DISCOVERY OF EIGHTz∼ 6 QUASARS IN THE SLOAN DIGITAL SKY SURVEY OVERLAP REGIONS

We present the discovery of eight quasars at identified in the Sloan Digital Sky Survey (SDSS) overlap regions. Individual SDSS imaging runs have some overlap with each other, leading to repeat observations over an area spanning >4000 deg 2 (more than one-fourth of the total footprint). These overlap regions provide a unique data set that allows us to select high-redshift quasars more than 0.5 mag fainter in the z band than those found with the SDSS single-epoch data. Our quasar candidates were first selected as i -band dropout objects in the SDSS imaging database. We then carried out a series of follow-up observations in the optical and near-IR to improve photometry, remove contaminants, and identify quasars. The eight quasars reported here were discovered in a pilot study utilizing the overlap regions at high galactic latitude ( ). These quasars span a redshift range of and a flux range of mag. Five of them are fainter than mag, the typical magnitude limit of quasars used for the SDSS single-epoch images. In addition, we recover eight previously known quasars at that are located in the overlap regions. These results validate our procedure for selecting quasar candidates from the overlap regions and confirming them with follow-up observations, and they provide guidance to a future systematic survey over all SDSS imaging regions with repeat observations.