Stellar population analysis on the stacked spectra of double-peaked
  emission-line galaxies
  The double-peaked emission-line galaxies has long been perceived as objects
related with merging galaxies or other phenomena of disturbed dynamical
activities, such as outflows and disk rotation. In order to find the connection
between the unique activities happening in these objects and their stellar
population physics, we study the stellar populations of the stacked spectra
drawn from double-peaked emission-line galaxies in the Large Sky Area
Multi-object Fiber Spectroscopic Telescope (LAMOST) Data Release 4 (DR4) and
Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) database. We group the
selected double-peaked emission-line objects into 10 different types of pairs
based on the Baldwin-Phillips-Terlevich (BPT) diagnosis for each pair of
blue-shifted and red-shifted components, and then stack the spectra of each
group for analysis. The software STARLIGHT is employed to fit each stacked
spectra, and the contributions of stars at different ages and metallicities are
quantified for subsequent comparative study and analysis. To highlight the
commonness and uniqueness in these double-peaked emitting objects, we compare
the population synthesis results of the stacked spectra of double-peaked
emission-line galaxies with that of their counterpart reference samples
appearing single-peaked emission features. The reference sample are also
selected from LAMOST DR4 and SDSS DR7 databases, respectively. From the
comparison results, we confirm the strong correlations between the stellar
populations and its spectral classes, and find that the double-peaked emitting
phenomena is more likely to occur in the `older' stellar environment and the
subgroups hosting different BPT components will show obvious heterogeneous star
formation history.
