Stellar population analysis on the stacked spectra of double-peaked emission-line galaxies

Abstract

Double-peaked emission-line galaxies have long been perceived as objects related to merging galaxies or other phenomenawith 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 the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) databases. 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 blueshifted and redshifted components, and then stack the spectra of each group for analysis. The software STARLIGHT is employed to fit each stacked spectrum, and the contributions of stars at different ages and metallicities are quantified for subsequent comparative study and analysis. To highlight the commonality 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 those of their counterpart reference samples displaying single-peaked emission features. The reference samples are also selected from the LAMOST DR4 and SDSS DR7 databases. From the comparison results, we confirm the strong correlations between stellar populations and their spectral classes, and find that the double-peaked emitting phenomenon is more likely to occur in an ‘older’ stellar environment and the subgroups hosting different BPT components will show an obvious heterogeneous star formation history.