Double-peaked narrow emission-line galaxies from Sloan Digital Sky Survey. I. Sample and basic properties

Abstract: Recently, much attention has been given to double-peaked narrow emission-line galaxies, some of which are suggested to be related with merging galaxies. We make a systematic search to build the largest sample of these sources from Data Release 7 of Sloan Digital Sky Survey (SDSS DR7). With reasonable criteria of fluxes, full-width-half-maximum of emission lines and separations of the peaks, we select 3,030 double-peaked narrow emission-lines galaxies. In light of the existence of broad Balmer lines and the locations of the two components of double-peaked narrow emission lines distinguished by the Kauffmann et al. (2003) criteria in the Baldwin-Phillips-Terlevich (BPT) diagram, we find that there are 81 type I AGN, 837 double-type II AGN (2-type II), 708 galaxies with double star forming components (2-SF), 400 with mixed star forming and type II AGN components (type II + SF) and 1,004 unknown-type objects. As a by-product, a sample of galaxies (12,582) with asymmetric or top-flat profiles of emission lines is established. After inspecting the SDSS images of the two samples visually, we find 54 galaxies with dual cores. The present samples can be used to study the dynamics of merging galaxies, the triggering mechanism of black hole activity, the hierarchical growth of galaxies and dynamics of narrow line regions driven by outflows and rotating disk.