# Radiation-pressure Waves and Multiphase Quasar Outflows

## TL;DR

This study analyzes quasar outflow spectra to reveal a multiphase stratified outflow structure influenced by radiation pressure, with specific ion behaviors correlating with outflow velocity and density.

## Contribution

It introduces evidence for a multiphase stratified outflow model driven by radiation pressure, explaining ion-specific trends and outflow dynamics in quasars.

## Key findings

- OVI and NV line equivalent widths correlate with outflow velocity and electron density.
- No dependence of outflow properties on quasar magnitude or redshift.
- Support for a multiphase outflow structure influenced by radiation pressure.

## Abstract

We report on quasar outflow properties revealed by analyzing more than 60 composite outflow spectra built from $\sim 60\,000$ CIV absorption troughs in the SDSS-III/BOSS DR12QBAL catalog. We assess the dependences of the equivalent widths of many outflow metal absorption features on outflow velocity, trough width and position, and quasar magnitude and redshift. The evolution of the equivalent widths of the OVI and NV lines with outflow velocity correlates with that of the mean absorption-line width, the outflow electron density, and the strength of lines arising from collisionally-excited meta-stable states. None of these correlations is found for the other high- or low-ionization species, and different behaviors with trough width are also suggested. We find no dependence on quasar magnitude or redshift in any case. All the observed trends can be reconciled by considering a multiphase stratified outflow structure, where inner regions are colder, denser and host lower-ionization species. Given the prevalence of radiative acceleration in quasar outflows found by Mas-Ribas & Mauland (2019), we suggest that radiation pressure sweeps up and compresses the outflowing gas outwards, creating waves or filaments where the multiphase stratified structure could take form. This scenario is supported by the suggested correlation between electron density and outflow velocity, and the similar behavior observed for the line and line-locking components of the absorption features. We show that this outflow structure is also consistent with other X-ray, radiative transfer, and polarization results, and discuss the implications of our findings for future observational and numerical quasar outflow studies.