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An HI line search for optically identified dwarf galaxy candidates in the M81 group

W. van Driel·R. C. Kraan-Korteweg·B. Binggeli·W. K. Huchtmeier
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Abstract

Sensitive 21cm HI line observations were performed for 23 dwarf members and possible members of the nearby M81 group of galaxies, including five objects of a clustering of extremely low-surface brightness objects of unknown nature. With the Nancay decimetric radio telescope the radial velocity range of -529 to 1826 km/s was searched to an rms noise of ~3-5 mJy. Only three objects were detected. However, their high radial velocities (between 600 and 1150 km/s) show them to lie behind the M81 group. These three objects, classified as dS0: (UGC 4998) and Im (Kar 1N and UGC 5658), have HI masses of 0.5, 2.0 and 2.5 10^8 Msun, for the assumed distance of 4 Mpc, and HI mass-to-blue light ratios of 0.05, 0.91 and 0.22 Msun/LBsun, 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 M81 group ( = 101 km/s, sigma=114 km/s) suggest that the HI emission of low velocity HI-rich members of the M81 group may still remain hidden within the strong Galactic HI emission (typically -150 < v < 115 km/s) or, for the 6 dwarf candidates in the immediate vicinity of M81, overshadowed by the very extended HI envelope encompassing M81, M82, NGC 3077, and NGC 2976 (-280 < v < 355 km/s).

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W. van Driel, R. C. Kraan-Korteweg, B. Binggeli, W. K. Huchtmeier. 1997-06-09. An HI line search for optically identified dwarf galaxy candidates in the M81 group. https://arxiv.org/abs/astro-ph/9706081

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