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