UC Santa Cruz

Active galactic nuclei (AGN) driven feedback has been proposed to be one of the most efficient ways to quench star formation and help maintain quiescence in massive galaxies. However, direct evidence of feedback in typical quiescent galaxy populations has been restricted to only a handful of sources. This thesis presents a series of evidence that large-scale winds in a new (and relatively common) class of early-type galaxy, known as `red geysers', may represent AGN radio mode feedback in action. The work is primarily based on integral field spectroscopic data from the SDSS IV- MaNGA survey that has completed observing 10,010 galaxies in the optical wavelength at $z<0.1$. The main focus of this work is utilizing a multi-wavelength approach to understand the detailed physics of the red geyser galaxies and place them in the context of global quenching of star formation in typical red and dead galaxies.

Radio data from the combined surveys of Faint Images of the Radio Sky at Twenty Centimeters (FIRST), VLA Sky survey (VLASS), and LOFAR Two Meter Sky Survey (LoTSS) reveal that red geysers preferentially host low luminosity radio mode AGNs with average radio luminosity $\rm L_{1.4 \ GHz} \sim 10^{21} - 10^{22} \ W\ Hz^{-1} $. Red geysers exhibit a wide range of radio morphologies: from double-lobed large-scale jets to compact and moderately extended features with average radio sizes between 5 - 30 kpc. However, the majority of the red geysers show a compact radio structure, closely resembling the `FR0' radio galaxies, which are the low luminosity counterparts of the more luminous FRI/FRII sources and often host small scale jets. Optical long-slit spectroscopy from the Keck ESI instrument and resolved spectroscopy from the SDSS IV- MaNGA survey shows that the turbulent ionized gas kinematics with `winged' emission line profiles are consistent with geometric projections through an outflowing broad conical wind.

In addition to the ample amount of ionized gas ($\sim \rm 10^{5}-10^6 \ M_{\odot}$), a large fraction of red geysers also host a significant amount of cold gas reservoir in the interstellar medium. Traced by the Sodium doublet absorption line, the signature is particularly enhanced for the radio bright red geysers indicating some underlying connection between the gas supply and the AGN activity. A detailed stellar population modeling and subsequent extraction of absorption-line kinematics using a Markov Chain Monte Carlo (MCMC) framework show that a large part of this cool gas is infalling towards the galaxy, with an average velocity $\sim \rm 60 \ km\ s^{-1}$. The origin of this cool inflowing gas is predicted to be a combination of internal sources like stellar mass loss and external accretion events like minor mergers. The emerging hypothesis is that this gas is inflowing towards the center to possibly fuel the central radio-mode AGNs, which can then trigger the outflowing wind visible in the ionized phase. This hypothesis is in agreement with the observed duty cycle of the red geysers, which matches the minor merger frequency in the local universe (0.1 $\rm Gyr^{-1}$). The minor mergers can provide the bulk of the multi-phase gas detected in these galaxies but cannot rejuvenate star formation, perhaps due to the feedback effect of the wind. The estimated kinetic energy from the wind $\rm \dot{E} \sim 10^{39} \ erg \ s^{-1}$ is energetically sufficient to suppress any residual star formation in the host galaxy. Red geysers are expected to be an episodic but short-lived phenomenon that possibly occurs in any red sequence galaxy. They can play an energetically important role in suppressing gas cooling and star formation at late times.