By Adam Watts
[email protected]
Galaxies grow by forming new stars, and the ability for a galaxy to form stars is set primarily by its reservoir of gas. Understanding the physical process that supply and deplete these gas reservoirs is essential to forming a complete picture of star formation. Massive stars, those greater than 8 times the mass of our own Sun, end their lives in supernova explosions within a few tens of millions of years of being born. Commonly referred to as ‘star formation feedback’, these explosions inject significant energy and heat into the surrounding gas, driving gas away in ‘outflows’ and halting the production of new stars within their local vicinity. Observing the impact of these gas outflows on the surrounding galaxy is hard, because the gas is many times fainter than the light from the galaxy itself. As such, we have observed outflows in only a handful of galaxies in the nearby Universe, and every new galaxy we find gives us important new information about the physics of star formation.
In our new research paper, we present the first high-resolution map of a massive star formation feedback-driven outflow from the nearby galaxy NGC 4383. The data were taken with ESO’s Multi Unit Spectroscopic Explore (MUSE) instrument, as part of the Australian-led ESO Large Programme called MAUVE (MUSE and ALMA Unveiling the Virgo Environment). The MUSE data let us map the complex and clumpy distribution of outflowing gas, shown below in Fig. 1 in red, as it is traveling away from the galaxy. MUSE is an integral field spectrograph, which means that every pixel within a picture it takes contains a spectrum of light, much like how a rainbow shows us the spectrum of sunlight. This spectrum encodes information about how fast the gas is moving in NGC 4383, and the mass of gas contained within it. We estimate that the outflowing gas is moving at mind-boggling speeds up to 340 kilometres per second away from the galaxy, and contains a mass of 50 million times the mass of our own Sun. While this gas will not escape the galaxy completely, it will be a while before it makes it back down to participate in future star formation.
The supernovae explosions that drive outflows deposit heavy elements, such as Nitrogen, Oxygen, Sulphur, and even Nickel into the surrounding gas. Outflows thus are a key process for distributing these elements throughout galaxies. The same MUSE spectra that let us measure the motions of the gas also give us information about the chemical elements that are present. In Fig. 2 below we show the amount of heavy elements contained in the outflow (coloured lines) and the galaxy (black lines) for increasing distances from the galaxy centre. The coloured lines are almost always above the black line, signifying the chemically enriched nature of the outflowing gas as it travels away from the galaxy. Eventually, these elements will be incorporated into future stars and even planets, while others might float in space forever.
In summary, we created the first high-resolution map of a massive gas outflow from the nearby galaxy NGC 4383, which we have used to measure the speed, mass, and chemical properties of the outflowing gas. As such outflows are hard to find, these new data give us important new information about the physics of processes that regulate star formation in galaxies.
