High- z Quasar Candidate Archive: A Spectroscopic Catalog of Quasars and Contaminants in Various Quasar Searches by Da-Ming Yang et al. on Wednesday 30 November

We present the high-$z$ quasar candidate archive (HzQCA), summarizing the

spectroscopic observations of 174 $z\gtrsim5$ quasar candidates using

Keck/LRIS, Keck/MOSFIRE, and Keck/NIRES. We identify 7 candidates as $z\sim 6$

quasars 3 of them newly reported here, and 51 candidates as brown dwarfs. In

the remaining sources, 74 candidates are unlikely to be quasars; 2 sources are

inconclusive; the others could not be fully reduced or extracted. Based on the

classifications we investigate the distributions of quasars and contaminants in

color space with photometry measurements from DELS ($z$), VIKING/UKIDSS

($YJHK_s$/$YJHK$), and un\textit{WISE} ($W1W2$). We find that the identified

brown dwarfs are not fully consistent with the empirical brown dwarf model that

is commonly used in quasar candidate selection methods. To refine spectroscopic

confirmation strategies, we simulate synthetic spectroscopy of high-$z$ quasars

and contaminants for all three instruments. The simulations utilize the

spectroscopic data in HzQCA. We predict the required exposure times for quasar

confirmation and propose and optimal strategy for spectroscopic follow-up

observations. For example, we demonstrate that we can identify a $m_J=21.5$ at

$z=7.6$ or a $m_J=23.0$ at $z=7.0$ within 15\,min of exposure time with LRIS.

With the publication of the HzQCA we aim to provide guidance for future quasar

surveys and candidate classification.

arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.16996v1