PHANGS-MUSE Catalog: Unpublished Images of Young Star Galaxies

From gas clouds to stars, an international team of astronomers delivers Friday with the PHANGS-MUSE catalog of 19 galaxies close to our own, a picture with unparalleled resolution of star nurseries.

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This is the result of a campaign, launched in 2017, to observe existing galaxies, to the farthest distance, about 60 million light-years, and only to the nearest 5, the outer suburbs of our Milky Way.

“It gives us, for the first time, a view of star-forming galaxies in the nearby universe, with a level of detail that allows us to look at the entities in which these stars are formed, the gas clouds,” an astronomer at the European Southern Observatory (ESO), which Participate in campaign leadership.

Like NGC 4303, also called M61, which extends the galaxy’s long spiral arms, in a symphony of orange-brown colors of gas clouds, they turn golden as stars are born, by the billions, and turn bluish as they age.


The MUSE instrument, a spectrometer installed on ESO’s Very Large Telescope in Chile, played a major role in the observation campaign. Its data, including more than thirty thousand images of hot gas nebulae and 15 million spectra, will be made available to the scientific community in the coming days.

The goal is to try to understand “what stimulates or prevents star formation somewhere in the galaxy,” continues Eric Emselm, on loan from the Astrophysical Research Center in Lyon.

MUSE is a program of the PHANGS International Collaboration, bringing together scientists from several continents, and aims to study the different phases of the baryonic cycle, which leads to star matter.

The program benefits from the contribution of two primary instruments, ESO’s ALMA Radio Telescope, and the Hubble Space Telescope.

All this makes it possible to “reconstruct a movie” of stellar creation, according to Eric Emselm, thanks to the number of galaxies observed.

With ALMA, astronomers see cold gas condensing to form molecular gas, the “fuel” of star formation.

Gas bubbles

With MUSE, “we see the following stages, when gas clouds create a large group of stars,” the largest of which will evolve very quickly, “over a few million years,” and some of them will explode, by expelling the gas. “We see these gas bubbles that open and redistribute the material” in the surrounding space.

So Meuse sees hot gas, young stars, and old stars. Using Hubble, which has greater analytical power, we begin to identify star clusters, seeing bubbles of gas and dust, with an accuracy of less than 30 light-years.

The mass of data provided, including the temperature, density, and chemical composition of stars and gas, will feed the flow of scientific articles for years to come.

While waiting for new machines that will help to better understand how stars are born.

Because “the resolution of the map we produce (using PHANGS) is only enough to identify and characterize the clouds that form stars, but not enough to see in detail what’s going on inside,” notes astronomer Eva Schinnerer, of the Max Planck Institute for Astronomy, in an ESO press release.

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The veil will continue to rise with the arrival this year of the James Webb Space Telescope, for which PHANGS has already assigned an observation window, and which will allow you to see better in clouds of gas and dust.

Then a time will come, later in this decade, from ESO’s European Giant Telescope (ELT). With the “colossal decision”, perhaps it will allow to unravel the secret of star nurseries.

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