The SINS Survey: Broad Emission Lines in High-Redshift Star-Forming Galaxies

TL;DR

This study analyzes high-redshift star-forming galaxies, revealing broad emission lines indicative of galactic winds or active black holes, with implications for galaxy evolution and black hole growth.

Contribution

It provides the first high-quality spectra showing broad emission lines in z~2 galaxies and explores their origins and implications for galaxy and black hole evolution.

Findings

Broad emission lines are more common in massive, active galaxies.

Mass outflow rates from winds are comparable to star formation rates.

Black hole masses inferred are lower than local universe predictions.

Abstract

High signal-to-noise, representative spectra of star-forming galaxies at z~2, obtained via stacking, reveal a high-velocity component underneath the narrow H-alpha and [NII] emission lines. When modeled as a single Gaussian, this broad component has FWHM > 1500 km/s; when modeled as broad wings on the H-alpha and [NII] features, it has FWHM > 500 km/s. This feature is preferentially found in the more massive and more rapidly star-forming systems, which also tend to be older and larger galaxies. We interpret this emission as evidence of either powerful starburst-driven galactic winds or active supermassive black holes. If galactic winds are responsible for the broad emission, the observed luminosity and velocity of this gas imply mass outflow rates comparable to the star formation rate. On the other hand, if the broad line regions of active black holes account for the broad feature, the corresponding black holes masses are estimated to be an order of magnitude lower than those predicted by local scaling relations, suggesting a delayed assembly of supermassive black holes with respect to their host bulges.