The Rest Frame Ultraviolet Spectra of UV-Selected Active Galactic Nuclei at z ~ 2-3

TL;DR

This study analyzes the UV spectra of 33 high-redshift UV-selected AGNs, revealing unique emission and absorption features, outflow characteristics, and differences from non-AGN star-forming galaxies, providing new insights into AGN-host galaxy interactions at z ~ 2-3.

Contribution

First detailed comparison of high-redshift star-forming galaxies with and without AGN activity based on UV spectral features.

Findings

Detection of NIV]1486 emission line in AGNs.

Blueshifted SiIV absorption indicates high-velocity outflows (~1000 km/s).

Differences in Ly-alpha emission and extinction trends compared to non-AGN galaxies.

Abstract

We present new results for a sample of 33 narrow-lined UV-selected active galactic nuclei (AGNs), identified in the course of a spectroscopic survey for star-forming galaxies at z ~ 2-3. The rest-frame UV composite spectrum for our AGN sample shows several emission lines characteristic of AGNs, as well as interstellar absorption features seen in star-forming Lyman Break Galaxies (LBGs). We report a detection of NIV]1486, which has been observed in high-redshift radio galaxies, as well as in rare optically-selected quasars. The UV continuum slope of the composite spectrum is significantly redder than that of a sample of non-AGN UV-selected star forming galaxies. Blueshifted SiIV absorption provides evidence for outflowing highly-ionized gas in these objects at speeds of ~ 10^(3) km/s, quantitatively different from what is seen in the outflows of non-AGN LBGs. Grouping the individual AGNs by parameters such as Ly-alpha equivalent width, redshift, and UV continuum magnitude allows for an analysis of the major spectroscopic trends within the sample. Stronger Ly-alpha emission is coupled with weaker low-ionization absorption, which is similar to what is seen in the non-AGN LBGs, and highlights the role that cool interstellar gas plays in the escape of Ly-alpha photons. However, the AGN composite does not show the same trends between Ly-alpha strength and extinction seen in the non-AGN LBGs. These results represent the first such comparison at high-redshift between star-forming galaxies and similar galaxies that host AGN activity.