Constructing massive blue elliptical galaxies in the local universe
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Over cosmic time, galaxy mass assembly has transitioned from low-mass, starforming disk galaxies to massive, quiescent elliptical galaxies. The merger hypothesis for the formation of new elliptical galaxies provides one physical explanation to the observed buildup of this population, a key prediction of which is a brief phase of morphological transformation from highly-disturbed remnant to blue elliptical. We study 12 plausible new ellipticals with varying degrees of morphological peculiarities visually selected from a larger parent sample of nearby (0.01 ≤ z ≤ 0.04), massive (M∗ ≥ 10¹ ⁰ M⊙), concentrated (Petrosian R90/R50 ≥ 2.6), and optically blue galaxies from the SDSS DR4 catalog. Using integral field spectroscopy, we construct two-dimensional spectra of the stellar populations and azimuthally bin them into concentric annuli to determine the relative ages of the stellar populations as a function of radius. Using this data and conclusions from simulations, we seek to distinguish post-mergers from galaxies undergoing other modes of mass assembly. We find that 1/3 of our sample is consistent with having undergone a recent, gas-rich major merger. Another 1/3 of our sample is consistent with having undergone a 'frosting' of recent star formation. The final 1/3 of our sample is either inconsistent with or inconclusive of having undergone a recent, gas-rich major merger.
Table of Contents
Introduction -- Sample selection and observations -- Data reduction -- Data preparation -- Spectroscopic analysis -- Qualitative radial star formation histories -- Conclusions -- Appendix A. Thumbnail images -- Appendix B. Variance map fits -- Appendix C. Emission-subtracted spectra -- Appendix D. Radial index measurements -- Appendix E. Star-Formation history model plane