4, 1.6 and , for the assumed distance of 4 Mpc, and H I mass-to-blue light ratios of 0.04, 0.73 and 0.18 , 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 is quite low. However, the mean redshift and velocity dispersion of the M 81 group ( , ) suggest that the H I emission of low velocity H I -rich members of the M 81 group may still remain hidden within the strong Galactic H I emission (typically 115 ) or, for the 6 dwarf candidates in the immediate vicinity of M 81, overshadowed by the very extended H I envelope encompassing M 81, M 82, NGC 3077, and NGC 2976 ( ).
Key words: galaxies: distances and redshifts / galaxies: irregular / galaxies: ISM / radio lines: galaxies / galaxies: clusters of: M 81 group
© European Southern Observatory (ESO), 1998