Census of the Local Universe (CLU) Narrowband Survey. I. Galaxy Catalogs from Preliminary Fields

We present the Census of the Local Universe (CLU) narrowband survey to search for emission-line (H alpha) galaxies. CLU-H alpha has imaged approximate to 3 pi of the sky (26,470 deg(2)) with four narrowband filters that probe a distance out to 200 Mpc. We have obtained spectroscopic follow-up for galaxy candidates in 14 preliminary fields (101.6 deg(2)) to characterize the limits and completeness of the survey. In these preliminary fields, CLU can identify emission lines down to an Ha. flux limit of 10(-14) erg s(-1) cm(-2) at 90% completeness, and recovers 83% (67%) of the H alpha flux from cataloged galaxies in our search volume at the Sigma = 2.5 (Sigma = 5) color excess levels. The contamination from galaxies with no emission lines is 61% (12%) for Sigma = 2.5 (Sigma = 5). Also, in the regions of overlap between our preliminary fields and previous emission-line surveys, we recover the majority of the galaxies found in previous surveys and identify an additional approximate to 300 galaxies. In total, we find 90 galaxies with no previous distance information, several of which are interesting objects: 7 blue compact dwarfs, 1 green pea, and a Seyfert galaxy; we also identify a known planetary nebula. These objects show that the CLU-H alpha survey can be a discovery machine for objects in our own Galaxy and extreme galaxies out to intermediate redshifts. However, the majority of the CLU-H alpha galaxies identified in this work show properties consistent with normal star-forming galaxies. CLU-H alpha galaxies with new redshifts will be added to existing galaxy catalogs to focus the search for the electromagnetic counterpart to gravitational wave events.