# Physical properties of the first quasars

## TL;DR

This paper reviews the properties of high-redshift quasars, emphasizing recent (sub-)millimeter observations, and discusses challenges and strategies for understanding early galaxy and black hole formation.

## Contribution

It provides a comprehensive overview of the latest observational results and discusses open issues and future strategies in studying early universe quasars.

## Key findings

- High-$z$ quasars reveal rapid supermassive black hole growth.
- Recent (sub-)millimeter data shed light on host galaxy properties.
- Open challenges remain in theoretical modeling of early galaxy evolution.

## Abstract

Since the beginning of the new millennium, more than 100 $z\sim 6$ quasars have been discovered through several surveys and followed-up with multi-wavelength observations. These data provided a large amount of information on the growth of supermassive black holes at the early epochs, the properties of quasar host galaxies and the joint formation and evolution of these massive systems. We review the properties of the highest-$z$ quasars known so far, especially focusing on some of the most recent results obtained in (sub-)millimeter bands. We discuss key observational challenges and open issues in theoretical models and highlight possible new strategies to improve our understanding of the galaxy-black hole formation and evolution in the early Universe.