Gas falling towards the center of a galaxy is a major driver of new star formation and the growth of supermassive black holes. Most of this gas is hydrogen, but it also includes more complex molecules, particularly water. However, astronomers have many questions about the details of how the inflow translates to star formation, some of which have now been answered by using telescopes that can see in the infrared to detect the spectral lines from water and other molecules.
ESO 320-G030 is a “starburst galaxy” emitting around a hundred times as much energy as the Milky Way, and forming stars 18 times as fast. This is driven by the inflow of gas, but efforts to observe the connection have been hindered by dust blocking light from around the galactic center at optical wavelengths just as we struggle to see into the core of our own galaxy.
Professor Eduardo Gonzalez-Alfonso of the University of Alcalá, Spain, used infrared observations of ESO 320-G030 taken with the Herschel Space Observatory and the ALMA submillimeter facility, both of which can see longer wavelengths than the majority of large telescopes.
In Astronomy & Astrophysics, Gonzalez-Alfonso and co-authors used the diversity of spectral lines produced by water molecules under different conditions to measure the rate of inflow of gas to ESO 320-G030's central regions at 18 solar masses a year. This exactly matches the rate at which new stars are being formed. Such rapid flow is only expected to last around 20 million years, after which star formation will presumably slow as well. The authors then observed the spectra of 17 other gas molecules that also form part of the flow to explore the chemistry of the galactic core, disk, and surrounding envelope.
ESO 320-G030 is 160 million light-years away. Although close by the standards of the entire universe, that is still much further than the galaxies we study in the most detail. It is, however, “exceptional in the local universe” according to the paper, in light of its brightness and rapid development, particularly considering it shows no signs of a recent merger with another galaxy.
Moreover, ESO 320-G030 is a barred spiral, and the authors think it may be key to understanding this galactic class. As the name suggests barred spiral galaxies appear to have a solid bar extending either side of the central bulge, with the spiral arms starting from the ends. Approximately two-thirds of the spiral galaxies in the universe today are barred, and the proportion is rising. This alone would make understanding the role bars play in galaxy evolution crucial, even without the discovery our own Milky Way has a substantial bar.
The authors conclude the nuclei of galaxies with “strong nuclear bars” are probably characterized by the short timescales (by the standards of galaxies) on which they evolve, and by the rapid growth of their black holes.
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