Red Geyser Galaxies and the Suppression of Star Formation

University Of California-Santa Cruz, Santa Cruz CA

Investigators

Abstract

For most of cosmic time, typical galaxies grow continuously by turning hydrogen and helium gas into new stars. However, in the last few billion years (roughly the most recent 25% of cosmic history), many galaxies stopped forming stars and seem to have entered a permanent state of quiescence. Our own Milky Way galaxy may be undergoing a similar fate. Astronomers are not only trying to understand what initially stops star formation in these galaxies, but what keeps it from re-starting when fresh supplies of gas become available. This project seeks to understand a newly-discovered phenomenon that may play a role. So-called "red geyser" galaxies host super-massive black holes at their centers that periodically emanate a wind of hot gas that spreads through the entire galaxy. This hot gas may be able to heat up cooler reservoirs and prevent them from collapsing into new stars. This project will confirm the relationship between red geysers and central black holes and study red geyser winds in detail to understand how they impact their host galaxies. This program will also contribute to training in research methods for students. It will support the use of specialized Jupyter-type Marvin notebooks for astronomical research through training classes for high school students and early undergraduates. This training will provide experience and job-skills for next generation researchers. These investigators have recently discovered a new class of quiescent, relatively common early- type galaxy that hosts large-scale, AGN-driven winds. These "red geysers''---found in 5-10% of the quiescent population---may be the missing energy source needed to maintain low levels of star formation in galaxies where star formation in general ceased long ago. Initial integral field observations from the relatively low resolution (R~2000; 2.5 arcsec FWHM) MaNGA Survey revealed characteristic ionized gas velocity fields. This project addresses two key issues through follow-up observations with the Keck Observatory. Investigators seek to determine (1) whether the tell-tale enhanced emission is due to shocks or gas over-densities, and (2) how the wind energy couples to the cooler ambient gas in order to suppress star formation. Both questions will be addressed by analyzing recently obtained Keck spectroscopic data that spatially and spectrally resolves the multicomponent gas structure with finer detail, allowing the investigators to search for shocks and turbulence at the interface between the wind and cooler material. These Keck observations, obtained for six red geysers over two nights, will also constrain a quantitative wind model to confirm the role of red geysers in suppressing late-time star formation. Finally, they will test the hypothesis that these winds are driven by low-luminosity AGN feedback by stacking the available but shallow radio flux observations to determine whether radio AGN activity is more often associated with optical identification of the red geyser phenomenon. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.