ESA Herschel Observatory: Researchers discover young galaxies not behaving as predicted

The young galaxy SDSS090122.37+181432.3. It is distorted because of gravitational lensing. 

Credit: NASA/STScI; S. Allam and team; and the Master Lens Database (masterlens.org), L. A. Moustakas, K. Stewart, et al (2014).

New Herschel Space Observatory findings have given scientists a remarkable insight into the internal dynamics of two young galaxies.

Surprisingly, they have shown that just a few billion years after the big bang, some galaxies were rotating in a mature way, seemingly having completed the accumulation of their gas reservoirs.

When galaxies form, they accumulate mass by gravitationally attracting vast, external gas clouds. As the gas clouds are consumed by the galaxy, they fall into haphazard orbits.

These disordered paths cause turbulence in the host galaxies, which can drive star formation.

James Rhoads

To investigate the internal conditions of forming galaxies, James Rhoads and Sangeeta Malhotra, both from Arizona State University, and colleagues targeted two young galaxies, known as SDSS0901 and the Clone.

The light from both galaxies has taken 10 billion years to reach us across space. Thus, we are seeing them when they were comparatively young.

Rhoads studies galaxy formation, galaxy evolution and the reionization of intergalactic hydrogen by early galaxies.

Malhotra's research ranges from properties of dust and gas in the (relatively nearby) interstellar medium to some of the farthest known galaxies.

Sangeeta Malhotra

In recent years they have also collaborated on finding and characterizing galaxies in the cosmic dawn, when the universe was less than a billion years old.

The current project focuses on a somewhat later time, the high noon of star formation in the universe – a time when the universe was about 3 billion years old, and when star birth in galaxies was much more active than it is today.

"The purpose of this project is to study the physical conditions of gas in those galaxies. We wanted to know: 'Are they similar to the galaxies around us, or is there some difference in their physical conditions?'" says Rhoads.

The two galaxies they choose to study are average galaxies for that time in cosmic history. This means that they are about 10 to 20 percent the size of our Milky Way, which is considered an average galaxy in the present-day universe.

Studying galaxies so far away is usually challenging because they appear too dim to study effectively, but in this case, the researchers were helped by a cosmic mirage known as a gravitational lens.

The two galaxies both sit behind intervening groups of galaxies, whose gravity warps space.

As described by Albert Einstein's General Theory of Relativity, this warping acts like a lens.

Although it distorts the images of the young galaxies, it helps by magnifying their light, thus bringing them within reach of ESA Herschel's HIFI instrument.

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