High-redshift Post-starburst Galaxies from the Sloan Digital Sky Survey

Abstract

Post-starburst galaxies are a rare class of galaxy that show the spectral signature of recent, but not ongoing, star-formation activity, and are thought to have their star formation suddenly quenched within the one billion years preceding the observations. In other words, these are galaxies in the transitional stage between blue, star-forming galaxies and red, quiescent galaxies, and therefore hold important information regarding our understanding of galaxy evolution. This class of objects can be used to study the mechanisms responsible for star-formation quenching, which is an important unsettled question in galaxy evolution.

In this thesis, we study this class of galaxies through a number of different approaches. First of all, we systematically selected a large, statistical sample of post-starburst galaxies from the spectroscopic dataset of the Sloan Digital Sky Survey (SDSS). This sample contains 13219 objects in total, with redshifts ranging from local universe to z ∼ 1.3 and median redshift zmedian = 0.59. This is currently the largest sample of post-starburst galaxies available in the literature.

Using this sample, we calculated the luminosity functions for a number of redshift bins. A rapid downsizing redshift evolution of the luminosity function is observed, whereby the number density of post-starburst galaxies at fixed luminosity is larger at higher redshift. From the luminosity functions, we calculated the amount of star-formation quenching accounted for in post-starburst galaxies, and compared to the amount required by the global decline of star-formation rate of the universe. We found that only a small fraction (∼ 0.2%) of all star-formation quenching in the universe goes through the post-starburst galaxy channel, at least for the luminous sources in our sample.

We also searched the SDSS spectroscopic database the post-starburst quasars, which are an even more special class of objects that show both a post-starburst stellar population and AGN activity in the same object. Given that AGN feedback is thought to be a likely mechanism responsible for quenching star-formation, post-starburst quasars provide ideal laboratory for

studying this link. We explored various ways to identify post-starburst quasars, and construct our sample with more than 600 objects at high-redshift. This is the largest sample of post-starburst quasars available in the literature, and will be useful for AGN feedback studies.

Finally, we studied the clustering properties of post-starburst galaxies through cross-correlation with CMASS galaxies. The real-space cross correlation function is a power-law with correlation length r0 ∼ 9.2 Mpc, and power-law index γ ∼ 1.8. We also measure the linear bias of post-starburst galaxies to be bPSG ∼ 1.74 at redshift z = 0.62, corresponding to a dark matter halo mass of Mhalo ∼ 1.5 × 1013 M⊙. We found no evidence for redshift evolution in clustering properties for post-starburst galaxies.