The youngest and most remote galaxy ever seen by ALMA

Atacama Large Millimeter/submillimeter Array(ALMA) observed a gravitationally-lensed galaxy at z=8.38!

The Atacama Large Millimeter/submillimeter Array (ALMA) at Chile, was used by an international team of astronomers, led by Nicolas Laporte of University College London, to observe A2744_YD4, the youngest and most remote galaxy ever seen by ALMA. This galaxy was observed shortly after its formation, when the Universe was only four percent (4%) of its present age (~13.7billion years), and is the most distant galaxy in which dust has been detected.

The team of astronomers studyied the observational data and found that galaxy A2744_YD4 contained an abundance of interstellar dust — dust formed by the deaths of an earlier generation of stars. 

Dr. Nicolas Laporte commented: “Not only is A2744_YD4 the most distant galaxy yet observed by ALMA, but the detection of so much dust indicates early supernovae must have already polluted this galaxy.”

The enormous distnace to A2744_YD4, at a redshift of z=8.38 or when the Universe was only ~600 million years old, was confirmed by follow-up observations using the X-shooter instrument on ESO’s Very Large Telescope, located at an altitute of 2’635m atCerro Paranal, Chile.

The dusty galaxy A2744_YD4 lies behind a massive galaxy cluster called Abell 2744 (3.5 billion light-years away or at redshift z=0.308), that is thought to be the result of four smaller galaxy clusters colliding. Abell 2744 acted like a giant cosmic “telescope” to magnify the more distant A2744_YD4 by about 1.8 times, a result of a phenomenon called gravitational lensing.

Astronomers estimated that A2744_YD4 contained an amount of dust equivalent to 6 million times the mass of our Sun, while the galaxy’s total stellar mass (the mass of all its stars) is estimated around to 2 billion times the mass of our Sun. They also measured the star formation rate of A2744_YD4 and found that stars are forming at a rate of 20 solar masses per year (for our Milky Way is just one solar mass per year)

Prof. Richard Ellis (ESO and University College London) a co-author of the study noted: “This rate is not unusual for such a distant galaxy, but it does shed light on how quickly the dust in A2744_YD4 formed. Remarkably, the required time is only about 200 million years — so we are witnessing this galaxy shortly after its formation.”

And Dr. Laporte concludes: “Further measurements of this kind offer the exciting prospect of tracing early star formation and the creation of the heavier chemical elements even further back into the early Universe.”

The galaxy cluster Abell 2744 (NASA/ESA Hubble Space Telescope) and the very faint galaxy called A2744_YD4, as seen when the Universe was only about 600 million years old. The new observations of this galaxy with ALMA, shown in red, have demonstrated that it is rich in dust.
Credit: ALMA (ESO/NAOJ/NRAO), NASA, ESA, ESO and D. Coe (STScI)/J. Merten (Heidelberg/Bologna)
Credits (text & video): European Southern Observatory