H I 21 centimeter observations and I-band CCD surface photometry of spiral galaxies behind the Virgo Cluster and toward its antipode

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Abstract

In a companion paper we describe a project in which we seek to resolve the controversies over corrections for the peculiar velocity of the Local Group toward the Virgo Cluster and the Malmquist bias. The former is particularly important for galaxies at low redshift, out to perhaps twice the distance to the Virgo Cluster, while the latter affects more distant, flux-limited samples. To this end we have selected two samples of disk galaxies (S0 or later). The first sample consists of 123 bright disk galaxies complete to B_T_ = 14.5 in two volumes in the local space. One is located in the direction of, but behind, the Virgo Cluster (10^h^30^m^ < α < 13^h^30^m^, 0 < δ < 20^deg^ and 2500 <v_h_ < 4500 km s^-1^, where v_h_ is the heliocentric velocity), while the other is toward the antipode (22^h^ <α < 2^h^, 0 < δ < 20^deg^ and v_h_ < 3000 km s^-1^) The second sample consists of 44O "faint" blue galaxies with 14.5 < B_T_ <~ 15.5 which was originally generated directly by scanning a few Palomar Sky Survey Plates in the above two directions. We are especially interested in the galaxies located in the two local volumes defined above, that is, all the bright spiral galaxies plus those faint galaxies with appropriate velocities. We describe in this paper the following observations and their results: (1) We have obtained high signal-to-noise and high-velocity-resolution 21 cm line spectra for all the bright galaxies, either from the literature or from our own observations presented in this paper. (2) We observed all the faint galaxies in H I 21 cm to identify those in our chosen local volumes. Seventy-seven such galaxies were found, and follow-up observations have yielded high-quality spectra similar to those in (1). (3) I-band CCD photometry was obtained for all the bright galaxies and part of the sample of faint galaxies in the two local volumes.

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