HI observations of the high-velocity cloud in the direction of M 92

Abstract

We present wide-field neutral hydrogen (H i) Lovell telescope multibeam, and Dominion Radio Astrophysical Observatory H i synthesis observations, of the high velocity cloud (HVC) located in the general direction of the globular cluster M 92. This cloud is part of the larger Complex C and lies at velocities between ~-80 and -130 km s-1 in the Local Standard of Rest. The Lovell telescope observations, of resolution 12 arcmin spatially and 3.0 km s-1 in velocity, fully sampling a 3.112.6° RA-Dec grid, have found that this part of HVC Complex C comprises two main condensations, lying approximately north-south in declination, separated by ~2° and being parallel to the Galactic plane. At this resolution, peak values of the brightness temperature and H i column density of ~1.4 K and ~51019 cm-2 are determined, with relatively high values of the full width half maximum velocity (FWHM) of ~22 km s-1 being observed, equivalent to a gas kinetic temperature, in the absence of turbulence and geometric effects of ~10 000 K. Each of these properties, as well as the sizes of the clouds, are similar in the two components. The DRAO observations, towards the Northern HVC condensation, are the first high-resolution H i spectra of Complex C. When smoothed to a resolution of 3 arcmin, they identify several H i intensity peaks with column densities in the range 4-71019 cm-2. Further smoothing of these data to 6 arcmin resolution tentatively indicates that parts of the HVC consist of two velocity components, of similar brightness temperature, separated by ~7 km s-1 in velocity, and with FWHM velocity widths of ~5-7km s-1. No IRAS 60 or 100 micron flux is associated with the M 92 HVC. Cloud properties are briefly discussed and compared to previous observations of HVCs.