Star Formation Suppression Due to Jet Feedback in Radio Galaxies with Shocked Warm Molecular Gas

TL;DR

This study uses Herschel data to show that jet-driven shocks in radio galaxies suppress star formation by injecting turbulence into the interstellar medium, with suppression factors up to 6, independent of jet power.

Contribution

It provides the first direct evidence linking jet-driven shocks to star formation suppression in radio galaxies, highlighting turbulence as a key mechanism.

Findings

Star formation is suppressed by a factor of 3-6.

Approximately 25% of galaxies show suppression over 10 times.

Suppression does not correlate with jet power or warm H2 emission.

Abstract

We present Herschel observations of 22 radio galaxies, selected for the presence of shocked, warm molecular hydrogen emission. We measured and modeled spectral energy distributions (SEDs) in 33 bands from the ultraviolet to the far-infrared to investigate the impact of jet feedback on star formation activity. These galaxies are massive, early-type galaxies with normal gas-to-dust ratios, covering a range of optical and infrared colors. We find that the star formation rate (SFR) is suppressed by a factor of ~3-6, depending on how molecular gas mass is estimated. We suggest this suppression is due to the shocks driven by the radio jets injecting turbulence into the interstellar medium (ISM), which also powers the luminous warm H2 line emission. Approximately 25% of the sample shows suppression by more than a factor of 10. However, the degree of SFR suppression does not correlate with indicators of jet feedback including jet power, diffuse X-ray emission, or intensity of warm molecular H2 emission, suggesting that while injected turbulence likely impacts star formation, the process is not purely parameterized by the amount of mechanical energy dissipated into the ISM. Radio galaxies with shocked warm molecular gas cover a wide range in SFR-stellar mass space, indicating that these galaxies are in a variety of evolutionary states, from actively star-forming and gas-rich to quiescent and gas-poor. SFR suppression appears to have the largest impact on the evolution of galaxies that are moderately gas-rich.