DESI survey of S IV absorption outflows in quasars: Contribution to AGN feedback and comparison with [O III] emission outflows

¹ Department of Physics, Virginia Tech, Blacksburg, VA 24061, USA
² Department of Physics and Astronomy, University of Kentucky, Lexington KY 40506, USA

^⋆ Corresponding author: mayanksh@vt.edu

Received: 25 April 2025
Accepted: 16 June 2025

Abstract

Aims. Quasar outflows play a crucial role in the evolution of their host galaxies through various feedback processes. This effect is thought to be particularly important when the Universe was only 2–3 billion years old, during the period known as cosmic noon. By utilizing existing observations from the Dark Energy Spectroscopy Instrument (DESI), we conducted a survey of high-ionization quasar outflows at cosmic noon, aiming to double the current sample of such outflows with distance and energetics determination. We also aimed to compare these properties with those derived from spatially resolved outflows in similar quasars probed through integral field spectroscopy.

Methods. We performed Monte Carlo simulations on a sample of 130 quasars and detect signatures of high-ionization outflows in the form of S IV troughs in eight objects. The absorption features of each outflow were then individually analyzed to characterize their physical conditions by determining the total hydrogen column density (N_H), the ionization parameter (U_H), and the electron number density (n_e). Through these parameters, we determined the distance of the outflows from their central source (R), their mass outflow rate, and their kinetic luminosity.

Results. The detected outflows show complex kinematic structures with a wide range of blueshifted velocities (100–4600 km s⁻¹). We locate five of the eight outflows at distances between 240–5500 pc from the central source. Only upper limits could be obtained for two outflows, placing them closer than 100 and 900 pc, respectively; for one outflow, the distance could not be determined. From the combined sample of 15 high-ionization S IV outflows at cosmic noon, we find that a high fraction (up to 46%) are powerful enough to contribute significantly to multistage active galactic nucleus feedback processes. Their energetics are also consistent with spatially resolved outflows in a luminosity- and redshift-matched sample of quasars. Comparison with previous spectra reveals interesting variations in some objects, including two cases of emerging high-velocity broad absorption line features with velocities of –8000 and –39 000 km s⁻¹. An impressive case of four line-locked Si IV outflow systems is also revealed in one object.