Cosmic Noon Galaxies Drive Faster and Stronger Galactic Outflows
Galaxies at the peak of the universe’s star formation roughly 10 billion years ago drove higher outflow rates and stronger outflows than nearby galaxies of similar stellar mass, according to a study accepted for publication in The Astrophysical Journal and detailed on astrobites.org. The research evaluates 387 galaxies spanning a wide range of redshifts from the Keck Observatory’s MOSFIRE Survey, offering new empirical data on how galactic winds regulate stellar growth across cosmic time.
The Tech TL;DR:
- Researchers analyzed a joint sample of 387 galaxies using data from the Keck Observatory’s MOSFIRE Survey to track galactic outflows across cosmic time.
- Data show that approximately 30% of the galaxies in the sample exhibit detectable outflows, with Cosmic Noon galaxies displaying higher velocities and stronger mass outflow rates than local counterparts.
- The mass loading factor increases alongside star formation rate density, indicating that concentrated star formation generates greater pressure to overcome host galaxy gravitational pull.
Keck Observatory MOSFIRE Survey Captures 387 Galaxies Across Cosmic Time
Galaxies continuously exchange matter with the surrounding circumgalactic medium, pulling in gas to fuel star formation while expelling material via outflows driven by supernovae and supermassive black holes. Measuring these dynamics in the distant universe has historically proven difficult due to limited spectral resolution and signal-to-noise ratios in high-redshift samples. To overcome this, authors Tiffany Liou, Xinfeng Xu, Allison L. Strom, Nathalie A. Korhonen Cuestas, Claude-André Faucher-Giguère, Tim B. Miller, Gwen Rudie, Ryan F. Trainor, Naveen A. Reddy, Charles C. Steidel, and Yuguang Chen evaluated a joint sample of 387 galaxies from the Keck Observatory’s MOSFIRE Survey.
The research team identified outflows by separating a broad emission-line component—which traces high-velocity outflowing gas—from a narrow component produced by the stationary interstellar medium. Fitting these components simultaneously across several emission lines allowed the authors to isolate galaxies with active outflows.
Cosmic Noon Outflow Rates Outpace Modern Galactic Measurements
Approximately 30% of the galaxies in the MOSFIRE sample display detectable outflows. During Cosmic Noon, the period roughly 10 billion years ago when star formation and supermassive black hole activity peaked, galaxies generally exhibited higher outflow rates than nearby galaxies of similar stellar mass. While the local Universe displays a strong correlation between mass outflow rate and stellar mass, that relationship becomes more moderate at Cosmic Noon.
At redshifts above four, the study found no significant trend, a limitation driven by a narrow range of stellar masses within that subset and observational biases toward brighter galaxies with higher star formation rates. Nonetheless, intermediate- and high-redshift outflows consistently demonstrate higher velocities than those observed locally.
Mass Loading Factor Scales With Star Formation Concentration
To quantify how efficiently outflows remove gas relative to star formation, the authors tracked the mass loading factor, defined as the mass outflow rate divided by the star formation rate. Observations at Cosmic Noon reveal a strong positive relationship between the mass loading factor and star formation rate density.
When star formation is more concentrated within a galaxy, the resulting outflows experience greater internal pressure. This elevated pressure helps the gas overcome the gravitational pull of the host galaxy, successfully driving material out into the circumgalactic medium where it can eventually be recycled.