The properties of Spheroidal Post-Mergers in the Local Universe
Abstract
Galaxy merging is a fundamental aspect of the standard hierarchical galaxy formation paradigm. A large, homogeneous catalogue of mergers was compiled, through direct visual inspection of the entire SDSS spectroscopic sample using the Galaxy Zoo project. We explore a subset of galaxies from this catalogue that are spheroidal ``post-mergers'' (SPMs) - where a single remnant is in the final stages of relaxation and shows evidence for a dominant bulge, making them plausible progenitors of early-type galaxies. The SPMs have bluer colours than the general early-type galaxy population due to merger-induced star formation. An emission line analysis using optical emission line ratios indicates that 68% of our SPMs exhibit LINER or Seyfert-like activity, while the rest are classified as ``star forming'' (16%) or ``quiescent'' (26%). A comparison to emission line activity in a sample where the mergers are still in progress indicates that the AGN fraction rises in the post-mergers galaxies, while star-formation rates is higher in the mergers. The results indicate that the starburst episodes peak during the merger phase, while the AGN switches on at a later stage. The timing of mergers evolving into post-mergers is consistent with the starburst-AGN time delay we found in the literature.
- Publication:
-
The Starburst-AGN Connection under the Multiwavelength Limelight
- Pub Date:
- November 2011
- Bibcode:
- 2011sacm.confE..12C