Nancay blind 21cm line survey of the Canes Venatici group region

Abstract

A radio spectroscopic driftscan survey in the 21cm line with the Nancay Radio Telescope of 0.08 steradians of sky in the direction of the constellation Canes Venatici covering a heliocentric velocity range of -350 < V_hel < 2350 km/s produced 53 spectral features, which was further reduced to a sample of 33 reliably detected galaxies by extensive follow-up observations. With a typical noise level of rms = 10 mJy after Hanning smoothing, the survey is -- depending on where the detections are located with regard to the center of the beam -- sensitive to M(HI)=1-2x10^8 Msun at 23 Mpc and to M(HI)=4-8x10^7 Msun throughout the CVn Groups (Ho=100). The survey region had been previously examined on deep optical plates by Binggeli et al. 1990 and contains loose groups with many gas-rich galaxies as well as voids. No galaxies that had not been previously identified in these deep optical surveys were uncovered in our HI survey, neither in the groups nor the voids. The implication is that no substantial quantity of neutral hydrogen contained in gas-rich galaxies has been missed in these well-studied groups. All late-type members of our sample are listed in the Fisher and Tully (1981b) optically selected sample of nearby late-type galaxies; the only system not contained in Fisher and Tullys' Catalog is the S0 galaxy NGC 4203. Within the well--sampled CVn group volume with distances corrected for flow motions, the HI mass function is best fitted with the Zwaan et al. (1997) HI mass function (alpha=-1.2) scaled by a factor of f=4.5 in account of the locally overdense region.