New observations by the Atacama Large Millimeter/submillimeter Array (ALMA) provide a close look at a galaxy that may be in the process of shutting down its star formation.
Transitioning a Galaxy

We think that galaxies transition from blue spirals actively forming stars (left) to red, quiescent ellipticals (right). [Hubble/Galaxy Zoo]
Since galaxies form stars out of cold gas, we could assume that star formation stops only when the cold gas supply is depleted. But observations suggest that star formation can shut down across a galaxy much more quickly than the timescale for using up the gas supply — sometimes turning off within just a few tens of millions of years. Such a rapid shutdown is termed “violent quenching”.

Top: Hubble images of SDSS J1341–0321. Bottom: Contours show the location of the galaxy’s molecular gas: all CO J(2 → 1) molecular gas (left), just the gas moving rapidly toward us (middle) and just the gas moving rapidly away from us (right). [Geach et al. 2018]
Options for Violent Quenching
What mechanisms could suddenly prevent cold gas from contracting into stars in the disk of a galaxy? The most efficient approach is the rapid removal or destruction of the molecular gas.
In one common picture of rapid gas removal, powerful jets emitted from the supermassive black hole in a galaxy’s active nucleus (AGN) play a key role. In this model, the jets blow out the galaxy’s molecular gas on short timescales — and in so doing, they both clear out gas available for star formation, and also propel metal-enriched gases into the circumgalactic medium.
But new observations have challenged the picture of AGN-driven outflows as the standard violent-quenching mechanism. In a recent study led by Jim Geach (University of Hertfordshire, UK), a team of scientists presents a new view of a quenching galaxy that doesn’t seem to have an AGN.
Look to the Stars
Using ALMA, Geach and collaborators trace the molecular gas in SDSS J1341–0321, a massive and compact galaxy thought to have recently undergone a major merger and now showing signs of early-stage quenching. Despite this galaxy hosting no evidence of an active nucleus, the ALMA observations reveal an outflow of cool gas moving at a speedy 1,000 km/s relative to the stars.

The Antennae Galaxies are an example of a starburst galaxy with rapid star-formation activity driven by a recent merger. [NASA, ESA, and the Hubble Heritage Team (STScI/AURA)-ESA/Hubble Collaboration]
If this model correctly describes SDSS J1341–0321, the next question is whether similar stellar outflows could account for violent quenching in other compact, massive galaxies across the universe. While we don’t yet know the answer, it seems likely that future high-resolution observations — perhaps also made with ALMA — will help us to find out!
Citation
“Violent Quenching: Molecular Gas Blown to 1000 km s−1 during a Major Merger,” J. E. Geach et al 2018 ApJL 864 L1. doi:10.3847/2041-8213/aad8b6
9 Comments
Pingback: AAS Nova – New
Pingback: How to Turn Off a Galaxy’s Star Formation – CityGov
Pingback: How to Turn Off a Galaxy's Star Formation – Sky & Telescope | SPACE FORCE
Pingback: How to Turn Off a Galaxy’s Star Formation – Sky & Telescope - monsterbizx
Pingback: How to Turn Off a Galaxy’s Star Formation – Sky & Telescope - MillionaireBiz
Pingback: Cómo apagar la formación de estrellas en una galaxia – Observatori Astronòmic
Pingback: Octubre 2018 – Observatori Astronòmic
Pingback: Cómo apagar la formación de estrellas en una galaxia « SEDA / LIADA - RedLIADA - Cursos LIADA - Cielo del Mes - Fenómenos Astronómicos - RELEA
Pingback: How to Turn Off a Galaxy’s Star Formation – AstroBrief