Galaxies at Cosmic Noon drove significantly faster and stronger outflows than nearby galaxies of similar stellar mass today, according to new research accepted for publication in The Astrophysical Journal. The study connects data from 387 galaxies across a wide range of redshifts, offering a clearer picture of how matter cycles between galaxies and their surrounding mediums during a period when the universe reached its peak of star formation and supermassive black hole activity roughly 10 billion years ago.
Keck Observatory Data Tracks 387 Galaxies Across Cosmic Time
Galaxies constantly exchange matter with the circumgalactic medium, taking in gas that fuels star formation and expelling material through powerful outflows driven by supernovae and supermassive black holes. Extending outflow measurements to higher redshifts has historically proved difficult due to limited spectral resolution and signal-to-noise ratios in distant samples. To solve this, researchers analyzed a joint sample of 387 galaxies from the Keck Observatory’s MOSFIRE Survey. This dataset bridges low-redshift observations at $z approx 0–1$ with the distant Cosmic Noon era at $z approx 2–3$.
Cosmic Noon Outflows Outpace Local Universe Velocities
Galaxies at Cosmic Noon display higher outflow rates than nearby counterparts of similar mass. At redshifts above four, however, researchers found no significant trend, largely because those observed galaxies span a narrow mass range and are heavily biased toward brighter systems with high star formation rates. Even with these observational biases, intermediate- and high-redshift outflows clearly exhibit higher velocities and stronger forces than those observed in the local universe.
Concentrated Star Formation Drives Higher Mass Loading Factors
To evaluate how efficiently outflows remove gas relative to star formation, the study utilizes the mass loading factor $eta = dot{M}_{text{out}}/text{SFR}$. Observations from Cosmic Noon demonstrate a strong positive relationship between this mass loading factor and the star formation rate surface density. When star formation is more concentrated, outflows experience greater pressure. This pressure helps the gas overcome the gravitational pull of the host galaxy and transport more material outward.
Galactic Fountains Recycle Gas Back Into Host Galaxies
Expelled gas does not automatically escape into the intergalactic medium permanently. By comparing maximum outflow velocities with galaxy escape velocities, the authors determined that most observed outflows move too slowly to escape their host galaxies entirely. Instead, this material remains bound, travels into the circumgalactic medium, and eventually falls back in a galactic fountain cycle that feeds future generations of stars.
Frequently Asked Questions About Cosmic Noon Outflows
What is Cosmic Noon?
Cosmic Noon is the period approximately 10 billion years ago when the universe reached the peak of its star formation and supermassive black hole activity. This era provides astronomers with an ideal window to study rapid galaxy growth.
Why do Cosmic Noon galaxies drive stronger outflows?
Galaxies during this epoch had higher star formation rate surface densities. This concentration of star formation creates greater pressure, driving faster and stronger gas outflows compared to galaxies of similar mass today.
Does all outflowing gas escape into deep space?
No, most outflowing gas does not reach the escape velocity of its host galaxy. The material typically remains gravitationally bound and eventually returns to the galaxy through a galactic fountain cycle.
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