W. K. Huchtmeier — Page 2

arXiv1997

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

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).

astro-ph↗

arXiv1996

HI Observations of two Molecular Clouds with Extremely Large Velocity Dispersions

We have mapped two molecular clouds at (l, b) = (3.2 degrees, + 0.3 degrees) and (l, b) = (5.4 degrees, -0.5 degrees) in 21-cm line and continuum emission. These clouds show unusually large velocity dispersions of more than 100 km/s (FWHM) which has also been seen in $^{12}$CO, $^{13}$CO, and CS emissions. This dispersion is roughly an order of magnitude larger compared to giant molecular clouds. From our HI observation we estimate that the atomic mass of the cloud at l = 3.2 degrees is about $1.5\times 10^5 M_\odot$ and the mass of the cloud at l = 5.4 degrees is $7\times 10^4 M_\odot$. The ratio of total molecular mass to atomic mass for these clouds appears to be normal for clouds near the galactic center. The main peculiar feature of these clouds is their abnormally large velocity dispersion; the extent in velocity is from about 0 km/s (LSR) to 200 km/s. These clouds are connected, in the l-v plane, to high velocity ridges that extend over several degrees of the longitude. These properties, we believe, provide important clues to the physical process responsible for their large velocity dispersion.

astro-ph↗