Fast outflows and star formation quenching in quasar host galaxies

TL;DR

This study uses integral-field spectroscopy to investigate the impact of quasar-driven outflows on star formation in host galaxies at z~2.4, providing evidence for both suppression and potential positive feedback effects.

Contribution

It presents detailed observations of ionised outflows and star formation regions in quasar hosts, revealing the complex dual role of outflows in galaxy evolution.

Findings

Outflows are spatially anti-correlated with star formation regions.

Star formation rates remain high despite the presence of outflows.

Outflows may both suppress and potentially promote star formation.

Abstract

Negative feedback from active galactic nuclei (AGN) is considered a key mechanism in shaping galaxy evolution. Fast, extended outflows are frequently detected in the AGN host galaxies at all redshifts and luminosities, both in ionised and molecular gas. However, these outflows are only "potentially" able to quench star formation and we are still missing a decisive evidence of negative feedback in action. Here we present Spectrograph for INtegral Field Observations in the Near Infrared (SINFONI) H- and K-band integral-field spectroscopic observations of two quasars at $z\sim$2.4 characterised by fast, extended outflows detected through the [OIII]$\lambda$5007 line (Carniani et al. 2015). The high signal-to-noise ratio of our observations allows us to identify faint narrow (FWHM $< 500$ km/s), and spatially extended components in [OIII]$\lambda$5007 and H$\alpha$ emission associated with star formation in the host galaxy. Such star-formation powered emission is spatially anti-correlated with the fast outflows. The ionised outflows therefore appear to be able to suppress star formation in the region where the outflow is expanding. However the detection of narrow, spatially-extended H$\alpha$ emission indicates star formation rates of at least $\sim 50-90$ M$_{\odot}$/yr, suggesting either that AGN feedback does not affect the whole galaxy or that many feedback episodes are required before star formation is completely quenched. On the other hand, the narrow H$\alpha$ emission extending along the edges of the outflow cone may lead also to a positive feedback interpretation. Our results highlight the possible twofold role of galaxy-wide outflows in host galaxy evolution.