New observations by the Atacama Giant Millimeter/submillimeter Array (ALMA) present an in depth take a look at a galaxy that could be within the means of shutting down its star formation.
Transitioning a Galaxy
Although we all know rather more concerning the processes of galaxy formation and evolution than we did even a decade in the past, many key factors nonetheless elude us. One explicit puzzle is that of how star formation ends in a galaxy. We expect that galaxies ultimately transition from vibrant, blue, star-forming disks into pink and quiescent ellipticals — however what causes star formation in a galaxy to close down throughout this transition?
Since galaxies type stars out of chilly fuel, we may assume that star formation stops solely when the chilly fuel provide is depleted. However observations recommend that star formation can shut down throughout a galaxy rather more shortly than the timescale for utilizing up the fuel provide — generally turning off inside just some tens of thousands and thousands of years. Such a fast shutdown is termed “violent quenching”.
Choices for Violent Quenching
What mechanisms may instantly stop chilly fuel from contracting into stars within the disk of a galaxy? Essentially the most environment friendly strategy is the fast elimination or destruction of the molecular fuel.
In a single widespread image of fast fuel elimination, highly effective jets emitted from the supermassive black gap in a galaxy’s lively nucleus (AGN) play a key function. On this mannequin, the jets blow out the galaxy’s molecular fuel on quick timescales — and in so doing, they each filter out fuel out there for star formation, and in addition propel metal-enriched gases into the circumgalactic medium.
However new observations have challenged the image of AGN-driven outflows as the usual violent-quenching mechanism. In a current examine led by Jim Geach (College of Hertfordshire, UK), a crew of scientists presents a brand new view of a quenching galaxy that doesn’t appear to have an AGN.
Look to the Stars
Utilizing ALMA, Geach and collaborators hint the molecular fuel in SDSS J1341–0321, a large and compact galaxy thought to have not too long ago undergone a significant merger and now exhibiting indicators of early-stage quenching. Regardless of this galaxy internet hosting no proof of an lively nucleus, the ALMA observations reveal an outflow of cool fuel transferring at a speedy 1,000 km/s relative to the celebrities.
Geach and collaborators recommend that this outflow is violent quenching in one other type: a strong stellar outflow at present expelling round 300 photo voltaic lots of fuel per 12 months. They argue that this outflow was launched inside the final 5 million years from a central starburst — a area of compact, vigorous star formation — triggered by SDSS J1341–0321’s current merger. On this mannequin, the celebrities themselves blow out all of the fuel — and as soon as the fuel is gone, star formation will flip off and the galaxy will seem pink and quiescent.
If this mannequin appropriately describes SDSS J1341–0321, the following query is whether or not related stellar outflows may account for violent quenching in different compact, huge galaxies throughout the universe. Whereas we don’t but know the reply, it appears probably that future high-resolution observations — maybe additionally made with ALMA — will assist us to search out out!
“Violent Quenching: Molecular Fuel Blown to 1000 km s−1 throughout a Main Merger,” J. E. Geach et al 2018 ApJL 864 L1. doi:10.3847/2041-8213/aad8b6
This publish initially appeared on AAS Nova, which options analysis highlights from the journals of the American Astronomical Society.