# Predicting the Yields of $z$ > 6.5 Quasar Surveys in the Era of Roman and Rubin

**Authors:** Wei Leong Tee, Xiaohui Fan, Feige Wang, Jinyi Yang, Sangeeta Malhotra, James E. Rhoads  
**arXiv:** [2308.12278](https://arxiv.org/abs/2308.12278)  
**Date:** 2023-08-23  
**Summary page:** https://www.summarizepaper.com/en/paper/2308.12278v1/

## Key points

- Study focuses on predicting yields of high-redshift quasar surveys in the era of Roman and Rubin observatories
- Currently, around 70 luminous quasars discovered with redshifts greater than 6.5, but biased towards bright end
- Roman/Rubin survey expected to yield three times more quasars and probe broader range of luminosities
- Survey aims to identify high-redshift quasars, galactic dwarfs, and low-redshift compact galaxies as potential quasar candidates
- Mock catalogs based on population models used to evaluate selection completeness and efficiency
- Color dropout method in z and Y bands used for primary candidate selection, followed by Bayesian method for confirmation
- Overall selection completeness estimated to be >80% with efficiency of ~10% for redshifts between 6.5 and 9
- Predicted around 180 quasars at redshifts >6.5, 20 at redshifts >7.5, and 2 at redshifts >8.5 (dependent on assumptions)
- Proper motion information can be used to reject brown dwarfs as false positives for brighter stars (<mag 25) up to rejection rate of 50%
- Low-redshift galaxies dominate as contaminants at fainter magnitudes
- Roman/Rubin observatories have potential to discover statistical sample of early and faint quasars in universe
- Datasets from survey valuable for follow-up studies using James Webb Space Telescope and Extremely Large Telescopes
- Future observations will help determine faint end slope of quasar luminosity function and provide constraints on growth of supermassive black holes in early universe

## Summary

This study focuses on predicting the yields of high-redshift quasar surveys in the era of the Roman and Rubin observatories. Currently, there have been around 70 luminous quasars discovered with redshifts greater than 6.5, but these discoveries are strongly biased towards the bright end, providing a limited understanding of quasar abundance beyond cosmic dawn. The authors present the expected results of the Roman/Rubin high-redshift quasar survey, which is anticipated to yield three times more quasars and probe a broader range of luminosities. The survey aims to identify high-redshift quasars, galactic dwarfs, and low-redshift compact galaxies that have similar colors as potential quasar candidates. To evaluate selection completeness and efficiency, mock catalogs based on population models are created. The classical color dropout method in the z and Y bands is utilized to select primary quasar candidates, followed by a Bayesian selection method to confirm their identification as quasars. The results show that the overall selection completeness is estimated to be greater than 80% with an efficiency of approximately 10% for redshifts between 6.5 and 9. Specifically, it is predicted that there will be around 180 quasars at redshifts greater than 6.5, 20 at redshifts greater than 7.5, and 2 at redshifts greater than 8.5. However, these predictions depend on assumptions about the shape of the quasar luminosity distribution and its evolution with redshift. To reject brown dwarfs as false positives, proper motion information can be used for stars brighter than magnitude 25 with up to a rejection rate of 50%. At fainter magnitudes, low-redshift galaxies dominate as contaminants in the sample. The authors highlight that the Roman/Rubin observatories have the potential to discover a statistical sample of early and faint quasars in the universe. The datasets obtained from this survey will be valuable for follow-up studies using the James Webb Space Telescope and Extremely Large Telescopes. These future observations will help determine the faint end slope of the quasar luminosity function and provide constraints on the growth of supermassive black holes in the early universe. In summary, this study presents predicted results from a high-redshift quasar survey using Roman/Rubin observatories which has important implications for understanding early universe phenomena such as black hole growth through probing faint end unexplored regions of space beyond cosmic dawn . This survey is expected to provide a more comprehensive view into current knowledge gaps regarding abundance levels by identifying previously unseen faint sources which can guide future observational efforts in studying properties related to them .