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Session 66 - Galaxies.
Display session, Thursday, June 11
Atlas Ballroom,
\par We present the Arecibo Dual-Beam Survey, a 21 cm HI driftscan search for galaxies out to cz = 8000 km/s. The primary goal of this survey is to identify galaxies independent of their stellar properties. By using two telescope feeds simultaneously pointed 1.6\deg apart on the sky, the survey area was doubled while also allowing us to excise interference which appeared in both feeds. Observations of the same region of the sky taken on different days were used to confirm detections. Over 400 square degrees of the sky were covered in the main beam, resulting in over 450 galaxy detections. \par A subsample of 73 low-velocity sources (<3000 km/s) was selected for follow-up observations using the VLA D-array. At present, accurate positions and HI fluxes exist only for sources in this follow-up sample. The number counts of the low-mass sources appear to be consistent with the steeply increasing low-mass end of the mass function presented in Schneider et al. (1998). In addition, the subsample contains seven optically intriguing sources: galaxies detected at 21 cm but with little or no optical emission on the Digitized POSS II. One blank-field source appears to be isolated, having no identified neighbor within one degree. \par Unlike previous 21 cm galaxy searches, we have tested our detection algorithms (by-eye and using computer algorithms) on artificial sources in an effort to quantify our completeness. Without a detailed understanding of the completeness, one cannot reliably determine the mass function. We introduce artificial sources with a wide range of fluxes and widths prior to the reduction process to determine, for example, which sources might be suppressed by baseline subtraction procedures. These efforts have shown the dependence of our detection limits on both the signal-to-noise and the line width of the sources.
